EMERGENCY SURGERY OF THE URINARY TRACT

Transcription

1 EMERGENCY SURGERY OF THE URINARY TRACT Theresa W. Fossum DVM, MS, PhD, Diplomate ACVS Professor of Veterinary Surgery; Midwestern University, Glendale, AZ Urinary tract trauma is common in dogs and cats and may be life-threatening if diagnosis is delayed or therapy is inappropriate. Cystolithiasis, neoplasia, and rupture are the most common abnormalities of the urinary bladder in small animals. Urinary obstruction may occur if calculi become lodged in the urethra or if a tumor obstructs the proximal urethra or trigone. Male cats with FIC may develop penile urethral obstruction. Obstruction to urinary flow may cause a distended urinary bladder, postrenal azotemia, and hyperkalemia. Bladder rupture primarily occurs after motor vehicular trauma, but may also be caused by necrotic bladders (e.g., following damage to its blood supply or prolonged urethral obstruction) or as a complication of bladder surgery. Urinary leakage into the abdominal cavity causes uremia, dehydration, hypovolemia, hyperkalemia, and death if undiagnosed or untreated. Urinary obstruction and uroperitoneum are medical emergencies, not surgical emergencies. Hyperkalemia associated with these conditions makes the animal prone to cardiac arrhythmias; therefore fluid and electrolyte abnormalities should be corrected before anesthesia. Hyperkalemia causes bradycardia, absent or flattened P waves, prolongation of the P-R interval, widened QRS complexes, and/or tented or spiked T waves in addition to predisposing to cardiac arrhythmias. Potassium concentrations greater than 7 meq/l may cause irregular idioventricular rhythms, and potassium concentrations exceeding 9 meq/l commonly cause atrial standstill. Mild or moderate hyperkalemia may be treated with intravenous (IV) fluids (i.e., 0.9% saline for dilution; Box 26-1). LRS and 0.9% saline have both been shown to be effective in resolving metabolic acidosis, hyperkalemia, and postrenal azotemia associated with urethral obstruction in cats; however, LRS was more efficient at restoring acid-base and electrolyte imbalances. If the animal has concurrent hyponatremia, 5% dextrose solution (D5W) and half-strength saline should be avoided. Fluid correction, especially with LRS, should be performed after relieving the obstruction and should occur over 4-6 hours. Hyperkalemia from uroabdomen responds well to abdominal drainage plus intravenous fluid therapy. Hyperkalemia caused by urethral obstruction responds well to intravenous fluids plus elimination of the obstruction. Although seldom required, life-threatening hyperkalemia may be treated with sodium bicarbonate. Bicarbonate therapy drives potassium into cells in exchange for hydrogen ions. Patients with life-threatening hyperkalemia are often moribund and poorly responsive. Additionally, these patients may have respiratory acidosis associated with poor ventilation. Moribund patients should immediately be intubated and hyperventilated to correct respiratory acidosis and improve hyperkalemia. Similar to administering bicarbonate, hyperventilating the patient raises ph and drives potassium intracellularly. Alternatively, life-threatening hyperkalemia can be treated with insulin and dextrose administration. Insulin facilitates cellular uptake of potassium, whereas dextrose prevents hypoglycemia following insulin administration. If the hyperkalemia appears immediately life threatening, 10% calcium gluconate given slowly intravenously may protect the heart until other therapy lowers the plasma potassium concentration. Preventing reabsorption of electrolytes and waste products by abdominal drainage, urinary catheterization, and IV fluid therapy is the best way to treat hyperkalemia and azotemia in animals with uroperitoneum. Penrose drains are ineffective for abdominal drainage of more than 12 to 24 hours because they are quickly isolated from the abdominal cavity by omentum and fibrin; closed systems (e.g., peritoneal catheters, sump drains) are more appropriate for abdominal drainage because they can be attached to an empty fluid bag, allowing for a closed system and quantification of abdominal fluid loss to gauge amount of IV fluid replacement. The goal of abdominal drainage in these patients is to normalize serum electrolytes and decrease azotemia, making the animal a better candidate for general anesthesia. Fluid therapy plus abdominal drainage for 6 to 12 hours is often adequate for this purpose. Peritoneal dialysis may be useful when treating patients with concurrent renal dysfunction. Urethral trauma (e.g., gunshot or bite wounds, rupture caused by vehicular trauma, and obstruction Page 1 of 8

