Hyponatraemia Quiz

See Euvolaemic. The best description is near-normal total body sodium with increased total body water, C. Serum sodium is a concentration, so adding water can lower the result without a major depletion of sodium stores. Euvolaemic means the person has no obvious clinical signs of extracellular fluid depletion or overload. It does not mean that total body water must be unchanged. Much of the retained water is distributed beyond the circulating compartment, and sodium regulation can limit obvious extracellular expansion. This is why water-retaining conditions can cause hyponatraemia without peripheral oedema.

Losing both sodium and water (A), with proportionally greater sodium loss, describes hypovolaemic hyponatraemia. Increasing both stores with a greater increase in water (E) describes hypervolaemic hyponatraemia, as can occur in heart failure. Isolated sodium depletion with unchanged water (D) can reduce sodium concentration but does not describe the usual euvolaemic water-excess model. Losing water while keeping sodium stores normal (B) concentrates sodium and tends towards hypernatraemia instead.