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Nonsurgical Management of Canine Obstructive Urolithopathy
Canine Urolithiasis II
Nonsurgical Management of Canine Obstructive U rol ithopathy
Carl A. Osborne, D.V.M., Ph.D.,* and David]. Polzin, D.V.M., Ph.D.t "There are some patients whom we cannot help, there are none whom we cannot harm." A. L. BLOOMFIELD
INDICATIONS Obstruction of the Upper Urinary Tract Obstruction to urine outflow may cause varying degrees of damage to the upper urinary tract. For example, persistent obstruction of the urethra or both ureters of a patient with previously normal renal function will cause death within a few. days. Therefore, re-establishment of urine outflow should receive emergency priority. Likewise, unilateral ureteral or renal pelvic obstruction caused by uroliths may rapidly (within a few days) lead to acute generalized pyelonephritis, septicemia, and possibly death. Prolonged persistent obstruction of one ureter in the absence of infection is usually not an immediate threat to life, but it will cause progressive and irreversible destruction of the associated kidney. Results of experimental and clinical studies underscore the fact that varying degrees of recovery of renal function may occur following elimination of the cause of obstruction. For example, in one study of dogs with unilateral renal obstruction of 2, 4, or 6 weeks' duration, there was 38.7 per cent recovery of renal function after 2 weeks of obstruction, 9.8 per cent recovery after 4 weeks of obstruction and 2 per cent after 6 weeks of obstruction. 14 In another study in dogs, glomerular filtration rate (GFR) returned to 68 per cent of normal values following 7 days of complete unilateral ureteral obstruction. 15 *Diplomate, American College of Veterinary Internal Medicine; Professor, Department of Small Animal Clinical Sciences, University of Minnesota College of Veterinary Medicine, St. Paul, Minnesota tDiplomate, American College of Veterinary Internal Medicine; Assistant Professor, Department of Small Animal Clinical Sciences, University of Minnesota College of Veterinary Medicine, St. Paul, Minnesota Veterinary Clinics of North America: Small Animal Practice-Val. 16, No. 2, March 1986
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Sequential studies in dogs with unilateral ureteral obstruction revealed that recovery of renal function is inversely proportional to the duration of obstruction. 16 After 28 days of complete unilateral obstruction, GFR was only 22 per cent of preobstruction GFR. However, after contralateral nephrectomy, GFR in the previously obstructed kidneys increased to 95 to 114 per cent of control values. It is obvious that, in absence of infection, kidneys have a remarkable ability to recover function after relatively long periods of obstruction. Increased renal function after contralateral nephrectomy is also noteworthy. Results of these studies are of great clinical significance. They prevent adoption of an overly pessimistic view about recovery of renal function following correction of obstruction. In the absence of conclusive evidence of irreversibility, efforts to decompress the urinary tract and to eliminate the cause(s) of obstruction should be considered, because at least partial restoration of renal function is likely. Obstruction of the Lower Urinary Tract Partial or complete obstruction of the urethra may result in severe or chronic distension of the urinary bladder. Over-stretching of the bladder wall may damage "tight junctions" between smooth muscle fibers of the detrusor muscle, causing impaired conduction of the motor nerve impulses and a weak or ineffectual detrusor reflex. Damage to sensory nerve endings may also contribute to a poor detrusor reflex. Following removal of urethroliths, the urinary bladder may be hypotonic or atonic, resulting in further urine retention, overflow incontinence, and urinary tract infection. However, if the duration of overdistention is short and the bladder lumen is }s.ept relatively empty for l to 2 weeks by intermittent catheterization or use of a closed indwelling urinary catheter drainage system, damage to the bladder is usually reversible. As bladder function begins to return, the strength of detrusor contraction may be enhanced by administration of bethanecol at a dosage of 5 to 25 mg given orally every 8 hours in dogs, or 2.5 to 5.0 mg given orally every 8 hours in cats. 26 Follow-up Therapy Nonsurgical and percutaneous techniques have been developed to reestablish complete patency of the urinary outflow tract by displacing or bypassing uroliths. In some situations, nonsurgical methods may result in removal of the urolith(s). However, follow-up medical and/or surgical therapy is usually required (see the articles about medical dissolution of uroliths and "Surgical Removal of Canine Uroliths"). NONSURGICAL MANAGEMENT OF UROLITHS IN THE URETHRA AND/OR BLADDER NECK Cystocentesis If obstruction to urine outflow causes overdistention of the urinary bladder, it may be decompressed by cystocentesis. 24 • 25 Timing of Procedure. Because solutions used to flush the urethral
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lumen may alter the composition of urine in the bladder lumen and, therefore, alter results of diagnostic tests (urinalyses, urine culture, and so on), serious consideration should be given to collection of a urine sample by cystocentesis prior to the attempt to restore urethral patency with reverse flushing solutions. This strategy has advantages and disadvantages. In addition to preserving the diagnostic values of a urine sample, simultaneous decompression of an overdistended urinary bladder by removing most (but not all) of the urine provides a mechanism to temporarily halt the continued adverse effects of obstructive uropathy, irrespective of cause. This may provide additional time to remove or bypass the obstructive urethral lesion without further deterioration of renal function. It may also decrease intraluminal pressure at the proximal site of urethal obstruction, which in turn may facilitate repulsion of uroliths into the bladder lumen. In addition, the gross character of aspirated urine may provide valuable clues about the nature of the obstructive disorder. The following are potential disadvantages of the procedure: (1) it may result in extravasation of urine into the bladder wall and/or peritoneal cavity, and (2) it may injure the bladder wall or surrounding structures. Although these complications could be severe in patients with a devitalized bladder wall, in our experience this has been the exception rather than the rule if the majority of the urine is removed from the bladder. Loss of a small quantity of urine into the peritoneal cavity is usually of little consequence, especially if it does not contain pathogens. The potential of trauma to the bladder and adjacent structures can be avoided by good technique. We are not advocating an "always or never" recommendation regarding diagnostic and therapeutic cystocentesis. Clinical judgment is required regarding its use in each patient. However, it is preferable to decompress the urinary bladder by cystocentesis (saving an aliquot for appropriate diagnostic tests) prior to use of reverse flushing procedures in patients that are (1) likely to have adequate integrity of the bladder wall (that is, they do not have an atonic detrussor muscle), and (2) in which immediate overdistention of the bladder lumen is not allowed to recur. Equipment. We routinely use 22-gauge needles. Depending on the size of the patient and the distance of the ventral bladder wall from the ventral abdominal wall, 1.5-inch hypodermic or 3-inch spinal needles* may be selected. We usually use large-capacity (20 to 60 ml) syringes for therapeutic cystocentesis. Alternately, therapeutic cystocentesis may be performed with 6- to 12-ml syringes and a two-way or three-way valve. t If desirable, a 22gauge needle may be transected midway between its tip and hub and reconnected with a section of flexible polyethylene tubing. :j: Site. We recommend that the needle be inserted through the ventral or ventrolateral wall of the bladder in order to minimize the chance of trauma to the ureters and major abdominal vessels (Fig. 1). 24 The needle should be inserted close to the junction of the bladder with the urethra rather than at the vertex of the bladder (see Fig. 1). This will permit *Yale Spinal Needle. Becton-Dickinson Co., Rutherford, New Jersey. tPharmaseal Inc., Toa Alto, Puerto Rico. :j:PE 60., Clay Adams Inc., Parsippany, New Jersey.
