To compare the short-term effects on acid base, electrolyte status and urine output of a single fluid bolus of saline to that of the balanced solution Plasmalyte® in critically ill patients.

Prospective, randomized, controlled trial. Adult patients (≥ 18 years) admitted to the ICU receiving a fluid bolus were randomized to receive 1 L of saline (NaCl 0.9%, Baxter) or a balanced fluid [Plasmalyte® (Baxter)]. Blood samples and urine output were collected just before (T0), just after (T1), 2 h after (T2) (only for urinary output) and three hours after termination of the fluid bolus (T4). The effect of fluid boluses on serum chloride, apparent strong ion difference, base excess, urinary output and blood pressure or vasopressor need were analyzed.

Patients who received a 1 L saline fluid bolus had a significant increase in serum chloride (1.60; 95% CI 1.10 to 2.10; P < 0.001) and short-term decrease in apparent strong ion difference (− 1.85; 95% CI − 2.71 to − 0.99; P < 0.001) and base excess (− 0.90; 95% CI − 1.31 to − 0.50; P < 0.001). We observed a 17% increase in patients developing hyperchloremia in the saline group (0.17; 95% CI 0.05 to 0.29; P = 0.005). No significant difference in urinary output, blood pressure or vasopressor need was observed in either group.

Even a single, small bolus of saline, administered to critically ill patients, causes a significant increase in chloride concentration and a decrease in apparent strong ion difference and base excess, and an increase in the number of patients developing hyperchloremia. No difference in effect on urinary output, blood pressure or vasopressor need was observed between the two groups.

2014-001005-41; date of registration: 28/10/2014.

EC project number 2014/038.