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Management of Rectal Injuries
Advances in Equine Abdominal Surgery
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Management of Rectal Injuries Mark C. Rick, DVM*
RECTAL TEARS Iatrogenic injuries to the equine rectum and terminal small colon occur rarely in relation to the total number of rectal palpations performed for reproductive and other diagnostic purposes. Rectal injuries can also occur from overzealous use of enemas or from a misdirected stallion penis during natural service. Discussions and written articles concerning rectal injuries always seem to find them selves relegated to the last topics at scientific meetings and the last chapters in books. Whether this is strictly due to anatomic consid erations, or more likely, an aversion to the remote possibility that a rectal tear might befall a clinician at any time is a matter open for debate. Whatever the case may be, should a practitioner ever cause or encounter a rectal tear, several very important decisions need to be made expeditiously to maximize the health of the horse and to defuse liability considerations. Anytime there is fresh blood on a rectal sleeve or there is a sudden "feeling of release of pressure" on the arm when performing a rectal exam, immediate determination of the presence and/or extent of a rectal tear needs to be made. Also, open discussion with the owner or agent of the horse needs to be established. There is no room for casual dismissal or a "wait and see" approach for these types of injuries. To be summoned by the anxious horse owner a few hours following the suspected or known occurrence of a rectal injury to see why the mare is sweating, has a "splinted" abdomen and is uncomfortable does not demonstrate good judgment. There are many techniques currently available that offer in creased chances for survival of the horse with an injured or torn *Private Practitioner, Alamo Pintado Equine Medical Center, Los Olivos, California Veterinary Clinics of North America: Equine Practice-Vol. 5, No. 2, August 1989
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rectum if the problems are attacked forthrightly. 3-S, 7• 8• 14• 19· 21• 23• 27 Basic medical and perhaps surgical decisions need to be made within 30 minutes of the rectal injury. That is not to say that the horse needs to be immediately taken to surgery in all instances, but, following proper evaluation of the tear and discussion with the client, well-intended and well-informed approaches can be used in dealing with the problem. It may come up in the discussion with the owner or client as to who is liable and who will pay for the horse's medical expenses. These questions require careful consideration on the part of the veterinarian, since he or she is responsible for following a good standard of practice whenever performing a rectal examination. 22 If there was adequate and safe restraint of the horse, if lubricants were used to gently clear the rectum of feces, and if any rectal contractures were not overtly fought, then the veterinarian can safely feel and openly discuss that this injury was not caused by malpractice, and, hence, the care and expense should not be expected to be borne by the veterinarian. As insurance adjusters would remind us, and it so states in their written recommendations, no admission of guilt need or should be made. This holds true for all cases in which everything was done properly, following skilled and well executed procedures. If you feel otherwise at the time of the injury, then it would be up to your judgment and ethics as to the approach you would suggest to the client. When we receive horses at our medical center that have been referred for evaluation and possible repair of torn rectums, our discussions are directed entirely at the client/owner as to the course of action we propose to take. The referring veterinarian is, of course, later informed of all the diagnostics and course of treatments, but we try to be sure that he or she is removed from the decision making process. This is our attempt to establish a firm commitment on the part of the owner to be solely responsible for all decisions and financial obligations. At this point, our staff has reached a general agreement upon the way in which the rectal injury occurred, it has been or is about to be evaluated, and the owner/client �s been informed of the injury. EVALUATION
The three most important parameters, which can be immedi ately determined in most instances, are the location of the tear, its overall size, and its depth or the number of tissue layers actually penetrated. Also, the lapsed time since occurrence and diagnosis of
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the tear is very important to ascertain. Most tears, although com monly referred to as "rectal tears, " would be more correctly termed "small colon tears."9 The rectum does not enlarge to form the ampulla recti until it enters the retroperitoneal cavity, which is approximately 30 cm (12 in) farther down from the anus. Because of the presence of the pararectal fossa dorsally and the rectogenital pouch ventrally, the distance from the anus to the peritoneal cavity can actually be less than 15 cm (6 in). Most tears occur somewhere just past the pelvic inlet, which means that the majority of these tears are within the peritoneal cavity.2• 5• 9 Most tears are located dorsally and are usually of a longitudinal configuration.2• 5• 18 Possibly the tear occurs dorsally because horses will sometimes adversely react to rectal palpation and simultaneously strain and lean down. The tail often clamps down so that the arm is forced upwards and this may push the knuckles or the ultrasound probe up through the dorsal wall. To evaluate location, size, and depth of the tear, the horse should be well tranquilized and the rectum carefully evacuated. Xylazine (0.3 mg/kg intravenously [IV]) and butorphanol tartrate (0.1 mg/kg IV) combinations work extremely well to sedate and relax the horse and to allow for a safe inspection to proceed. I prefer to cut the fingers off the normal rectal sleeve and use a latex exam or surgical glove placed over the rectal sleeve. Lidocaine enemas, caudal epidural anesthesia, or probanthine (0.014 mg/kg IV) can be used to relax the rectum and facilitate fecal evacuation. In most instances, though, I have found the xylazine/butorphanol tartrate combination sufficient for a very thorough exam with the decreased risk of patient wobbliness from the epidural. The tear can sometimes be visualized with the aid of a glass or Caslick speculum; however, the rectal mucosa usually infolds around the speculum, making direct visualization difficult. Of more importance is the digital evaluation of the tear. Once the tear has been located it should be very gently felt for position, distance in from the anal sphincter, size, and, if possible, depth. Any feces in or around the tear should be very carefully removed. Liberal use of nonirritating lubricants will facili tate this part of the exam. The tear can be classified according to the layers torn: Grade I = mucosa or mucosa and submucosa; Grade 2 = muscularis only; Grade 3 = mucosa, submucosa, and muscular layer, including tears into the dorsal mesentery; Grade 4 = complete tear of the rectal wall into the abdominal cavity.2 Patient evaluation includes measuring and recording all vital signs, hematologic parameters, and rectal findings. An evaluation of the abdominal fluid also is extremely important. Peritoneal fluid changes may occur very quickly; for example, a gelding was admitted
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to the hospital for removal of a urinary calculus via a perineal urethrostomy and lithotripsy technique. The horse was sedated, had a caudal epidural, and his rectum fully evacuated. A rectal exam was performed to feel the calculus, and the rectum was inadvertently torn (Grade 3). Within 30 minutes, with no passage of feces by the tear, the peritoneal fluid had increased in amount, was cloudy yellow in color, and had a nucleated cell count in excess of 50, 000 cells/ mm. This horse underwent surgery for a primary rectal wall closure and was treated aggressively for the peritonitis. His recovery was uneventful and the cystic calculus was removed 6 months later, by a perineal approach. TREATMENT
Once the patient and the tear have been thoroughly evaluated, decisions need to be made as to the best course of action. Grade I Tears Grade 1 tears (mucosa or mucosa and submucosa) (Fig. I), are amenable to medical treatment alone or can be treated with direct suturing techniques in the standing animal using epidural anes thesia. 3· 5 These horses should be monitored very closely for 4 to 8 days and placed on a laxative type of diet such as green grass or water-soaked alfalfa pellets, combined with regular administration of mineral oil by nasogastric tube. Broad-spectrum antibiotics should be administered. Serial hemograms (complete blood count and
Figure 1. Grade 1 rectal injury, with disruption of the mucosa! layer only.
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fibrinogen) as well as peritoneal fluid analyses aid in monitoring the patient. If the horse is only slightly dehydrated, oral fluid supple mentation may be all that is necessary for adequate volume replace ment. For more severe dehydration (>8 per cent), intravenous fluid administration may be required to restore circulating volume, ensure tissue perfusion, and to prevent bowel stasis and possible colon impaction. These horses should not be palpated for at least 30 days to avoid enlargement or deeper penetration of the tear. Grade 2 Tears Grade 2 rectal tears are likely to occur only in rare circumstances in which the muscular layer tears but the more elastic mucosa and submucosa stretch without tearing (Fig. 2). These may be felt upon subsequent rectal palpations as a variable-sized diverticulum that is more accurately described as a mucosal-submucosal hernia. 2 Horses with large Grade 2 tears may present with signs of tenesmus or with rectal impactions. The hernia or diverticulum is detected after manual evacuation of the rectum. These tears are usually manageable with conservative measures such as dietary control aimed at keeping the feces soft. Grade 3 Tears Medical Management. Grade 3 tears that disrupt the mucosa, submucosa, and muscular layers (Fig. 3) dictate prompt and aggres sive medical as well as surgical intervention. 3-S, 8• 14• 18• 21• 23 The immediate concern is to prevent enlargement or perforation of the
Figure 2. Grade 2 rectal injury, demonstrating mucosal-submucosal diverticulum, which can occur when the muscular layer has been disrupted.