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Fig~re 1. Schematic drawing illustrating correct and incorrect sites of insertion of a needle into the bladder for the purpose of evacuating most of the urine from within its lumen. The needle should be inserted in the ventral or ventrolateral surface of the wall a short distance cranial to the junction of the bladder and urethra rather than at the vertex of the bladder. This will permit removal of urine and decompression of the bladder without need for reinsertion of the needle into the bladder lumen. (Medical illustration by Michael P. Schenk, University of Minnesota College of Veterinary Medicine, St. Paul, Minnesota. )
removal of urine and decompression of the bladder without reqmnng reinsertion of the needle into the bladder lumen. If the needle is placed in or adjacent to the vertex of the bladder, it may not remain within the bladder lumen because the bladder progressively decreases in size following aspiration of urine. · · We also recommend that the needle be directed through the bladder wall at approximately a 45° angle so that an oblique needle tract will be created (see Fig. 1). By directing the needle through the bladder wall in an oblique fashion, the elasticity of the vesical musculature and the interlacing arrangement of individual muscle fibers will provide a better seal for the small pathway created by the needle when it is removed. In addition, subsequent distention of the bladder wall as the lumen refills with urine will tend to force the walls of the needle tract into apposition in a fashion somewhat analogous to the flap valve of the ureterovesical junction. Procedure. The ventral abdominal skin penetrated by the needle should be cleansed with an antiseptic solution each time cystocentesis is performed. Excessive hair should be removed with a clipper if necessary. We usually drench the area with alcohol. Appropriate caution should be used to avoid iatrogenic trauma to, or infection of, the urinary bladder and surrounding structures. It is usually easiest to perform the proced1.1re with the patient in lateral or dorsal recumbency. Because insertion and withdrawal of a 22-gauge needle through the walls of the abdomen and bladder are associated with little discomfort, general or local anesthesia is usually unnecessary.
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Following localization and immobilization of the urinary bladder, the needle should be inserted through the ventral abdominal wall and advanced to the caudoventral aspect of the bladder. The needle should be inserted through the bladder wall at an oblique angle and directed so that it will enter the bladder lume n cranial to the junction of the bladder with the urethra. E xcessive digital pressure should not be applied to the bladder wall while the needle is in its lumen. 24 This will prevent urine from being forced around the needle into the peritoneal cavity (Fig. 2). Appropriate caution should be used to prevent laceration of the bladder as a result of careless movement of the needle. The bladder should be emptied as completely as is consistent with atraumatic technique. It is undesirable to attempt complete evacuation of the bladde r lumen because this will allow the sharp point of the needle to damage the bladder wall. The need for prophylactic antibacterial therapy following cystocentesis must be determined on the basis of the status of the patient and retrospective evaluation of technique. If it is probable that the dog has urinary tract infection or if subsequent restoration of urethral patency requires intermittent or indwelling catheterization, antimicrobial therapy should be considered. Palpation
Unidirectional massage of a urethral urolith with a finge r inserted into the vagina or rectum of female dogs has frequently been effective in
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Figure 2. Schematic illustration of urine escaping through bladder wall as a result of excessive digital pressure used to localize and immob ilize th e bladder . (S = skin of abdominal wall; B = wall of urinary bladder. )
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Figure 3. Survey lateral abdominal radiograph of a 5-year-old spayed female Miniature Schnauzer with obstruction of the proximal urethra and distal ureters caused by a large struvite/calcium apatite urocystolith. The urocystolith was dislodged following lubrication and digital palpation through the abdomen.
dislodging urethral uroliths. Likewise, manipulation of a urolith lodged in the neck of the bladder and proximal urethra by palpation per abdomen will usually result in restoration of urine outflow (Fig. 3). Prior to palpation, a liberal quantity of l:l mixture of sterilized physiologic saline solution (or a comparable nonirritating physiologic solution) and aqueous lubricant should be injected through a catheter into the urethral lumen adjacent to the urolith. This maneuver helps to lubricate the urolith(s) and the urethrq) mucosa, which is often inflamed and swollen. We recommend that this mixture be prepared by connecting the tips of two large-capacity syringes, one partially filled with an aqueous lubricant and the other partially filled with saline solution, using a three-way valve. Injection of these materials back and forth between the syringes will allow rapid mixing without loss of sterility (Fig. 4). Aqueous lubricants should not be injected into the urinary tract of patients known to have tears in the wall of the urethra or urinary bladder, because lubricants have been implicated in the formation of periurethral granulomas in human beings30 and rabbits . 3 U rohydropropulsion
U roliths lodged in the urethra of male and female dogs may be moved back into the lumen of the urinary bladder by urohydropropulsion. 23 • 27 The technique is based on dilatation of a portion of the urethra with fluid under pressure. Restraint and Anesthesia. The disposition of the patient may warrant sedation or general anesthesia. Pharmacologic agents dependent on renal metabolism or excretion for inactivation and elimination from the body should be avoided. If an uncooperative patient is an anesthetic risk because of a uremic crisis, topical application of lidocaine gel to the urethral mucosa in combination with parenteral administration of a low dose of analgesic may provide adequate patient restraint. General anesthesia should be used if uroliths cannot be removed from the urethra of nonanesthetized patients by urohydropropulsion. We have
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Figure 4. Schematic diagram illustrating technique to mix sterilized aqueous lubricant (L) with physiologic saline solution (S) in two syringes connected by a three-way valve . (From Osborne, C. A. , et aL: Nonsurgical removal ofuroliths from the urethra of female dogs. J. Am. Vet. Med. Assoc., 182:47-50, 1983; with permission.)
not had any patients in which urethral uroliths could not be removed by this technique while under general anesthesia. Appropriate caution should be used since patients in renal failure are more sensitive to general anesthesia than normal patients. Short-acting barbiturates (thiamylal) may be used, because they are inactivated primarily by the liver. Inhalant anesthetics such as halothane may also be considered because they are not dependent on the kic,lneys for inactivation and excretion from the body. Male Dogs
To remove uroliths by urohydropropulsion, follow this procedure:27 (1) Inject a libe ral quantity of a 1:1 mixture of sterilized saline solution and aqueous lubricant through a flexible catheter into the urethral lumen adjacent to the uroliths (consult the section on palpation). (2) Next, an assistant should insert an index finger into the rectum and firmly occlude the lumen of the pelvic urethra by applying digital pressure against the ischium through the ventral wall of the rectum (Fig. 5). (3) A bovine teat cannula (or suitable facsimile) with an attached 35- to 60-ml syringe filled with sterilized saline should then be inserted into the lumen of the penile urethra via the external urethral orifice. The penile urethra should be compressed around the shaft of the teat cannula by digital pressure . As a result of these maneuvers, a portion of the urethra from the external urethral orifice to the bony pelvis becomes a closed system . (4) Saline should be injected into the urethra until a marked increase in the diameter of the pelvic urethra is perceived by the assistant (see Fig. 5). Confirmation that the urethra has been markedly distended is of great importance, because diste ntion of the urethra to its maximum capacity must be achieved before a sufficient degree of pressure can be created within the urethral
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lumen to advance the uroliths. At this point, the lumen of all portions of the isolated urethra, except that located in the ventral groove of the os penis, will be markedly dilated (see Fig. 5). Dilation of the lumen of the segment of the urethra located in the ventral groove of the os penis is limited to that caused by stre tching of the ventral portion of the urethral wall (see Fig. 5). (5) At this point in the manuever, the teat cannula should be removed rapidly from the distal urethra. Simultaneously, digital pressure applied to the distal penile urethra should be released rapidly in order to permit forceful expulsion of saline out of the urethra (see Fig. 5). Digital pressure applied to the pelvic urethra must be maintained. If the uroliths are small enough to pass through the distended portion of the urethra located in the ventral groove of the os penis, they will be carried with the fluid toward the external urethral orifice. It is usually necessary to repeat the procedure several times to move the urolith(s) from the caudal end of the os penis to the external urethral orifice . The movement of uroliths
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Figure 5. Re moval of urethrolith in a male dog by urohydropropulsion. (1) Urethrolith originating from the urinary bladder has lodged behind the os penis. (2) Dilation of the urethral lume n by injecting fluid with pressure. Digital pressure applied to the external urethral orifice and the pelvic urethra has created a closed system. (3) Sudden release of digital pressure at the external m ethral orifice and subsequent movement of fluid and urethroliths toward the external ure thral orifice. (4) Sudde n release of digital pressure at the pelvic urethra and subsequent movement of fluid and urethrolith toward the urinary bladder. (From Piermattei, D . L. , and Osborne, C. A. : Urohydropropulsion: Nonsurgical removal of urethral calculi in male dogs. In Kirk, R. W. (ed.): Current Veterinary Therapy. Volume 6. Philadelphia, W. B. Saunders Co., 1977, pp. 1195-1196.)
