Urethral Obstruction in Small Animals

Mechanical obstruction of the urethra can occur as a result of urethroliths, urinary tract neoplasia, stricture, prostatic disease, or extraluminal compression from adjacent organs. Functional obstruction of the urethra can also occur. 

Male cats are uniquely predisposed to UO as a complication of lower urinary tract disease, and urethral plugs are responsible for UO in most cases.

Obstruction of urine flow leads to accumulation of metabolic wastes and postrenal azotemia and uremia.

Animals with UO might exhibit frequent nonproductive attempts to urinate. Obstructed animals might also vocalize during attempts to urinate. Owners of cats, in particular, might mistake the signs of UO for constipation. 

Complete UO causes uremia within 36–48 hours, which leads to depression, vomiting, diarrhea, dehydration, coma, and death within approximately 72 hours. 

On physical examination, animals with UO typically have a hard, distended, and painful bladder. 

The pelvic urethra can be readily palpated on rectal examination in dogs and might reveal a stone, prostatomegaly, or mass. 

External genitalia should be examined to look for evidence of blood, trauma, or stone material. 

Depending on the severity and chronicity of UO, the animal might be depressed or dehydrated, show signs of shock, and have bradyarrhythmia.

• Physical examination

• Radiography

• Blood work and urinalysis

Diagnosis of UO is usually suspected from physical examination findings.

An ECG should be monitored and blood collected for point-of-care evaluation including assessment of electrolyte concentrations, renal values, and acid-base status. 

Diagnostic workup of UO should always include radiography to evaluate for uroliths, urinalysis, and blood work to evaluate kidney function and electrolytes. The timing of these diagnostic tests depends on patient stability before urethral catheterization.

Advanced diagnostic tests—such as contrast urethrography, CT, ultrasonography, or urethrocystoscopy—might be indicated in some UO cases. 

• Stabilization

• Decompressive cystocentesis

• Relief of obstruction

UO is an emergency condition, and stabilization should be prioritized in severely affected patients. 

Venous access should be obtained, and IV fluid therapy with a crystalloid solution (eg, lactated Ringer's solution or 0.9% NaCl) should be administered. With dehydration or hypovolemia, an initial bolus might be required as part of fluid resuscitation.

Life-threatening hyperkalemia can develop with UO and should be addressed promptly. When severe (serum potassium concentration > 7.5 mEq/dL), hyperkalemia can cause life-threatening cardiac arrhythmias and requires prompt intervention. All patients with severe hyperkalemia should have ECG monitoring. 

Ten percent calcium gluconate (0.5–1.5 mL/kg, slow IV over 15–30 minutes while monitoring ECG for arrhythmias) is often chosen as first-line treatment for hyperkalemia because of its effect within minutes. Note that calcium gluconate decreases membrane excitability of the cardiac myocytes but does not lower serum potassium concentration. 

One or more therapies to promote intracellular translocation of potassium are typically administered along with calcium gluconate. Fifty percent dextrose can be administered (0.5–1 mL/kg, diluted 1:4 in saline solution and administered IV slowly) alone or along with regular insulin (0.25–0.5 U/kg, IV). If regular insulin is given, after an initial dextrose bolus, 2.5–5% dextrose should be continued in IV fluids until the effect of the insulin has worn off to prevent hypoglycemia (2–6 hours). 

Other drugs that promote intracellular translocation of potassium include sodium bicarbonate (1–2 mEq/kg, slow IV) and beta-2-adrenergic receptor agonists (bronchodilators) such as terbutaline (0.01 mg/kg, IV) or albuterol (1–2 puffs using a metered-dose inhaler [90 mcg/actuation], delivered via an appropriately sized spacer and face mask). 

These therapies are a temporary way to mitigate arrhythmias and decrease serum potassium before restoring renal excretion of potassium by relieving urinary tract obstruction.  

Decompressive cystocentesis should be performed in animals too unstable for the heavy sedation or anesthesia needed to relieve UO. Despite historical controversy and concerns for bladder rupture, the procedure appears to be generally safe (1).

Ultimately, UO must be relieved. In dogs, relief might be straightforward and accomplished by passing a urinary catheter. If an intraluminal obstruction is encountered and the catheter cannot be easily passed, a smaller-diameter catheter can be used, or attempts can be made to retropulse the obstructing object back into the bladder by instilling saline solution (0.9% NaCl) with or without sterile lubricant through the urinary catheter while occluding the distal urethra digitally to allow for fluid distention of the urethra. 

In male cats, relief of UO should be done under general anesthesia whenever possible, with care taken to provide adequate pain management because of the risk of urethrospasm, tearing, or stricture development associated with the procedure. Detailed descriptions of how to unblock a male cat can be found in other resources (2).

Depending on the etiology of UO, additional urinary diversion options might be required if catheterization is either unsuccessful or provides only temporary relief (eg, with tumors or stricture). 

Other possible procedures to address UO include placement of a urethral stent, cystostomy tube placement, urethral surgery to bypass a structure or mass, and laser lithotripsy to remove an obstructing urethral stone.

• George CM, Grauer GF. Feline urethral obstruction: diagnosis and management. Today’s Vet Pract. 2016;6(4):36-46.  

• Cooper ES. Controversies in the management of feline urethral obstruction. J Vet Emerg Crit Care (San Antonio). 2015;25(1):130-137.

• Also see pet owner content regarding urethral obstruction in dogs and cats.

1. Gerken KK, Cooper ES, Butler AL, Chew DJ. Association of abdominal effusion with a single decompressive cystocentesis prior to catheterization in male cats with urethral obstruction. J Vet Emerg Crit Care (San Antonio). 2020;30(1):11-17. doi:10.1111/vec.12914

2. George CM, Grauer GF. Feline urethral obstruction: diagnosis and management. Today's Vet Pract. 2016;6(4):36-46.