2 with stones) or neoplasia may result in urinary obstruction. If the prostatic or penile urethra is torn, subcutaneous urine leakage may occur. Spontaneous rupture of the urethra is uncommon but may occur in dogs. Initial signs of subcutaneous urine leakage are bruising and/or swelling, especially of the inguinal tissue of male dogs. The skin and subcutaneous tissue can necrose if left untreated. Management of patients with urethral rupture before surgery may necessitate placement of an indwelling urinary catheter and/or cutaneous urinary diversion (tube cystostomy). URETHROTOMY Urethrotomy is performed in male dogs to remove urethral calculi that cannot be retrohydropropulsed into the bladder and to facilitate placement of catheters into the bladder. Occasionally, urethrotomy is performed for a biopsy of obstructive lesions (i.e., strictures, scar tissue, and neoplasms). Prescrotal or perineal urethrotomy may be performed depending on the level of the obstructive lesion. NOTE: To prevent possible postoperative urethral stricture, cystotomy is preferred over urethrotomy if calculi can be advanced back into the bladder by retrohydropulsion. Prescrotal urethrotomy. Prescrotal urethrotomy is used to remove calculi from the distal penile urethra in dogs or to place Foley catheters into the urinary bladder if the catheter is of sufficient length and if the obstruction is distal to the proposed urethrotomy incision. Occasionally, urethrotomy can be performed under local anesthesia with opioid sedation in severely depressed or uremic patients. Prescrotal urethrotomies can be left to heal by secondary intention; however, hemorrhage should be expected from the surgical site for 3 to 5 days (particularly during urination). Primary closure is preferred if the mucosa is healthy and if adequate apposition of the urethral mucosa can be achieved because this decreases postoperative bleeding. Perineal urethrotomy. Perineal urethrotomy is occasionally used to remove calculi lodged at the ischial arch and to place catheters into the bladder of large male dogs. Perineal urethrotomy is less commonly indicated than urethrotomy at other sites. This urethrotomy site should be closed to prevent subcutaneous urine leakage. URETHROSTOMY Urethrostomy is indicated for (1) recurrent, obstructive calculi that cannot be managed medically; (2) calculi that cannot be removed by retrohydropropulsion or urethrotomy; (3) urethral stricture; (4) urethral or penile neoplasia or severe trauma; and (5) preputial neoplasia requiring penile amputation. Depending on the site of the lesion, ureterostomy can be prescrotal, scrotal, perineal, or prepubic in dogs. Scrotal urethrostomy is preferred if castration is an option and if the lesion is distal to the scrotum. Perineal urethrostomy is routinely performed in cats; however, prepubic and subpubic urethrostomy are also described. SURGERY OF THE KIDNEY AND URETER Renal disease or ureteral trauma or obstruction may cause signs of acute or chronic renal failure. The minimum database for urinary dysfunction includes BUN, creatinine, urinalysis, hematocrit, total protein, albumin, electrolytes (especially potassium), total CO 2, and an ECG, if electrolytes are not readily available. These animals may have significant metabolic derangements, besides azotemia. Acute renal disease usually causes moderate or severe dehydration. Although most oliguric animals have acute renal failure, many animals with nonobstructive acute renal failure are not oliguric. Preoperative intravenous fluid therapy is needed to restore circulating blood volume and urine production; however, fluids must be administered judiciously to avoid overloading these patients. Diuretics may also be helpful to enhance urine production in animals that are adequately hydrated. Urine production of hydrated animals on maintenance Page 2 of 8

