Proceedings of the World Small Animal Veterinary Association Sydney, Australia 2007

Transcription

1 Proceedings of the World Small Animal Veterinary Association Sydney, Australia 2007 Hosted by: Australian Small Animal Veterinary Association (ASAVA) Australian Small Animal Veterinary Association (ASAVA) Australian Small Animal Veterinary Association (ASAVA) Next WSAVA Congress

2 SURGICAL DECISION MAKING IN DOGS AND CATS WITH ACUTE URETHRAL OBSTRUCTION D.J. Brockman BVSc CVR CSAO DipACVS DipECVS ILTM MRCVS Department of Small Animal Medicine & Surgery, Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Herts AL9 7TA History and physical examination: Historically, affected animals may have suffered from oliguria, stranguria, and dysuria for hours to days, with little to no urination. Occasionally (more frequently in cats) the animal is presented because of lethargy, weakness and collapse. Physical examination findings reflect the degree of cardiovascular compromise and the presence of a large very firm bladder on gentle abdominal palpation. Pathophysiological changes seen in these patients include azotaemia (hyperkalaemia), metabolic acidosis, hypovolaemia. Initial evaluation and stabilization: This will require initial blood tests: PCV, total protein, electrolytes as a minimum. Ideally, full haematology and serum biochemistry and urinalysis should be done. An ECG strip should be obtained or continuous ECG monitoring performed. Therapy will require intravenous access and should consist of these main elements: 1. intravascular fluid volume replacement 2. cardioprotection 3. correction of electrolyte abnormalities 4. relief of the urinary obstruction. A balanced electrolyte solution may be used at initial doses of 10ml 60ml/kg/hr depending on the degree of hypovolaemia. 0.9% saline may help correct the electrolyte abnormalities more rapidly. Life-threatening hypokalaemic bradycardia can be treated by administering calcium gluconate ( mg/kg) to provide cardioprotection while the potassium falls in response to fluid therapy and urine drainage. Insulin or insulin + glucose therapy (to shift potassium into cells) and bicarbonate administration are alternative or adjunctive strategies to aid in the management of hyperkalaemia. Initial stabilization can be aided by cystocentisis, making the patient a better sedation/anaesthetic candidate. The majority of urethral obstructions can be relieved without surgery using trans-urethral cystic catheter placement along with retropulsion of any plugs or stones. Occasionally, obstructions require surgical relief. Once the obstruction is relieved and urine flow is established, the GFR will increase and a postobstructional diuresis will commence, any metabolic acidosis and electrolyte abnormalities should gradually return to normal over the follwing24 hours. THE ROLE OF SURGERY IN THE MANAGEMENT OF URETHRAL OBSTRUCITON: CYSTOTOMY: A. Indications

3 a. When urethral calculi have been retropulsed into the bladder of either the male dog or cat. B. Technical comments: Prepare prepuce and penis tip aseptically. Ventral midline coeliotomy. Ventral cystotomy. Flush from penis tip back to bladder not the other way around. Count stones, if possible, if too many/too small, perform retrograde urethrography at the end of the procedure. Stones for culture and analysis. CANINE URETHROTOMY/URETHROSTOMY A. Indications 1. Urethrotomy is most often employed with obstruction at the base of the os penis, and the urethra is assessed to be fully patent after calculus removal. b. Urethrotomy within the os penis frequently results in stricture formation and is not recommended. c. Urethrotomy incisions can be allowed to heal by second intention, healing in 7-10 days; also can be closed primarily with 4-0 or 5-0 synthetic absorbable suture followed by routine skin closure. d. Haemorrhage may be profuse intermittently, especially after urination or at times of sexual excitement. 2. Permanent urethrostomy is indicated with calculi lodged within the os penis, strictures 2 to previous trauma, or severe acute penile/urethral injury. B. Choosing the Appropriate Location for Urethrostomy 1. Scrotal urethrostomy is the procedure of choice when a permanent urethral opening is desired. Castration / scrotal ablation must accompany this procedure in the intact male. i. The membranous urethra in the region of the scrotum is larger and more distensible than at the base of the os penis, allowing the passage of larger calculi and decreasing the risk of stricture formation. ii. The scrotal urethra is more superficial and surrounded by less cavernous tissue than the perineal urethra. Hemorrhage is more easily controlled, and surgical exposure is better than with other regions of the urethra. 2. Prescrotal urethrostomy is advocated by some surgeons, "saving" the scrotal urethra in the event the prescrotal urethrostomy develops an occlusive stricture. 3. Perineal and antepubic urethrostomy are indicated if stricture or irreparable laceration/crushing exists proximal to the scrotal urethra. i. Perineal urethrostomy may produce persistent urine scald of the perineal epithelium, and increased risk of urine extravasation into the periurethral tissues post-operatively.

