Clinical settings and vasopressin function in hyponatraemic children.

Hyponatraemia is one of the most common electrolyte abnormalities in hospitalised children. In a prospective study we tested whether hyponatraemia is associated with sustained release of the antidiuretic hormone arginine vasopressin (AVP). Out of 27 children with persistent hyponatremia (serum sodium < 130 mmol/l), 25 had measurable plasma concentrations of AVP [median and quartiles 5.0 pg/ml (1.5-8.3)]. Volume contraction as consequence of sodium loss caused hyponatraemia in 16 patients. Hyponatraemia in the presence of extracellular volume expansion and reduced effective arterial blood volume occurred in 5 patients. Only 3 patients had normovolaemic hyponatraemia (so-called syndrome of inappropriate antidiuretic hormone secretion) and 3 suffered from chronic renal failure. It is concluded that plasma AVP concentration is measurable in most children with hyponatraemia. Non-osmotic stimulation of AVP release and lack of suppression of this hormone is an important pathogenetic mechanism of hyponatraemia in children.