Hyponatraemia--a prospective analysis of surgical patients.

A prospective study of 71 patients with hyponatraemia was undertaken over an 18-month period in one surgical unit at King Edward VIII Hospital, Durban, to study the incidence and pattern of hyponatraemia. Electrolytes and urea values were measured serially in all patients. Hyponatraemia was defined as a serum sodium level of < 130 mmol/l. The incidence of hyponatraemia was 2.2%, the most common type being normovolaemic hypotonic hyponatraemia. Hyponatraemia was either mild (sodium level 120-130 mmol/l) or moderate (111-120 mmol/l). No patient had severe hyponatraemia (< 110 mmol/l). Hyponatraemia was corrected within 1-6 days using normal saline; in 73% of patients it was corrected within 24 hours. No patient developed neurological symptoms. A mortality rate of 28% was attributed to underlying illness, and hyponatraemia per se was asymptomatic in this study. Aggressive sodium correction was therefore not indicated.