Potassium

Hyperkalaemia: The Three-Step Emergency

Potassium is the most abundant ion inside your cells and the most tightly guarded ion in your blood — and for good reason. Let the level in the serum drift up by a couple of millimoles and the heart's electrical membrane begins to fail: the ECG deforms through a predictable, sinister sequence and can end in a flat line. What makes hyperkalaemia a favourite of examiners and a terror on the ward is that the fix is not one drug but a choreographed three-step protocol — protect the heart, shift the potassium, remove it — and getting the order and the logic right is the whole game.

Hypokalaemia: Safe Replacement and the Magnesium Link

Potassium is the most abundant ion inside your cells, and the gradient it holds across every membrane is what lets nerves fire and the heart beat in rhythm. Move that number a little — a diuretic here, a bout of vomiting there — and the same ion that runs the heart can stop it. Hypokalaemia is one of the commonest electrolyte disturbances on any ward, and much of it is made by the drugs we prescribe. This chapter is about reading the danger early, replacing potassium without killing the patient in the process, and the one companion ion — magnesium — that quietly decides whether your replacement works at all.