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within the urethral lumen may be monitored with the aid of a urethral catheter or, if necessary, by means of radiography. If the urethroliths are too large to pass through the ventral groove of the os penis, the procedure should be modified. Instead of releasing digital pressure applied to the distal portion of the urethra, digital pressure applied to the pelvic urethra should be rapidly released (see Fig. 5). Pressure should be maintained in the urethral lumen by forcing the syringe plunger forward until the assistant has released digital pressure applied through the rectal wall. This variation in technique forcibly advances fluid, and usually urethroliths, into the urinary bladder (see Fig. 5). On occasion, the urolith may suddenly become free from adjacent tissues and rapidly return to the bladder lumen. However, as was the situation with the antegrade flush, it may be necessary to repeat the procedure several times before the uroliths reach the urinary bladder. The position of the urolith(s) may be monitored by means of palpation of the perineal and pelvic urethra, with the aid of a urethral catheter or by means of radiography. A combined procedure utilizing cystotomy and retrograde flushing of the urethra to remove silica uroliths located in the bladder and urethra has been described. 12 The objective is to eliminate the need for urethrotomy in addition to cystotomy in patients with uroliths lodged in the urethra. Following cystotomy and removal of urocystoliths, a relatively small catheter is advanced to the site of obstructing uroliths. The catheter should be small enough in diameter to allow passage of urethral uroliths while the catheter is positioned in the urethra. Large quantities of a nonirritating isotonic solution are then injected into the urethra in an attempt to flush the uroliths back into the bladder lumen. In order to facilitate retrograde flushing of the urethra, it may be necessary to have an assistant occlude the distal end of the urethra with digital pressure applied to the tip of the penis. Female Dogs U rohydropropulsion may be used to remove uroliths lodged in the urethra of female dogs: 23 (1) Inject a liberal quantity of a 1:1 mixture of sterilized saline solution and aqueous lubricant through a flexible catheter into the urethral lumen adjacent to the uroliths. With an index finger in the rectum or preferably the vagina, firmly occlude the lumen of the distal end of the urethra around a catheter (Fig. 6). This creates a closed system between the occluding urolith and the site of digital compression of the urethra. (2) Next, inject saline solution through the catheter to distend the urethra to its maximum. Dilation of the urethra combined with pressure generated by the intraluminal saline solution usually causes the urolith to move back into the bladder lumen. Gentle digital manipulation of the urolith may aid in moving it toward the bladder lumen. Movement of a large urolith lodged in the neck of the bladder and proximal portion of the urethra may require digital manipulation of the urolith per abdomen by an assistant while saline solution is injected through the catheter. If intraurethral pressure is lost owing to reflux of saline solution through the external urethral orifice, it may be necessary to repeat the procedure several times before the uroliths reach the urinary bladder. The position of
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Figure 6. Schematic illustration of uroh ydropropulsion in a female dog with a solitary urethrolith using a conventional urinary catheter. A, Urolith originating from the urinarv bladder has become lodged in .the urethra. B , Small portion of the urethral lumen distal to the urethrolith and proximal to a site occluded by digital pressure applied through the vaginal wall has been expanded by injecting saline solution through a catheter. C, The urolith has been forced back into the bladder lumen, eliminating obstruction to urine outflow. (From Osborne, C. A., eta!.: Nonsurgical removal of uroliths from the urethra offemale dogs. J. Am. Vet. Med. Assoc., 1 82: 47~50 , 1983; with permission.)
the urolith(s) may be monitored by digital palpation, attempts to advance the catheter, or radiography. If difficulty is encountered in occluding the external urethral orifice around the catheter, a 4 to 7 French Swan-Ganz balloon catheter or pediatric Foley catheter may be used (Fig. 7). Inflation of the balloon after it has been inserted into th~ urethra combined with firm digital pressure may be effective in minimizing reflux of saline solution through the external urethral orifice. Urethral Catheterization
Attempts to Dislodge Urethroliths. Although urethral uroliths may be pushed back into the bladder with the aid of a catheter, this technique
Figure 7. Schematic illustration of urohydropropulsion utilizing a Swan-Ganz balloon catheter. Inflation of the balloon with air helps to prevent reflux of saline solution out of the external urethral orifice. (From Osborne, C. A. , et al.: Nonsurgical removal of uroliths from the urethra offemale dogs. J. Am. Vet. Med. Assoc. , 182:47- 50, 1983; with permission.)
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Figu re 8. Lateral view of a retrograde positive-contrast urethrogram of an 8-year-old male Labrador Retriever. The tip of the urinary catheter has pen etrated the caudodorsal aspect of the urethral wall at a site just distal to a ureth rolith (arrow). (From Osborne, C . A. , et al.: Nonsurgical removal of uroliths from the urethra of femal e dogs. J. Am. Vet. Med. Assoc., 182:47-50, 1983; with permission. )
often is unsuccessful and is associated with risk of urethral trauma and secondary infection (Fig. 8). If the urolith can be moved easily by inserting a catheter into the urethral lumen, our experience has been that it also can be moved readily by digital pressure applied through the vaginal or rectal wall. Judicious use of a catheter to attempt to dislodge urethral uroliths may be justified as a last resort. The diameter of the catheter should be as large as is consistent with atraumatic technique. A rigid catheter is more likely to be associated with success than a flexible one; it also is more likely to cause urethral injury. The catheter should be liberally coated with sterilized, water-soluble lubricant. Unless there is a tear in the urethral wall, a liberal quantity of a 1:1 mixture of saline solution and water-soluble lubricant should be injected through the catheter as the urolith is advanced toward the urinary bladder. If there is a tear in the urethra, only nonirritating isotonic solutions such as physiologic saline solution or lactated Ringer's solution should be used . Caution must be used to avoid trauma to the urethra; excessive force should never be used . Stone baskets have been designed to retrieve small uroliths from the ureters of human beings. The Mitchell Stone Basket* has been used for removal of uroliths from the urethra of male dogs. They may be of value in small female dogs with urethral uroliths; however, we have had no clinical experience with this technique. Flexible foreign body forcepst may also be of value in some patients. Temporary Bypass of Urethroliths. At one time, a commonly used nonsurgical method to attempt to re-establish patency of a urethra occluded with one or more uroliths was urethral catheterization. However, this *Mitchell Stone Basket. C. R. Bard Co., Murray Hill, New Jersey. tForeign Body Forceps. R. Wolf Medical Instruments Corp., Rosemont , Illinois.
