{"id":8861,"date":"2022-01-28T19:05:32","date_gmt":"2022-01-28T19:05:32","guid":{"rendered":"https:\/\/tvn.tv-multi-theme.com.216-70-96-51.jvv2-rfnp.accessdomain.com\/?p=8861"},"modified":"2025-11-12T15:06:40","modified_gmt":"2025-11-12T15:06:40","slug":"subcutaneous-ureteral-bypass-as-a-treatment-option-for-urolithiasis-in-cats","status":"publish","type":"post","link":"https:\/\/navc.sitepreview.app\/todaysveterinarynurse.com\/urology-renal-medicine\/subcutaneous-ureteral-bypass-as-a-treatment-option-for-urolithiasis-in-cats\/","title":{"rendered":"Subcutaneous Ureteral Bypass (SUB) as a Treatment Option for Urolithiasis in Cats"},"content":{"rendered":"

The subcutaneous ureteral bypass (SUB) system has revolutionized the treatment of upper urinary tract urolithiasis in cats over the past 10 years. This completely indwelling system bypasses the ureter and diverts urine from the kidney to the bladder through a locking-loop nephrostomy tube and cystostomy tube, respectively. Both tubes join at a connector within the abdomen; an accessory tube from the connector to a subcutaneous shunting port allows percutaneous access to the system (FIGURE 1<\/span><\/strong>).<\/p>\n

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Figure 1. SUB 3.0 showing the X-connector with the cystostomy tube (black arrows) secured to the cranial portion of the connector along with the accessory tube (red arrows). The bilateral nephrostomy tubes (white arrows) are secured at the caudal portion of the connector.<\/p><\/div>\n

Knowledge of the disease process of feline upper urinary tract urolithiasis and current treatment recommendations is important for veterinary nurses. Effective client education involves understanding available treatment options, indications for intervention, and associated risks and complications. In patients that receive a SUB, long-term management of the device after placement is also required; therefore, understanding the various components is essential for a successful outcome.<\/span><\/p>\n

Feline Ureterolithiasis<\/h2>\n

Feline ureteral obstructions are increasingly being reported.1<\/sup> This increase in incidence may be attributed to greater awareness, better diagnostics, and owners electing to pursue treatment; however, these obstructions continue to be challenging to manage. More than 90% of feline ureteroliths retrieved are composed exclusively of calcium oxalate (CaOx)2<\/sup> and are not amenable to dissolution. To further complicate matters, numerous stones may be present, with a median of 2 to 4 stones per ureter3,4<\/sup> and up to 85% of cats with evidence of concurrent nephrolithiasis.4<\/sup> Partial obstructions may be monitored, but resolution of even partial obstructions can be beneficial and may maximize renal function in a cat with known ureterolithiasis due to preexisting renal disease. <\/span><\/p>\n

Obstructive Nephropathy<\/h2>\n

The luminal diameter of the feline ureter is 0.4 mm1<\/sup> and not likely to accommodate even small uroliths. A postrenal obstruction creates back pressure that is transmitted proximally from the site of obstruction and directly to the renal tubules. After an initial increase in both renal blood flow and glomerular pressure, both fall rapidly, resulting in a significant decrease in the glomerular filtration rate (GFR).4<\/sup> Depending on the duration of obstruction, interstitial inflammation, ischemia, tubular atrophy, fibrosis, and renal cell death may occur.5<\/sup> The longer the obstruction, the more significant the damage; therefore, timing is critical for restoring function to the affected kidney. Left untreated, renal injury may become irreversible with a permanent reduction in GFR and destruction of the renal parenchyma.<\/span><\/p>\n

The presence of azotemia on bloodwork indicates that GFR has decreased to 25% of normal. When this is the result of obstruction, it indicates that the obstruction is bilateral or the unobstructed contralateral kidney is dysfunctional. Otherwise, in cases of unilateral obstruction, the contralateral kidney should be able to compensate for the decrease in GFR. Decreased renal function of the contralateral kidney may be due to a prior undetected episode of ureteral obstruction or concurrent chronic kidney disease (CKD), as up to 20% of all cats are affected by CKD during their lifetime.6<\/sup> Cats with preexisting renal compromise are at the greatest risk for an acute onset of severe azotemia with even a partial obstruction. Any delay in care may contribute to a further decrease in kidney function.<\/span><\/p>\n

Physical Examination and Clinical Findings<\/h3>\n

Clinical signs of upper urinary tract obstruction can vary in severity at presentation, depending on factors such as duration and degree of obstruction, degree of impairment of each kidney, degree of prerenal azotemia, and presence of pyelonephritis. Cats may be asymptomatic, with ureterolithiasis diagnosed as an incidental finding or obtunded in critical condition due to uremia. Most commonly, cats present with nonspecific signs such as inappetence, vomiting, lethargy, weight loss, polyuria and polydipsia, and lower urinary tract signs (e.g., stranguria, pollakiuria, periuria, hematuria). Owing to the high incidence of ureterolithiasis, diagnostic imaging is recommended for cats with chronic nonspecific clinical signs with or without evidence of renal disease.2<\/sup><\/span><\/p>\n

Azotemia, metabolic acidosis, hyperphosphatemia, hyperkalemia, anemia, and leukocytosis may be present on bloodwork.2<\/sup> Urine sediment may or may not be indicative of inflammation or infection and, in cases with a complete obstruction, may only represent the nonobstructed kidney (as no urine from the obstructed kidney will be present in the <\/span>bladder). If possible, a urine sample should be submitted for culture to look for a urinary tract infection (UTI) and prior to initiation of antimicrobials. A sample from the renal pelvis at time of intervention is also typically submitted for aerobic <\/span>culture. Abdominal pain may be appreciated on physical examination due to stimulation at the site of obstruction and\/or dilation of the collection system and renal capsule.5<\/sup> Bilateral renomegaly may be present with <\/span>bilateral obstruction or big kidney-little kidney palpated due to renal fibrosis of the non-obstructed kidney. <\/span><\/p>\n

Diagnostic Imaging<\/h3>\n

The combination of radiography and ultrasonography can identify and diagnose ureteroliths, nephroliths, and signs of complete or partial obstruction.2<\/sup> Increased renal size and radiodense uroliths may be easily detected on radiographs of the upper urinary tract (<\/span>FIGURE 2<\/span><\/strong>). Hydroureter seen on ultrasonography is the result of the ureteral lumen expanding with urine and is typically proximal to the occlusion (<\/span>FIGURE 3<\/span><\/strong>). The ureter often becomes tortuous as ureteral peristalsis increases in an attempt to relieve the obstruction.5<\/sup> This distention and increase in intraluminal pressures can result in mild to marked renal pelvic dilation, or hydronephrosis, seen on ultrasonography as the collection system fills with urine (<\/span>FIGURE 4<\/span><\/strong>). The finding of a small contralateral kidney is not uncommon with unilateral obstruction (FIGURE 2<\/span><\/strong><\/span>).<\/span><\/p>\n