As an approximation, a decrease in plasma pH of 0.1 units results in an increase in plasma potassium of approx. 0.6 mmol/l 1. ECF/ICF distribution. Normally, cell membrane sodium pump (Na-K-ATPase) keeps intracellular sodium low (approx. 10 mmol/l) and the intracellular potassium high (approx. 140 mmol/l). Hypokalaemia (plasma K+ < 3.3 mmol/l), and Hyperkalaemia (plasma K+ > 5 mmol/l) are both common and potentially lethal, particularly if acute. (a) Acid base status