Alteration of anion gap and strong ion difference caused by hydroxyethyl starch 6% (130/0.42) and gelatin 4% in children

Background: Synthetic colloid administration is a common practice for preventing perioperative hypovolemia and consecutive circulatory failure in children. This prospective, randomized study was conducted to investigate the effects of two different unbalanced synthetic colloid solutions on acid–base equilibrium in children. Methods: Fifty pediatric patients (aged 0–12 years) scheduled for major pediatric surgery were randomized to receive either 10 ml·kg^?1 of 6% hydroxyethyl starch solution 130/0.42 (HES) or 4% modified fluid gelatin (GEL) to maintain adequate systemic hemodynamics. Before and after colloid administration, a blood sample was collected to analyze hemoglobin, hematocrit, electrolytes, and acid–base parameters. The anion gap and the strong ion difference (SID) were calculated using standard formulas. Results: Both HES and GEL administration caused a significant increase in plasma chloride concentration (P < 0.01) and an accompanying decrease in SID (P < 0.01). In the HES group, the anion gap decreased significantly (P < 0.01) whereas the anion gap remained stable in the GEL group. In both groups, initial actual base excess and pH did not change significantly after colloid administration. Conclusions: Moderate intraoperative plasma replacement with unbalanced synthetic colloids HES and GEL leads to a decrease in SID and, in the case of HES, to a significant decrease in the anion gap in children. These alterations may result in a possible misinterpretation when the anion gap and SID are used for differential diagnosis of metabolic disturbances during major pediatric surgery.