Hyperkalaemia. Poisoning is usually minimal below 6.5 mmol per litre but may be severe above 8 mmol per litre.
However, comparatively low doses may cause adverse effects when excretion is delayed as in renal insufficiency. The absolute toxicity is dependent on other electrolytes and acid-base levels.
Hyperkalaemic symptoms include paraesthesia of the extremities, listlessness, mental confusion, weakness, paralysis, hypotension, cardiac arrhythmias, heart block and cardiac arrest.
Hyperkalaemia is often asymptomatic. However, increasing serum potassium levels can be detected by changes in the ECG; initially the appearance of tall, peaked T waves, followed by a widening of the QRS complex bending into the abnormal T waves. P-wave voltage decreases and the PR interval is prolonged.
Severe cardiac toxicity may be treated with calcium gluconate (10-20ml of a 10% injection given over 1-5 minutes with ECG monitoring). The effect may be transient and the injection may need to be repeated.
Raised serum potassium levels respond to administration of dextrose (300-500ml/hr of 10 or 25% solution), dextrose and insulin (as for dextrose with 10 units of insulin per 20 g dextrose), or sodium bicarbonate solution.
Cation exchange resins may be used, or in severe cases peritoneal dialysis or haemodialysis may be necessary.
Caution should be exercised in patients who are digitalised and who may experience acute digitalis intoxication in the course of potassium removal.