Acid base and electrolyte changes after hypertonic saline (7.5%) infusion: a randomized controlled clinical trial

Hypertonic saline solutions are effective in the treatment of haemorrhagic and septic shock, elevated intracranial pressure and perioperative fluid deficits. Infusion, however, causes electrolyte and acid-base imbalance. In a randomized double-blind study, the effects of a 10-min infusion of 4 ml/kg 7.5% NaCl or 0.9% NaCl were evaluated in 14 fasting women before hysterectomy. Venous blood from the forearm was collected at baseline, 10, 20, 30, 60 and 120 min after start of the infusion for the determination of plasma electrolytes and acid-base balance. We found that 1) a median increase in plasma sodium of 11 mmol/l (range 9-13 mmol/l) and chloride of 14 mmol/l (range 9-16 mmol/l) immediately after the infusion followed by a small decrease after 2 h, 2) a minor decrease in plasma potassium in relation to the infusion followed by a significant increase of 0.3 mmol/l (range 0.1-1.4 mmol/l) above baseline after 1 h, 3) a decrease in pH of 0.05 (range 0.02-0.07) and, finally, 4) a decrease in base excess of 1.9 mmol/l (range 0.8-2.7 mmol/l). It is concluded that infusion of 7.5% NaCl in a clinical relevant dose increases plasma potassium and causes minor changes in the acid-base balance in normovolaemic women.