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technique is associated with a high risk of urethral trauma (abrasion, contusion, laceration, or puncture), a high risk of secondary urinary tract infection, and a high rate of failure. Nonetheless, it may be considered if attempts to remove urethroliths by other nonsurgical methods have failed and there is immediate need to re-establish urethral patency. If advancement of a catheter beyond a urethrolith cannot be achieved without excessive trauma, it should be abandoned in favor of other nonsurgical or surgical methods (for example, cystocentesis, tube cystostomy) (consult the article 13ntitled "Surgical Removal of Canine Uroliths"). Successful insertion of a catheter beyond the site of an obstructing urethrolith may be enhanced by the following: (1) selection of human ureteral catheters with tips (spiral filaform tips*) designed to bypass narrowed lumens; (2) proper restraint and/or sedation of the patient; (3) injecting a liberal quantity of a 1:1 mixture of saline solution and watersqluble lubricant around the urolith(s) (consult the section on palpation); (4) manipulation of the catheter tip and urolith through overlying tissues by palpatiop; (5) dilation of the urethral lumen by the same technique as used for urohydropropulsion (if necessary); and/or (6) gradual dilation of the urethral lumen adjacent to the urolith by use of firm and steady pressure on the catheter (in contrast to intermittent and forceful pressure). Cqtheters, lubricants, irrigating solutions, specula, and other instruments should be sterile~owever, because the distal portion of the urethra normally contains a commensal population of bacteria, it is impossible to aseptically catheterize the patient. 18 Ascending migration of bacteria through the lumen of the catheter may be minimized by use of closed drainage systems that prevent reflux of urine from the collection receptacle back into the urinary tract. 18 If an open system of indwelling catheterization is used, the question is not whether urinary tract infection will occur, but rather when urinary tract infection will occur. If the purpose of the indwelling catheter is to bypass the site of urethral obstruction, if the detrusor muscle is functional, and if the micturition reflex is intact, there is usu~lly no need to extend the tip of the catheter into the bladder lumen. Over-insertion of excessive lengths of catheter should be avoided to minimize trauma to the bladder, and/or to prevent the catheter from becoming knotted or entangled within the bladder and/or urethral lumens.
NONSURGICAL AND PERCUTANEOUS TECHNIQUES FOR MANAGEMENT OF URETEROLITHS AND NEPHROLITHS Use of percutaneous nephropyelostomy techniques to decompress the upper urinary tract, and to detect, localize, extract, and/or dissolve nephroliths and ureteroliths has gained widespread attention in human beings. 33 With the aid of fluoroscopy, contrast radiography, real-time ultrasound, and/or computer-assisted tomography, needles, catheters, cannulas, nephroscopes (endourology), and stone baskets are percutaneously inserted *American Cystoscope Makers Inc., Pellham Manor, New York.
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through the renal parenchyma into the renal pelves and urethers. 17• 21 • 22 · 35 The key to successful percutaneous extraction and/or dissolution of nephroliths and ureteroliths is the capacity to introduce relatively large tubes into the renal pelvis. Once access to the upper urinary tract has been attained, uroliths may be removed by (1) mechanical extraction with stone baskets, 5 (2) mechanical extraction following fragmentation by hydraulic shock waves initiated by an electrical discharge (electrohydraulic lithotripsy), 4 • 9 • 10• 29 • 36 (3) mechanical extraction following fragmentation with ultrasound (ultrasonic lithotripsy), 1· 20 · 31 and/or (4) flushing with stone solvents (chemolysis). 11 · 32 • 34 A technique of percutaneous nephropyelostomy applicable to dogs has been reported. 2 • 19 However, the technique is more difficult to perform in dogs than in human beings because of greater mobility of the kidneys and smaller size of the renal pelves. Although it may be used to decompress the upper urinary tract, further studies are needed to develop a procedure that permits passage of catheters of sufficient size to remove or dissolve renoliths and ureteroliths in dogs and cats. Electrohydraulic ureterolithotripsy has been used under experimental conditions to disintegrate ureteral stones in dogs. 28 Extracorporeal shock-wave lithotripsy (ESWL) has been recently developed as a noninvasive technique of disintegration of human uroliths. 6 • 7 · 8 · 13 Basically, the technique involves in-vivo disintegration of uroliths as a result of subjecting them to repeated (1000 to 2000) focused shock waves. The focused shock waves are generated in a tub of water (containing the patien~y an electrical discharge across a spark gap positioned at the first focal point of a hemi-ellipsoidal reflector. Pressure (or shock) waves originating from the first focal point are reflected in such fashion that they (and their energy) become focused at the second focal point of the ellipse. With the aid of fluoroscopY,, the urolith to be disintegrated is precisely placed at the second focal point of the ellipsoid. The concept of extracorporeal shockwave lithotripsy appears to be applicable to dogs. In fact, during early phases of development, dogs were utilized in development of protocols to disintegrate nephroliths. However, cost (approximately $2 million for purchase, installation, and maintenance of equipment) and lack of availability of shock-wave lithotripter units preclude its use in veterinary medicine at this time.
REFERENCES l. Aiken, P.: Percutaneous ultrasonic destruction of renal calculi. Urol. Clin. North Am., 9:145-151, 1982. 2. Barbaric, Z. L., Gothlin, J. H., and Davies, R. S.: Transluminal dilatation and stent placement in obstructed ureters in dogs through use of percutaneous nephropyelostomy. Invest. Radio!., 12:534-536, 1977. 3. Blaine, G.: Experimental observations on absorbable alginale products in surgery. Ann. Surg., 125:102-114, 1947. 4. Bulow, H., and Frohmuller, G. W.: Electrohydraulic lithotripsy with aspiration of the fragments under vision. J. Urol., 126:454-456, 1981. 5. Casteneda-Zuniga, W. R., Miller, R. P., and Amplatz, K.: Percutaneous removal of kidney stones. Urol. Clin. North Am., 9:113-119, 1982.
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6. Chaussy, C., Brendel, W., and Schmiedt, E.: Extracorporeally induced destruction of kidney stones by shock waves. Lancet, 2:1265-1268, 1980. 7. Chaussy, C., and Schmiedt, E.: Shock wave treatment for stones in the upper urinary tract. Urol. Clin. North Am., 10:743-750, 1983. 8. Chaussy, C., Schmiedt, E., and Jocham, D.: Extracorporeal shock-wave lithotripsy for treatment of urolithiasis. Urology, 23:59-66, 1984. 9. Clayman, R. V.: Techniques in percutaneous removal of renal calculi: Mechanical extraction and electrohydraulic lithotripsy. Urology, 23:11-19, 1984. 10. Clayman, R. V., Miller, R. P., Reinke, D. B., et al.: Nephroscopy: Advances and adjuncts. Urol. Clin. North Am., 9:51-60, 1982. 11. Dretler, S. P., and Pfister, R. C.: Percutaneous dissolution of renal calculi. Ann. Rev. Med., 34:359-366, 1983. 12. Egger, E. L., and Rigg, D. L.: Treatment of silica urethral obstruction in a dog by retrograde urohydropropulsion. Compend. Contin. Ed. Pract. Vet., 5:147-150, 1983. 13. Finlayson, R., and Thomas, W. C.: Extracorporeal shock-wave lithotripsy. Ann. Intern. Med., 101:387-389, 1984. 14. Gillenwater, J. Y.: Clinical aspects of urinary tract obstruction. Semin. Nephrol., 2:4654, 1982. 15. Kerr, W. S., Jr.: Effect of complete ureteral obstruction for one week on kidney function. J. Appl. Physiol., 6:762-772, 1954. 16. Kerr, W. S., Jr.: Effects of complete ureteral obstruction in dogs on kidney function. Am. J. Physiol., 184:521-526, 19&6. 17. Leadbetter, G. W.: Diagnostic urologic instrumentation. In Campbell's Urology. Edition 4. Volume l. Philadelphia, W. B. Saunders Co., 1978, pp. 358-376. 18. Lees, G. E., and Osborne, C. A.: Use and misuse of intermittent and indwelling urinary catheters. In Kirk, R. W. (ed.): Current Veterinary Therapy. Volume 8. Philadelphia, W. B. Saunders Co., 1983, pp. 1097-1100. 19. Ling, G. V., Ackerman, N., Lowenstone, L. J., et al.: Percutaneous nephropyelocentesis and nephropyelostomy in dogs. A description of the technique. Am. J. Vet. Res., 40:1605-1612, 1979. 20. Marberger, M.: Disintegration of renal and ureteral calculi with ultrasound. Urol. Clin. North Am., 10:729-742, 1983. 21. Miller, R. P., Reinke, D. B., Clayman, R. V., et al.: Percutaneous approach to the ureter. Urol. Clin. North Am., 9:31-40, 1982. 