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Medical Management of Feline Urethral Obstruction
DISORDERS OF THE FELINE LOWER URINARY TRACT II
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MEDICAL MANAGEMENT OF FELINE URETHRAL OBSTRUCTION Carl A. Osborne, DVM, PhD, John M. Kruger, DVM, PhD, Jody P. Lulich, DVM, PhD, Joseph W. Bartges, DVM, PhD, and David J. Polzin, DVM, PhD
MEDICAL TREATMENT
Irrespective of the cause(s) of urethral obstruction, predictable clinical and biochemical abnormalities subsequently develop. They are characterized by systemic deficits and/ or excesses in fluids (dehydration) and electrolytes (hyperkalemia, hyperphosphatemia), acid-base (metabolic acidosis) imbalance, and retention of metabolic wastes (creatinine, urea, other protein catabolites). The magnitude of these systemic abnormalities varies with the degree and duration of obstruction. (See the article entitled "Pathophysiology of Feline Urethral Obstruction"). Obstructive uropathy that persists longer than about 24 hours usually results in postrenal azotemia. This occurs because increased back pressure induced by obstruction to outflow impairs glomerular filtration, renal blood flow, and tubular function. After obstruction of the urethra of normal cats, death occurs in 3 to 6 days. Damage to the mucosal surface of the urinary bladder may shorten survival time. Despite the potentially catastrophic outcome of urethral obstruction, the biochemical consequences of this disorder are potentially reversible provided appropriate supportive and symptomatic parenteral therapy is given. (See the article entitled "Management of Postrenal Azotemia" for further details.)
From the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota, St. Paul, Minnesota (CAO, JPL, DJP); and the Department of Small Animal Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan (JMK); and the Department of Small Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, Georgia (JWB)
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In severe cases, initiation of supportive therapy to correct hyperkalemia, metabolic acidosis, and volume depletion should be initiated immediately after decompression of the excretory pathway by cystocentesis. The immediate need to remove urethral plugs within hours of their discovery precludes attempts to cause their dissolution over a period of days or weeks. However, repulsion of urethral plugs into the bladder lumen is often possible. Thus the question arises: can such plugs be dissolved by medical therapy? As described in the article entitled "Feline Urethral Plugs: Etiology and Pathophysiology," urethral plugs contain a substantially greater quantity of matrix than do classic uroliths. Though it is probable that medical protocols effective in inducing sterile struvite urolith dissolution would also be effective in dissolving the struvite crystalline component of urethral plugs located in the bladder lumen, such therapy may not result in dissolution of plug matrix. Furthermore, Calcium oxalate and ammonium urate crystals have been identified in a few naturally occurring feline urethral plugs. These factors may account for lack of expected response to therapy in some patients. Attempts to dissolve struvite crystals with urine acidifiers or diets designed to promote acid urine should not be initiated in cats with postrenal azotemia. The metabolic sequela of urethral obstruction, particularly severe metabolic acidosis, must be corrected before diets designed to acidify urine are utilized. RESTORATION OF URETHRAL PATENCY Overview
Obstructive urethropathy may be caused by one or more intraluminal, mural, or extramural abnormalities located at one or more sites (Table 1, Figs. 1, 2, 3, and 4). Hence, reverse flushing solutions may be very effective in dissolving urethral plugs, but would have no effect on obstructive lesions located in the urethral wall or periurethral tissue. Inability to restore patency by flushing the urethral lumen with a solution should arouse one's suspicion of a mural or periurethral lesion in addition to, or instead of, a firmly lodged urethral plug or urethrolith. Physical and Chemical Restraint
Physical restraint, alone or in combination with topical anesthesia, may be sufficient for obstructed patients that are particularly docile or severely depressed. Wrapping the cat in a bath towel may help to protect the patient and the assistant. If local anesthetics are used to anesthetize the urethral mucosa, they should be administered only in a quantity sufficient to accomplish this goal. We do not recommend use of local anesthetic agents as primary reverse flushing solutions because they may induce systemic toxicity if
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Table 1. POSSIBLE CAUSES OF URETHRAL OBSTRUCTION IN MALE CATS Primary Causes
Perpetuating Causes
Intraluminal Urethral plugs (matrix and/or crystals; see Figs. 2 & 3) Urethroliths Tissue sloughed from urinary bladder or urethra
Intraluminal Increased production of mucoprotein, red and white blood cells and fibrin Sloughed tissue
Mural or extramural Strictures (see Fig. 1) Prostatic lesions Urethral neoplasms Anomalies (see Fig. 4) Reflex dysynergia Combinations Others?
Mural Inflammatory swelling Muscular spasm (reflex dyssynergia?) Strictures Combinations Others?
Iatrogenic Causes
Tissue damage Reverse flushing solutions Catheter trauma Catheter-induced foreign body reaction Catheter-induced infection Postsurgical dysfunction
Figure 1. Antegrade positive contrast cystourethrogram of a 2-year-old neutered male domestic shorthaired cat. The flexure of the preprostatic urethra was caused by caudal displacement of the urinary bladder. Note the stricture of the penile urethra.
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Figure 2. Retrograde positive contrast urethrocystogram of a 7-year-old neutered male domestic shorthaired cat illustrating obstruction of the preprostatic and penile (arrow) urethra with struvite urethral plugs.
Figure 3. Survey radiograph of the lower urinary tract of a neutered adult male cat at the time of necropsy. Note the varied diameter and interrupted continuity of the matrix crystalline plug in the penile. postprostatic, and prostatic urethra. Radiodense crystalline material is apparent in the bladder lumen. The crystals in the urethral plug and urinary bladder are composed of struvite.