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Figure 3. Grade 3 rectal injury in which the mucosa, submucosa, and muscular layers have all been disrupted, leaving only the thin serosal layer intact.
tear. This is accomplished with tranquilization of the horse, manual rectal evacuation of feces, temporary meticulous packing of the torn area with an antiseptic soaked gauze pack, and possible use of epidural anesthesia, probanthine, or atropine to decrease gastroin testinal motility. The use of atropine, a parasympatholytic drug, is felt to be somewhat controversial. Indiscriminate usage of atropine has led to gastrointestinal complications. It does have the advantage of being readily available to almost all primary care practitioners, and I feel it is an excellent and safe adjunct, at the correctly specified dose, to depress intestinal motility while the horse is in transit. A single dose of 0. 044 mg/kg (20 mg for a 450-kg horse) given intramuscularly (IM) or subcutaneously (SQ) will decrease intestinal motility for up to 12 hr. Larger or repeated doses could lead to prolonged ileus with subsequent tympanic viscus distension, mild-to-moderate abdominal pain, and an elevated heart rate. 6 At the low-dose rate and following single-dose administration, the bowel stasis would only rarely be a " problem. Initiation of high levels of broad-spectrum systemic antimicro bials, tetanus toxoid inoculation, and administration of fecal laxatives such as mineral oil should also be a part of the preliminary treatment. En route to a surgical facility or shortly after arrival, IV fluids should be administered to rehydrate or overhydrate the horse in anticipation of an extensive surgical procedure and to counter the adverse hemodynamic effects of endotoxins. The technique chosen to repair the rectal injury depends largely on the location or the tear, the preference and expertise of the
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surgeon, and the availability of necessary equipment such as a rectal liner or expandable basket. Much of the following discussion of surgical options for Grade 3 tears would also apply for Grade 4 tears, in which there is total perforation into the abdominal cavity (Fig. 4). The most significant difference between Grade 3 and Grade 4 tears is the amount of direct contamination of the abdomen in Grade 4 tears put into perspective with the value of the animal, poorer prognosis, increased expense, and the likelihood of multiple post operative complications of most Grade 4 tears. Direct Closure. In certain patients that are tractable and have the rare combination of expandable or retractable rectums, minimal mucosa} and submucosal edema or necrosis, and an available surgeon with a high degree of patience and manual dexterity, the Grade 3 tears can be sutured directly (Meagher DM; personal communica tion, 1988). The surgeon must be meticulous in the closure to avoid both further damage to the edges of the tear and incorporating nearby mucosa} folds into the tear, as this would reduce the rectal diameter. Also, incomplete suturing of the tear would allow for continual packing with feces and eventual breakdown or dissection under the mucosa. Contractions of the wide muscular bands and circular smooth muscle increase the risks of dehiscience of the sutured tears. The direct suturing methods have been aided in recent years by the development of specialized surgical instruments, most notably the expandable rectal speculum or wire basket (Robert N. Roland, Davis, CA 95616) and long-handled instruments (Figs. 5 through
Figure 4. Grade 4 rectal injury, in which there has been perforation of the rectal wall, allowing access directly into the peritoneal cavity.
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Figure 5. Cut-away side view of the expandable rectal speculum in the closed position, as it is inserted into the rectum.
7). 19 Transection of the anal sphincter will allow improved exposure. Increased success with the direct suturing method has also been achieved by combining it with simultaneous ventral midline celi otomy and evacuation of the large colon via pelvic flexure enterot omy.12 This essentially decreases the ingesta that would normally pass through the rectum during the critical first 48 hours and, hence, lessens chances of impaction, mucosal dissection, or severe contam-
Figure 6. View of the expandable rectum speculum in the open position, which is used to allow visualization of and access to the rectal injury.
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Figure 7. Diagrammatic rep resentation of the expandable rec tal speculum in place, and utiliza tion of long-handled pistol-grip needle holder and auxiliary light source to directly suture a dorsally positioned Grade 3 rectal tear. The schematic in the lower left dem onstrates an idealized two-layered closure of such a tear.
ination. For instances in which the rectal tear is accessible to direct suturing, a simple continuous pattern utilizing size O or 1 absorbable suture material, with a swaged-on, taper-point, half-circle needle, incorporating all layers, is the method of choice. A recently described surgical procedure, utilizing a temporary indwelling rectal liner, has been successfully used in a number of cases. 23• 28 Ventral midline celiotomy provides adequate exterioriza tion of the small colon to situate the liner as well as allowing evacuation of the large colon, should that be deemed beneficial. An assistant not participating in the laparotomy passes the plastic rectal ring and sleeve through the anus and small colon until it can be surgically placed proximal to the tear. The plastic ring is anchored to the wall of the small colon with retention sutures, which are then oversewn so as to infold the wall. Feces that enter the ring are contained within the liner until passed through the anus. In a reported series of horses, some of which were euthanized because of complications, luminal strictures were not apparent at the site of ring attachment in the small colon. One complication described was the formation of a complete ostomy at the site of the original tear between the intestinal mucosa and peritoneal cavity, with subsequent fatal peritonitis after the ring and liner were passed (average, 9 to 12 days after implantation). 23 The liner not only protects the tear but
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also effectively limits access to the tear for any manual debridement to cleanse the edges. Direct suturing was recommended to decrease the lesion size, provide support, and decrease the likelihood of ostomy formation from intestinal mucosa to peritoneal lumen. 23 Another method of direct closure of the tear involves approach ing the injury via a ventral midline celiotomy. 5 The location of most tears, dorsally in the mesocolon or mesorectum and so far caudally, often makes exposure poor and, hence, very seriously limits visual ization. If the tear is inaccessible because of its dorsal position but is far enough cranial to be approached via a ventral midline celi otomy, a direct suture repair via an enterotomy on the antimesenteric side of the small colon may be possible. Evacuation of the contents, traction, and possibly elevation of the horse's hindquarters, or assistance by someone's hand pushing back on the rectum may all be necessary to allow access to the tear. 5 Performance of the midline celiotomy, small colon enterotomy and evacuation of feces, exposure and meticulous closure of the tear itself, and then closure of the enterotomy site all would require a good deal of time and effort. The likely necessity of evacuating the large colon as well would almost mandate that two surgical teams perform these procedures simultaneously, in order to keep the operating time at a safe limit. Accessibility to the tear would still be the key factor. If closure is not deemed possible, options still exist for other procedures such as placement of a temporary rectal liner or colostomy. Colostomy. The use of a temporary diverting colostomy, loop or end-on, for the management of rectal tears deserves lengthy discussion, owing to the inherent advantage of diverting most or all feces away from the tear. :.--s. 8• 14• 21 The loop colostomy provides some continuity to the small colon with diversion of the feces out the stoma created in the antimesenteric side of the small colon and exiting through the flank incision. The end-on colostomy, which totally diverts all feces out through a low flank incision, requires a more complicated reanastomosis after the tear has healed. The surgical technique requires general anesthesia in the ma jority of patients to allow for the abdomiQal manipulations that will be necessary. In the presence of peritooeal inflammation, the un anesthetized horse may be very reluctant and unwilling to permit the traction and manipulations necessary on the bowel. This does not preclude all standing flank surgeries, especially if a general anesthesia is not possible or poses serious health risks to the patient, but most surgeons prefer the added time and ease of tissue handling with the patient in lateral or dorsal recumbency. The end-on colostomy can be performed through one or two incisions. 4• 8• 14• 21 A routine paralumbar flank incision can be utilized to make the initial manipulations and exploration of the abdomen.
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Figure 8. Ideal position for placement of the stoma for the end on colostomy in the lower left Hank region.
The lower flank incision is then used as the exit site for the cranial small colon (Fig. 8). When dealing with an incomplete rectal tear without serious peritoneal contamination, the low flank incision alone can suffice for the bowel manipulations.8 In either case, the small colon is exteriorized in the lower flank region and readied for surgical transection. The section of small colon to be utilized should be located several feet cranial to the rectal injury. This allows adequate mobilization of the small colon from its attachment as well as the eventual and more technically difficult reattachment (Fig. 9). The caudal portion of the small colon is emptied of remaining ingesta with manual milking or by use of a tube passed forward from the
Figure 9. Preparing the two ends of the small colon for the end-on colostomy. The cranial section, depicted in the left hand, will exit the body wall at the lower stoma site, as shown in Figure 8. The distal segment on the right will be oversewn in two inverting layers and left loose within the abdominal cavity until eventual reattachment.
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Figure 10. Schematic representation of the proximal small colon being pulled through the lower flank stoma site. The mesentery of the proximal segment can be attached to the body wall if the paralumbar flank approach was utilized, but this is not necessary and not possible if the lower approach was used alone.
rectum, past the tear, until warm water can be safely flushed cranial.4 The caudal stump end is then closed with a double-row inverting pattern, utilizing size 2-0 absorbable suture material. We routinely utilize an antibiotic lavage during these and any other possibly contaminated procedures. The cranial segment is then oversewn and brought through the lower flank incision or clamped and carefully pushed through the hole, where it is firmly attached with a multiple layered closure (Figs. 10 and 11).
Figure 11. Diagrammatic rep resentation of multiple tissue layer closure and attachment of the colon at the stomal site.
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It is very important that a circular incision, slightly smaller than the small colon diameter (7 to 10 cm, average) is made through the skin, fascia, and fibrous layer of the external abdominal oblique muscle. Otherwise the stoma will not provide a large enough lumen for safe and unrestricted passage of feces. Some surgeons prefer to fold back and suture the end of the small colon into a cuff. 4• 14 This may not be necessary but does seem to lessen the submucosal hemorrhage, which will persist for several hours. We prefer to bring about 6 cm of cranial small colon out, so as to keep it away from the incision for the first day and make the deeper layers of suturing less likely to be contaminated. A row of simple interrupted sutures are utilized to attach the small colon serosa to the transverse abdominal muscle layer. A second layer of sutures, placed in simple interrupted pattern, attaches the serosa to the internal abdominal oblique mus cles. Again, with simple interrupted sutures of size O or size 1 absorbable material, the small colon is further attached to the external abdominal oblique fibrous layer. The fascia and skin are sutured to the small colon, utilizing nonabsorbable sutures in a simple interrupted pattern. Fastidious closure techniques are very important to prevent fecal contamination of the stoma site. Localized infection and later abscessation can be avoided by careful attention to closure of all dead space, by allowing for adequate size of the stoma, and by close postoperative attention to diet to avoid impaction at the surgical site. Lush green grass pasture is the ideal food source. Otherwise, water soaked alfalfa pellets and frequent administration of mineral oil will ensure soft but formed fecal consistency. The loop colostomy procedure has the advantages of greater
Figure 12. Loop colostomy procedure, demonstrating the pull through of the small colon (cranial segment at the top); attachment of the colon wall to the external abdominal oblique muscle; and the attachment of the mucosa! lining to the skin.
