Four percent gelatine is an alkaline compound due to NH2 groups, whereas 6% hydroxyethyl starch 130/0.4 (HES130) has acidic features. We investigated whether these solutions lead to differences in acid–base balance in pigs during acidaemia and correction of pH.

Anaesthetized pigs were randomized to HES130 or gelatine infusion (n = 5 per group). Animals received acid infusion (0.4 M solution of lactic acid and HCl diluted in normal saline) and low tidal volume ventilation (6–7 mL kg−1, PaCO2 of 80–85 mmHg, pH 7.19–7.24). Measurements were made before and after induction of acidaemia, before and after correction of pH with haemofiltration (continuous venovenous haemofiltration) and tris-hydroxymethylaminomethane infusion. We measured parameters describing acid–base balance according to Stewart’s approach, ketone body formation, oxygen delivery, haemodynamics, diuresis and urinary pH.

Acid–base balance did not differ significantly between the groups. In HES130-treated pigs, the haemodilution-based drop of haemoglobin (1.4 ± 1.0 g dL−1, median ± SD) was paralleled by an increase in the cardiac output (0.5 ± 0.4 L min−1). Lacking increases in cardiac output, gelatine-treated pigs demonstrated a reduction in oxygen delivery (149.4 ± 106.0 mL min−1). Tris-hydroxymethylaminomethane volumes required for pH titration to desired values were significantly higher in the gelatine group (0.7 ± 0.1 mL kg−1 h−1 vs. HES130: 0.5 ± 0.2 mL kg−1 h−1).

The buffer capacity of gelatine did not lead to favourable differences in acid–base balance in comparison to HES130.