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Medical treatment includes  uid therapy, diuresis
with mannitol, analgesia, symptomatic treatment of uremic signs and amitriptyline or alpha-sympatholytic drugs (e.g. tamsulosin or prazosin). Medical treatment has been shown to be effective in only around 10% of cats. If medical treatment is not successful after 24 to
48 hours, or if the patient is unstable (hyperkalemic, oliguric, overhydrated) immediate intervention is indicated to decrease the intrarenal pressure and to reestablish urine  ow. During medical management, the renal pelvis should be checked for further enlargement.
Traditional surgery on feline ureters which have a diameter of only 0.4 mm is technically demanding. Perioperative mortality rates of 21% and perioperative complication rates of 30% have been reported (9, 10). The most common complications of ureteral surgery are perioperative leakage, stricture formation and recurrent obstruction, which are observed in around 40% of cats with ureteral stones.
Interventional techniques with surgical assistance for renal decompression and reestablishment of urine  ow such as ureteral stents and the subcutaneous ureteral bypass device (SUB) have been developed in the last decade and have improved the prognosis for cats with ureteral obstructions.
With the placement of feline double pigtail ureteral stents urine is diverted from the renal pelvis to the
urinary bladder. The success rate of stent placement in
a study with 69 cats (79 obstructed ureters) was 96%
(2). The perioperative mortality was 7.5%. Procedural complications were seen in 6/69 cats (urine leakage, pollakiuria/stranguria), post-operative complications (< 1 week) in 6/66 cats (stanguria, pollakiuria, urine leakage, stent dislodgement), short term complications (< 1 month) in 6/61 cats (stranguria, pollakiuria, stent migration) and long term complications in 20/60 cats requiring a stent exchange or SUB device in 19/60 cats. The median survival time was 498 days, and the 1-year survival rate of all stented patients was 65%. In another study with 26 cats (31 obstructed ureters) the mortality rate before discharge was 15%. In this study, obstructions were due to ureteric calculi (21 cats), ureteric strictures (4 cats) and due to traumatic bilateral obstructions (1 cat) (11). Eight of the
cats that survived to discharge were later euthanized due
to marked azotemia, and three cats were euthanized due to severe dysuria refractory to medical treatment. In 8 cats, stent replacement was necessary due to stent migration, fracture, mineralization causing luminal obstruction or sterile cystitis. The median survival time in this study was 265 days and the 1-year survival rate was 44%. Based on this study, the prognosis of cats with stent placement remains guarded because of the presence of chronic renal disease but also because of intervention related complications, such as dysuria, which is seen in up to 35% of cats with ureteral stents, stent migration or fracture.
An Urban Experience
The SUB system includes a nephrostomy tube and
a cystotomy tube, which are placed permanently and
are connected via a subcutaneously placed shunting tube. With this system, urine can  ow through the attached catheters from the renal pelvis to the bladder. Implantation of a SUB device was originally developed
as a salvage procedure for cats in which a stent could not be placed due to a very narrow lumen of the ureter or excessive ureteral stones. In recent years, it has
been shown that the SUB device is advantageous over stents for all causes of ureteral obstruction in cats with regard to mortality and long-term complications. In a retrospective study of 137 cats with ureteral obstruction due to ureterolithiasis (67%), stricture (13%), stricture and stones (20%) or pyonephrosis (0.5%) placement of the SUB device was successful in all cases. Perioperative complications were device leakage (3.4%), kinking
(5%), occlusion with blood clots (7.5%) and catheter mineralization (25%). Of the 137 cats, 94% survived
to discharge and the median survival time was 827
days (12). Dysuria which is a common complication
in cats with ureteral stents (>30%), is an uncommon complication in cats with an SUB device (<5%). A smaller study that investigated initial outcomes and complications of the SUB procedure at two university hospitals reported a need for blood transfusion in the peri- or post-operative period in 8/19 cats, pleural effusion in 2/19 cats, and a 21% rate of bacterial urinary tract infections within 10 days of surgery (13). None
of these cats had a positive culture or an active urine sediment before surgery. Two patients had recurrent multi-drug-resistant UTI infections. Recurrent and resistant infections and the potential for bio lms are therefore a signi cant concern in SUB patients. The median disease-free interval was 180 days, the 1-year survival rate was 83%.
Ureteral obstructions in cats are increasing in frequency. Adequate diagnostics should be performed as soon
as possible in order to identify this condition and to improve the chance for recovery of renal function with earlier intervention. Good collaboration between primary care veterinarians, medicine and surgery specialists is necessary for the management of affected cats. Despite the promising results with interventional procedures, owners also need to understand possible short and long- term complications of these interventions.
1. Osborne CA, Lulich JP, Kruger JM, Ulrich LK, Koehler LA. Analysis of 451,891 canine uroliths, feline uroliths, and feline urethral plugs from 1981 to 2007: perspectives from the Minnesota Urolith Center. Vet Clin North Am Small Anim Pract. 2009;39(1):183-97.
2. Berent AC, Weisse CW, Todd K, Bagley DH. Technical and clinical outcomes of ureteral stenting in cats with benign ureteral obstruction: 69 cases (2006-2010). J Am Vet Med Assoc. 2014;244(5):559-76.
3. Wilson DR. Renal function during and following obstruction. Annu Rev Med. 1977;28:329-39.
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