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ease of surgery and allowing continual access to and partial use of the distal segment. This can aid in the prevention of atrophy of the distal segment. The possible passage of feces through the distal segment could, of course, be a major disadvantage as well. The surgical approach utilizes the standard left paralumbar flank grid and then exteriorizes the small colon. The colon is situated so that the cranial segment is attached at the top of the flank incision. 5 • 18 A loop of intestine with the antimesenteric surface pointed outward, ap proximately 8-cm long, is then sutured to the edges of the external abdominal oblique muscle and fascia, with size 0 absorbable suture, in a simple interrupted pattern. A 6-cm incision is then made through the antimesenteric band into the lumen, and the mucosa! lining is sutured to the skin using size 2-0 nonabsorbable suture in a simple interrupted pattern (Fig. 12). POSTOPERATIVE MANAGEMENT
For either of the two colostomy methods, intensive postopera tive management is crucial, time consuming, and expensive. The horse should be maintained on high levels of broad-spectrum anti biotics. We routinely use potassium penicillin G (40, 000 U/kg IV QID) and gentamicin sulfate (2. 2 mg/kg IV TID or QID). Also nonsteroidal antiinflammatories, preferably flunixin meglumine (0. 25 mg/kg IV or IM QID) and dietary management are integral to the successful management of these patients. Low-dose heparin admin istration (15, 000 to 30, 000 IU IV or SQ QID) may aid in preventing adhesion formation and is part of our protocol. Ileus
The horse with a Grade 3 rectal injury is the perfect candidate for rapid development of postoperative ileus. Perhaps atropine, a parasympatholytic drug, was administered to prevent passage of feces through the tear. There will likely be some degree of perito nitis, both from the tear itself and from surgical manipulations. And there will be slight anesthetic depre�ion of bowel motility as well. This deleterious triad could easily lead to severe, possibly irreversi ble, ileus. Naturally the effects of the atropine and anesthetic will subside with time. The peritonitis can be dealt with using appropriate antibiotics and peritoneal drainage and/or lavage. I strongly contend that neostigmine, used early in the course of the disease, plays an integral role in preventing ileus and decreasing patient morbidity and mortality. The risk of anastomotic dehiscence has not been a problem. Neostigmine methylsulfate is administered intravenously via a slow-drip system (Travenol Infusor, Deerfield,
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IL, 60015) of 2 ml per hour (0. 01 mg/kg/hour) connected to the IV catheter. If the horse shows mild discomfort, the neostigmine is further diluted. Only when the horse shows no tolerance for the intestinal stimulation do we discontinue its administration altogether. The horse is maintained on the infusion of neostigmine for the first 48 to 96 hours postoperatively. Neostigmine, which is felt to pri marily enhance propulsive motility of the large colon, and metoclo promide, which enhances gastroduodenal motor activity, may be used separately or in combination to prevent or treat ileus 1 (see Gerring). Waiting for the bowel to become severely distended or for other metabolic problems to arise definitely decreases the intestinal motility enhancement and the survival of the patient. Correcting all electrolyte disturbances, walking the horse hourly, feeding a diet of lush green grass, administration of analgesics, and control of perito nitis all play equally critical roles in minimizing occurrence of ileus. 1 Edema and Inflammation Often the colostomy site becomes edematous within the first 24 hours after surgery. This may necessitate careful administration of warm water enemas to keep the lumen open and to prevent impaction and patient discomfort. Later, if a local abscess should develop at the stoma, it is important that it be aggressively treated by drainage and lavage so as to allow for tissue healing in time for the reanastomosis. If peritoneal fluid analysis indicates the presence of severe inflammation or possible sepsis, then peritoneal lavage is begun. Serial peritoneal fluid nucleated cell counts and cytological exams assist in making the distinction between normal postoperative inflam matory changes versus more severe changes. 17 If the patient is febrile, depressed, anorectic, has ileus and also has increased quan tities of abdominal fluid with a nucleated count above 150, 000 cells per mm, 3 high protein, and presence of bacteria, then serious attention to the treatment of the peritonitis must begin. Often, at the time of surgery, the surgeon can determine the need for peritoneal lavage, and a drain or drains can be inserted at that time. Several methods for peritoneal lavage have been described. 13• 26 I prefer the use of a large-bore (30 F) mushroom or urological catheter placed through the linea alba in the cranial abdomen. Using large volumes (3 to 10 L) of warmed isotonic saline or lactated Ringer's solution, flushed in a retrograde fashion through the drain over a 1-hour period and then allowed to drain back out, has given good results without the need for a separate ingress portal. After a few days, the return flow may become hampered, as the omentum or fibrin clots seal the openings of the catheter. A sterile infusion pipette or Chambers catheter can sometimes dislodge these obstruc-
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tions and allow for adequate outflow. After insertion of the lavage solutions, the horse can be walked or hand-grazed for a period of time. At no time is the horse to be left unattended while the catheter remains open, so as to avoid accidental soilage of the end. The catheters are sealed with a 3-ml syringe and firmly taped to the horse's body wall with encircling elastic wrap before leaving the horse unattended. Assessment of Healing
Assessment of healing of a rectal tear is very important. If the tear was not sutured, it may require periodic cleaning and delicate debridement with gauze sponges to hasten the healing process and prevent formation of an abscess, a permanent ostomy, a diverticulum, or a rectal stricture. The uncomplicated Grade 3 tear can be expected to heal within 2 to 4 weeks. Several months have elapsed before some colostomies have been reanastomosed, but, generally, the earlier it is attempted the easier it is to rejoin the bowel. Avoidance of extreme atrophy of the caudal segment and maturation of adhesions are two reasons to attempt early reanastomosis. Reanastomosis
It seems that many times the horse is just getting over the critical part of after-care, returning to a positive metabolic state, and getting the few localized stomal problems under control when one is looking at another long and difficult surgery and its associated problems. This is not the time to put off the surgery for a few more days if everything is deemed ready.4 A day before the reanastomosis of the small colon the horse is held off feed. Twelve hours prior to surgery the horse is given 1 gallon of mineral oil via nasogastric tube. The surgical approach for the reanastomosis of the end-on colostomy is usually the ventral midline celiotomy. The advantages to this approach are adequate assessment and breakdown of adhesions from the tear or colostomy and adequate room to manipulate the two small colon segments for the anastomosis and for emptying of the large colon, should it be necessapY. Prior to anesthetizing the horse, the stoma is prepared in an aseptic manner, and the small colon is packed with Betadine-soaked cotton. If there is evidence of infection or an abscess around the stoma, the small colon is transected and oversewn within the abdomen, and the stomal and short segment of small colon are dealt with separately. This eliminates the possibility of peritoneal soilage from the abscess site. The proximal segment and distal segment are transected a few centimeters from their ends. An end-to-end hand-sewn anastomosis is performed, using a simple interrupted pattern, crushing technique, with size 2-0 absorbable
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suture material (chromic gut) followed by a continuous inverting pattern with size 3-0 absorbable suture material. 16 The mesentery is closed in a simple continuous pattern, using size O absorbable suture material. Routine closure of the abdominal incision is per formed. The horse is then rotated into lateral recumbency and the stoma and possibly short segment of small colon are handled separately. After removal of the remaining small colon portion and minimal debridement of the edges, the transverse and internal abdominal oblique muscle layers are closed in a simple interrupted pattern. The ring left in the external abdominal oblique fibrous layer is closed with size 2 or 3 absorbable suture material in a simple interrupted pattern. External fascia and subcutaneous tissues layers are apposed. A penrose drain may be inserted between the fascia and the skin in the likely event of postsurgical seroma or sepsis. The skin is closed with nonabsorbable suture material in a vertical mattress pattern. The method of closure for the loop colostomy essentially involves the reverse of the creation of the stoma. The attachments to the skin and the external abdominal oblique muscle are carefully dissected free from the edge of the small colon. If the small colon is felt to be excessively traumatized in this dissection, a short segment should be brought out of the incision and an end-to-end resection and anastomosis performed. Otherwise, the antimesenteric band is closed with double-inverting layers, utilizing 2-0 absorbable suture mate rial, and vigorously cleansed and replaced in the abdomen. The flank incision is then closed in a routine manner. Peristomal herniation, abscessation, or dehiscence are the most frequently described problems with the end-on colostomy. These problems can be avoided with careful selection of the site, low enough in the flank to allow for unrestricted fecal passage yet not so low as to invite bowel herniation. Also, careful multiple-layered closure of the tissues decreases the dead space and prevents stomal infection. Broodmares that are left with permanent colostomies present special problems in advanced pregnancy and during parturition. Unusual pressures are placed against the stomal site, and increased likelihood for herniation exists. RECTAL PROLAPSE The occurrence of rectal prolapse in horses is rare, when one considers the overall incidence of alimentary tract diseases in this species. Other large species, cattle and pigs for instance, have a much higher incidence of rectal prolapse in comparison with that in
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horses. Any condition that causes protracted tenesmus can lead to the development of a prolapsed rectum. Causes would include such conditions as diarrhea, intestinal parasitism, urinary obstructions, dystocia, Grade 2 rectal tears, constipation, or neoplastic diseases of the rectum.5• 9 • 20 • 24 • 25
EVALUATION
Rectal prolapses have been divided into four main classifications, from Type I to Type IV, with each higher designation corresponding to increasingly more involved tissues and structures, a more involved repair, and a somewhat worsened prognosis. A Type I rectal prolap se is a protrusion of the rectal mucosa and submucosa only. This is the most common type of rectal prolapse and usually presents as a large, doughnut-shaped swelling at the anus. The Type II prolap se involves all or part of the ampu lla recti and usually differs from the Type I in that it is larger and more cylindrical in appearance. The Type III prolap se appears similar to the Type II until palpated and it is determined that part of the small colon has invaginated into the rectum, which results in a much firmer and thicker-feeling prolapse than the Type II. The T ype IV prolapse is an actual intussusception of the peritoneal rectum and/or small colon through the anus. In the Type IV prolapse there is a "trench" between the prolapse and the anus that can be easily felt with a finger sliding in past what would normally be the mucocutaneous junction. An initial concern when dealing with a rectal prolapse is to determine the primary cause of the tenesmus, concurrently treating that condition as well as addressing the prolapse itself. Careful attention to the patient's history is very important as it may aid in determining the underlying cause of the tenesmus, which might not be readily apparent. The clinical exam is also very important, and the condition of the prolapsed tissues will determine whether con servative or surgical methods will be necessary.