3 fluids that do not have abnormal extrarenal losses should be at least 50 ml/kg/day or greater than 2 ml/kg/hr. Various electrolyte and acid-base abnormalities may occur, depending on the severity and duration of the renal or ureteral disease. Hyperkalemia is often present in acute obstructive renal disorders and some acute renal parenchymal disorders. Hypokalemia may occur with acute or chronic renal disease and diuretic therapy. Both conditions predispose to cardiac arrhythmias and should be corrected before surgery. Clinically important hypocalcemia is occasionally associated with chronic renal disease. Metabolic acidosis may also be present in animals with acute or chronic renal disease. Animals with chronic renal failure may be anemic because of decreased levels of erythropoietin. Erythropoietin is produced by the kidneys and acts to stimulate red cell production in the bone marrow. Elevated plasma levels of parathyroid hormone may have a negative effect on erythropoietin concentrations. Gastric ulceration, bleeding, or increased red cell fragility may occur in uremic patients. Coagulation profiles may be warranted in animals with chronic renal disorders. Normally hydrated animals with a PCV of less than 20% or hemoglobin of less than 5 g/dl may benefit from preoperative blood transfusions. ANESTHETIC CONSIDERATIONS Anemic patients should be given oxygen before induction and during recovery. Anticholinergic drugs are used to prevent bradycardia. Systemic arterial blood pressure and urine output should be monitored during surgery. Because of intrinsic properties of the kidney, renal blood flow tends to remain constant, despite variations in systemic arterial pressure between 75 and 160 mm Hg, a phenomenon termed autoregulation. However, hypotension during surgery may cause renal vasoconstriction, decreased blood flow, and subsequent renal damage. Hypotensive drugs (e.g., acetylpromazine) should be avoided in animals with renal impairment. If the animal is oliguric but normotensive, low-dose dopamine (1 to 2 µg/kg/min intravenously), with or without furosemide (0.2 mg/kg intravenously), can be used. Alternatively, mannitol (1 4 to 1 2 g/kg intravenously) may be used in cats. If both oliguria and hypotension coexist, dopamine (2 to 10 µg/kg/min intravenously) or dobutamine (2 to 10 µg/kg/min intravenously) may be administered. Thiobarbiturates should be avoided if arrhythmias are present. Isoflurane or sevoflurane are the inhalation agent of choice in arrhythmic patients. General anesthetic principles that should be considered in animals with renal disease include the following. They may be premedicated with an anticholinergic (i.e., atropine or glycopyrrolate) and oxymorphone, butorphanol, or buprenorphine. If the animal has minimal renal compromise, a thiobarbiturate, propofol, or a mask can be used for induction. Ketamine should be avoided in cats with renal compromise. If the dog is severely depressed, oxymorphone plus diazepam may allow intubation. If additional drugs are needed, etomidate or a reduced dose of thiobarbiturate or propofol may be administered intravenously, or mask induction may be used if the animal is not vomiting. Urine output should be monitored during and after surgery. ANTIBIOTICS Perioperative antibiotic therapy should be considered in animals with renal disease or obstruction, even if there is no evidence of infection. Animals with renal calculi or ectopic ureters may have concurrent infections and should be placed on appropriate antibiotics, based on urine culture and susceptibility. Alternatively, antibiotics can be withheld until appropriate intraoperative cultures have been taken. If possible, potentially nephrotoxic antibiotics (i.e., aminoglycosides, tetracycline [except doxycycline], and sulfonamides) should be avoided. Penicillin drugs (i.e., penicillin G, ampicillin, amoxicillin, and combinations of clavulanic acid and amoxicillin) are highly concentrated in urine. They are bactericidal and Page 3 of 8

4 generally effective against gram-positive organisms. Cephalosporins (e.g., cefazolin, 20 mg/kg intravenously at induction) have an enhanced gram-negative spectrum, are excreted in the urine, and are often used for perioperative antibiotic therapy. Fluoroquinolones (e.g., enrofloxacin) have a broad activity against aerobic gram-negative bacteria. Drug doses or dosing frequency should be altered as required by the degree of renal compromise. SURGICAL ANATOMY The kidneys lie in the retroperitoneal space lateral to the aorta and caudal vena cava. They have a fibrous capsule and are held in position by subperitoneal connective tissue. The cranial pole of the right kidney lies at the level of the thirteenth rib. In an average-sized dog, the cranial pole of the left kidney lies about 5 cm caudal to the upper third of the last rib. The renal pelvis is the funnel-shaped structure that receives urine and directs it into the ureter. There are generally five to six