Urolithiasis of the lower urinary tract (Proceedings)

Uroliths can be found in the renal pelvis, the ureter, the bladder, or the urethra. The most common locations are the bladder and the urethra. A higher incidence of calcium oxalate has been reported in the ureter and kidney in cats. This higher incidence seems to parallel the diet changes instituted several years ago to prevent stones in the lower urinary tract. Different types of uroliths have been identified in veterinary medicine such as struvite or magnesium ammonium phosphate, calcium oxalate, ammonium urate, silicate and cystine. Pathophysiology behind each type of urolith needs to be well understood in order to accomplish a successful surgical treatment.

Hematuria, stranguria, and pollakiuria are the most common clinical signs associated with uroliths. Blood work, urinalysis, radiographic evaluation of the urinary system and ultrasounds are required to diagnosed urolithiasis in dogs and cats.

Indications

Detection of uroliths is not in itself an indication for surgery. Along with medical management, surgical intervention has an important role in the therapy for urolithiasis. Surgical candidates include:

     • Patients with urolith induced obstruction to urine outflow that cannot be corrected by non-surgical techniques

     • Patients with uroliths that are refractory to current methods of medical dissolution: silica, calcium oxalate, and calcium phosphate uroliths

     • Patients with uroliths that are increasing in size while under medical therapy

     • Patients with nephroliths and renal dysfunction

     • Patients with anatomical defects that predispose to UTI

     • Patients not responding to therapy because of poor owner compliance.

Evaluation of patients before surgery

If an obstruction is present several metabolic changes can occur that will compromise the patient. First a post-renal azotemia will develop. This azotemia should be reversible as soon as the urine can flow freely. This azotemia may not develop if the obstruction is only compromising one ureter or one kidney. Electrolyte imbalance will develop very quickly with urinary obstruction or uroabdomen. Uroabdomen can appear if an obstruction has been sustained for a long period of time. Hyperkalemia will induce serious bradycardia with tall T wave (K >5.5 mEq/L), prolongation of QRS complex (K>6.5 mEq/L), decrease amplitude of P wave and prolongation of P wave (K>7.5 mEq/L), and disappearance of P wave when K>8.5 mEq/L. High potassium concentration will induce a temporary atrial standstill. It is important to recognize those changes because induction of anesthesia in such a patient is not indicated. To lower the potassium concentration induction of diuresis is the best option. Either a small urinary catheter can be placed in the urethra to bypass the obstruction or a cystocenthesis can be performed to empty the bladder as much as possible. If a uroabdomen is present an abdominal drain can be placed under local anesthesia. If diuresis does not lower the level of potassium a combination of insulin glucose and bicarbonate can be used. Potassium concentration will decrease for a period of time allowing a safe induction of anesthesia to perform surgery. Finally if insulin is not helping injection of calcium gluconate will help protect the heart against the effect of potassium.

Surgical removal of bladder stones

Removal of uroliths from the bladder is not technically difficult. Appropriate care should be taken to remove all uroliths from the bladder, bladder neck, and the urethra. Anatomical defect predisposing to urinary infection should be corrected, if possible. A urinary catheter should be placed in the urethra before the beginning of the surgery especially if the stones are small in diameter.

After a midline incision in the caudal abdomen, the bladder is pack off the rest of the abdomen with laparotomy sponges to minimize contamination and catch stones that might escape. A ventral cystotomy is performed and the incision should extend from the apex of the bladder to the trigone area. Four stay sutures are placed in the wall of the bladder. Stay sutures help prevent urine spillage in the abdomen but also help manipulating the bladder wall without touching it with hand or instruments. Manipulation of the bladder wall triggers severe edema and bleeding from the mucosa.

Following a ventral cystotomy the uroliths are removed either with a spoon, or suction. The bladder neck and lumen should be explore with a finger to detect remaining large uroliths. A biopsy of bladder wall should be performed then for culture and sensitivity. Bladder wall culture gives more reliable results regarding bacterial infection than urine culture. Bladder neck is flushed with warm sterile saline to remove small urolith. The urethra is flushed with the catheter placed prior to surgery. A surgery technician can access this catheter underneath the surgery drapes and flush sterile saline while withdrawing the catheter. Then a catheter is introduced in the proximal urethra and large amounts of saline are used to flush the urethra. Before closing the bladder a catheter is introduced from the bladder in the urethra to confirm patency of the urethra. The bladder is closed with a 4-0 monofilament absorbable suture in a simple continuous pattern. The sutures are placed full-thickness. It is not necessary to maintain a urinary catheter postoperatively. Complications from a cystotomy are: dehiscence (rare) and uroabdomen. Bladder stones can also be removed with a laparoscopy assisted cystotomy in dogs and cats.

Surgical management of stones in the urethra

Uroliths are lodged in the urethra causing partial or complete obstruction and urethritis.Generally, small cystic calculi migrate to the neck of the bladder during micturition and pass into the urethra.

In the male, urethral calculi most commonly lodge caudal to the os penis. In the female, calculi may lodge at any location along the length of the urethra. Urethral obstruction is more common in the male than female.

In animals with complete obstruction of a duration long enough to cause azotemia, temporary urinary diversion is provided by either passing a urinary catheter along side the calculus, performing a prepubic cystostomy, or frequent cystocenteses. Azotemia is treated with crystalloid IV therapy prior to calculus removal. Hyperkalemia can develop in cat or dog with complete chronic obstruction.