TREATMENT
Conservative measures, commonly employed in Types I and II rectal prolapses, are most successful if initiated soon after the prolapse occurs.5 • 25 Severely edematous or necrotic rectal mucosa necessitate surgical correction to achieve satisfactory long-term re sults. The conservative therapy usually entails reduction of mucosal edema with the application of topical demulcents, of which glycerin
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is the most commonly used. Caudal epidural anesthesia provides cessation of straining and allows for gentle replacement of the prolapsed tissues and insertion of a purse-string suture in the anal sphincter. Also, if a rectal mass is felt such as a polyp, leiomyoma, or lipoma, it can be removed at this time by careful dissection and closure of the tissue layers. Along with replacement of the prolapsed tissues, administration of muscle relaxants, tranquilizers, antiinflam matories, and laxatives should be part of the protocol. The edematous rectal tissues and the purse-string suture lead to a high rate of obstipation, which then complicates the prolapse repair. Ensuring easy passage of feces, controlling minor pain and inflammation, and depressing sensitivity all play important roles in prevention of recurrence.27 Submucosal Resection
Should the conservative treatment fail outright, if the prolapse recurs at some future time, or if the rectal mucosa was badly damaged upon presentation, the surgical correction by submucosal resection should be opted for on Types I to III rectal prolapses. The method of submucosal resection has met with high success and is a relatively uncomplicated surgery when certain important steps are followed carefully in the preparation and surgical execution.10• 24 Either caudal epidural or general anesthesia may be utilized, largely depending upon the temperament of the animal. Multiple previous epidural anesthesias may make it more difficult to successfully repeat this type of anesthesia and, hence, may necessitate general anesthesia. After careful cleansing of the prolapsed tissues and surrounding perinea! area, two 18-gauge, 6-inch long spinal needles are inserted perpendicular to each other through the external anal sphincter to fix the prolapse in position and prevent its sliding inward as the dissection proceeds. Two circumferential incisions are made at the junctions of healthy and unhealthy mucosal layers, one at the outward apex of the prolapse and one at the anal sphincter. The plane of dissection between the damaged mucosa and submucosal layers is then carried out, with great care being taken to stay outside the muscular layer. Hemorrhage may be a slight problem during the dissection but can usually be controlled with the aid of electrocautery or ligation of the vessels. Once the dissection of the damaged layers has proceeded all around the prolapsed portion, the closure is begun. It is sometimes helpful, due to slight disparity in size of the two rings, to divide them into equal quadrants using the retention needles as landmarks. This ensures more accurate alignment of the two rings as the closure proceeds. The incised edges are apposed using size O chromic catgut in a simple interrupted pattern, burying the knots. Owing to frequent
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postoperative swelling or, possibly, to the necessity of manual evacuation of the rectum, it is not uncommon to have a few of the sutures pull loose. Slight dehiscence has not been a problem, but use of a continuous suture pattern could lead to major dehiscence and should therefore carefully be considered prior to use. The results of a major dehiscence may not be immediately evident, but with subsequent wound contracture, it could lead to rectal stricture and constipation. Type III rectal prolapses can be managed by submucosal resec tion with the additional necessity of ventral midline celiotomy if the invaginated small colon cannot be manually reduced. If there is any question or doubt about the viability of the internal portion or its return to a normal position, then early surgical exploration would allow for a more simplified correction. To delay the surgery and wait for the horse to show signs of dysfunction or necrotic internal bowel is to invite the development of more severe problems and increase the likelihood of small colon resection and anastomosis being re quired. Colostomy
Type IV rectal prolapses present with actual intussusception of variable lengths (more than 30 cm) of small colon through the anal sphincter. Some degree of vascular compromise or frank mesenteric rupture means that aggressive surgical approaches need to be initi ated early on, to preserve the possibility of resection and anasto mosis.24 If there is insufficient or considerably compromised tissue with which to perform the distal anastomosis, the colostomy, with consideration of permanent colostomy, can be performed. Some owners do not find the idea of permanent colostomy a desirable alternative; therefore, careful evaluation and open discussion need to be undertaken at the time of surgery. DYSTOCIA AND RECTAL PROLAPSE
The Type IV rectal prolapse is most eommonly associated with dystocia in the brood mare. Veterinarians that have participated in several equine dystocias will testify to the mare's intense abdominal straining and to the strong force that often accompanies each abdom inal press. If the mare becomes extremely violent or agitated, she often literally throws herself down at the same time that she puts on her abdominal press. It is at these moments that foaling attendants and veterinarians have described small colon intussuceptions or small colon vaginal prolapses as occurring. Therefore, rapid assess ment of the mare's condition and temperament, along with fetal
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manipulations and equally rapid administration of tranquilizers, muscle relaxants, and insertion of large-bore stomach tube into the trachea to prevent epiglottic closure, can all assist with the dystocia as well as prevent small colon complications due to intense straining. Although these comments might be better placed in a section on mare dystocia, their inclusion here was felt to be warranted on personal experience. Treatment of the overanxious mare should begin early, both to assist the foaling process as well as to avoid difficult sequelae; this will prevent learning about these unfortunate sequelae "the hard way. "
REFERENCES 1. Adams SB: Recognition and management of ileus. Vet Clin North Am [Equine Pract] 4:91, 1988 2. Arnold JS, Meagher DM, Lohse CL: Rectal tears in the horse. J Equine Med Surg 2:55, 1978 3. Arnold JS, Meagher DM: Management of rectal tears in the horse. J Equine Med Surg 2:64, 1978 4. Azzie MAJ: Temporary colostomy in the management of rectal tears in the horse. J S Afr Vet Assoc 46: 121, 1975 5. Brown MP: Conditions of the rectum. Vet Clin North Am [Large Anim Pract] 4: 185, 1982 6. Ducharme NG, Fubini SL: Gastrointestinal complications associated with the use of atropine in horses. J Am Vet Med Assoc 182:229, 1983 7. Embertson RM, Hodge RJ, Vachon AM: Near-circumferential rectal tear in a pony. J Am Vet Med Assoc 188:738, 1986 8. Herthel DJ : Colostomy in the mare. In Proc Am Assoc Equine Practnr 20: 187, 1974 9. Keller SD, Horney DF: Diseases of the equine small colon. Compend Contin Educ Pract Vet 7:Sl l3, 1985 10. Levine SB : Surgical treatment of recurrent rectal prolapse in a horse. J Equine Med Surg 2:228, 1978 11. Livesey MA, Keller SD: Segmental ischemic necrosis following mesocolic rupture in postparturient mares. Compend Contin Educ Pract Vet 8:763, 1986 12. Markel MD, Stover SM, Pascoe JR, et al: Evacuation of the large colon in horses. Compend Contin Educ Pract Vet 10:96, 1988 13. Markel MD: Prevention and management of peritonitis in horses. Vet Clin North Am [Equine Pract] 4: 145, 1988 14. Mcilwraith CW, Turner AS: Temporary diverting colostomy for management of rectal tears. In Mcilwraith CW, Turner AS (eds): Equine Surgery: Advanced Techniques. Philadelphia, Lea & Febiger, 1987, p 326 15. Mcilwraith CW: The acute abdominal patient. Vet Clin North Am [Large Anim Pract] 4: 167, 1982 16. Ramey DW: Healing in the small colon of the pony: Stapling vs. suturing. In Moore JN, White NA, Becht JL (eds): Equine Colic Research. Proceedings of the Second Georgia Symposium. Edition 2. Lawrenceville, New Jersey, Veterinary Learning Systems, 1986, p 166 17. Santschi EM, Grindem CB, Tate LP, et al: Peritoneal fluid analysis in ponies after abdominal surgery. Vet Surg 17:6, 1988 18. Shires GMH : Rectal tears. In Robinson NE (ed): Current Therapy in Equine Medicine. Edition 2. Philadelphia, WB Saunders, 1987, p 75 19. Spensley MS, Meagher DM, Hughes JP: Instrumentation to facilitate surgical repair of rectal tears in the horse: A preliminary report. In Proc Am Assoc Equine Practnr 553, 1985
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20. Snyder JR, Pascoe JR, Williams JW: Rectal prolapse and cystic calculus in a burro. J Am Vet Med Assoc 187:421, 1985
21. Stashak TS, Knight AP: Temporary diverting colostomy for management of small colon tears in the horse: A case report. J Equine Med Surg 2: 196, 1978 22. Stauffer VD: Equine rectal tears-A malpractice problem. J Am Vet Med Assoc 178:798,
1981 23. Taylor TS, Watkins JP, Schumacher J: Temporary indwelling rectal liner for use in horses with rectal tears. J Am Vet Med Assoc 191:677, 1987 24. Turner TA, Fessler JF: Rectal prolapse in the horse. J Am Vet Med Assoc 177: 1028, 1980
25. Turner TA: Rectal prolapse. In Robinson NE (ed): Current Therapy in Equine Medicine. Edition 2. Philadelphia, WB Saunders, 1987, p 73 26. Valdez H, Scruthfield WL: Peritoneal lavage in the horse. J Am Vet Med Assoc 175:388,
1979 27. Walker DF: Management of rectal injuries. In Walker DF, Vaughan JT (eds): Bovine and Equine Urogenital Surgery. Philadelphia, Lea & Febiger, 1980, p 217 28. Watkins JP, Taylor TS, Schumacher J: Temporary rectal liner as an aid in management
of rectal tears. In Moore JN, White NA, Becht JL (eds): Equine Colic Research. Proceedings of the Second Georgia Symposium. Edition 2. Lawrenceville, New Jersey, Veterinary Leaming Systems, 1986, p 322
Alamo Pintado Equine Medical Center P. O. Box 249 Los Olivos, CA 93441
0749----0739/89 $0.00 + .20
Management of Rectal Injuries Mark C. Rick, DVM*
