Unblock that cat, STAT!
The ins and outs of treating urinary obstruction in your feline veterinary patients.
absolutimages / stock.adobe.comUrethral obstruction is a common emergency in cats. Cats with blocked urine outflow quickly develop metabolic disturbances that can be fatal. At the 2018 meeting of the American Association of Feline Practitioners, held in September in Charlotte, North Carolina, Elke Rudloff, DVM, DACVECC, of Lakeshore Veterinary Specialists in Milwaukee, Wisconsin, discussed emergency treatment of blocked cats and the importance of addressing cardiovascular instability before attempting to remove the obstruction.
Causes of urethral obstruction
Urethral plugs are made of either crystalline or cellular matrix. The most common crystal type in cats is struvite, Dr. Rudloff says, but other types of crystals also occur. Cellular-matrix plugs are collections of sloughed tissue, inflammatory cells or red blood cells.
Not all urethral obstructions are caused by plugs. Urethral inflammation, muscle spasms, stricture, neoplasia and reflex dyssynergia (incoordination of the bladder detrusor and urethral sphincter muscles) can also block outflow.
Male animals are much more likely than females to develop urethral obstruction due to their longer, narrower urethra, but obstruction is possible in females. Other risk factors are younger age, increased weight and a diet of only dry food, Dr. Rudloff says.
Cat owners may report crying, restlessness, bloody urine, frequent trips to the litter box, attempts to urinate outside the litter box, frequent licking of the genitals or vomiting in their pets. Owners sometimes mistake straining to urinate for constipation.
Physical examination may reveal pale mucous membranes and hypothermia. The patient's heart rate could be increased, decreased or normal. Dr. Rudloff reminds veterinarians that cats in hypovolemic shock tend to have bradycardia, not tachycardia. Severe biochemical changes can result in altered mentation. Abdominal palpation must be gentle to minimize pain and avoid rupturing the bladder, which is large and firm in blocked cats.
Stabilizing the patient
Dr. Rudloff stresses that cats in critical condition must be stabilized before bladder decompression is attempted. For a cat with circulatory compromise, “putting a urinary catheter in … is not going to save his life,” she points out. “It's not worthwhile to decompress his bladder until you've addressed the circulatory problems,” she adds.
Intravenous catheterization and the laboratory database. Dr. Rudloff recommends placing a peripheral intravenous (IV) catheter immediately. IV fluid treatment (with an isotonic crystalloid such as lactated Ringer's solution) can begin if the urinary obstruction will be removed soon. If urethral catheterization will be delayed, IV fluid therapy can wait.
Initial blood tests should include packed cell volume, total protein, electrolyte levels, glucose level and venous blood gases. Dr. Rudloff notes, however, that treatment should not be delayed if blood tests cannot be obtained right away. Some biochemical abnormalities can be inferred from the patient's condition, and an electrocardiogram (ECG) can show evidence of hyperkalemia without a blood test.
Managing hyperkalemia and dysrhythmias. Dysrhythmias caused by hyperkalemia require emergency treatment, Dr. Rudloff says. Electrocardiographic changes that indicate hyperkalemia include bradycardia, tall T waves, prolonged P-R interval, sinoventricular rhythm and asystole. “There is no set potassium level that predicts a dysrhythmia,” so treatment of hyperkalemia depends on ECG findings, she says.
Hyperkalemia in cats with adequate perfusion and a normal heart rhythm usually can be corrected with IV fluids alone, Dr. Rudloff says. Cats with dysrhythmias, poor perfusion, or altered mentation caused by hyperkalemia should receive an IV bolus of regular insulin to drive potassium into cells. The insulin bolus should be followed by a continuous IV infusion of dextrose. Calcium gluconate can be administered intravenously to protect the heart from the effects of hyperkalemia.
Relieving the obstruction
Once you've stabilized the patient, it's time to address the obstruction, Dr. Rudloff says.
Analgesia and sedation. Cats with urethral obstruction need immediate pain relief, possibly even before IV catheterization, Dr. Rudloff says. She recommends sedating cats for urethral catheterization with a combination of a narcotic and a tranquilizer (such as ketamine plus midazolam or propofol plus midazolam). She suggested that a combination of midazolam and either etomidate or alfaxalone could be safest in cats with cardiovascular instability.
To unblock cats, Dr. Rudloff usually does not use inhalation anesthesia or sedate cats to a level requiring intubation. She notes that isoflurane and sevoflurane cause vasodilation. An epidural or coccygeal anesthetic block can be helpful, she says. She also recommends applying lidocaine gel to the urinary catheter.
Unblocking the urethra. The unblocking procedure is done with sterile technique, including clipping the hair and placing a sterile drape. The initial catheterization should be done with a 3.5-F, open-ended polypropylene (tomcat) catheter. Warm saline mixed with water-soluble lubricant can be flushed through the catheter to retropulse the obstruction into the bladder. Dr. Rudloff recommends using a 1-ml tuberculin syringe to flush the catheter because it can generate higher pressures than a 3- or 6-ml syringe.
After the bladder has been decompressed and lavaged, the polypropylene catheter is replaced with a soft, 3.5-F red rubber tube, which is sutured into place. Another option is a multipurpose polypropylene urinary catheter that is suitable both for unblocking and for leaving in place. The indwelling urinary catheter should be connected to a closed collection system, Dr. Rudloff said. If the obstruction cannot be removed with a urinary catheter, the bladder can be decompressed with cystocentesis.
Here's what to keep an eye on while the patient is undergoing the procedure.
Fluid replacement. The IV fluid rate should account for maintenance needs and rehydration. Some cats become polyuric because of postobstructive diuresis, Dr. Rudloff says. She recommends measuring urine output every four hours and adjusting the fluid rate accordingly.
If urine output appears to decline despite adequate IV fluid replacement, check the collection system for kinks or clogs, she suggests. Bladder rupture, bladder atony and acute renal failure can also cause urine output to drop.
Expected complications. Cats with urethral blockage should be monitored for dehydration, azotemia, postobstructive diuresis, hyperkalemia or hypokalemia, urethral damage, hemorrhage, uroperitoneum and hypothermia. Cats need ongoing pain relief after bladder decompression.
Further diagnostic tests
Because inflammation affects urinalysis results, Dr. Rudloff suggests repeating urinalysis after the cat has recovered. Urinary tract infection is uncommon in male cats with first-time urethral obstruction, she says, so urine culture is not necessarily indicated in these cats. She recommends culturing the urine of blocked female cats and cats with repeat obstructions. Calculi flushed from the bladder should be submitted for laboratory analysis.
Diagnostic imaging can be performed after the patient is stable and the obstruction has been relieved. Partially inflating the bladder with sterile saline can make calculi and masses in the bladder easier to see on radiographs. Gently compressing the bladder with a wooden spoon (with the cat in lateral recumbency) improves the visibility of calculi on radiographs, Dr. Rudloff says. Ultrasound may reveal abdominal fluid and radiolucent or small calculi.
Interstitial cystitis is another feline urological condition that responds well to environmental enrichment. Read more in "FIC: It's not about the bladder."
Reported recurrence rates range from 14% to 57%, Dr. Rudloff says. Various medications (e.g. prazosin) have been used to prevent recurrence, but none have been shown to decrease the reobstruction rate. Dietary modification, increasing the amount of water ingested, and environmental enrichment are the best options for preventing reobstruction, she said.
Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. She is a practicing companion animal veterinarian and a certified editor in the life sciences (ELS). She owns Walden Medical Writing and writes and edits materials for healthcare professionals and the general public.