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.

The objective of the study was to determine regional pulmonary filling characteristics in 20 mechanically ventilated patients with acute lung injury.

Regional filling characteristics were calculated from tracings of regional tidal volumes vs. global tidal volumes measured by electrical impedance tomography (EIT). These plots were fitted to a polynomial function of the second degree. Regional polynomial coefficients of the second degree characterized the curve linearity of the plots. Near-zero values of the polynomial coefficient indicated a homogeneous increase in regional tidal volumes during the whole inspiration. Positive values hinted at initial low regional tidal volume change suggesting lung volume recruitment. Negative values indicated late low regional tidal volume change implying hyperinflation of this lung region.

We found a broad heterogeneity of regional lung filling characteristics. The minimal regional polynomial coefficients varied from −2.80 to −0.56 (median −1.16), while the maximal regional polynomial coefficients varied from 0.58 to 3.65 (median 1.41).

Measurements of regional filling characteristics by EIT may be a helpful tool to adjust the respiratory settings during mechanical ventilation to optimize lung recruitment and to avoid overdistension. It applies a non-pressure-related assessment to the mechanics of lung inflation and gives a view of the real problems underlying ventilatory strategies dependent on global characteristics.