4 ii. Antepubic urethrostomy is technically difficult because vascular and nervous supply to the bladder neck must be preserved. C. Approach, Surgical Manipulation, Closure (for scrotal urethrostomy) a. Scrotal ablation and castration (for intact males) performed (Urethral catheter passed preoperatively if possible) b. Retractor penis muscle retracted ± sutured laterally, and corpus spongiosum penis (= corpus cavernosum urethra) and urethra are incised on caudoventral midline, with a desired stoma 1-2 cm long c. Surgery is completed by suturing urethral mucosa to the surrounding skin edge with 3-0 or 4-0 monofilament material (nylon or polypropylene) d. Urethrostomy at other sites requires similar manipulations D. Complications: a. Increased risk of ascending bacterial infection vs. normal anatomy not borne out by the information currently available. b. Cavernous tissues will hemorrhage for up to 10 days postoperatively, especially after urination or sexual stimulation c. Subcutaneous urine extravasation produces profound cellulitis and systemic illness/sepsis: investigate periurethral trauma or cellulitis thoroughly and without delay FELINE PERINEAL URETHROSTOMY A. Indications: 1. Obstruction that cannot be relieved with catheterisation (a surgical emergency) 2. Stricture 2 to distal urethral obstruction Perineal urethrostomy is performed less frequently now than it was years ago, probably as a result of the improved success of treating Feline Lower Urinary Tract Disease (FLUTD) with aggressive medical therapeutics (antibiotics when indicated, dietary management, careful relief of urethral obstruction) and the recognition of the complications associated with restructuring the male urogenital tract. B. Approach, Surgical Manipulation, Closure: ventral recumbency, in a rectal stand, with a purse string suture inserted into the anus elliptical incision from just dorsal to the scrotum to ventral to the prepuce; castration is included in this procedure if not already performed penis is mobilized with blunt and sharp dissection close to the shaft, and the sharp incision of ventral ligamentous attachments to the ischiatic symphysis and the crus of the penis; the crus may hemorrhage profusely if not subsequently ligated further dissection is employed until penis is freed approx. 1 cm proximal to the paired bulbourethral glands; avoid damage to the rectum, anus, and anal sacs dorsally

5 after application of a tourniquet, the penis is amputated just distal to the crura, the urethral lumen is catheterised, and the urethra is incised dorsally to the cranial aspect of the bulbourethral glands simple interrupted sutures of 4-0 nylon (Ethilon), polypropylene (Prolene), or similar are used to appose the full thickness of the urethra to the perineal skin penis is fully amputated once a triangular stoma has been established, and the cut ends of the corpus spongiosum are sewn together skin incision is completed with a Penrose drain ventral to the pelvic urethra petroleum jelly is applied to the urethrostomy site twice daily, Elizabethan collar used as needed, and the sutures are removed in days under sedation (usually). C. Complications: Aggressive periurethral dissection may produce striated-muscle urethral sphincter dysfunction 2 to pudendal nerve damage Asymptomatic bacterial cystitis has been reported in about ¼ of the cats with perineal urethrostomies, followed long term. Stricture and/or urethral obstruction secondary to calculi may occur. TUBE CYSTOSTOMY Indications: Temporary urinary diversion following urethral rupture repair, or following temporary urethral obstruction. Additional equipment: DePezzer mushroom-tipped or Foley balloon-tipped urologic catheter of appropriate size. Approach: Caudal ventral mid-line coeliotomy; from umbilicus to pubis. Manipulations: The urinary bladder is examined to ensure that adequate blood supply remains. A location in the ventrolateral bladder wall is identified mid-way between the trigone and the apex of the bladder. A purse-string suture of 2-0 (3 Ph Eur) or 3-0 (4 Ph Eur) polydioxanone is placed. If a Foley catheter is used, the catheter is placed through a stab incision in the body wall approximately 2cm lateral to the ventral midline at a level that will minimally distort bladder position before the catheter tip is placed into the bladder. The catheter is then inserted into the bladder lumen through a stab incision in the centre of the purse-string suture. The balloon of the Foley catheter is then inflated but kept away from the bladder wall to avoid inadvertent catheter balloon puncture. Once the catheter tip is inside the bladder, the other end of the catheter should be occluded using artery forceps or similar. If a mushroom tipped catheter is being used, once it placed into the bladder the other end must be fed through the body wall in a similar position as previously described for the Foley catheter. Four cystopexy sutures

6 of polydioxanone are preplaced in a box configuration around the abdominal and bladder wall incisions. Ideally, the pexy sutures should pass through the seromuscular layers of the bladder wall and partial thickness through the body wall. The sutures are then tied and the catheter tip is drawn up to the bladder wall. The tube is secured with either a Chinese finger trap suture or tape tabs sutured to the skin. Abdominal closure is routine. The catheter is attached to a closed collection system initially. After a period of a few days, intermittent drainage can be undertaken. Summary: Success in treatment of lower urinary tract disease requires careful attention to the preanaesthetic medical work-up and stabilization of the patient. The decision to perform a surgical procedure will depend on whether obstructing calculi can be retropulsed into the bladder and if they cannont, the position of the obstruction and the presence or absence of catheter related urethral injuries. A good outcome for return of renal function can be expected for all these treatments, providing attention is given to the post-operative requirements of these animals, especially with respect to fluid requirements during post-obstructional diuresis.