Validation of extravascular lung water measurement by transpulmonary thermodilution in a pediatric animal model

OBJECTIVE: The measurement of extravascular lung water using the transpulmonary thermodilution technique enables the bedside quantification of the amount of pulmonary edema. Children have higher indexed to body weight values of extravascular lung water compared with adults. Transpulmonary thermodilution measurements of extravascular lung water in children have not yet been validated. The purpose of this study was to validate the extravascular lung water measurements with the transpulmonary thermodilution method over a wide range of lung water values in a pediatric animal model. DESIGN: Experimental animal intervention study. SETTING: Animal laboratory at the Radboud University Nijmegen, The Netherlands. SUBJECTS: Eleven lambs. INTERVENTION: Pulmonary edema was induced using a surfactant washout model. MEASUREMENTS AND MAIN RESULTS: Between the lavages, extravascular lung water index was estimated using transpulmonary single and double indicator dilution. Two additional lambs were used to estimate extravascular lung water index in lungs without pulmonary edema. The final extravascular lung water index results were compared with the extravascular lung water index estimations by postmortem gravimetry (EVLWIG). The results were analyzed using both correlation and Bland-Altman statistics. Extravascular lung water index by transpulmonary thermodilution (EVLWITPTD) correlated significantly with either EVLWIG (r = 0.88) or with extravascular lung water index by transpulmonary double indicator dilution (EVLWITPDD) (r = 0.98). The mean bias with EVLWIG was 12.2 mL/kg (limits of agreement +/- 10.9 mL/kg) and with EVLWITPDD 2.4 mL/kg (limits of agreement +/- 3.8 mL/kg). The percentage errors were 41% and 14%, respectively. The bias became more positive when the mean of EVLWITPTD and EVLWIG increased (r = 0.72; p = 0.003). CONCLUSIONS: EVLWITPTD was significantly correlated to the postmortem gravimetric gold standard, although a significant overestimation was demonstrated with increasing pulmonary edema