Extravascular lung water and intrathoracic blood volume: double versus single indicator dilution technique

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Abstract
Objective: The accuracy of single thermodilution was assessed in measuring extravascular lung water (EVLW) and intrathoracic blood volume (ITBV). Design: Single thermodilution (ST) was prospectively compared with thermo-dye dilution (TD) in 13 mechanically ventilated pigs using the Pulsion Cold Z-021 monitor. Interventions: Lung injury was induced with oleic acid injection. Results: EVLWITD increased from 4.3 ± 1.4 to 11.3 ± 4.5 ml/kg (p = 0.0014) and ITBVTD decreased from 581 ± 66 to 540 ± 85 ml (p = 0.039) after induction of lung injury. EVLWST was systematically overestimated (0.5–1 ml/kg) and ITBVST was slightly underestimated (15–20 ml) when calculated automatically by the Pulsion Cold Z-021 monitor. This bias could be removed by adjusting two coefficients needed for the computation of ITBVST and EVLWST so that the following regression equations were obtained: EVLWIST = 0.98 · EVLWITD + 0.27 (r = 0.94, p < 10–6) and ITBVST = 1.0 · ITBVTD + 0 (r = 0.87, p < 10–6). Conclusions: Single thermodilution allows estimation of ITBV and EVLW values with reasonable accuracy and therefore provides useful information about the cardiac preload and the severity of lung injury. However, automatic calculation of EVLWIST and ITBVST using the Pulsion Cold Z-021 might be biased. Therefore, researchers and clinicians should validate single thermodilution for the given settings, before employing this method to estimate EVLW and ITBV.

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