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Figure 4. Retrograde positive contrast urethrogram illustrating strictures of the penile and postprostatic urethra of a 5-month-old male domestic shorthair cat with urethral obstruction. Note the vesicourachal diverticulum.
absorbed in sufficient quantity. Their absorption may be enhanced by damage to the urothelium, and their toxic potential may be enhanced by postrenal azotemia. Because of the increased risk of adverse drug reactions associated with obstructive uropathy, pharmacologic restraint should be avoided when feasible. However, the risk of adverse drug reactions must be weighed against the possibility of iatrogenic trauma to the urethra in an uncooperative patient. If the disposition of the patient is such that attempts to dislodge the urethral obstruction are likely to be associated with additional damage to the urethra, or if high risk of iatrogenic urinary tract infection exists, some form of pharmacologic restraint should be considered. Short-acting barbiturates (thiamylal) that are metabolized by the liver, propofol, and/ or inhalant anesthetics may be considered if general anesthesia is required. Anesthetics must be given cautiously because doses less than those recommended for patients with normal renal function are required in patients with postrenal azotemia. If ketamine hydrochloride is used, similar caution is indicated because it is excreted in active form by the kidneys. Low doses of ketamine (1 to 2 mg/kg given intravenously) and diazepam (0.2 mg/kg given intravenously) have been successfully used by many clinicians. However, if difficulty is encountered in relieving outflow obstruction, admin-
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istration of additional quantities of ketamine should be given with caution. Correction of Intraluminal Urethral Obstruction
We recommend a step-by-step priority of procedures when attempting to restore urethral patency in an obstructed male cat. In order of priority they are (1) massage of the distal urethra, (2) attempts to induce voiding by gentle palpation of the urinary bladder, (3) cystocentesis, (4) retrograde urethral flushing, (5) combinations of 1 through 4, (6) diagnostic radiology to determine if the cause of urethral obstruction is intraluminal, mural, and/ or extramural, and, if absolutely necessary, (7) surgical procedures. Gentle Massage of the Urethra
Gentle massage of the penis between the thumb and fingers may help to dislodge plugs located in the penile urethra (Fig. 5). If necessary, the penis may be manipulated while it is retracted within the prepuce. Plugs located in the preprostatic (abdominal) or membranous (pelvic) urethra may occasionally be dislodged by massaging the urethra per rectum. Though these methods are often ineffective, their simplicity and occasional success make them worth trying before considering cystocentesis or catheterization. In addition, they may disrupt material in urethral
Figure 5. A 3-year-old male domestic shorthaired cat with urethral obstruction. Note the matrix crystalline plug at the external urethral orifice (arrow).
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Figure 6. The 3·year-old domestic shorthair cat described in Figure 5 after digital manipulation of the distal urethra and manual compression of the urinary bladder. Fragments of urethral plug are visible on the microscope slide (arrows).
plugs confined to the penile urethra to such a degree that subsequent palpation of the urinary bladder may dislodge them. Palpation of the Urinary Bladder
Inability of a cat to void urine spontaneously indicates that increasing intraurethral pressure by digitally compressing the urinary bladder . is unlikely to be effective. However, if this technique is utilized after urethral massage, sufficient intraluminal pressure may be generated to dislodge fragments of urethral precipitates (Fig. 6). Appropriate caution should be used to prevent iatrogenic damage to the urinary bladder. If urinary tract infection is likely, the consequences of inducing vesicoureteral reflux during palpation should be considered because microbes may be forced into the upper urinary tract. Cystocentesis
In general, cystocentesis should be performed if the aforementioned techniques are ineffective in reestablishing urethral patency (Fig. 7). The advantages of performing decompressive cystocentesis before flushing the urethral lumen via a catheter are (1) a urine sample suitable for analysis and culture is obtained; (2) 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 obstruc-
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Figure 7. Technique of decompressive cystocentesis . A large capacity syringe and threeway stopcock are connected to a 1.5-inch long 22-gauge hypodermic needle via a flexible intravenous extension set. Bloody urine has been aspirated from an overdistended urinary bladder into the syringe.
tive urethropathy (irrespective of cause); (3) decompression of an overdistended urinary bladder and proximal urethra may facilitate repulsion of a urethral plug or urolith into the bladder lumen; and (4) the gross character of aspirated urine may provide valuable clues about the nature of the obstructive disorder (intraluminal precipitates of matrix and crystalline material versus extraluminal compression). Urine that contains large quantities of visible precipitates suggests a greater likelihood of reobstruction after subsequent flushing of the urethral lumen. The potential disadvantages of performing cystocentesis are (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. Though 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, but not all, 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 proper technique. We are not advocating an "always or never" recommendation regarding decompressive cystocentesis. Clinical judgment is required regarding its use in each patient. However, decompressing the urinary bladder by cystocentesis (saving an aliquot for appropriate diagnostic
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tests) before use of reverse flushing procedures is preferable in patients (1) likely to have adequate integrity of the bladder wall and (2) in which immediate overdistension of the bladder lumen is not allowed to recur. We recommend that a 22-gauge needle be attached to a flexible intravenous extension set which in turn is attached to a large capacity syringe (20 to 60 mL). One individual should immobilize the urinary bladder and 22-gauge needle, while another aspirates urine from the bladder lumen (see Fig. 7). Gentle agitation of the bladder in an up-anddown motion before cystocentesis may disperse particular matter or crystals throughout the urine, and thus facilitate their aspiration into the collection system. We recommend that the needle be inserted through the ventral or ventrolateral wall of the bladder to minimize the chance of trauma to the ureters and major abdominal vessels (Fig. 8). The needle should be inserted midway between the vertex of the bladder and the junction of the bladder with the urethra rather than at the vertex of the bladder. This will permit removal of urine and decompression of the bladder without requiring 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 after aspiration of urine. We also recommend that the needle be directed through the bladder wall at approximately a 45-degree angle so that an oblique needle tract is created (see Fig. 8). By directing the needle through the bladder wall in an oblique fashion, the elasticity of the vesical musculature and the interlacing
Figure 8. Correct site of insertion of a needle into the bladder for the purpose of evacuating urine. The needle should be inserted in the ventral or ventrolateral surface of the wall a short distance cranial to the junction of the bladder with the urethra rather than at the vertex of the bladder. This position permits removal of urine and decompression of the bladder without need for reinsertion of the needle into the bladder lumen.