RECTAL TEARS Iatrogenic injuries to the equine rectum and terminal small colon occur rarely in relation to the total number of rectal palpations performed for reproductive and other diagnostic purposes. Rectal injuries can also occur from overzealous use of enemas or from a misdirected stallion penis during natural service. Discussions and written articles concerning rectal injuries always seem to find them selves relegated to the last topics at scientific meetings and the last chapters in books. Whether this is strictly due to anatomic consid erations, or more likely, an aversion to the remote possibility that a rectal tear might befall a clinician at any time is a matter open for debate. Whatever the case may be, should a practitioner ever cause or encounter a rectal tear, several very important decisions need to be made expeditiously to maximize the health of the horse and to defuse liability considerations. Anytime there is fresh blood on a rectal sleeve or there is a sudden "feeling of release of pressure" on the arm when performing a rectal exam, immediate determination of the presence and/or extent of a rectal tear needs to be made. Also, open discussion with the owner or agent of the horse needs to be established. There is no room for casual dismissal or a "wait and see" approach for these types of injuries. To be summoned by the anxious horse owner a few hours following the suspected or known occurrence of a rectal injury to see why the mare is sweating, has a "splinted" abdomen and is uncomfortable does not demonstrate good judgment. There are many techniques currently available that offer in creased chances for survival of the horse with an injured or torn *Private Practitioner, Alamo Pintado Equine Medical Center, Los Olivos, California Veterinary Clinics of North America: Equine Practice-Vol. 5, No. 2, August 1989
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rectum if the problems are attacked forthrightly. 3-S, 7• 8• 14• 19· 21• 23• 27 Basic medical and perhaps surgical decisions need to be made within 30 minutes of the rectal injury. That is not to say that the horse needs to be immediately taken to surgery in all instances, but, following proper evaluation of the tear and discussion with the client, well-intended and well-informed approaches can be used in dealing with the problem. It may come up in the discussion with the owner or client as to who is liable and who will pay for the horse's medical expenses. These questions require careful consideration on the part of the veterinarian, since he or she is responsible for following a good standard of practice whenever performing a rectal examination. 22 If there was adequate and safe restraint of the horse, if lubricants were used to gently clear the rectum of feces, and if any rectal contractures were not overtly fought, then the veterinarian can safely feel and openly discuss that this injury was not caused by malpractice, and, hence, the care and expense should not be expected to be borne by the veterinarian. As insurance adjusters would remind us, and it so states in their written recommendations, no admission of guilt need or should be made. This holds true for all cases in which everything was done properly, following skilled and well executed procedures. If you feel otherwise at the time of the injury, then it would be up to your judgment and ethics as to the approach you would suggest to the client. When we receive horses at our medical center that have been referred for evaluation and possible repair of torn rectums, our discussions are directed entirely at the client/owner as to the course of action we propose to take. The referring veterinarian is, of course, later informed of all the diagnostics and course of treatments, but we try to be sure that he or she is removed from the decision making process. This is our attempt to establish a firm commitment on the part of the owner to be solely responsible for all decisions and financial obligations. At this point, our staff has reached a general agreement upon the way in which the rectal injury occurred, it has been or is about to be evaluated, and the owner/client �s been informed of the injury. EVALUATION
The three most important parameters, which can be immedi ately determined in most instances, are the location of the tear, its overall size, and its depth or the number of tissue layers actually penetrated. Also, the lapsed time since occurrence and diagnosis of
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the tear is very important to ascertain. Most tears, although com monly referred to as "rectal tears, " would be more correctly termed "small colon tears."9 The rectum does not enlarge to form the ampulla recti until it enters the retroperitoneal cavity, which is approximately 30 cm (12 in) farther down from the anus. Because of the presence of the pararectal fossa dorsally and the rectogenital pouch ventrally, the distance from the anus to the peritoneal cavity can actually be less than 15 cm (6 in). Most tears occur somewhere just past the pelvic inlet, which means that the majority of these tears are within the peritoneal cavity.2• 5• 9 Most tears are located dorsally and are usually of a longitudinal configuration.2• 5• 18 Possibly the tear occurs dorsally because horses will sometimes adversely react to rectal palpation and simultaneously strain and lean down. The tail often clamps down so that the arm is forced upwards and this may push the knuckles or the ultrasound probe up through the dorsal wall. To evaluate location, size, and depth of the tear, the horse should be well tranquilized and the rectum carefully evacuated. Xylazine (0.3 mg/kg intravenously [IV]) and butorphanol tartrate (0.1 mg/kg IV) combinations work extremely well to sedate and relax the horse and to allow for a safe inspection to proceed. I prefer to cut the fingers off the normal rectal sleeve and use a latex exam or surgical glove placed over the rectal sleeve. Lidocaine enemas, caudal epidural anesthesia, or probanthine (0.014 mg/kg IV) can be used to relax the rectum and facilitate fecal evacuation. In most instances, though, I have found the xylazine/butorphanol tartrate combination sufficient for a very thorough exam with the decreased risk of patient wobbliness from the epidural. The tear can sometimes be visualized with the aid of a glass or Caslick speculum; however, the rectal mucosa usually infolds around the speculum, making direct visualization difficult. Of more importance is the digital evaluation of the tear. Once the tear has been located it should be very gently felt for position, distance in from the anal sphincter, size, and, if possible, depth. Any feces in or around the tear should be very carefully removed. Liberal use of nonirritating lubricants will facili tate this part of the exam. The tear can be classified according to the layers torn: Grade I = mucosa or mucosa and submucosa; Grade 2 = muscularis only; Grade 3 = mucosa, submucosa, and muscular layer, including tears into the dorsal mesentery; Grade 4 = complete tear of the rectal wall into the abdominal cavity.2 Patient evaluation includes measuring and recording all vital signs, hematologic parameters, and rectal findings. An evaluation of the abdominal fluid also is extremely important. Peritoneal fluid changes may occur very quickly; for example, a gelding was admitted
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to the hospital for removal of a urinary calculus via a perineal urethrostomy and lithotripsy technique. The horse was sedated, had a caudal epidural, and his rectum fully evacuated. A rectal exam was performed to feel the calculus, and the rectum was inadvertently torn (Grade 3). Within 30 minutes, with no passage of feces by the tear, the peritoneal fluid had increased in amount, was cloudy yellow in color, and had a nucleated cell count in excess of 50, 000 cells/ mm. This horse underwent surgery for a primary rectal wall closure and was treated aggressively for the peritonitis. His recovery was uneventful and the cystic calculus was removed 6 months later, by a perineal approach. TREATMENT
Once the patient and the tear have been thoroughly evaluated, decisions need to be made as to the best course of action. Grade I Tears Grade 1 tears (mucosa or mucosa and submucosa) (Fig. I), are amenable to medical treatment alone or can be treated with direct suturing techniques in the standing animal using epidural anes thesia. 3· 5 These horses should be monitored very closely for 4 to 8 days and placed on a laxative type of diet such as green grass or water-soaked alfalfa pellets, combined with regular administration of mineral oil by nasogastric tube. Broad-spectrum antibiotics should be administered. Serial hemograms (complete blood count and
Figure 1. Grade 1 rectal injury, with disruption of the mucosa! layer only.
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fibrinogen) as well as peritoneal fluid analyses aid in monitoring the patient. If the horse is only slightly dehydrated, oral fluid supple mentation may be all that is necessary for adequate volume replace ment. For more severe dehydration (>8 per cent), intravenous fluid administration may be required to restore circulating volume, ensure tissue perfusion, and to prevent bowel stasis and possible colon impaction. These horses should not be palpated for at least 30 days to avoid enlargement or deeper penetration of the tear. Grade 2 Tears Grade 2 rectal tears are likely to occur only in rare circumstances in which the muscular layer tears but the more elastic mucosa and submucosa stretch without tearing (Fig. 2). These may be felt upon subsequent rectal palpations as a variable-sized diverticulum that is more accurately described as a mucosal-submucosal hernia. 2 Horses with large Grade 2 tears may present with signs of tenesmus or with rectal impactions. The hernia or diverticulum is detected after manual evacuation of the rectum. These tears are usually manageable with conservative measures such as dietary control aimed at keeping the feces soft. Grade 3 Tears Medical Management. Grade 3 tears that disrupt the mucosa, submucosa, and muscular layers (Fig. 3) dictate prompt and aggres sive medical as well as surgical intervention. 3-S, 8• 14• 18• 21• 23 The immediate concern is to prevent enlargement or perforation of the
Figure 2. Grade 2 rectal injury, demonstrating mucosal-submucosal diverticulum, which can occur when the muscular layer has been disrupted.