22. Mitty, H. A., and Gribetz, M. E.: The status ofinterventional uroradiography. J. Urol., 127:2-9, 1982. 23. Osborne, C. A., Abdullahi, S., Klausner, J. S., et al.: Nonsurgical removal of uroliths from the urethra offemale dogs. J. Am. Vet. Med. Assoc., 182:47-50, 1983. 24. Osborne, C. A., Lees, G. E., and Johnston, G. R.: Diagnostic and therapeutic cystocentesis. In Bojrab, M. J., et al. (eds.): Current Techniques in Small Animal Surgery. Edition 2. Philadelphia, Lea & Febiger, 1983, pp. 321-324. 25. Osborne, C. A., Lees, G. E., and Johnston, G. R.: Cystocentesis. In Kirk, R. W. (ed.): Current Veterinary Therapy. Volume 7. Philadelphia, W. B. Saunders Co., 1980, pp. 1150-1153. 26. Osborne, C. A., Polzin, D. J., Feeney, D. R., et al.: The urinary system: Pathophysiology, diagnosis, treatment. In Gourley, I. M., and Vasseur, P. B. (eds.): General Small Animal Surgery. Philadelphia, J. B. Lippincott Co., 1985, p. 546. 27. Piermattei, D. L., and Osborne, C. A.: Nonsurgical removal of calculi from the urethra of male dogs. J. Am. Vet. Med. Assoc., 159:1755-1757, 1971. 28. Purohit, G. S., Pham, D., Raney, A. M., et al.: Electrohydraulic ureterolithotripsy: An experimental study. Invest. Urol., 17:462-464, 1980. 29. Raney, A. M., and Handler, J. H.: Electrohydraulic nephrolithotripsy. Urology, 6:439442, 1975. 30. Read, R. J., Smith, J. L., and Sternberg, W. H.: Granulomas induced by surgical lubricating jelly. Am. J. Clin. Pathol., 36:41-48, 1961. 31. Sequra, J. W., and LeRoy, A. J.: Percutaneous ultrasonic lithotripsy: Urology, 23:7-10, 1984. 32. Sheldon, C. A., and Smith, A. D.: Chemolysis of calculi. Urol. Clin. North Am., 9:121130, 1982.
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33. Smith, A. D.: Symposium on endourology. Ural. Clin. North Am., 9:15-196, 1982. 34. Smith, A. D., and Lee, W. J.: Percutaneous stone removal procedures including irrigation. Ural. Clin. North Am., 10:719-727, 1983. 35. Stables, D. P.: Percutaneous nephrostomy: Techniques, indications, and results. Ural. Clin. North Am., 9:15-29, 1982. 36. Tessler, A. N., and Kossow, J.: Electrohydraulic stone disintegration. Urology, 5:470474, 1975. Department of Small Animal Clinical Sciences College of Veterinary Medicine University of Minnesota St. Paul, Minnesota 55108
Nonsurgical Management of Canine Obstructive U rol ithopathy
Carl A. Osborne, D.V.M., Ph.D.,* and David]. Polzin, D.V.M., Ph.D.t "There are some patients whom we cannot help, there are none whom we cannot harm." A. L. BLOOMFIELD
INDICATIONS Obstruction of the Upper Urinary Tract Obstruction to urine outflow may cause varying degrees of damage to the upper urinary tract. For example, persistent obstruction of the urethra or both ureters of a patient with previously normal renal function will cause death within a few. days. Therefore, re-establishment of urine outflow should receive emergency priority. Likewise, unilateral ureteral or renal pelvic obstruction caused by uroliths may rapidly (within a few days) lead to acute generalized pyelonephritis, septicemia, and possibly death. Prolonged persistent obstruction of one ureter in the absence of infection is usually not an immediate threat to life, but it will cause progressive and irreversible destruction of the associated kidney. Results of experimental and clinical studies underscore the fact that varying degrees of recovery of renal function may occur following elimination of the cause of obstruction. For example, in one study of dogs with unilateral renal obstruction of 2, 4, or 6 weeks' duration, there was 38.7 per cent recovery of renal function after 2 weeks of obstruction, 9.8 per cent recovery after 4 weeks of obstruction and 2 per cent after 6 weeks of obstruction. 14 In another study in dogs, glomerular filtration rate (GFR) returned to 68 per cent of normal values following 7 days of complete unilateral ureteral obstruction. 15 *Diplomate, American College of Veterinary Internal Medicine; Professor, Department of Small Animal Clinical Sciences, University of Minnesota College of Veterinary Medicine, St. Paul, Minnesota tDiplomate, American College of Veterinary Internal Medicine; Assistant Professor, Department of Small Animal Clinical Sciences, University of Minnesota College of Veterinary Medicine, St. Paul, Minnesota Veterinary Clinics of North America: Small Animal Practice-Val. 16, No. 2, March 1986
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Sequential studies in dogs with unilateral ureteral obstruction revealed that recovery of renal function is inversely proportional to the duration of obstruction. 16 After 28 days of complete unilateral obstruction, GFR was only 22 per cent of preobstruction GFR. However, after contralateral nephrectomy, GFR in the previously obstructed kidneys increased to 95 to 114 per cent of control values. It is obvious that, in absence of infection, kidneys have a remarkable ability to recover function after relatively long periods of obstruction. Increased renal function after contralateral nephrectomy is also noteworthy. Results of these studies are of great clinical significance. They prevent adoption of an overly pessimistic view about recovery of renal function following correction of obstruction. In the absence of conclusive evidence of irreversibility, efforts to decompress the urinary tract and to eliminate the cause(s) of obstruction should be considered, because at least partial restoration of renal function is likely. Obstruction of the Lower Urinary Tract Partial or complete obstruction of the urethra may result in severe or chronic distension of the urinary bladder. Over-stretching of the bladder wall may damage "tight junctions" between smooth muscle fibers of the detrusor muscle, causing impaired conduction of the motor nerve impulses and a weak or ineffectual detrusor reflex. Damage to sensory nerve endings may also contribute to a poor detrusor reflex. Following removal of urethroliths, the urinary bladder may be hypotonic or atonic, resulting in further urine retention, overflow incontinence, and urinary tract infection. However, if the duration of overdistention is short and the bladder lumen is }s.ept relatively empty for l to 2 weeks by intermittent catheterization or use of a closed indwelling urinary catheter drainage system, damage to the bladder is usually reversible. As bladder function begins to return, the strength of detrusor contraction may be enhanced by administration of bethanecol at a dosage of 5 to 25 mg given orally every 8 hours in dogs, or 2.5 to 5.0 mg given orally every 8 hours in cats. 26 Follow-up Therapy Nonsurgical and percutaneous techniques have been developed to reestablish complete patency of the urinary outflow tract by displacing or bypassing uroliths. In some situations, nonsurgical methods may result in removal of the urolith(s). However, follow-up medical and/or surgical therapy is usually required (see the articles about medical dissolution of uroliths and "Surgical Removal of Canine Uroliths"). NONSURGICAL MANAGEMENT OF UROLITHS IN THE URETHRA AND/OR BLADDER NECK Cystocentesis If obstruction to urine outflow causes overdistention of the urinary bladder, it may be decompressed by cystocentesis. 24 • 25 Timing of Procedure. Because solutions used to flush the urethral
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lumen may alter the composition of urine in the bladder lumen and, therefore, alter results of diagnostic tests (urinalyses, urine culture, and so on), serious consideration should be given to collection of a urine sample by cystocentesis prior to the attempt to restore urethral patency with reverse flushing solutions. This strategy has advantages and disadvantages. In addition to preserving the diagnostic values of a urine sample, simultaneous decompression of an overdistended urinary bladder by removing most (but not all) of the urine provides a mechanism to temporarily halt the continued adverse effects of obstructive uropathy, irrespective of cause. This may provide additional time to remove or bypass the obstructive urethral lesion without further deterioration of renal function. It may also decrease intraluminal pressure at the proximal site of urethal obstruction, which in turn may facilitate repulsion of uroliths into the bladder lumen. In addition, the gross character of aspirated urine may provide valuable clues about the nature of the obstructive disorder. The following are potential disadvantages of the procedure: (1) it may result in extravasation of urine into the bladder wall and/or peritoneal cavity, and (2) it may injure the bladder wall or surrounding structures. Although these complications could be severe in patients with a devitalized bladder wall, in our experience this has been the exception rather than the rule if the majority of the urine is removed from