General Principles in Urinary Tract Surgery
Urinary obstruction and uroperitoneum are medical emergencies and should be corrected before any surgery is planned. Hyperkalemia associated with these conditions makes the animal more prone to cardiac arrhythmias; therefore, fluid and electrolyte abnormalities should be corrected before anesthesia.
Urolithiasis is the main indication for urinary tract surgery. Whenever the urethra is obstructed, the patient should be first stabilized and deobstructed before surgery. This is achieved by the mean of retropulsion. Retropulsion should be done on emergency in order to:
Re-establish urethral patency
Decompress the bladder
Prevent post-renal renal failure
However, in cases of urolithiasis but when the patient is not fully obstructed, retropulsion should also be attempted before surgery in order to flush the calculi back into the bladder and to avoid urethrotomies.
Retropulsion is best achieved with the patient under deep sedation or general anesthesia to relieve as much urethral spasm and pain as possible during the procedure. A well-lubricated, smooth urinary catheter should be used. Once the stone has been flushed back into the bladder, the catheter is left in place in a closed manner and the patient is monitored until surgery.
When a patient is obstructed but retropulsion is impossible there are two possibilities:
1. The first option is emergency surgery of the urethra (urethrotomy or urethrostomy). Because of risk of bleeding or of stricture the procedure should be avoided as much as possible.
2. The second option is the placement of a percutaneous cystostomy tube. In the short term, the cystostomy tube offers immediate relief of obstruction. When the tube is left in place for a longer time, the decrease in intra-bladder pressure and inflammation can relieve some of the urethral pressure and spasm. Different types of percutaneous cystostomy tubes (Foley-type, pigtail-type, over-the-mandrin, out-of-the mandrin) have been described for both use in dogs or in cats.
In operating, respecting atraumatic surgical principles allows better healing, diminishes the infection rate and induces less pain. Because of the detrimental effect of post-operative swelling and pain on the urinary tract, these principles should be cautiously applied. Once exposed, the urinary bladder should be constantly flushed. Any suture should be placed without tension: this will limit local ischemia, fibrosis and dehiscence risk. Use of atraumatic instruments is mandatory. Traction sutures or atraumatic de Bakey forceps are recommended. Beside general a surgery pack, laparotomy sponges, suction apparatus and flushing solutions are needed. Well lubricated urinary catheters should always be available. Sutures and ligatures should always be as small as possible and not penetrate the mucosa (see below).
Anatomy of the urinary tract should also be well-known, mainly in respect to vessels and nerve localization. The bladder receives its blood supply from the cranial and caudal vesicular arteries, which are branches of the umbilical and urogenital arteries, respectively. Sympathetic innervation is from the hypogastric nerves, whereas parasympathetic innervation is via the pelvic nerve. The pudendal nerve supplies somatic innervation to the external bladder sphincter and striated musculature of the urethra. The urethra in male dogs is divided into prostatic membranous and penile portions.
Although the dorsal approach has been described, the ventral cystotomy is always preferred. By performing a ventral cystotomy, the neurovascular bundles as well as the ureters can be avoided. The risk of adhesions between the abdominal wall and bladder was formerly claimed as a reason not to perform a ventral cystotomy. These adhesions do not actually occur. A ventral cystotomy is performed as follows:
The caudal abdomen is packed with laparotomy sponges
A traction suture is placed at the apex of the bladder
Bladder opening is made in an avascular zone
Specimen collection for histopath, calculi and culture is made
Surgical retropulsion of calculi trapped in the trigone or into the urethra is carried out
The trigone, bladder wall and urethra are examined endoscopically (when available)
With a very well vascularized epithelium, bladder healing is usually very prompt. During the lag phase, which lasts 1 to 4 days, bladder resistance relies on the fibrin clot and suture material. The proliferation phase starts immediately after this and lasts up to 2 weeks after which the bladder wall usually gains 80% of its initial strength. Under normal conditions, the bladder wall will regain 100% of its initial strength within 3 weeks. Substantial portions of the bladder can be safely resected. As long as the trigone is undamaged, the bladder will expand (due to epithelial regeneration, scar tissue formation and remodeling, hypertrophy and proliferation of smooth muscle) until it again functions as an effective reservoir.
Suture material used to close the bladder wall should be chosen cautiously. Urine is a specific medium in which specific bacteria can grow. Most sutures appear to lose tensile strength faster in alkaline urine (such as that seen with Proteus infections) than in acidic urine or sterile urine. As a general rule, in order to avoid contact between urine and suture material, extra-mucosal sutures should be used. In addition, because multifilament materials can act as a nidus for calculi, they should be avoided. 3/0 to 5/0 monofilament absorbable (quickly absorbable is preferred) sutures on a round needle are usually recommended.
Cystotomy closure can be summarized as follows:
One layer appositional closure
Simple continuous or simple interrupted sutures
3-5/0 monofilament absorbable on a round needle
Animals with bladder or urethral calculi often have concurrent infections and should be treated with appropriate antibiotics based on urine culture and susceptibility. If the patient has already received a significant amount of antibiotic drugs, further antibiotic therapy should be withheld until intraoperative cultures are taken. Tissue (bladder wall) or calculi culture carry a greater chance of producing a positive result than a urine sample.
Urination should be closely monitored in patients after urinary tract surgery. Urinary catheters should be used cautiously as they may allow ascending bacterial infection or cause fibrosis and stricture.