Hyperkalaemia
Raised extracellular potassium partially depolarises cardiac myocytes and slows conduction, so the lethal risk is arrhythmia and cardiac arrest rather than the number on the result.
Definition
A serum potassium concentration of 5.5 mmol/L or more, adopting the European Resuscitation Council threshold. The UK Kidney Association grades it mild at 5.5 to 5.9 mmol/L, moderate at 6.0 to 6.4 and severe at 6.5 or more. Any ECG change attributable to hyperkalaemia is an emergency regardless of the band.
First principles
Severity is graded by the number, but the ECG says whether harm has already started
The severity bands set the treatment thresholds, but they do not measure the heart. About two thirds of patients in the severe band show ECG changes, so a normal trace is common and only partly reassuring. In one series every patient who deteriorated within six hours had a preceding abnormal ECG, and almost all events occurred before any treatment was given. That is why an abnormal trace triggers calcium at any level, while the number alone drives the shifting and removal steps.
This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.