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arrangement of individual muscle fibers provides a better seal for the small pathway created when the needle is removed. Jn addition, subsequent distention of the bladder wall as the lumen refills with urine tends to force the walls of the needle tract into apposition in a fashion somewhat analagous to the flap valve of the ureterovesical junction. Excessive digital pressure should not be applied to the bladder wall while the needle is in its lumen lest urine be forced around the needle into the peritoneal cavity. 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. Attempting complete evacuation of the bladder lumen is undesirable because the sharp point of the needle may then damage the bladder wall. We recommend that 15 to 20 mL of urine remain in the bladder. Jn the event patency of the urethra is not established before the bladder fills with urine again, decompressive cystocentesis should be repeated. On occasion, we have performed serial decompressive cystocenteses over a span of several days until urethral patency was reestablished. The need for prophylactic antibacterial therapy after cystocentesis must be determined on the basis of the status of the patient and retrospective evaluation of technique. If subsequent restoration of urethral patency requires intermittent or indwelling catheterization, appropriate antimicrobial therapy should be considered (see the article entitled "Use and Misuse of Indwelling Urethral Catheters"). Flushing the Urethral Lumen
Flushing the urethral lumen with sterilized solutions after urethral catheterization may dislodge urethral plugs and uroliths. However, urethral obstruction may be caused by a combination of intraluminal precipitates (uroliths or urethral plugs), swelling of the urethral wall, and/ or spasm of the urethral musculature (see Table 1). Reverse flushing solutions should be selected cautiously because accumulation and absorption of large quantities of acid or anesthetic solutions from an inflamed urinary bladder may cause systemic toxicity. In addition, the coating of glycosaminoglycans (GAGS) that lines the surface of the urothelium may be damaged. Glycosaminoglycans normally minimize adherence of crystals and microbes to the urethral mucosa.'' 2 Adherence of crystals to the urothelium is most likely to occur if acidic solutions are used to dissolve struvite crystals. Pending results of further studies, we prefer physiologic saline or lactated Ringer's solution because these fluids are readily available, sterilized, nontoxic, nonirritating, and economical. The general guidelines to be followed when reverse flushing feline urethras to reestablish patency are outlined in the box on page 497. Use of proper restraint, atraumatic urethral catheters (Figs. 9 through 15), and nonirritating flushing solutions greatly minimizes damage to the urethral mucosa and surrounding structures.
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em l"llllllllllllllllll 1 2
SPEC. Figure 9. Minnesota olive-tipped urethral catheters (Ejay International, Glendora, CA). The catheters are 0.5, 1.0, and 1.5 inches in length.
Figure 10. Saline-filled syringe, intravenous extension set, and Minnesota olive-tipped catheter used to flush the urethra of male cats with matrix-crystalline urethral plugs.
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Figure 11. Technique of catheterization of an obstructed urethra of a male cat with a Minnesota olive-tipped catheter attached to a flexible intravenous extension set, three-way valve, and large capacity syringe.
Figure 12. The beneficial effects of flushing without occlusion of the urethra around the catheter. A portion of the matrix-crystalline plug has been flushed out of the external urethral orifice.
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Figure 13. Normal caliber of urine stream of the cat described in Figure 11 . We would not routinely use an indwelling transurethral catheter in this circumstance.
Figure 14. Antegrade positive contrast urethrogram of a 4-year-old neutered male Persian cat illustrating extravasation of contrast medium from the penile urethra (arrow). Damage to the urethra was caused by a forceful attempt to bypass a distal urethral plug with a polypropylene catheter.
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Figure 15. Retrograde positive contrast urethrocystogram of a 6-year-old neutered male domestic shorthaired cat illustrating extravasation of contrast medium from the postprostatic urethra into adjacent tissue. Damage to the urethra was caused by a forceful attempt to bypass a urethral plug with a polypropylene catheter.
