Hyperkalaemia in the blocked cat: ECG changes and treatment
4-year-old neutered male cat with 48 hours of unproductive attempts to urinate. He is recumbent, hypothermic and has a large, firm bladder. ECG and blood work:
| Parameter | Result | Reference |
|---|---|---|
| Heart rate | 120 bpm | 140–240 bpm |
| P wave | Absent | Present |
| QRS | 0.07 s, wide | ≤ 0.04 s |
| T wave | Tall and peaked | Small |
| Potassium | 9.4 mmol/L | 3.5–5.5 |
| Creatinine | 8.2 mg/dL | 0.8–2.0 |
| Ionised calcium | 0.85 mmol/L | 1.10–1.40 |
What is the most appropriate first therapeutic measure?
chevron_right Show answer and explanation
A. IV lidocaine, because the wide complexes indicate a ventricular rhythm
The wide QRS is due to hyperkalaemia, not a ventricular arrhythmia. Lidocaine does not correct the cause and in cats has a narrow margin for neurological and cardiac toxicity.
B. Slow IV 10% calcium gluconate with ECG monitoring, together with fluid therapy
Correct. Calcium does not lower potassium, but it restores the difference between resting and threshold potential and protects the myocardium within minutes for about 20–30 min. This cat's ionised hypocalcaemia also worsens cardiotoxicity. Then: insulin with glucose, decompression and unblocking.
C. IV atropine to correct the bradycardia
The bradycardia results from hyperkalaemia, not vagal tone, and does not respond to atropine. The potassium must be treated.
D. General anaesthesia and immediate urethral catheterisation before anything else
Anaesthetising a cat with potassium of 9.4 mmol/L and these ECG changes carries a high risk of arrest. Stabilise first; unblocking comes afterwards.
lightbulb Key takeaway
A blocked cat in pain and shock should be tachycardic: bradycardia is a red flag for hyperkalaemia. Record an ECG on admission. Order: IV calcium (protects the heart), insulin with glucose (shifts potassium into cells), fluids and unblocking; monitor blood glucose after insulin.
Test yourself with 10 random questions
Cardiology · 100 questions, a different test every time
Related questions
Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.