BackgroundThe intent of this study was to evaluate the impact of the commonly used colloids—hetastarch and albumin—on in vivo acid–base balance. From this evaluation, a better understanding of the mechanism of dilutional acidosis was expected.MethodsIn a prospective, randomized fashion, 11 healthy volunteers were administered 15 ml/kg hetastarch solution, 6%, or 15 ml/kg albumin, 5%, intravenously over 30 min. Four weeks later, the study subjects were administered the other colloid. Arterial blood gas and electrolyte parameters were measured at baseline and at 30, 60, 90, 120, 210, and 300 min after colloid administration. Pre- and postlaboratory values were compared within groups using a pairedttest and a Wilcoxon signed rank test and between groups using repeated-measures analysis of variance and a Wilcoxon rank sum test.ResultsThirty min after infusion, subjects who were administered hetastarch showed statistically significant changes (P< 0.05) in base excess (from 2.5 ± 0.9 mEq/l to 0.7 ± 1.1 mEq/l), HCO3−concentration (from 27 ± 1.0 mEq/l to 25 ± 1.3 mEq/l), Cl−concentration (from 108 ± 2 mEq/l to 112 ± 2 mEq/l), albumin concentration (from 4.4 ± 0.2 g/dl to 3.5 ± 0.5 g/dl), and arterial carbon dioxide tension (Paco2; from 40.8 ± 2.3 mmHg to 39.2 ± 3.2 mmHg), whereas only the albumin concentration (from 4.4 ± 0.2 g/dl to 4.8 ± 0.6 g/dl) changed significantly in the albumin-treated group.ConclusionsDecreases in base excess were observed for 210 min after hetastarch administration but not after albumin. The mechanism for this difference is discussed.