Extravascular lung water assessed by transpulmonary single thermodilution and postmortem gravimetry in sheep

Acute lung injury is associated with accumulation of extravascular lung water (EVLW). The aim of the present study was to compare two methods for quantification of EVLW: transpulmonary single thermodilution (EVLWST) and postmortem gravimetric (EVLWG).

Eighteen instrumented and awake sheep were randomly assigned to one of three groups. All groups received Ringer's lactate (5 ml/kg per hour intravenously). To induce lung injury of different severities, sheep received Escherichia coli lipopolysaccharide 15 ng/kg per min intravenously for 6 hours (n = 7) or oleic acid 0.06 ml/kg intravenously over 30 min (n = 7). A third group (n = 4) was subjected to sham operation. Haemodynamic variables, including EVLWST, were measured using a PiCCOplus monitor (Pulsion Medical Systems, Munich, Germany), and the last measurement of EVLWST was compared with EVLWG.

At the end of experiment, values for EVLWST (mean +/- standard error) were 8.9 +/- 0.6, 11.8 +/- 1.0 and 18.2 +/- 0.9 ml/kg in the sham-operated, lipopolysaccharide and oleic acid groups, respectively (P < 0.05). The corresponding values for EVLWIG were 6.2 +/- 0.3, 7.1 +/- 0.6 and 11.8 +/- 0.7 ml/kg (P < 0.05). Ranges of EVLWIST and EVLWIG values were 7.5-21.0 and 4.9-14.5 ml/kg. Regression analysis between in vivo EVLWST and postmortem EVLWG yielded the following relation: EVLWST = 1.30 x EVLWG + 2.32 (n = 18, r = 0.85, P < 0.0001). The mean bias +/- 2 standard deviations between EVLWST and EVLWG was 4.9 +/- 5.1 ml/kg (P < 0.001).

In sheep, EVLW determined using transpulmonary single thermodilution correlates closely with gravimetric measurements over a wide range of changes. However, transpulmonary single thermodilution overestimates EVLW as compared with postmortem gravimetry.