the bladder. Loss of a small quantity of urine into the peritoneal cavity is usually of little consequence, especially if it does not contain pathogens. The potential of trauma to the bladder and adjacent structures can be avoided by good technique. We are not advocating an "always or never" recommendation regarding diagnostic and therapeutic cystocentesis. Clinical judgment is required regarding its use in each patient. However, it is preferable to decompress the urinary bladder by cystocentesis (saving an aliquot for appropriate diagnostic tests) prior to use of reverse flushing procedures in patients that are (1) likely to have adequate integrity of the bladder wall (that is, they do not have an atonic detrussor muscle), and (2) in which immediate overdistention of the bladder lumen is not allowed to recur. Equipment. We routinely use 22-gauge needles. Depending on the size of the patient and the distance of the ventral bladder wall from the ventral abdominal wall, 1.5-inch hypodermic or 3-inch spinal needles* may be selected. We usually use large-capacity (20 to 60 ml) syringes for therapeutic cystocentesis. Alternately, therapeutic cystocentesis may be performed with 6- to 12-ml syringes and a two-way or three-way valve. t If desirable, a 22gauge needle may be transected midway between its tip and hub and reconnected with a section of flexible polyethylene tubing. :j: Site. We recommend that the needle be inserted through the ventral or ventrolateral wall of the bladder in order to minimize the chance of trauma to the ureters and major abdominal vessels (Fig. 1). 24 The needle should be inserted close to the junction of the bladder with the urethra rather than at the vertex of the bladder (see Fig. 1). This will permit *Yale Spinal Needle. Becton-Dickinson Co., Rutherford, New Jersey. tPharmaseal Inc., Toa Alto, Puerto Rico. :j:PE 60., Clay Adams Inc., Parsippany, New Jersey.
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Fig~re 1. Schematic drawing illustrating correct and incorrect sites of insertion of a needle into the bladder for the purpose of evacuating most of the urine from within its lumen. The needle should be inserted in the ventral or ventrolateral surface of the wall a short distance cranial to the junction of the bladder and urethra rather than at the vertex of the bladder. This will permit removal of urine and decompression of the bladder without need for reinsertion of the needle into the bladder lumen. (Medical illustration by Michael P. Schenk, University of Minnesota College of Veterinary Medicine, St. Paul, Minnesota. )
removal of urine and decompression of the bladder without reqmnng reinsertion of the needle into the bladder lumen. If the needle is placed in or adjacent to the vertex of the bladder, it may not remain within the bladder lumen because the bladder progressively decreases in size following aspiration of urine. · · We also recommend that the needle be directed through the bladder wall at approximately a 45° angle so that an oblique needle tract will be created (see Fig. 1). By directing the needle through the bladder wall in an oblique fashion, the elasticity of the vesical musculature and the interlacing arrangement of individual muscle fibers will provide a better seal for the small pathway created by the needle when it is removed. In addition, subsequent distention of the bladder wall as the lumen refills with urine will tend to force the walls of the needle tract into apposition in a fashion somewhat analogous to the flap valve of the ureterovesical junction. Procedure. The ventral abdominal skin penetrated by the needle should be cleansed with an antiseptic solution each time cystocentesis is performed. Excessive hair should be removed with a clipper if necessary. We usually drench the area with alcohol. Appropriate caution should be used to avoid iatrogenic trauma to, or infection of, the urinary bladder and surrounding structures. It is usually easiest to perform the proced1.1re with the patient in lateral or dorsal recumbency. Because insertion and withdrawal of a 22-gauge needle through the walls of the abdomen and bladder are associated with little discomfort, general or local anesthesia is usually unnecessary.
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Following localization and immobilization of the urinary bladder, the needle should be inserted through the ventral abdominal wall and advanced to the caudoventral aspect of the bladder. The needle should be inserted through the bladder wall at an oblique angle and directed so that it will enter the bladder lume n cranial to the junction of the bladder with the urethra. E xcessive digital pressure should not be applied to the bladder wall while the needle is in its lumen. 24 This will prevent urine from being forced around the needle into the peritoneal cavity (Fig. 2). Appropriate caution should be used to prevent laceration of the bladder as a result of careless movement of the needle. The bladder should be emptied as completely as is consistent with atraumatic technique. It is undesirable to attempt complete evacuation of the bladde r lumen because this will allow the sharp point of the needle to damage the bladder wall. The need for prophylactic antibacterial therapy following cystocentesis must be determined on the basis of the status of the patient and retrospective evaluation of technique. If it is probable that the dog has urinary tract infection or if subsequent restoration of urethral patency requires intermittent or indwelling catheterization, antimicrobial therapy should be considered. Palpation
Unidirectional massage of a urethral urolith with a finge r inserted into the vagina or rectum of female dogs has frequently been effective in
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Figure 2. Schematic illustration of urine escaping through bladder wall as a result of excessive digital pressure used to localize and immob ilize th e bladder . (S = skin of abdominal wall; B = wall of urinary bladder. )
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Figure 3. Survey lateral abdominal radiograph of a 5-year-old spayed female Miniature Schnauzer with obstruction of the proximal urethra and distal ureters caused by a large struvite/calcium apatite urocystolith. The urocystolith was dislodged following lubrication and digital palpation through the abdomen.
dislodging urethral uroliths. Likewise, manipulation of a urolith lodged in the neck of the bladder and proximal urethra by palpation per abdomen will usually result in restoration of urine outflow (Fig. 3). Prior to palpation, a liberal quantity of l:l mixture of sterilized physiologic saline solution (or a comparable nonirritating physiologic solution) and aqueous lubricant should be injected through a catheter into the urethral lumen adjacent to the urolith. This maneuver helps to lubricate the urolith(s) and the urethrq) mucosa, which is often inflamed and swollen. We recommend that this mixture be prepared by connecting the tips of two large-capacity syringes, one partially filled with an aqueous lubricant and the other partially filled with saline solution, using a three-way valve. Injection of these materials back and forth between the syringes will allow rapid mixing without loss of sterility (Fig. 4). Aqueous lubricants should not be injected into the urinary tract of patients known to have tears in the wall of the urethra or urinary bladder, because lubricants have been implicated in the formation of periurethral granulomas in human beings30 and rabbits . 3 U rohydropropulsion
U roliths lodged in the urethra of male and female dogs may be moved back into the lumen of the urinary bladder by urohydropropulsion. 23 • 27 The technique is based on dilatation of a portion of the urethra with fluid under pressure. Restraint and Anesthesia. The disposition of the patient may warrant sedation or general anesthesia. Pharmacologic agents dependent on renal metabolism or excretion for inactivation and elimination from the body should be avoided. If an uncooperative patient is an anesthetic risk because of a uremic crisis, topical application of lidocaine gel to the urethral mucosa in combination with parenteral administration of a low dose of analgesic may provide adequate patient restraint. General anesthesia should be used if uroliths cannot be removed from the urethra of nonanesthetized patients by urohydropropulsion. We have
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Figure 4. Schematic diagram illustrating technique to mix sterilized aqueous lubricant (L) with physiologic saline solution (S) in two syringes connected by a three-way valve . (From Osborne, C. A. , et aL: Nonsurgical removal ofuroliths from the urethra of female dogs. J. Am. Vet. Med. Assoc., 182:47-50, 1983; with permission.)
