Cat with Urethral Obstruction and Severe Hyperkalemia
Tiger is a 5-year-old male castrated Domestic Shorthair, 5.6 kg, brought in at 23:10 after 14 hours of straining to urinate with only drops produced. He is vocalizing, has a tense painful abdomen, and a firm bladder the size of a baseball. HR 170, weak femoral pulses, RR 36, temperature 36.1 C, pale mucous membranes, CRT 2 seconds. He is laterally recumbent and minimally responsive. The veterinarian placed an IV catheter and ran bloodwork: potassium 8.4 mmol/L, sodium 141 mmol/L, BUN 82 mg/dL, creatinine 7.9 mg/dL, glucose 240 mg/dL, PCV 42%, TS 7.6 g/dL. The ECG shows bradycardia with no visible P waves, spiked T waves and a widened QRS. The practice has 10% calcium gluconate, regular insulin, 50% dextrose, 0.9% NaCl, lactated Ringer's solution and a fluid pump. The veterinarian is on the phone with the owner about cost.
1. Interpret the ECG and list the immediate interventions, with doses, in the order you would give them.
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Interpretation. Absent P waves, spiked T waves, wide QRS and bradycardia indicate a sinoventricular rhythm from severe hyperkalemia - a pre-arrest rhythm at risk of ventricular fibrillation or asystole. This is a membrane emergency, not a number to recheck later.
Order.
- Oxygen, ECG continuously, minimal handling.
- 10% calcium gluconate 0.5-1.0 mL/kg IV slowly over 10-15 minutes with ECG monitoring (2.8-5.6 mL for this cat). It stabilizes myocardium within minutes but does not lower potassium; it lasts 30-60 minutes, so the next steps must follow.
- Regular insulin 0.1-0.2 U/kg IV (0.6-1.1 U) with dextrose 1-2 g per unit, given as a diluted bolus, then monitor glucose at 30, 60 and 120 minutes for hypoglycemia.
- 0.9% NaCl bolus 10-20 mL/kg over 15-20 minutes to restore perfusion and dilute potassium.
- Consider nebulized albuterol as an adjunct.
- Relieve the obstruction as soon as the rhythm allows - do not wait for potassium to normalize before decompressing.
2. Which fluid would you choose for the first hour and why, and what is the plan once the obstruction is relieved?
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First hour. 0.9% NaCl. Balanced crystalloids such as lactated Ringer's contain potassium (about 4-5 mmol/L) and, more importantly, the cat needs volume and sodium loading to improve perfusion; normal saline is the conventional choice during the hyperkalemic crisis. Give 10-20 mL/kg (56-112 mL) over 15-20 minutes, reassess perfusion, mentation and lung sounds, and repeat only if indicated - this cat is small and can be overloaded.
After relief. Switch to a balanced crystalloid once potassium is trending down, because the post-obstructive diuresis will waste potassium and the cat can become hypokalemic. Measure urine output with a closed collection system. Output above roughly 2-3 mL/kg/hour is post-obstructive diuresis; replace losses milliliter for milliliter with a balanced fluid while accounting for maintenance, then reassess every few hours.
Monitoring. Potassium, BUN, creatinine, PCV/TS, body weight, blood pressure and urine output. Watch for hypokalemia, dehydration, re-obstruction and bladder rupture; keep the cat hospitalized until he is eating and producing adequate urine without a catheter.
3. Describe how you would relieve the obstruction and what could go wrong during and after the procedure.
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Technique. Once the ECG is improving and analgesia is on board, clip and aseptically prepare the perineum. Use a sterile, lubricated tomcat catheter with lidocaine gel; advance gently with steady pressure, never force. If the plug is at the tip, flush with sterile saline using a three-way tap at low pressure. If the catheter will not pass, stop and let the veterinarian consider cystocentesis for temporary decompression or a perineal urethrostomy - repeated blind trauma causes strictures.
During. Watch for vagal bradycardia, bladder rupture, hemorrhage, and sudden release of a distended bladder causing decompensation. Do not empty a very distended bladder completely in one go; decompress slowly and leave a closed system in place if indicated.
After. Expect hematuria for 24-48 hours. Monitor for re-obstruction, which is common in the first 72 hours, and for urine leaking into the abdomen. Discuss diet (dissolution or prevention depending on stone type), water intake, stress reduction and a recheck plan with the owner, and warn them that recurrence is a when-not-if problem.