diverticula that curve outward from the renal pelvis. The renal artery normally bifurcates into dorsal and ventral branches; however, variations are common. The ureter begins at the renal pelvis and enters the dorsal surface of the bladder obliquely, by means of two slit-like orifices. The blood supply to the ureter is from the cranial ureteral artery (from the renal artery) and the caudal ureteral artery (from the prostatic or vaginal artery). SURGICAL TECHNIQUES For the kidney, a ventral midline abdominal incision is performed from the xiphoid to caudal to the umbilicus. If the distal ureter must be transected (i.e., for nephrectomy) or a cystotomy is necessary, the incision should extend to the pubis. Balfour retractors are used to retract the abdominal wall and expose the kidney. The entire abdominal contents should be inspected before exploring the urinary tract. The right kidney is exposed by elevating the duodenum and displacing the other loops of intestine toward the animal s left side. Similarly, the left kidney is exposed by elevating the mesocolon so that the small intestine is retracted to the animal s right side. The kidney can be isolated from the remaining abdominal contents with moistened laparotomy sponges.renal Biopsy Renal biopsy may be indicated to diagnose the cause of renal insufficiency (especially acute renal failure), hematuria (rare), or proteinuria. It may be performed at surgery, or percutaneously, with the aid of ultrasound, laparoscopy, a keyhole abdominal incision, or blindly. Of the percutaneous techniques, ultrasound-guided biopsy is preferable. Percutaneous biopsy should be avoided in patients with bleeding disorders, large intrarenal cysts, perirenal abscesses, or obstructive uropathy. Giving fluids before, during, and shortly after biopsy to initiate and maintain a mild diuresis may decrease the formation of blood clots within the renal pelvis, that could cause hydronephrosis. Surgical biopsies may be performed using a biopsy instrument (e.g., Vim Tru-Cut or Franklin modified Vim-Silverman biopsy needles) or a wedge resection. The latter allows a larger sample to be obtained. Page 4 of 8

5 Needle biopsy. Perform a needle biopsy with a Tru-Cut instrument by placing the tip of the instrument on the kidney capsule, with the obturator specimen rod fully retracted within the outer cannula. Push the specimen rod into the lesion by advancing the plastic handle. Then advance the outer sheath of the needle into the tissue to sever the biopsy sample. Withdraw the needle, with the outer sheath over the specimen rod. Apply digital pressure to the site to control hemorrhage. Be sure that the sample is primarily cortical tissue. Wedge biopsy. For a wedge biopsy, make an incision into the renal parenchyma with a No. 15 scalpel blade. Make another incision at an angle to the first incision to remove a wedged-shaped piece of parenchyma. Be sure to include cortex in the sample. Close the incision with a mattress suture of 3-0 absorbable suture material. Nephrectomy Nephrectomy is indicated for renal neoplasia, severe trauma resulting in uncontrollable hemorrhage or urine leakage, pyelonephritis that is resistant to medical therapy, hydronephrosis, and ureteral abnormalities (i.e., avulsion, stricture, rupture, or calculi) that defy surgical repair. Before nephrectomy, renal function in the opposite kidney should be assessed by determining its glomerular filtration rate (GFR), if possible. Excretory urograms are not innocuous and can produce anuric/oliguric renal failure in animals with previously mild or moderate renal disease. If excretory urograms are done, avoid large doses of contrast material and maintain good renal perfusion. Bilateral renal dysfunction may warrant a guarded prognosis. If renal neoplasia is suspected, radiography (thoracic and abdominal) and ultrasonography should be performed to help rule out metastasis (including to the opposite kidney). To avoid unintentional transection, the opposite ureter should always be identified; this is particularly critical when removing large neoplasms. Grasp the peritoneum over the kidney and incise it. Free the kidney from its sublumbar attachments, using a combination of blunt and sharp dissection. Elevate the kidney and retract it medially to locate the renal artery and vein on the dorsal surface of the renal hilu. Identify any branches of the renal artery. Double ligate the renal artery with absorbable (e.g., polydioxanone, polyglyconate, or poliglecaprone 25) or nonabsorbable (e.g., cardiovascular silk) suture close to the abdominal aorta, to ensure that all branches have been ligated. Identify the renal vein and ligate it similarly. The left ovarian and testicular veins drain into the renal vein and should not be ligated in intact dogs. Avoid ligating the renal artery and vein together to prevent an arteriovenous fistula from forming. Ligate the ureter near the bladder. Remove the kidney and ureter, and after procuring appropriate culture specimens, submit them for histologic examination. Page 5 of 8