not had any patients in which urethral uroliths could not be removed by this technique while under general anesthesia. Appropriate caution should be used since patients in renal failure are more sensitive to general anesthesia than normal patients. Short-acting barbiturates (thiamylal) may be used, because they are inactivated primarily by the liver. Inhalant anesthetics such as halothane may also be considered because they are not dependent on the kic,lneys for inactivation and excretion from the body. Male Dogs
To remove uroliths by urohydropropulsion, follow this procedure:27 (1) Inject a libe ral quantity of a 1:1 mixture of sterilized saline solution and aqueous lubricant through a flexible catheter into the urethral lumen adjacent to the uroliths (consult the section on palpation). (2) Next, an assistant should insert an index finger into the rectum and firmly occlude the lumen of the pelvic urethra by applying digital pressure against the ischium through the ventral wall of the rectum (Fig. 5). (3) A bovine teat cannula (or suitable facsimile) with an attached 35- to 60-ml syringe filled with sterilized saline should then be inserted into the lumen of the penile urethra via the external urethral orifice. The penile urethra should be compressed around the shaft of the teat cannula by digital pressure . As a result of these maneuvers, a portion of the urethra from the external urethral orifice to the bony pelvis becomes a closed system . (4) Saline should be injected into the urethra until a marked increase in the diameter of the pelvic urethra is perceived by the assistant (see Fig. 5). Confirmation that the urethra has been markedly distended is of great importance, because diste ntion of the urethra to its maximum capacity must be achieved before a sufficient degree of pressure can be created within the urethral
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lumen to advance the uroliths. At this point, the lumen of all portions of the isolated urethra, except that located in the ventral groove of the os penis, will be markedly dilated (see Fig. 5). Dilation of the lumen of the segment of the urethra located in the ventral groove of the os penis is limited to that caused by stre tching of the ventral portion of the urethral wall (see Fig. 5). (5) At this point in the manuever, the teat cannula should be removed rapidly from the distal urethra. Simultaneously, digital pressure applied to the distal penile urethra should be released rapidly in order to permit forceful expulsion of saline out of the urethra (see Fig. 5). Digital pressure applied to the pelvic urethra must be maintained. If the uroliths are small enough to pass through the distended portion of the urethra located in the ventral groove of the os penis, they will be carried with the fluid toward the external urethral orifice. It is usually necessary to repeat the procedure several times to move the urolith(s) from the caudal end of the os penis to the external urethral orifice . The movement of uroliths
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Figure 5. Re moval of urethrolith in a male dog by urohydropropulsion. (1) Urethrolith originating from the urinary bladder has lodged behind the os penis. (2) Dilation of the urethral lume n by injecting fluid with pressure. Digital pressure applied to the external urethral orifice and the pelvic urethra has created a closed system. (3) Sudden release of digital pressure at the external m ethral orifice and subsequent movement of fluid and urethroliths toward the external ure thral orifice. (4) Sudde n release of digital pressure at the pelvic urethra and subsequent movement of fluid and urethrolith toward the urinary bladder. (From Piermattei, D . L. , and Osborne, C. A. : Urohydropropulsion: Nonsurgical removal of urethral calculi in male dogs. In Kirk, R. W. (ed.): Current Veterinary Therapy. Volume 6. Philadelphia, W. B. Saunders Co., 1977, pp. 1195-1196.)
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within the urethral lumen may be monitored with the aid of a urethral catheter or, if necessary, by means of radiography. If the urethroliths are too large to pass through the ventral groove of the os penis, the procedure should be modified. Instead of releasing digital pressure applied to the distal portion of the urethra, digital pressure applied to the pelvic urethra should be rapidly released (see Fig. 5). Pressure should be maintained in the urethral lumen by forcing the syringe plunger forward until the assistant has released digital pressure applied through the rectal wall. This variation in technique forcibly advances fluid, and usually urethroliths, into the urinary bladder (see Fig. 5). On occasion, the urolith may suddenly become free from adjacent tissues and rapidly return to the bladder lumen. However, as was the situation with the antegrade flush, it may be necessary to repeat the procedure several times before the uroliths reach the urinary bladder. The position of the urolith(s) may be monitored by means of palpation of the perineal and pelvic urethra, with the aid of a urethral catheter or by means of radiography. A combined procedure utilizing cystotomy and retrograde flushing of the urethra to remove silica uroliths located in the bladder and urethra has been described. 12 The objective is to eliminate the need for urethrotomy in addition to cystotomy in patients with uroliths lodged in the urethra. Following cystotomy and removal of urocystoliths, a relatively small catheter is advanced to the site of obstructing uroliths. The catheter should be small enough in diameter to allow passage of urethral uroliths while the catheter is positioned in the urethra. Large quantities of a nonirritating isotonic solution are then injected into the urethra in an attempt to flush the uroliths back into the bladder lumen. In order to facilitate retrograde flushing of the urethra, it may be necessary to have an assistant occlude the distal end of the urethra with digital pressure applied to the tip of the penis. Female Dogs U rohydropropulsion may be used to remove uroliths lodged in the urethra of female dogs: 23 (1) Inject a liberal quantity of a 1:1 mixture of sterilized saline solution and aqueous lubricant through a flexible catheter into the urethral lumen adjacent to the uroliths. With an index finger in the rectum or preferably the vagina, firmly occlude the lumen of the distal end of the urethra around a catheter (Fig. 6). This creates a closed system between the occluding urolith and the site of digital compression of the urethra. (2) Next, inject saline solution through the catheter to distend the urethra to its maximum. Dilation of the urethra combined with pressure generated by the intraluminal saline solution usually causes the urolith to move back into the bladder lumen. Gentle digital manipulation of the urolith may aid in moving it toward the bladder lumen. Movement of a large urolith lodged in the neck of the bladder and proximal portion of the urethra may require digital manipulation of the urolith per abdomen by an assistant while saline solution is injected through the catheter. If intraurethral pressure is lost owing to reflux of saline solution through the external urethral orifice, it may be necessary to repeat the procedure several times before the uroliths reach the urinary bladder. The position of
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Figure 6. Schematic illustration of uroh ydropropulsion in a female dog with a solitary urethrolith using a conventional urinary catheter. A, Urolith originating from the urinarv bladder has become lodged in .the urethra. B , Small portion of the urethral lumen distal to the urethrolith and proximal to a site occluded by digital pressure applied through the vaginal wall has been expanded by injecting saline solution through a catheter. C, The urolith has been forced back into the bladder lumen, eliminating obstruction to urine outflow. (From Osborne, C. A., eta!.: Nonsurgical removal of uroliths from the urethra offemale dogs. J. Am. Vet. Med. Assoc., 1 82: 47~50 , 1983; with permission.)
the urolith(s) may be monitored by digital palpation, attempts to advance the catheter, or radiography. If difficulty is encountered in occluding the external urethral orifice around the catheter, a 4 to 7 French Swan-Ganz balloon catheter or pediatric Foley catheter may be used (Fig. 7). Inflation of the balloon after it has been inserted into th~ urethra combined with firm digital pressure may be effective in minimizing reflux of saline solution through the external urethral orifice. Urethral Catheterization
Attempts to Dislodge Urethroliths. Although urethral uroliths may be pushed back into the bladder with the aid of a catheter, this technique
Figure 7. Schematic illustration of urohydropropulsion utilizing a Swan-Ganz balloon catheter. Inflation of the balloon with air helps to prevent reflux of saline solution out of the external urethral orifice. (From Osborne, C. A. , et al.: Nonsurgical removal of uroliths from the urethra offemale dogs. J. Am. Vet. Med. Assoc. , 182:47- 50, 1983; with permission.)