Inability to establish adequate urethral patency by use of catheters and reverse flushing should arouse a high index of suspicion that the underlying cause is not a urethral plug (see Table 1). Appropriate diagnostic procedures should be considered. Overdistension of the bladder lumen may be prevented by serial decompressive cystocenteses. We do not recommend surgical intervention to correct obstructive urethropathy in uremic cats unless no reasonable alternative exists. Immediate Aftercare
After urine flow has been reestablished by nonsurgical techniques, most of the urine should be removed from the bladder lumen. Removing all the urine from the bladder lumen is unnecessary and inadvisable because trauma associated with such efforts may aggravate the severity of bladder lesions. Manual compression may be used provided substantial pressure is not required to induce voiding. Manual compression of the bladder is not necessarily the procedure of choice if an overdistended bladder has been recently decompressed by cystocentesis because it may cause extravasation of urine into the bladder wall or peritoneal cavity. Alternative methods include either use of a catheter and syringe or cystocentesis. Each of these procedures has advantages and disadvan-
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General Guidelines for Reverse Flushing Male Feline Urethras Obstructed with Intraluminal Materials 1. Make every effort to protect the patient from iatrogenic complications associated with catheterization of the urethra (especially trauma and urinary tract infection with bacteria; see Figs. 14 and 15). 2. Strive to use meticulous aseptic "feather-touch" technique. 3. Use only sterile catheters. 4. Cleanse the penis and prepuce with warm water before catheterization. 5. Select the shortest Minnesota olive-tipped feline urethral catheter• for initial catheterization of the urethra and attach it to a flexible intravenous connection set and a syringe (see Figs. 9, 10, & 11 ). 6. Coat the olive tip with sterile aqueous lubricant. 7. Before insertion of the catheter into the external urethral orifice, the extended penis should be displaced dorsally until the long axis of the urethra is approximately parallel to the vertebral column. 8. Carefully advance the catheter to the site of obstruction. If necessary, replace the short olive-tipped Minnesota needle with a longer one. Record the site of suspected obstruction, because this information may be of value when considering use of muscle relaxants and/or when considering urethral surgery to prevent recurrent obstruction. CAUTION: Do not mistake resistance induced by curvature of the feline male urethra for a site of obstruction, and never use excessive force when advancing the catheter (see Figs. 14 and 15). 9. Flush a large quantity of physiologic saline or lactated Ringer's solution (as much as several hundred mL) into the urethral lumen, and allow it to reflux out the external urethral orifice (see Fig. 12). When possible, the catheter may be advanced toward the bladder. As a result of this maneuver, the obstructed urethral plugs may be gradually dislodged and flushed around the catheter and out of the urethral lumen. Application of steady but gentle digital pressure to the bladder wall after the urethra has been flushed with physiologic saline or lactated Ringer's solution may result in expulsion of a urethral plug or urolith from the urethral lumen. Excessive pressure should not be used because it may result in (1) trauma to the bladder, (2) reflux of potentially infected urine into the ureters and renal pelvis, and/or (3) rupture of the bladder wall. 10. If the technique outlined in step 9 is unsuccessful, attempting repulsion of suspected urethral plugs or uroliths back into the bladder lumen by occluding the distal end of the urethra around the olive tip of the catheter before injecting fluid into the urethra may be necessary. By preventing reflux of solutions out of the external urethral orifice, this maneuver tends to dilute the urethral lumen. If the obstruction persists, an attempt may be made to gently advance the suspected plug or urolith toward the bladder. Excessive force should not be used. 11 . On occasion, allowing the reverse flushing solution to soften the obstructing urethral plugs (this technique is ineffective for most uroliths) before attempting to propel them back into the bladder is advantageous. Allowing a lapse of several hours between attempts to remove firmly lodged plugs by reverse flushing has been effective. *Minnesota feline olive-tipped urethral catheters are available from EJA Y International, Inc, Glendora, California
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tages that must be considered in light of the status of the urinary bladder and urethra of each patient. If the gross appearance of voided or aspirated urine suggests that reobstruction due to intraluminal debris is likely, removal of this material with saline or lactated Ringer's solution flushes of the bladder lumen may be of value in minimizing reobstruction. Particulate material located in the dependent portion of the bladder may be dispersed throughout the bladder lumen by digitally moving the bladder in an up-and-down fashion, which may in tum facilitate aspiration of crystals, inflammatory reactants, and blood clots into the catheter and syringe. Local instillation of antimicrobial agents into the bladder lumen in an attempt to prevent or treat urinary tract infection is of unproved value. Unless the bladder wall is hypotonic or atonic, the antimicrobial agent is likely to be voided soon after instillation. If circumstances dictate the need for antimicrobial agents, they should be given orally or parenterally to maximize their effectiveness. The urinary bladder should be periodically evaluated after restoration of adequate urethral patency to ensure that urethral obstruction has not recurred and/ or that the detrusor muscle is not hypotonic. Micturition induced by gentle digital compression of the bladder may facilitate evaluation of urethral patency. Caution must be used when selecting various drugs for azotemic cats. Though glucocorticoid therapy has been advocated to minimize inflammatory swelling of the urethra, glucocorticoids may aggravate the severity of potentially life-threatening uremia by inducing protein catabolism (via gluconeogenesis) and may predispose to bacterial urinary tract infection (see the article entitled "Prednisolone Therapy of Idiopathic Feline Lower Urinary Tract Disease"). Likewise, administration of acidifying agents to azotemic cats may aggravate the severity of existing metabolic acidosis. Indiscriminate use of any drug in patients with renal dysfunction must be avoided because of the potential adverse drug reactions associated with the uremic state. After relief of urethral obstruction, a transitory obligatory postobstructive diuresis may develop. Even though polyuric cats may consume some water, it is often insufficient to maintain proper fluid balance. Therefore, supplementing water intake by parenteral administration of rehydrating or maintenance fluids may be necessary. References 1. Khan SR, et a!: Crystal retention by injured urothelium of the rat urinary bladder. J Urol132:153, 1984 2. Pantazopoulos D, et a!: Effects of drugs on crystal adhesion to injured urothelium. Urology 36:255-259, 1990
Address reprint requests to Carl A. Osborne, DVM, PhD Department of Small Animal Clinical Sciences University of Minnesota College of Veterinary Medicine 1352 Boyd Avenue St. Paul, MN 55108
0195-5616/96 $0.00
+
.20
MEDICAL MANAGEMENT OF FELINE URETHRAL OBSTRUCTION Carl A. Osborne, DVM, PhD, John M. Kruger, DVM, PhD, Jody P. Lulich, DVM, PhD, Joseph W. Bartges, DVM, PhD, and David J. Polzin, DVM, PhD
MEDICAL TREATMENT
Irrespective of the cause(s) of urethral obstruction, predictable clinical and biochemical abnormalities subsequently develop. They are characterized by systemic deficits and/ or excesses in fluids (dehydration) and electrolytes (hyperkalemia, hyperphosphatemia), acid-base (metabolic acidosis) imbalance, and retention of metabolic wastes (creatinine, urea, other protein catabolites). The magnitude of these systemic abnormalities varies with the degree and duration of obstruction. (See the article entitled "Pathophysiology of Feline Urethral Obstruction"). Obstructive uropathy that persists longer than about 24 hours usually results in postrenal azotemia. This occurs because increased back pressure induced by obstruction to outflow impairs glomerular filtration, renal blood flow, and tubular function. After obstruction of the urethra of normal cats, death occurs in 3 to 6 days. Damage to the mucosal surface of the urinary bladder may shorten survival time. Despite the potentially catastrophic outcome of urethral obstruction, the biochemical consequences of this disorder are potentially reversible provided appropriate supportive and symptomatic parenteral therapy is given. (See the article entitled "Management of Postrenal Azotemia" for further details.)