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Figure 3. Grade 3 rectal injury in which the mucosa, submucosa, and muscular layers have all been disrupted, leaving only the thin serosal layer intact.
tear. This is accomplished with tranquilization of the horse, manual rectal evacuation of feces, temporary meticulous packing of the torn area with an antiseptic soaked gauze pack, and possible use of epidural anesthesia, probanthine, or atropine to decrease gastroin testinal motility. The use of atropine, a parasympatholytic drug, is felt to be somewhat controversial. Indiscriminate usage of atropine has led to gastrointestinal complications. It does have the advantage of being readily available to almost all primary care practitioners, and I feel it is an excellent and safe adjunct, at the correctly specified dose, to depress intestinal motility while the horse is in transit. A single dose of 0. 044 mg/kg (20 mg for a 450-kg horse) given intramuscularly (IM) or subcutaneously (SQ) will decrease intestinal motility for up to 12 hr. Larger or repeated doses could lead to prolonged ileus with subsequent tympanic viscus distension, mild-to-moderate abdominal pain, and an elevated heart rate. 6 At the low-dose rate and following single-dose administration, the bowel stasis would only rarely be a " problem. Initiation of high levels of broad-spectrum systemic antimicro bials, tetanus toxoid inoculation, and administration of fecal laxatives such as mineral oil should also be a part of the preliminary treatment. En route to a surgical facility or shortly after arrival, IV fluids should be administered to rehydrate or overhydrate the horse in anticipation of an extensive surgical procedure and to counter the adverse hemodynamic effects of endotoxins. The technique chosen to repair the rectal injury depends largely on the location or the tear, the preference and expertise of the
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surgeon, and the availability of necessary equipment such as a rectal liner or expandable basket. Much of the following discussion of surgical options for Grade 3 tears would also apply for Grade 4 tears, in which there is total perforation into the abdominal cavity (Fig. 4). The most significant difference between Grade 3 and Grade 4 tears is the amount of direct contamination of the abdomen in Grade 4 tears put into perspective with the value of the animal, poorer prognosis, increased expense, and the likelihood of multiple post operative complications of most Grade 4 tears. Direct Closure. In certain patients that are tractable and have the rare combination of expandable or retractable rectums, minimal mucosa} and submucosal edema or necrosis, and an available surgeon with a high degree of patience and manual dexterity, the Grade 3 tears can be sutured directly (Meagher DM; personal communica tion, 1988). The surgeon must be meticulous in the closure to avoid both further damage to the edges of the tear and incorporating nearby mucosa} folds into the tear, as this would reduce the rectal diameter. Also, incomplete suturing of the tear would allow for continual packing with feces and eventual breakdown or dissection under the mucosa. Contractions of the wide muscular bands and circular smooth muscle increase the risks of dehiscience of the sutured tears. The direct suturing methods have been aided in recent years by the development of specialized surgical instruments, most notably the expandable rectal speculum or wire basket (Robert N. Roland, Davis, CA 95616) and long-handled instruments (Figs. 5 through
Figure 4. Grade 4 rectal injury, in which there has been perforation of the rectal wall, allowing access directly into the peritoneal cavity.
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Figure 5. Cut-away side view of the expandable rectal speculum in the closed position, as it is inserted into the rectum.
7). 19 Transection of the anal sphincter will allow improved exposure. Increased success with the direct suturing method has also been achieved by combining it with simultaneous ventral midline celi otomy and evacuation of the large colon via pelvic flexure enterot omy.12 This essentially decreases the ingesta that would normally pass through the rectum during the critical first 48 hours and, hence, lessens chances of impaction, mucosal dissection, or severe contam-
Figure 6. View of the expandable rectum speculum in the open position, which is used to allow visualization of and access to the rectal injury.
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Figure 7. Diagrammatic rep resentation of the expandable rec tal speculum in place, and utiliza tion of long-handled pistol-grip needle holder and auxiliary light source to directly suture a dorsally positioned Grade 3 rectal tear. The schematic in the lower left dem onstrates an idealized two-layered closure of such a tear.
ination. For instances in which the rectal tear is accessible to direct suturing, a simple continuous pattern utilizing size O or 1 absorbable suture material, with a swaged-on, taper-point, half-circle needle, incorporating all layers, is the method of choice. A recently described surgical procedure, utilizing a temporary indwelling rectal liner, has been successfully used in a number of cases. 23• 28 Ventral midline celiotomy provides adequate exterioriza tion of the small colon to situate the liner as well as allowing evacuation of the large colon, should that be deemed beneficial. An assistant not participating in the laparotomy passes the plastic rectal ring and sleeve through the anus and small colon until it can be surgically placed proximal to the tear. The plastic ring is anchored to the wall of the small colon with retention sutures, which are then oversewn so as to infold the wall. Feces that enter the ring are contained within the liner until passed through the anus. In a reported series of horses, some of which were euthanized because of complications, luminal strictures were not apparent at the site of ring attachment in the small colon. One complication described was the formation of a complete ostomy at the site of the original tear between the intestinal mucosa and peritoneal cavity, with subsequent fatal peritonitis after the ring and liner were passed (average, 9 to 12 days after implantation). 23 The liner not only protects the tear but
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also effectively limits access to the tear for any manual debridement to cleanse the edges. Direct suturing was recommended to decrease the lesion size, provide support, and decrease the likelihood of ostomy formation from intestinal mucosa to peritoneal lumen. 23 Another method of direct closure of the tear involves approach ing the injury via a ventral midline celiotomy. 5 The location of most tears, dorsally in the mesocolon or mesorectum and so far caudally, often makes exposure poor and, hence, very seriously limits visual ization. If the tear is inaccessible because of its dorsal position but is far enough cranial to be approached via a ventral midline celi otomy, a direct suture repair via an enterotomy on the antimesenteric side of the small colon may be possible. Evacuation of the contents, traction, and possibly elevation of the horse's hindquarters, or assistance by someone's hand pushing back on the rectum may all be necessary to allow access to the tear. 5 Performance of the midline celiotomy, small colon enterotomy and evacuation of feces, exposure and meticulous closure of the tear itself, and then closure of the enterotomy site all would require a good deal of time and effort. The likely necessity of evacuating the large colon as well would almost mandate that two surgical teams perform these procedures simultaneously, in order to keep the operating time at a safe limit. Accessibility to the tear would still be the key factor. If closure is not deemed possible, options still exist for other procedures such as placement of a temporary rectal liner or colostomy. Colostomy. The use of a temporary diverting colostomy, loop or end-on, for the management of rectal tears deserves lengthy discussion, owing to the inherent advantage of diverting most or all feces away from the tear. :.--s. 8• 14• 21 The loop colostomy provides some continuity to the small colon with diversion of the feces out the stoma created in the antimesenteric side of the small colon and exiting through the flank incision. The end-on colostomy, which totally diverts all feces out through a low flank incision, requires a more complicated reanastomosis after the tear has healed. The surgical technique requires general anesthesia in the ma jority of patients to allow for the abdomiQal manipulations that will be necessary. In the presence of peritooeal inflammation, the un anesthetized horse may be very reluctant and unwilling to permit the traction and manipulations necessary on the bowel. This does not preclude all standing flank surgeries, especially if a general anesthesia is not possible or poses serious health risks to the patient, but most surgeons prefer the added time and ease of tissue handling with the patient in lateral or dorsal recumbency. The end-on colostomy can be performed through one or two incisions. 4• 8• 14• 21 A routine paralumbar flank incision can be utilized to make the initial manipulations and exploration of the abdomen.
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Figure 8. Ideal position for placement of the stoma for the end on colostomy in the lower left Hank region.
The lower flank incision is then used as the exit site for the cranial small colon (Fig. 8). When dealing with an incomplete rectal tear without serious peritoneal contamination, the low flank incision alone can suffice for the bowel manipulations.8 In either case, the small colon is exteriorized in the lower flank region and readied for surgical transection. The section of small colon to be utilized should be located several feet cranial to the rectal injury. This allows adequate mobilization of the small colon from its attachment as well as the eventual and more technically difficult reattachment (Fig. 9). The caudal portion of the small colon is emptied of remaining ingesta with manual milking or by use of a tube passed forward from the
Figure 9. Preparing the two ends of the small colon for the end-on colostomy. The cranial section, depicted in the left hand, will exit the body wall at the lower stoma site, as shown in Figure 8. The distal segment on the right will be oversewn in two inverting layers and left loose within the abdominal cavity until eventual reattachment.
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Figure 10. Schematic representation of the proximal small colon being pulled through the lower flank stoma site. The mesentery of the proximal segment can be attached to the body wall if the paralumbar flank approach was utilized, but this is not necessary and not possible if the lower approach was used alone.
rectum, past the tear, until warm water can be safely flushed cranial.4 The caudal stump end is then closed with a double-row inverting pattern, utilizing size 2-0 absorbable suture material. We routinely utilize an antibiotic lavage during these and any other possibly contaminated procedures. The cranial segment is then oversewn and brought through the lower flank incision or clamped and carefully pushed through the hole, where it is firmly attached with a multiple layered closure (Figs. 10 and 11).
Figure 11. Diagrammatic rep resentation of multiple tissue layer closure and attachment of the colon at the stomal site.
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It is very important that a circular incision, slightly smaller than the small colon diameter (7 to 10 cm, average) is made through the skin, fascia, and fibrous layer of the external abdominal oblique muscle. Otherwise the stoma will not provide a large enough lumen for safe and unrestricted passage of feces. Some surgeons prefer to fold back and suture the end of the small colon into a cuff. 4• 14 This may not be necessary but does seem to lessen the submucosal hemorrhage, which will persist for several hours. We prefer to bring about 6 cm of cranial small colon out, so as to keep it away from the incision for the first day and make the deeper layers of suturing less likely to be contaminated. A row of simple interrupted sutures are utilized to attach the small colon serosa to the transverse abdominal muscle layer. A second layer of sutures, placed in simple interrupted pattern, attaches the serosa to the internal abdominal oblique mus cles. Again, with simple interrupted sutures of size O or size 1 absorbable material, the small colon is further attached to the external abdominal oblique fibrous layer. The fascia and skin are sutured to the small colon, utilizing nonabsorbable sutures in a simple interrupted pattern. Fastidious closure techniques are very important to prevent fecal contamination of the stoma site. Localized infection and later abscessation can be avoided by careful attention to closure of all dead space, by allowing for adequate size of the stoma, and by close postoperative attention to diet to avoid impaction at the surgical site. Lush green grass pasture is the ideal food source. Otherwise, water soaked alfalfa pellets and frequent administration of mineral oil will ensure soft but formed fecal consistency. The loop colostomy procedure has the advantages of greater
Figure 12. Loop colostomy procedure, demonstrating the pull through of the small colon (cranial segment at the top); attachment of the colon wall to the external abdominal oblique muscle; and the attachment of the mucosa! lining to the skin.
