When large volume of intravenous saline are administered to correct extracellular fluid deficits, metabolic acidosis can result. Two theories have been proposed to explain metabolic acidosis, dilutional acidosis and hyperchloremic acidosis. This study was performed to evaluate the possible explanations for metabolic acidosis resulting from the infusion of large amounts of normal saline.

Thirty two adult patients who underwent upper abdominal surgery with general anesthesia were included in this study. All patients were allocated randomly to receive either normal saline (NS group, n = 16) or Hartmann's solution (HS group, n = 16) during anesthesia. We monitored arterial blood gas, electrolyte, and hematocrit values during the perioperative period. We also calculated the estimated postoperative HCO3- concentrations based on dilutional acidosis or hyperchloremic acidosis and compared these with the measured HCO3- concentrations. Statistical analyses were performed using the Fisher's exact test, unpaired t-test, paired t-test, and repeated measure ANOVA. Data are expressed as means ± SD.

The infusion of normal saline, but not of Hartmann's solution, caused metabolic acidosis with hyperchloremia. The estimated postoperative HCO3- concentration based on dilutional acidosis was almost the same as the measured HCO3- concentration. The estimated postoperative HCO3- concentration based on hyperchloremic acidosis was significantly lower than based on dilutional acidosis and the measured HCO3- concentration.

Infusion of large amounts of normal saline during anesthesia produced metabolic acidosis, which was not observed after the administration of Hartmann's solution. The appropriate term to describe this phenomenon is suggested to be dilutional acidosis.