From the Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota, St. Paul, Minnesota (CAO, JPL, DJP); and the Department of Small Animal Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, Michigan (JMK); and the Department of Small Animal Medicine, College of Veterinary Medicine, University of Georgia, Athens, Georgia (JWB)
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In severe cases, initiation of supportive therapy to correct hyperkalemia, metabolic acidosis, and volume depletion should be initiated immediately after decompression of the excretory pathway by cystocentesis. The immediate need to remove urethral plugs within hours of their discovery precludes attempts to cause their dissolution over a period of days or weeks. However, repulsion of urethral plugs into the bladder lumen is often possible. Thus the question arises: can such plugs be dissolved by medical therapy? As described in the article entitled "Feline Urethral Plugs: Etiology and Pathophysiology," urethral plugs contain a substantially greater quantity of matrix than do classic uroliths. Though it is probable that medical protocols effective in inducing sterile struvite urolith dissolution would also be effective in dissolving the struvite crystalline component of urethral plugs located in the bladder lumen, such therapy may not result in dissolution of plug matrix. Furthermore, Calcium oxalate and ammonium urate crystals have been identified in a few naturally occurring feline urethral plugs. These factors may account for lack of expected response to therapy in some patients. Attempts to dissolve struvite crystals with urine acidifiers or diets designed to promote acid urine should not be initiated in cats with postrenal azotemia. The metabolic sequela of urethral obstruction, particularly severe metabolic acidosis, must be corrected before diets designed to acidify urine are utilized. RESTORATION OF URETHRAL PATENCY Overview
Obstructive urethropathy may be caused by one or more intraluminal, mural, or extramural abnormalities located at one or more sites (Table 1, Figs. 1, 2, 3, and 4). Hence, reverse flushing solutions may be very effective in dissolving urethral plugs, but would have no effect on obstructive lesions located in the urethral wall or periurethral tissue. Inability to restore patency by flushing the urethral lumen with a solution should arouse one's suspicion of a mural or periurethral lesion in addition to, or instead of, a firmly lodged urethral plug or urethrolith. Physical and Chemical Restraint
Physical restraint, alone or in combination with topical anesthesia, may be sufficient for obstructed patients that are particularly docile or severely depressed. Wrapping the cat in a bath towel may help to protect the patient and the assistant. If local anesthetics are used to anesthetize the urethral mucosa, they should be administered only in a quantity sufficient to accomplish this goal. We do not recommend use of local anesthetic agents as primary reverse flushing solutions because they may induce systemic toxicity if
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Table 1. POSSIBLE CAUSES OF URETHRAL OBSTRUCTION IN MALE CATS Primary Causes
Perpetuating Causes
Intraluminal Urethral plugs (matrix and/or crystals; see Figs. 2 & 3) Urethroliths Tissue sloughed from urinary bladder or urethra
Intraluminal Increased production of mucoprotein, red and white blood cells and fibrin Sloughed tissue
Mural or extramural Strictures (see Fig. 1) Prostatic lesions Urethral neoplasms Anomalies (see Fig. 4) Reflex dysynergia Combinations Others?
Mural Inflammatory swelling Muscular spasm (reflex dyssynergia?) Strictures Combinations Others?
Iatrogenic Causes
Tissue damage Reverse flushing solutions Catheter trauma Catheter-induced foreign body reaction Catheter-induced infection Postsurgical dysfunction
Figure 1. Antegrade positive contrast cystourethrogram of a 2-year-old neutered male domestic shorthaired cat. The flexure of the preprostatic urethra was caused by caudal displacement of the urinary bladder. Note the stricture of the penile urethra.
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Figure 2. Retrograde positive contrast urethrocystogram of a 7-year-old neutered male domestic shorthaired cat illustrating obstruction of the preprostatic and penile (arrow) urethra with struvite urethral plugs.
Figure 3. Survey radiograph of the lower urinary tract of a neutered adult male cat at the time of necropsy. Note the varied diameter and interrupted continuity of the matrix crystalline plug in the penile. postprostatic, and prostatic urethra. Radiodense crystalline material is apparent in the bladder lumen. The crystals in the urethral plug and urinary bladder are composed of struvite.