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ease of surgery and allowing continual access to and partial use of the distal segment. This can aid in the prevention of atrophy of the distal segment. The possible passage of feces through the distal segment could, of course, be a major disadvantage as well. The surgical approach utilizes the standard left paralumbar flank grid and then exteriorizes the small colon. The colon is situated so that the cranial segment is attached at the top of the flank incision. 5 • 18 A loop of intestine with the antimesenteric surface pointed outward, ap proximately 8-cm long, is then sutured to the edges of the external abdominal oblique muscle and fascia, with size 0 absorbable suture, in a simple interrupted pattern. A 6-cm incision is then made through the antimesenteric band into the lumen, and the mucosa! lining is sutured to the skin using size 2-0 nonabsorbable suture in a simple interrupted pattern (Fig. 12). POSTOPERATIVE MANAGEMENT
For either of the two colostomy methods, intensive postopera tive management is crucial, time consuming, and expensive. The horse should be maintained on high levels of broad-spectrum anti biotics. We routinely use potassium penicillin G (40, 000 U/kg IV QID) and gentamicin sulfate (2. 2 mg/kg IV TID or QID). Also nonsteroidal antiinflammatories, preferably flunixin meglumine (0. 25 mg/kg IV or IM QID) and dietary management are integral to the successful management of these patients. Low-dose heparin admin istration (15, 000 to 30, 000 IU IV or SQ QID) may aid in preventing adhesion formation and is part of our protocol. Ileus
The horse with a Grade 3 rectal injury is the perfect candidate for rapid development of postoperative ileus. Perhaps atropine, a parasympatholytic drug, was administered to prevent passage of feces through the tear. There will likely be some degree of perito nitis, both from the tear itself and from surgical manipulations. And there will be slight anesthetic depre�ion of bowel motility as well. This deleterious triad could easily lead to severe, possibly irreversi ble, ileus. Naturally the effects of the atropine and anesthetic will subside with time. The peritonitis can be dealt with using appropriate antibiotics and peritoneal drainage and/or lavage. I strongly contend that neostigmine, used early in the course of the disease, plays an integral role in preventing ileus and decreasing patient morbidity and mortality. The risk of anastomotic dehiscence has not been a problem. Neostigmine methylsulfate is administered intravenously via a slow-drip system (Travenol Infusor, Deerfield,
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IL, 60015) of 2 ml per hour (0. 01 mg/kg/hour) connected to the IV catheter. If the horse shows mild discomfort, the neostigmine is further diluted. Only when the horse shows no tolerance for the intestinal stimulation do we discontinue its administration altogether. The horse is maintained on the infusion of neostigmine for the first 48 to 96 hours postoperatively. Neostigmine, which is felt to pri marily enhance propulsive motility of the large colon, and metoclo promide, which enhances gastroduodenal motor activity, may be used separately or in combination to prevent or treat ileus 1 (see Gerring). Waiting for the bowel to become severely distended or for other metabolic problems to arise definitely decreases the intestinal motility enhancement and the survival of the patient. Correcting all electrolyte disturbances, walking the horse hourly, feeding a diet of lush green grass, administration of analgesics, and control of perito nitis all play equally critical roles in minimizing occurrence of ileus. 1 Edema and Inflammation Often the colostomy site becomes edematous within the first 24 hours after surgery. This may necessitate careful administration of warm water enemas to keep the lumen open and to prevent impaction and patient discomfort. Later, if a local abscess should develop at the stoma, it is important that it be aggressively treated by drainage and lavage so as to allow for tissue healing in time for the reanastomosis. If peritoneal fluid analysis indicates the presence of severe inflammation or possible sepsis, then peritoneal lavage is begun. Serial peritoneal fluid nucleated cell counts and cytological exams assist in making the distinction between normal postoperative inflam matory changes versus more severe changes. 17 If the patient is febrile, depressed, anorectic, has ileus and also has increased quan tities of abdominal fluid with a nucleated count above 150, 000 cells per mm, 3 high protein, and presence of bacteria, then serious attention to the treatment of the peritonitis must begin. Often, at the time of surgery, the surgeon can determine the need for peritoneal lavage, and a drain or drains can be inserted at that time. Several methods for peritoneal lavage have been described. 13• 26 I prefer the use of a large-bore (30 F) mushroom or urological catheter placed through the linea alba in the cranial abdomen. Using large volumes (3 to 10 L) of warmed isotonic saline or lactated Ringer's solution, flushed in a retrograde fashion through the drain over a 1-hour period and then allowed to drain back out, has given good results without the need for a separate ingress portal. After a few days, the return flow may become hampered, as the omentum or fibrin clots seal the openings of the catheter. A sterile infusion pipette or Chambers catheter can sometimes dislodge these obstruc-
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tions and allow for adequate outflow. After insertion of the lavage solutions, the horse can be walked or hand-grazed for a period of time. At no time is the horse to be left unattended while the catheter remains open, so as to avoid accidental soilage of the end. The catheters are sealed with a 3-ml syringe and firmly taped to the horse's body wall with encircling elastic wrap before leaving the horse unattended. Assessment of Healing
Assessment of healing of a rectal tear is very important. If the tear was not sutured, it may require periodic cleaning and delicate debridement with gauze sponges to hasten the healing process and prevent formation of an abscess, a permanent ostomy, a diverticulum, or a rectal stricture. The uncomplicated Grade 3 tear can be expected to heal within 2 to 4 weeks. Several months have elapsed before some colostomies have been reanastomosed, but, generally, the earlier it is attempted the easier it is to rejoin the bowel. Avoidance of extreme atrophy of the caudal segment and maturation of adhesions are two reasons to attempt early reanastomosis. Reanastomosis
It seems that many times the horse is just getting over the critical part of after-care, returning to a positive metabolic state, and getting the few localized stomal problems under control when one is looking at another long and difficult surgery and its associated problems. This is not the time to put off the surgery for a few more days if everything is deemed ready.4 A day before the reanastomosis of the small colon the horse is held off feed. Twelve hours prior to surgery the horse is given 1 gallon of mineral oil via nasogastric tube. The surgical approach for the reanastomosis of the end-on colostomy is usually the ventral midline celiotomy. The advantages to this approach are adequate assessment and breakdown of adhesions from the tear or colostomy and adequate room to manipulate the two small colon segments for the anastomosis and for emptying of the large colon, should it be necessapY. Prior to anesthetizing the horse, the stoma is prepared in an aseptic manner, and the small colon is packed with Betadine-soaked cotton. If there is evidence of infection or an abscess around the stoma, the small colon is transected and oversewn within the abdomen, and the stomal and short segment of small colon are dealt with separately. This eliminates the possibility of peritoneal soilage from the abscess site. The proximal segment and distal segment are transected a few centimeters from their ends. An end-to-end hand-sewn anastomosis is performed, using a simple interrupted pattern, crushing technique, with size 2-0 absorbable
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suture material (chromic gut) followed by a continuous inverting pattern with size 3-0 absorbable suture material. 16 The mesentery is closed in a simple continuous pattern, using size O absorbable suture material. Routine closure of the abdominal incision is per formed. The horse is then rotated into lateral recumbency and the stoma and possibly short segment of small colon are handled separately. After removal of the remaining small colon portion and minimal debridement of the edges, the transverse and internal abdominal oblique muscle layers are closed in a simple interrupted pattern. The ring left in the external abdominal oblique fibrous layer is closed with size 2 or 3 absorbable suture material in a simple interrupted pattern. External fascia and subcutaneous tissues layers are apposed. A penrose drain may be inserted between the fascia and the skin in the likely event of postsurgical seroma or sepsis. The skin is closed with nonabsorbable suture material in a vertical mattress pattern. The method of closure for the loop colostomy essentially involves the reverse of the creation of the stoma. The attachments to the skin and the external abdominal oblique muscle are carefully dissected free from the edge of the small colon. If the small colon is felt to be excessively traumatized in this dissection, a short segment should be brought out of the incision and an end-to-end resection and anastomosis performed. Otherwise, the antimesenteric band is closed with double-inverting layers, utilizing 2-0 absorbable suture mate rial, and vigorously cleansed and replaced in the abdomen. The flank incision is then closed in a routine manner. Peristomal herniation, abscessation, or dehiscence are the most frequently described problems with the end-on colostomy. These problems can be avoided with careful selection of the site, low enough in the flank to allow for unrestricted fecal passage yet not so low as to invite bowel herniation. Also, careful multiple-layered closure of the tissues decreases the dead space and prevents stomal infection. Broodmares that are left with permanent colostomies present special problems in advanced pregnancy and during parturition. Unusual pressures are placed against the stomal site, and increased likelihood for herniation exists. RECTAL PROLAPSE The occurrence of rectal prolapse in horses is rare, when one considers the overall incidence of alimentary tract diseases in this species. Other large species, cattle and pigs for instance, have a much higher incidence of rectal prolapse in comparison with that in
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horses. Any condition that causes protracted tenesmus can lead to the development of a prolapsed rectum. Causes would include such conditions as diarrhea, intestinal parasitism, urinary obstructions, dystocia, Grade 2 rectal tears, constipation, or neoplastic diseases of the rectum.5• 9 • 20 • 24 • 25
EVALUATION
Rectal prolapses have been divided into four main classifications, from Type I to Type IV, with each higher designation corresponding to increasingly more involved tissues and structures, a more involved repair, and a somewhat worsened prognosis. A Type I rectal prolap se is a protrusion of the rectal mucosa and submucosa only. This is the most common type of rectal prolapse and usually presents as a large, doughnut-shaped swelling at the anus. The Type II prolap se involves all or part of the ampu lla recti and usually differs from the Type I in that it is larger and more cylindrical in appearance. The Type III prolap se appears similar to the Type II until palpated and it is determined that part of the small colon has invaginated into the rectum, which results in a much firmer and thicker-feeling prolapse than the Type II. The T ype IV prolapse is an actual intussusception of the peritoneal rectum and/or small colon through the anus. In the Type IV prolapse there is a "trench" between the prolapse and the anus that can be easily felt with a finger sliding in past what would normally be the mucocutaneous junction. An initial concern when dealing with a rectal prolapse is to determine the primary cause of the tenesmus, concurrently treating that condition as well as addressing the prolapse itself. Careful attention to the patient's history is very important as it may aid in determining the underlying cause of the tenesmus, which might not be readily apparent. The clinical exam is also very important, and the condition of the prolapsed tissues will determine whether con servative or surgical methods will be necessary.