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Figu re 8. Lateral view of a retrograde positive-contrast urethrogram of an 8-year-old male Labrador Retriever. The tip of the urinary catheter has pen etrated the caudodorsal aspect of the urethral wall at a site just distal to a ureth rolith (arrow). (From Osborne, C . A. , et al.: Nonsurgical removal of uroliths from the urethra of femal e dogs. J. Am. Vet. Med. Assoc., 182:47-50, 1983; with permission. )
often is unsuccessful and is associated with risk of urethral trauma and secondary infection (Fig. 8). If the urolith can be moved easily by inserting a catheter into the urethral lumen, our experience has been that it also can be moved readily by digital pressure applied through the vaginal or rectal wall. Judicious use of a catheter to attempt to dislodge urethral uroliths may be justified as a last resort. The diameter of the catheter should be as large as is consistent with atraumatic technique. A rigid catheter is more likely to be associated with success than a flexible one; it also is more likely to cause urethral injury. The catheter should be liberally coated with sterilized, water-soluble lubricant. Unless there is a tear in the urethral wall, a liberal quantity of a 1:1 mixture of saline solution and water-soluble lubricant should be injected through the catheter as the urolith is advanced toward the urinary bladder. If there is a tear in the urethra, only nonirritating isotonic solutions such as physiologic saline solution or lactated Ringer's solution should be used . Caution must be used to avoid trauma to the urethra; excessive force should never be used . Stone baskets have been designed to retrieve small uroliths from the ureters of human beings. The Mitchell Stone Basket* has been used for removal of uroliths from the urethra of male dogs. They may be of value in small female dogs with urethral uroliths; however, we have had no clinical experience with this technique. Flexible foreign body forcepst may also be of value in some patients. Temporary Bypass of Urethroliths. At one time, a commonly used nonsurgical method to attempt to re-establish patency of a urethra occluded with one or more uroliths was urethral catheterization. However, this *Mitchell Stone Basket. C. R. Bard Co., Murray Hill, New Jersey. tForeign Body Forceps. R. Wolf Medical Instruments Corp., Rosemont , Illinois.
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technique is associated with a high risk of urethral trauma (abrasion, contusion, laceration, or puncture), a high risk of secondary urinary tract infection, and a high rate of failure. Nonetheless, it may be considered if attempts to remove urethroliths by other nonsurgical methods have failed and there is immediate need to re-establish urethral patency. If advancement of a catheter beyond a urethrolith cannot be achieved without excessive trauma, it should be abandoned in favor of other nonsurgical or surgical methods (for example, cystocentesis, tube cystostomy) (consult the article 13ntitled "Surgical Removal of Canine Uroliths"). Successful insertion of a catheter beyond the site of an obstructing urethrolith may be enhanced by the following: (1) selection of human ureteral catheters with tips (spiral filaform tips*) designed to bypass narrowed lumens; (2) proper restraint and/or sedation of the patient; (3) injecting a liberal quantity of a 1:1 mixture of saline solution and watersqluble lubricant around the urolith(s) (consult the section on palpation); (4) manipulation of the catheter tip and urolith through overlying tissues by palpatiop; (5) dilation of the urethral lumen by the same technique as used for urohydropropulsion (if necessary); and/or (6) gradual dilation of the urethral lumen adjacent to the urolith by use of firm and steady pressure on the catheter (in contrast to intermittent and forceful pressure). Cqtheters, lubricants, irrigating solutions, specula, and other instruments should be sterile~owever, because the distal portion of the urethra normally contains a commensal population of bacteria, it is impossible to aseptically catheterize the patient. 18 Ascending migration of bacteria through the lumen of the catheter may be minimized by use of closed drainage systems that prevent reflux of urine from the collection receptacle back into the urinary tract. 18 If an open system of indwelling catheterization is used, the question is not whether urinary tract infection will occur, but rather when urinary tract infection will occur. If the purpose of the indwelling catheter is to bypass the site of urethral obstruction, if the detrusor muscle is functional, and if the micturition reflex is intact, there is usu~lly no need to extend the tip of the catheter into the bladder lumen. Over-insertion of excessive lengths of catheter should be avoided to minimize trauma to the bladder, and/or to prevent the catheter from becoming knotted or entangled within the bladder and/or urethral lumens.
NONSURGICAL AND PERCUTANEOUS TECHNIQUES FOR MANAGEMENT OF URETEROLITHS AND NEPHROLITHS Use of percutaneous nephropyelostomy techniques to decompress the upper urinary tract, and to detect, localize, extract, and/or dissolve nephroliths and ureteroliths has gained widespread attention in human beings. 33 With the aid of fluoroscopy, contrast radiography, real-time ultrasound, and/or computer-assisted tomography, needles, catheters, cannulas, nephroscopes (endourology), and stone baskets are percutaneously inserted *American Cystoscope Makers Inc., Pellham Manor, New York.
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through the renal parenchyma into the renal pelves and urethers. 17• 21 • 22 · 35 The key to successful percutaneous extraction and/or dissolution of nephroliths and ureteroliths is the capacity to introduce relatively large tubes into the renal pelvis. Once access to the upper urinary tract has been attained, uroliths may be removed by (1) mechanical extraction with stone baskets, 5 (2) mechanical extraction following fragmentation by hydraulic shock waves initiated by an electrical discharge (electrohydraulic lithotripsy), 4 • 9 • 10• 29 • 36 (3) mechanical extraction following fragmentation with ultrasound (ultrasonic lithotripsy), 1· 20 · 31 and/or (4) flushing with stone solvents (chemolysis). 11 · 32 • 34 A technique of percutaneous nephropyelostomy applicable to dogs has been reported. 2 • 19 However, the technique is more difficult to perform in dogs than in human beings because of greater mobility of the kidneys and smaller size of the renal pelves. Although it may be used to decompress the upper urinary tract, further studies are needed to develop a procedure that permits passage of catheters of sufficient size to remove or dissolve renoliths and ureteroliths in dogs and cats. Electrohydraulic ureterolithotripsy has been used under experimental conditions to disintegrate ureteral stones in dogs. 28 Extracorporeal shock-wave lithotripsy (ESWL) has been recently developed as a noninvasive technique of disintegration of human uroliths. 6 • 7 · 8 · 13 Basically, the technique involves in-vivo disintegration of uroliths as a result of subjecting them to repeated (1000 to 2000) focused shock waves. The focused shock waves are generated in a tub of water (containing the patien~y an electrical discharge across a spark gap positioned at the first focal point of a hemi-ellipsoidal reflector. Pressure (or shock) waves originating from the first focal point are reflected in such fashion that they (and their energy) become focused at the second focal point of the ellipse. With the aid of fluoroscopY,, the urolith to be disintegrated is precisely placed at the second focal point of the ellipsoid. The concept of extracorporeal shockwave lithotripsy appears to be applicable to dogs. In fact, during early phases of development, dogs were utilized in development of protocols to disintegrate nephroliths. However, cost (approximately $2 million for purchase, installation, and maintenance of equipment) and lack of availability of shock-wave lithotripter units preclude its use in veterinary medicine at this time.
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33. Smith, A. D.: Symposium on endourology. Ural. Clin. North Am., 9:15-196, 1982. 34. Smith, A. D., and Lee, W. J.: Percutaneous stone removal procedures including irrigation. Ural. Clin. North Am., 10:719-727, 1983. 35. Stables, D. P.: Percutaneous nephrostomy: Techniques, indications, and results. Ural. Clin. North Am., 9:15-29, 1982. 36. Tessler, A. N., and Kossow, J.: Electrohydraulic stone disintegration. Urology, 5:470474, 1975. Department of Small Animal Clinical Sciences College of Veterinary Medicine University of Minnesota St. Paul, Minnesota 55108