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Figure 4. Retrograde positive contrast urethrogram illustrating strictures of the penile and postprostatic urethra of a 5-month-old male domestic shorthair cat with urethral obstruction. Note the vesicourachal diverticulum.
absorbed in sufficient quantity. Their absorption may be enhanced by damage to the urothelium, and their toxic potential may be enhanced by postrenal azotemia. Because of the increased risk of adverse drug reactions associated with obstructive uropathy, pharmacologic restraint should be avoided when feasible. However, the risk of adverse drug reactions must be weighed against the possibility of iatrogenic trauma to the urethra in an uncooperative patient. If the disposition of the patient is such that attempts to dislodge the urethral obstruction are likely to be associated with additional damage to the urethra, or if high risk of iatrogenic urinary tract infection exists, some form of pharmacologic restraint should be considered. Short-acting barbiturates (thiamylal) that are metabolized by the liver, propofol, and/ or inhalant anesthetics may be considered if general anesthesia is required. Anesthetics must be given cautiously because doses less than those recommended for patients with normal renal function are required in patients with postrenal azotemia. If ketamine hydrochloride is used, similar caution is indicated because it is excreted in active form by the kidneys. Low doses of ketamine (1 to 2 mg/kg given intravenously) and diazepam (0.2 mg/kg given intravenously) have been successfully used by many clinicians. However, if difficulty is encountered in relieving outflow obstruction, admin-
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istration of additional quantities of ketamine should be given with caution. Correction of Intraluminal Urethral Obstruction
We recommend a step-by-step priority of procedures when attempting to restore urethral patency in an obstructed male cat. In order of priority they are (1) massage of the distal urethra, (2) attempts to induce voiding by gentle palpation of the urinary bladder, (3) cystocentesis, (4) retrograde urethral flushing, (5) combinations of 1 through 4, (6) diagnostic radiology to determine if the cause of urethral obstruction is intraluminal, mural, and/ or extramural, and, if absolutely necessary, (7) surgical procedures. Gentle Massage of the Urethra
Gentle massage of the penis between the thumb and fingers may help to dislodge plugs located in the penile urethra (Fig. 5). If necessary, the penis may be manipulated while it is retracted within the prepuce. Plugs located in the preprostatic (abdominal) or membranous (pelvic) urethra may occasionally be dislodged by massaging the urethra per rectum. Though these methods are often ineffective, their simplicity and occasional success make them worth trying before considering cystocentesis or catheterization. In addition, they may disrupt material in urethral
Figure 5. A 3-year-old male domestic shorthaired cat with urethral obstruction. Note the matrix crystalline plug at the external urethral orifice (arrow).
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Figure 6. The 3·year-old domestic shorthair cat described in Figure 5 after digital manipulation of the distal urethra and manual compression of the urinary bladder. Fragments of urethral plug are visible on the microscope slide (arrows).
plugs confined to the penile urethra to such a degree that subsequent palpation of the urinary bladder may dislodge them. Palpation of the Urinary Bladder
Inability of a cat to void urine spontaneously indicates that increasing intraurethral pressure by digitally compressing the urinary bladder . is unlikely to be effective. However, if this technique is utilized after urethral massage, sufficient intraluminal pressure may be generated to dislodge fragments of urethral precipitates (Fig. 6). Appropriate caution should be used to prevent iatrogenic damage to the urinary bladder. If urinary tract infection is likely, the consequences of inducing vesicoureteral reflux during palpation should be considered because microbes may be forced into the upper urinary tract. Cystocentesis
In general, cystocentesis should be performed if the aforementioned techniques are ineffective in reestablishing urethral patency (Fig. 7). The advantages of performing decompressive cystocentesis before flushing the urethral lumen via a catheter are (1) a urine sample suitable for analysis and culture is obtained; (2) 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 obstruc-
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Figure 7. Technique of decompressive cystocentesis . A large capacity syringe and threeway stopcock are connected to a 1.5-inch long 22-gauge hypodermic needle via a flexible intravenous extension set. Bloody urine has been aspirated from an overdistended urinary bladder into the syringe.
tive urethropathy (irrespective of cause); (3) decompression of an overdistended urinary bladder and proximal urethra may facilitate repulsion of a urethral plug or urolith into the bladder lumen; and (4) the gross character of aspirated urine may provide valuable clues about the nature of the obstructive disorder (intraluminal precipitates of matrix and crystalline material versus extraluminal compression). Urine that contains large quantities of visible precipitates suggests a greater likelihood of reobstruction after subsequent flushing of the urethral lumen. The potential disadvantages of performing cystocentesis are (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. Though 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, but not all, 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 proper technique. We are not advocating an "always or never" recommendation regarding decompressive cystocentesis. Clinical judgment is required regarding its use in each patient. However, decompressing the urinary bladder by cystocentesis (saving an aliquot for appropriate diagnostic
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tests) before use of reverse flushing procedures is preferable in patients (1) likely to have adequate integrity of the bladder wall and (2) in which immediate overdistension of the bladder lumen is not allowed to recur. We recommend that a 22-gauge needle be attached to a flexible intravenous extension set which in turn is attached to a large capacity syringe (20 to 60 mL). One individual should immobilize the urinary bladder and 22-gauge needle, while another aspirates urine from the bladder lumen (see Fig. 7). Gentle agitation of the bladder in an up-anddown motion before cystocentesis may disperse particular matter or crystals throughout the urine, and thus facilitate their aspiration into the collection system. We recommend that the needle be inserted through the ventral or ventrolateral wall of the bladder to minimize the chance of trauma to the ureters and major abdominal vessels (Fig. 8). The needle should be inserted midway between the vertex of the bladder and the junction of the bladder with the urethra rather than at the vertex of the bladder. This will permit removal of urine and decompression of the bladder without requiring 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 after aspiration of urine. We also recommend that the needle be directed through the bladder wall at approximately a 45-degree angle so that an oblique needle tract is created (see Fig. 8). By directing the needle through the bladder wall in an oblique fashion, the elasticity of the vesical musculature and the interlacing
Figure 8. Correct site of insertion of a needle into the bladder for the purpose of evacuating urine. The needle should be inserted in the ventral or ventrolateral surface of the wall a short distance cranial to the junction of the bladder with the urethra rather than at the vertex of the bladder. This position permits removal of urine and decompression of the bladder without need for reinsertion of the needle into the bladder lumen.
