Effect of mannitol on diuresis and acid-base equilibrium in critically ill patients.

BACKGROUND

Mannitol is the most commonly used osmotic diuretic, but its effect on plasma and urine electrolytes and on acid-base equilibrium have not been well investigated. The aim of this study was to evaluate the short-term effects of mannitol on diuresis and plasma and urine acid-base equilibrium in a group of critically ill patients according to the Stewart approach.

RESULTS

Prospective observational study enrolling all consecutive sedated and mechanically ventilated patients requiring mannitol infusion for clinical purpose. Plasma and urine acid-base variables and electrolytes were measured before mannitol infusion and every 60 and 30 min, respectively, following the infusion of 1 g/kg of ideal body weight of mannitol. Forty-two patients were enrolled. Diuresis increased significantly 30 min after the mannitol infusion was completed and remained significantly higher as compared with T0. Plasma sodium and chloride concentrations and plasma SID significantly decreased after mannitol infusion ended; urine sodium and chloride concentration remained unchanged, while urine ammonium increased increasing urine SID.

CONCLUSIONS

Since the end of the infusion, mannitol promoted a significant increase in diuresis, with a reduction in plasma electrolytes due to volume expansion, and a slight decrease in arterial pH due to dilutional acidosis. Kidney relative excretion pattern was unmodified during the study.