TREATMENT
Conservative measures, commonly employed in Types I and II rectal prolapses, are most successful if initiated soon after the prolapse occurs.5 • 25 Severely edematous or necrotic rectal mucosa necessitate surgical correction to achieve satisfactory long-term re sults. The conservative therapy usually entails reduction of mucosal edema with the application of topical demulcents, of which glycerin
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is the most commonly used. Caudal epidural anesthesia provides cessation of straining and allows for gentle replacement of the prolapsed tissues and insertion of a purse-string suture in the anal sphincter. Also, if a rectal mass is felt such as a polyp, leiomyoma, or lipoma, it can be removed at this time by careful dissection and closure of the tissue layers. Along with replacement of the prolapsed tissues, administration of muscle relaxants, tranquilizers, antiinflam matories, and laxatives should be part of the protocol. The edematous rectal tissues and the purse-string suture lead to a high rate of obstipation, which then complicates the prolapse repair. Ensuring easy passage of feces, controlling minor pain and inflammation, and depressing sensitivity all play important roles in prevention of recurrence.27 Submucosal Resection
Should the conservative treatment fail outright, if the prolapse recurs at some future time, or if the rectal mucosa was badly damaged upon presentation, the surgical correction by submucosal resection should be opted for on Types I to III rectal prolapses. The method of submucosal resection has met with high success and is a relatively uncomplicated surgery when certain important steps are followed carefully in the preparation and surgical execution.10• 24 Either caudal epidural or general anesthesia may be utilized, largely depending upon the temperament of the animal. Multiple previous epidural anesthesias may make it more difficult to successfully repeat this type of anesthesia and, hence, may necessitate general anesthesia. After careful cleansing of the prolapsed tissues and surrounding perinea! area, two 18-gauge, 6-inch long spinal needles are inserted perpendicular to each other through the external anal sphincter to fix the prolapse in position and prevent its sliding inward as the dissection proceeds. Two circumferential incisions are made at the junctions of healthy and unhealthy mucosal layers, one at the outward apex of the prolapse and one at the anal sphincter. The plane of dissection between the damaged mucosa and submucosal layers is then carried out, with great care being taken to stay outside the muscular layer. Hemorrhage may be a slight problem during the dissection but can usually be controlled with the aid of electrocautery or ligation of the vessels. Once the dissection of the damaged layers has proceeded all around the prolapsed portion, the closure is begun. It is sometimes helpful, due to slight disparity in size of the two rings, to divide them into equal quadrants using the retention needles as landmarks. This ensures more accurate alignment of the two rings as the closure proceeds. The incised edges are apposed using size O chromic catgut in a simple interrupted pattern, burying the knots. Owing to frequent
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postoperative swelling or, possibly, to the necessity of manual evacuation of the rectum, it is not uncommon to have a few of the sutures pull loose. Slight dehiscence has not been a problem, but use of a continuous suture pattern could lead to major dehiscence and should therefore carefully be considered prior to use. The results of a major dehiscence may not be immediately evident, but with subsequent wound contracture, it could lead to rectal stricture and constipation. Type III rectal prolapses can be managed by submucosal resec tion with the additional necessity of ventral midline celiotomy if the invaginated small colon cannot be manually reduced. If there is any question or doubt about the viability of the internal portion or its return to a normal position, then early surgical exploration would allow for a more simplified correction. To delay the surgery and wait for the horse to show signs of dysfunction or necrotic internal bowel is to invite the development of more severe problems and increase the likelihood of small colon resection and anastomosis being re quired. Colostomy
Type IV rectal prolapses present with actual intussusception of variable lengths (more than 30 cm) of small colon through the anal sphincter. Some degree of vascular compromise or frank mesenteric rupture means that aggressive surgical approaches need to be initi ated early on, to preserve the possibility of resection and anasto mosis.24 If there is insufficient or considerably compromised tissue with which to perform the distal anastomosis, the colostomy, with consideration of permanent colostomy, can be performed. Some owners do not find the idea of permanent colostomy a desirable alternative; therefore, careful evaluation and open discussion need to be undertaken at the time of surgery. DYSTOCIA AND RECTAL PROLAPSE
The Type IV rectal prolapse is most eommonly associated with dystocia in the brood mare. Veterinarians that have participated in several equine dystocias will testify to the mare's intense abdominal straining and to the strong force that often accompanies each abdom inal press. If the mare becomes extremely violent or agitated, she often literally throws herself down at the same time that she puts on her abdominal press. It is at these moments that foaling attendants and veterinarians have described small colon intussuceptions or small colon vaginal prolapses as occurring. Therefore, rapid assess ment of the mare's condition and temperament, along with fetal
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manipulations and equally rapid administration of tranquilizers, muscle relaxants, and insertion of large-bore stomach tube into the trachea to prevent epiglottic closure, can all assist with the dystocia as well as prevent small colon complications due to intense straining. Although these comments might be better placed in a section on mare dystocia, their inclusion here was felt to be warranted on personal experience. Treatment of the overanxious mare should begin early, both to assist the foaling process as well as to avoid difficult sequelae; this will prevent learning about these unfortunate sequelae "the hard way. "
REFERENCES 1. Adams SB: Recognition and management of ileus. Vet Clin North Am [Equine Pract] 4:91, 1988 2. Arnold JS, Meagher DM, Lohse CL: Rectal tears in the horse. J Equine Med Surg 2:55, 1978 3. Arnold JS, Meagher DM: Management of rectal tears in the horse. J Equine Med Surg 2:64, 1978 4. Azzie MAJ: Temporary colostomy in the management of rectal tears in the horse. J S Afr Vet Assoc 46: 121, 1975 5. Brown MP: Conditions of the rectum. Vet Clin North Am [Large Anim Pract] 4: 185, 1982 6. Ducharme NG, Fubini SL: Gastrointestinal complications associated with the use of atropine in horses. J Am Vet Med Assoc 182:229, 1983 7. Embertson RM, Hodge RJ, Vachon AM: Near-circumferential rectal tear in a pony. J Am Vet Med Assoc 188:738, 1986 8. Herthel DJ : Colostomy in the mare. In Proc Am Assoc Equine Practnr 20: 187, 1974 9. Keller SD, Horney DF: Diseases of the equine small colon. Compend Contin Educ Pract Vet 7:Sl l3, 1985 10. Levine SB : Surgical treatment of recurrent rectal prolapse in a horse. J Equine Med Surg 2:228, 1978 11. Livesey MA, Keller SD: Segmental ischemic necrosis following mesocolic rupture in postparturient mares. Compend Contin Educ Pract Vet 8:763, 1986 12. Markel MD, Stover SM, Pascoe JR, et al: Evacuation of the large colon in horses. Compend Contin Educ Pract Vet 10:96, 1988 13. Markel MD: Prevention and management of peritonitis in horses. Vet Clin North Am [Equine Pract] 4: 145, 1988 14. Mcilwraith CW, Turner AS: Temporary diverting colostomy for management of rectal tears. In Mcilwraith CW, Turner AS (eds): Equine Surgery: Advanced Techniques. Philadelphia, Lea & Febiger, 1987, p 326 15. Mcilwraith CW: The acute abdominal patient. Vet Clin North Am [Large Anim Pract] 4: 167, 1982 16. Ramey DW: Healing in the small colon of the pony: Stapling vs. suturing. In Moore JN, White NA, Becht JL (eds): Equine Colic Research. Proceedings of the Second Georgia Symposium. Edition 2. Lawrenceville, New Jersey, Veterinary Learning Systems, 1986, p 166 17. Santschi EM, Grindem CB, Tate LP, et al: Peritoneal fluid analysis in ponies after abdominal surgery. Vet Surg 17:6, 1988 18. Shires GMH : Rectal tears. In Robinson NE (ed): Current Therapy in Equine Medicine. Edition 2. Philadelphia, WB Saunders, 1987, p 75 19. Spensley MS, Meagher DM, Hughes JP: Instrumentation to facilitate surgical repair of rectal tears in the horse: A preliminary report. In Proc Am Assoc Equine Practnr 553, 1985
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20. Snyder JR, Pascoe JR, Williams JW: Rectal prolapse and cystic calculus in a burro. J Am Vet Med Assoc 187:421, 1985
21. Stashak TS, Knight AP: Temporary diverting colostomy for management of small colon tears in the horse: A case report. J Equine Med Surg 2: 196, 1978 22. Stauffer VD: Equine rectal tears-A malpractice problem. J Am Vet Med Assoc 178:798,
1981 23. Taylor TS, Watkins JP, Schumacher J: Temporary indwelling rectal liner for use in horses with rectal tears. J Am Vet Med Assoc 191:677, 1987 24. Turner TA, Fessler JF: Rectal prolapse in the horse. J Am Vet Med Assoc 177: 1028, 1980
25. Turner TA: Rectal prolapse. In Robinson NE (ed): Current Therapy in Equine Medicine. Edition 2. Philadelphia, WB Saunders, 1987, p 73 26. Valdez H, Scruthfield WL: Peritoneal lavage in the horse. J Am Vet Med Assoc 175:388,
1979 27. Walker DF: Management of rectal injuries. In Walker DF, Vaughan JT (eds): Bovine and Equine Urogenital Surgery. Philadelphia, Lea & Febiger, 1980, p 217 28. Watkins JP, Taylor TS, Schumacher J: Temporary rectal liner as an aid in management
of rectal tears. In Moore JN, White NA, Becht JL (eds): Equine Colic Research. Proceedings of the Second Georgia Symposium. Edition 2. Lawrenceville, New Jersey, Veterinary Leaming Systems, 1986, p 322
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