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arrangement of individual muscle fibers provides a better seal for the small pathway created when the needle is removed. Jn addition, subsequent distention of the bladder wall as the lumen refills with urine tends to force the walls of the needle tract into apposition in a fashion somewhat analagous to the flap valve of the ureterovesical junction. Excessive digital pressure should not be applied to the bladder wall while the needle is in its lumen lest urine be forced around the needle into the peritoneal cavity. 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. Attempting complete evacuation of the bladder lumen is undesirable because the sharp point of the needle may then damage the bladder wall. We recommend that 15 to 20 mL of urine remain in the bladder. Jn the event patency of the urethra is not established before the bladder fills with urine again, decompressive cystocentesis should be repeated. On occasion, we have performed serial decompressive cystocenteses over a span of several days until urethral patency was reestablished. The need for prophylactic antibacterial therapy after cystocentesis must be determined on the basis of the status of the patient and retrospective evaluation of technique. If subsequent restoration of urethral patency requires intermittent or indwelling catheterization, appropriate antimicrobial therapy should be considered (see the article entitled "Use and Misuse of Indwelling Urethral Catheters"). Flushing the Urethral Lumen
Flushing the urethral lumen with sterilized solutions after urethral catheterization may dislodge urethral plugs and uroliths. However, urethral obstruction may be caused by a combination of intraluminal precipitates (uroliths or urethral plugs), swelling of the urethral wall, and/ or spasm of the urethral musculature (see Table 1). Reverse flushing solutions should be selected cautiously because accumulation and absorption of large quantities of acid or anesthetic solutions from an inflamed urinary bladder may cause systemic toxicity. In addition, the coating of glycosaminoglycans (GAGS) that lines the surface of the urothelium may be damaged. Glycosaminoglycans normally minimize adherence of crystals and microbes to the urethral mucosa.'' 2 Adherence of crystals to the urothelium is most likely to occur if acidic solutions are used to dissolve struvite crystals. Pending results of further studies, we prefer physiologic saline or lactated Ringer's solution because these fluids are readily available, sterilized, nontoxic, nonirritating, and economical. The general guidelines to be followed when reverse flushing feline urethras to reestablish patency are outlined in the box on page 497. Use of proper restraint, atraumatic urethral catheters (Figs. 9 through 15), and nonirritating flushing solutions greatly minimizes damage to the urethral mucosa and surrounding structures.
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SPEC. Figure 9. Minnesota olive-tipped urethral catheters (Ejay International, Glendora, CA). The catheters are 0.5, 1.0, and 1.5 inches in length.
Figure 10. Saline-filled syringe, intravenous extension set, and Minnesota olive-tipped catheter used to flush the urethra of male cats with matrix-crystalline urethral plugs.
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Figure 11. Technique of catheterization of an obstructed urethra of a male cat with a Minnesota olive-tipped catheter attached to a flexible intravenous extension set, three-way valve, and large capacity syringe.
Figure 12. The beneficial effects of flushing without occlusion of the urethra around the catheter. A portion of the matrix-crystalline plug has been flushed out of the external urethral orifice.
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Figure 13. Normal caliber of urine stream of the cat described in Figure 11 . We would not routinely use an indwelling transurethral catheter in this circumstance.
Figure 14. Antegrade positive contrast urethrogram of a 4-year-old neutered male Persian cat illustrating extravasation of contrast medium from the penile urethra (arrow). Damage to the urethra was caused by a forceful attempt to bypass a distal urethral plug with a polypropylene catheter.
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Figure 15. Retrograde positive contrast urethrocystogram of a 6-year-old neutered male domestic shorthaired cat illustrating extravasation of contrast medium from the postprostatic urethra into adjacent tissue. Damage to the urethra was caused by a forceful attempt to bypass a urethral plug with a polypropylene catheter.
