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Subcutaneous Ureteral Bypass Catheter devices

In a normal cat, urine is produced in the kidneys and filters through into a collecting pool of the kidney called the "renal pelvis" before flowing down a tube called the ureter into the urinary bladder.

Ureteral obstructions occur when a blockage in the ureter prevents drainage of urine. Obstruction of urine flow can severely damage the kidneys.

Ureteral obstructions occur due to stones, blood clots or pus associated with infection. Other causes include ureteral strictures (scars) or ureteral cancer (this is rare).

The most common cause of ureteral obstruction in cats are due to kidney stones that move into and block the ureter. Stone formation accounts for approximately 80% of ureteral obstructions. Ureteral strictures or ureteral scars are the second most common cause and some patients have both. Most (>90%) stones are a type called calcium oxalate.

Ureteral obstructions may be partial or complete and involving one or both kidneys. If obstructions occur on both sides, life-threatening kidney failure can occur. Complete obstruction of both kidneys would be fatal within 48-72 hours if left untreated. Partial ureteral obstructions typically cause less severe damage to the kidneys and patients may achieve a greater return to function after relief of the obstruction.

Not only are stones the most common cause of ureteral obstruction, they also can serve as a risk for infection, leading to chronic urinary tract infections which can further complicate treatment.

Some patients have no clinical signs, especially if the non-obstructed kidney has normal function or if the obstruction is partial. Patients with obstructions on both sides have more severe signs. Possible signs include inappetence, vomiting, lethargy, weight loss, increased thirst and urination and straining to urinate.

Ultrasound is essential in identification of ureteral obstruction as the obstruction causes changes including enlarged kidneys, dilation of the ureters or urine draining portion of the kidney (renal pelvis) and bright tissue surrounding the kidneys. The stones themselves maybe seen with ultrasound, xray or sometimes a CT scan.

Subcutaneous Ureteral Bypass Catheter devices

Treatment

Many cases of ureteral obstruction ultimately require some sort of surgical intervention.

Medical management can be attempted using intravenous fluid therapy to increase urine production and drugs to relax ureteral smooth muscle, decrease ureteral inflammation and provide pain relief. Medical therapy has been shown to be effective in only a small number of cats (7.7-15%).

Unfortunately, kidney blood flow and the kidney's ability to produce urine, continues to deteriorate if the ureteral obstruction is not resolved and irreversible loss of kidney function can occur. Many patients are not candidates for medical management or do not respond to medical therapy, so other treatment options are typically needed.

Surgical removal of stones is very difficult due to the small size of the ureter in cats. Scar tissue commonly forms within the ureter that causes another obstruction after surgery is completed. For these reasons, surgical removal of the stones by opening the ureter is rarely performed.

Currently the recommended treatment is called Subcutaneous Ureteral Bypass or SUB.

SUBs are permanent "false or prosthetic ureters" - these are tubes placed into the kidney under the guidance of a "continuous xray machine" (fluoroscopy). The catheter is placed into the kidney into the region called the "renal pelvis", which is wider than usual due to the ureteral obstruction. The catheter is then joined to a metal port under the skin. A second catheter connects to the port, re-enters the abdomen and is placed into the urinary bladder. This system allows the urine to flow from the kidney to the urinary bladder but bypasses the obstructed ureter.

Ureteral obstruction and surgical intervention

One report assessed 134 cats with SUBS. Most cats (94%) survived to discharge. Complications included catheter blockage with blood clots (8.1%), catheter leakage (3.5%) and kinking of the catheter (4.6%). The most common long-term complication was mineralisation of the catheter which occurred in 24.2%. Long term survival times depends on how well the kidneys are functioning around 3 months after surgery. This is determined by blood and urine testing at that time.

Management of ureteral obstructions does not achieve a cure. Our aim is to restore and support kidney function. It is possible that some cats will have long-term kidney disease post-treatment and the long-term outcome depends on the stability of the kidney function. Cats with stable kidney disease after treatment will have a better outcome.

Sometimes once the pressure on the obstructed kidney is relieved by providing an alternative route for urine to drain, stones may move through to the bladder and drainage through the ureters recommences again.

Ongoing veterinary care is required for cats with SUBs. They need long term management of their SUB devices to try and prevent blockages or infection. This is done by "flushing the system" and is typically performed 7 days and 30 days after placement, then every 3 months thereafter for life. In most cats this procedure only takes an hour and is performed under sedation, however we typically ask you to drop your cat off for the day.

The placement of a SUB device is a new and advanced procedure. We have cared for many cats now using this life saving procedure and our experiences have been very positive.

Subcutaneous Ureteral Bypass Catheter devices

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