6 Partial Nephrectomy Partial nephrectomy is occasionally warranted for focal renal lesions, particularly if optimal preservation of renal function is necessary because of bilateral renal dysfunction. However, in most cases total nephrectomy is easier and has less risk of postoperative hemorrhage. If partial nephrectomy is performed, electrocoagulation of bleeding vessels should be avoided because this results in excessive parenchymal damage. Avoid partial nephrectomy in animals with clinically significant coagulopathies, as excessive blood loss may occur following this procedure. Nephrotomy If possible, strip the renal capsule from the area of the kidney to be excised. Use absorbable suture (No. 0 or 1) with two long, straight needles attached. Thread the needles into the kidney at the proposed resection site. Tie the thread into three separate ligatures, but avoid damaging the renal vessels or ureter. Excise the renal tissue distal to these ligatures. Ligate any bleeders and suture the exposed diverticula with absorbable suture material (2-0 or 3-0). Approximate the capsule over the end of the kidney, and anchor it to the sublumbar tissues to prevent rotation of the kidney. Alternatively, clamp the renal vessels with vascular forceps, and excise the kidney parenchyma. Ligate parenchymal vessels, and close the renal pelvis and diverticula. Suture the capsule and remove the clamps from the renal vessels. Nephrotomy is usually performed to remove calculi that are lodged within the renal pelvis, but it may also be performed to explore the renal pelvis for neoplasia or hematuria. Nephrotomy should be avoided in patients with severe hydronephrosis because ample parenchyma may not be available to prevent postoperative urine leakage. Additionally, nephrotomy may temporarily decrease renal function by 25% to 50%. Although bilateral nephrotomies can be performed, this could precipitate acute renal failure if renal function is sufficiently compromised preoperatively. Staged procedures are indicated in such patients. Closure of nephrotomy incisions may be accomplished without sutures or with transparenchymal horizontal mattress sutures. The latter may cause increased vascular strangulation, pressure necrosis, infarction, and postoperative hemorrhage. Cyanoacrylate adhesive provides rapid hemostasis; however, if the adhesive enters the renal diverticula, calculus formation may occur. Locate the renal vessels, and temporarily occlude them with vascular forceps, a tourniquet, or an assistant s fingers. Mobilize the kidney to expose the convex lateral surface. Make a sharp incision along the midline of the convex border of the kidney sufficient to allow removal of the calculi and inspection of the entire renal pelvis. Extend the incision from the capsule to the pelvic diverticula. Alternatively, make a sharp incision through the capsule, and bluntly separate the renal parenchyma with forceps. Culture the renal pelvis. Remove the calculi and flush the kidney with warm saline or lactated Ringer s solution. Assess the ureter for patency by placing a 31 2 French soft rubber catheter down the ureter and flushing it with warm fluids. Close the nephrotomy by apposing the cut tissues and applying digital pressure (for approximately 5 min), while restoring blood flow through the renal vessels (sutureless technique). Alternatively, appose the capsule with a continuous pattern of absorbable suture material. If adequate hemostasis is not achieved or urine leakage is a concern, place absorbable sutures through the cortex in a horizontal mattress fashion. Then suture the capsule with a continuous pattern of absorbable suture material. Replace the kidney in its original location. Sutures may be placed in the peritoneum where the kidney was elevated to help stabilize it. Page 6 of 8