All the efforts should be made to retroflux the uroliths in the bladder. It is easier to performed a cystotomy than an urethrotomy, and there is less morbidity associated.

     1. Retrograde hydropulsion (Figure 1)

          a. Thoroughly mix 45 cc of sterile saline and 15 cc of Surgilube in a 60 cc syringe and attach to the largest high density polyethylene urinary catheter that will pass through the os penis (5 to 8 French).

          b. Anesthetize the animal, pass the catheter up to and against the calculus. If the patient is a male place a gauze sponge around the tip of the penis and occlude the penis around the catheter by squeezing it with thumb and finger .

          c. Using a back and forth action on the catheter, simultaneously inject the saline/lubricant mix under pressure.

               i. The calculi and urethra are lubricated and the viscosity of the mix encourages the calculus to dislodge and flush into the bladder.

               ii. This technique is attempted regardless of how many stones are in the urethra.

          d. If the above technique fails, place a finger in the rectum, palpate the urethra, and occlude its lumen, repeat step 3 above and when maximum pressure is exerted on the urethra by the saline/lubricant mix, suddenly release digital urethralocclusion allowing lodged calculi to flush into the bladder. This technique allows maximal dilatation of the urethra.

Figure 1. Retrograde hydropulsion

If the stones are successfully retroflux in the bladder, the urinary catheter is left in place to prevent migration of the stones back into the urethra. A ventral midline celiotomy and cystotomy are then performed to remove all calculi. The catheter is used to flush the urethra in a retrograde fashion while it is removed. A normograde catheter is then placed from the cystotomy site and the urethra is flushed again with copious amount of saline.

If the stone cannot be retroflux in the bladder then a urethrotomy is performed.

     2. Urethrotomy (an incision over the calculi) may be performed to remove calculi that cannot be retropulsed. It is usually performed in the prescrotal because usually stones are lodged behind the os penis. With a urinary catheter in place to the level of the obstruction a 5 cm midline incision is made over the uroliths. The subcutaneous tissue is dissected and the retractor penis muscle is retracted on one side. A 15 scalpel blade is use to longitudinally incise the urethra over the uroliths. The uroliths are removed and the catheter advanced. If other uroliths are present they can either be retrieved through the urethrotomy or they can be flushed back in the bladder. Then a cystotomy is required. The urethrotomy incision can be left open or suture with an absorbable suture in a continuous pattern on the urethra . Subcutaneous tissue and skin are closed. If the incision is left open it is going to granulate and closed by second intention. Urine is leaking through the incision for several days. The corpus spongiosum will bleed when the dog urinates or becomes excited.

     3. Urethrostomy (a permanent opening to allow calculi to pass) may be indicated in animals that are chronic recurrent calculi formers (e.g., urate calculi in Dalmatians). Scrotal urethrostomy is the technique of choice for dogs because the urethra has a large diameter until it passes the level of the scrotum.

The dog is placed in dorsal recumbency and a urethral catheter is placed. After castration and scrotal ablation, the retractor penile muscle is retracted on the side to expose the ventral aspect of the urethra. The urethra is incised longitudinally over 3-4 cm (Figure 2). The periurethral tissue is sutured to the subcutaneous tissue with a 4-0 absorbable suture in a simple interrupted pattern. The urethral mucosa is then sutured to the skin with 4-0 non-absorbable monofilament in a simple continuous pattern. The urethra is more superficial in the scrotal area, surrounded by less cavernous tissue.

Figure 2.

Complications of an urethrostomy are hemorrhage, stricture, and dermatitis from urine scalding. Hemorrhage happens for 6 to 7 days after surgery when the dog urinates or becomes excited. Sedation might be required for a week to 10 days after surgery to help control bleeding. Stricture mostly occurs is the dogs is self-traumatizing the surgical site. An E collar is recommended for 10 days. After a urethrostomy dogs are at more risk of ascending UTI because the urethra is shorter.

In cats a perineal urethrostomy is performed. The cat is positioned in ventral recumbency at the end of the table. An elliptical incision is performed around the prepuce and the scrotum. The cat is castrated. The penis is isolated and the ischiocavernosus muscles are exposed by blunt dissection and transected to their attachment to the ischium. After care blunt dissection ventrally posterior displacement of the penis is possible. The retractor penile muscle is transected near the external anal sphincter muscle. The penile urethral is incised dorsal to the bulbourethral glands. At this point the urethra is wide (4 mm). The pelvic urethra and 3 cm of the penile urethra are sutured to the skin with 4-0 monofilament in a simple interrupted pattern. The remaining of the penile urethra and penis are amputated. An Elizabethan collar is used to prevent self-mutilation. Complications are hemorrhage, cystitis, urethral stricture, self-mutilation, and wound dehiscence.

Patient monitoring

     • Treatment for UTI and dietary management.

     • Medical management to prevent reoccurrence of urolith according to urolith analysis

     • Ureterotomy: uroabdomen

     • Cystotomy

          • Animals may pass small quantities of blood and blood clots for 2 - 3 days postoperatively.

          • Animals presenting with complete urinary obstruction and postrenal azotemia are continued on crystalloid IV therapy until serum urea nitrogen and creatinine return to normal.

     • Urethrotomy/urethrostomy

          • Hemorrhage from the urethral stoma is the most common immediate postsurgical complication. It generally occurs 4 - 5 days postoperatively, but occasionally will last up to 2 weeks.

          • Apply an Elizabethan collar to prevent self-mutilation.