Inability to establish adequate urethral patency by use of catheters and reverse flushing should arouse a high index of suspicion that the underlying cause is not a urethral plug (see Table 1). Appropriate diagnostic procedures should be considered. Overdistension of the bladder lumen may be prevented by serial decompressive cystocenteses. We do not recommend surgical intervention to correct obstructive urethropathy in uremic cats unless no reasonable alternative exists. Immediate Aftercare
After urine flow has been reestablished by nonsurgical techniques, most of the urine should be removed from the bladder lumen. Removing all the urine from the bladder lumen is unnecessary and inadvisable because trauma associated with such efforts may aggravate the severity of bladder lesions. Manual compression may be used provided substantial pressure is not required to induce voiding. Manual compression of the bladder is not necessarily the procedure of choice if an overdistended bladder has been recently decompressed by cystocentesis because it may cause extravasation of urine into the bladder wall or peritoneal cavity. Alternative methods include either use of a catheter and syringe or cystocentesis. Each of these procedures has advantages and disadvan-
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General Guidelines for Reverse Flushing Male Feline Urethras Obstructed with Intraluminal Materials 1. Make every effort to protect the patient from iatrogenic complications associated with catheterization of the urethra (especially trauma and urinary tract infection with bacteria; see Figs. 14 and 15). 2. Strive to use meticulous aseptic "feather-touch" technique. 3. Use only sterile catheters. 4. Cleanse the penis and prepuce with warm water before catheterization. 5. Select the shortest Minnesota olive-tipped feline urethral catheter• for initial catheterization of the urethra and attach it to a flexible intravenous connection set and a syringe (see Figs. 9, 10, & 11 ). 6. Coat the olive tip with sterile aqueous lubricant. 7. Before insertion of the catheter into the external urethral orifice, the extended penis should be displaced dorsally until the long axis of the urethra is approximately parallel to the vertebral column. 8. Carefully advance the catheter to the site of obstruction. If necessary, replace the short olive-tipped Minnesota needle with a longer one. Record the site of suspected obstruction, because this information may be of value when considering use of muscle relaxants and/or when considering urethral surgery to prevent recurrent obstruction. CAUTION: Do not mistake resistance induced by curvature of the feline male urethra for a site of obstruction, and never use excessive force when advancing the catheter (see Figs. 14 and 15). 9. Flush a large quantity of physiologic saline or lactated Ringer's solution (as much as several hundred mL) into the urethral lumen, and allow it to reflux out the external urethral orifice (see Fig. 12). When possible, the catheter may be advanced toward the bladder. As a result of this maneuver, the obstructed urethral plugs may be gradually dislodged and flushed around the catheter and out of the urethral lumen. Application of steady but gentle digital pressure to the bladder wall after the urethra has been flushed with physiologic saline or lactated Ringer's solution may result in expulsion of a urethral plug or urolith from the urethral lumen. Excessive pressure should not be used because it may result in (1) trauma to the bladder, (2) reflux of potentially infected urine into the ureters and renal pelvis, and/or (3) rupture of the bladder wall. 10. If the technique outlined in step 9 is unsuccessful, attempting repulsion of suspected urethral plugs or uroliths back into the bladder lumen by occluding the distal end of the urethra around the olive tip of the catheter before injecting fluid into the urethra may be necessary. By preventing reflux of solutions out of the external urethral orifice, this maneuver tends to dilute the urethral lumen. If the obstruction persists, an attempt may be made to gently advance the suspected plug or urolith toward the bladder. Excessive force should not be used. 11 . On occasion, allowing the reverse flushing solution to soften the obstructing urethral plugs (this technique is ineffective for most uroliths) before attempting to propel them back into the bladder is advantageous. Allowing a lapse of several hours between attempts to remove firmly lodged plugs by reverse flushing has been effective. *Minnesota feline olive-tipped urethral catheters are available from EJA Y International, Inc, Glendora, California
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tages that must be considered in light of the status of the urinary bladder and urethra of each patient. If the gross appearance of voided or aspirated urine suggests that reobstruction due to intraluminal debris is likely, removal of this material with saline or lactated Ringer's solution flushes of the bladder lumen may be of value in minimizing reobstruction. Particulate material located in the dependent portion of the bladder may be dispersed throughout the bladder lumen by digitally moving the bladder in an up-and-down fashion, which may in tum facilitate aspiration of crystals, inflammatory reactants, and blood clots into the catheter and syringe. Local instillation of antimicrobial agents into the bladder lumen in an attempt to prevent or treat urinary tract infection is of unproved value. Unless the bladder wall is hypotonic or atonic, the antimicrobial agent is likely to be voided soon after instillation. If circumstances dictate the need for antimicrobial agents, they should be given orally or parenterally to maximize their effectiveness. The urinary bladder should be periodically evaluated after restoration of adequate urethral patency to ensure that urethral obstruction has not recurred and/ or that the detrusor muscle is not hypotonic. Micturition induced by gentle digital compression of the bladder may facilitate evaluation of urethral patency. Caution must be used when selecting various drugs for azotemic cats. Though glucocorticoid therapy has been advocated to minimize inflammatory swelling of the urethra, glucocorticoids may aggravate the severity of potentially life-threatening uremia by inducing protein catabolism (via gluconeogenesis) and may predispose to bacterial urinary tract infection (see the article entitled "Prednisolone Therapy of Idiopathic Feline Lower Urinary Tract Disease"). Likewise, administration of acidifying agents to azotemic cats may aggravate the severity of existing metabolic acidosis. Indiscriminate use of any drug in patients with renal dysfunction must be avoided because of the potential adverse drug reactions associated with the uremic state. After relief of urethral obstruction, a transitory obligatory postobstructive diuresis may develop. Even though polyuric cats may consume some water, it is often insufficient to maintain proper fluid balance. Therefore, supplementing water intake by parenteral administration of rehydrating or maintenance fluids may be necessary. References 1. Khan SR, et a!: Crystal retention by injured urothelium of the rat urinary bladder. J Urol132:153, 1984 2. Pantazopoulos D, et a!: Effects of drugs on crystal adhesion to injured urothelium. Urology 36:255-259, 1990
Address reprint requests to Carl A. Osborne, DVM, PhD Department of Small Animal Clinical Sciences University of Minnesota College of Veterinary Medicine 1352 Boyd Avenue St. Paul, MN 55108