7 Pyelolithotomy Pyelolithotomy may be performed to remove renal calculi if the proximal ureter and renal pelvis are sufficiently dilated. This procedure avoids renal parenchymal trauma associated with nephrotomy. Pyelolithotomy is extremely difficult if the ureter is not dilated. Dissect the kidney from its sublumbar attachments, and expose the dorsal surface. Identify the ureter and renal vessels. Make an incision over the dilated pelvis and proximal ureter, and remove the calculi. Flush the renal pelvis and diverticula with warm saline to remove small debris. Next flush the ureter to ensure its patency. Close the incision with a continuous suture of 4-0 or 5-0 absorbable suture material. Ureterotomy Ureterotomy is occasionally performed to remove obstructive calculi. Because there is a risk of postoperative leakage and stricture formation, ureterotomy should be performed with care. If obstruction is not present, dietary dissolution of struvite calculi may be attempted. However, removal of calculi is indicated Page 7 of 8

8 if obstruction occurs or seems likely (e.g., hydroureter or hydronephrosis). Depending on the size of the animal, removal of the stones with a ureteroscope may be possible. Some stones located in the distal ureter may be flushed or pulled into the bladder through a cystotomy, making a ureterotomy unnecessary. Although ureteral mucosa will regenerate over a stent if the mucosa has not been completely disrupted, the use of stenting catheters is controversial because they may promote stricture formation and infection. If stents are used, they should be smaller than the diameter of the ureter. In some animals, ureteral stents may be placed so that they exit the urethral orifice and are sutured to the exterior. Transverse or longitudinal incisions may be made in the ureter; however, there may be less tension on transverse ureterotomies, and thus they may heal more readily. Make a transverse or longitudinal incision in the dilated ureter proximal to the calculi and remove them. Place a small, soft rubber catheter into the ureter proximal and distal to the incision, and flush the ureter with warm fluid. Be certain that all calculi have been removed and that the ureter is patent. Close the incision with simple interrupted sutures of 5-0 to 7-0 absorbable suture material. Alternatively, if the ureter is not dilated and stricture formation seems likely, make a longitudinal incision over the calculi, and close the incision in a transverse fashion. If the ureter has been damaged, perform a resection and anastomosis or proximal urinary diversion. Ureteral Anastomosis Ureteral anastomosis is technically difficult in small patients (i.e., small dogs and cats) and has a high rate of postoperative obstruction. If the ureter is transected or damaged near the bladder, ureteroneocystostomy may be performed. If the ureter is avulsed from the renal pelvis, urinary drainage can be performed by placing a catheter through the renal parenchyma into the ureter. The end of the catheter is exteriorized through the body wall. If function is adequate in the opposite kidney, nephrectomy may be considered, to minimize possible complications of leakage, stricture, or infection. Minimal dissection should be done around the ureter to avoid compromising its blood supply. To avoid damaging the ureter, stay sutures should be placed for manipulation, and traumatic forceps should be avoided. The amount of tension that can be placed on the ureter without causing stricture formation is unknown; therefore tension across the anastomotic site should be avoided. Various synthetic materials have been used to replace the ureter, but most are unacceptable because they promote fibrosis, calculus formation, or infection. A bladder-flap ureteroplasty has been described for ureteral trauma near the bladder. With this technique, a flap is elevated from the ventral surface of the bladder, and the ureter reimplanted into the flap. The flap is then closed as a tube. As with ureterotomy, stenting catheters should be used with caution because they may promote stricture formation. For ureteral anastomosis, suture the ureter directly, or spatulate it by making a longitudinal incision on opposite sides of each end of the ureter. Pre-place absorbable sutures (5-0 or 6-0) at the apex of the spatulated incisions and align the ureteral ends. Appose the ureteral ends with simple interrupted sutures, using the preplaced sutures. Close the remainder of the ureter with simple interrupted sutures. Ensure that the ends of the ureter are not twisted and that sufficient sutures have been placed to prevent leakage. Page 8 of 8