Measurement of end-expiratory lung volume by oxygen washin-washout in controlled and assisted mechanically ventilated patients

Objective: Assessing limits of agreement with helium dilution and repeatability of a new system (lung funcution, LUFU) that measures end-expiratory lung volume (EELV) in mechanically ventilated patients using the O2 washin (EELVWin) and washout (EELVWout) technique. LUFU consists of an Evita 4 ventilator, a side-stream oxygen analyzer, and a dedicated PC software. Design and setting: Prospective human study in a general ICU of a University hospital. Patients: Thirty-six mechanically ventilated patients. Interventions: We obtained 36 couples of both EELVWin and EELVWout measurements in each patient (5 with healthy lungs, 9 with ALI, 22 with ARDS). Measurements were obtained with patients ventilated either by assisted (ASB, 16 measurements) or controlled (CMV, 20 measurements) ventilation. In 19 of 20 cases in CMV, we obtained helium dilution measurements (EELVHe). Measurements and results: Bias for agreement with EELVHe was -16 ± 156 and 8 ± 161 ml, respectively, for EELVWin and EELVWout. Bias for agreement between EELVWin and EELVWout was 28 ± 78 and 23 ± 168 ml, respectively, for CMV and ASB. During CMV bias for repeatability were 8 ± 92 and 23 ± 165 ml, respectively, for EELVWin and EELVWout. During ASB bias for repeatability were 32 ± 160 and -15 ± 147 ml, respectively, for EELVWin and EELVWout. Conclusions: The LUFU method showed good agreement with helium, and good repeatability during partial and controlled mechanical ventilation. The technique is simple and safe.