Measuring end expiratory lung volume after cardiac surgery

The aim of this study was to evaluate the interest of end expiratory volume (EELV) measurement after cardiac surgery.

After stabilization, four EELV measurements were performed at one hour intervals during three hours using the nitrogen washout technique. EELV was compared to the predicted functional residual capacity (FRC) volume. The relationships between EELV and static compliance of the respiratory system, the PaO2/FiO2 ratio and the body mass index were studied. In addition, a recruitment maneuver was performed using a fixed 45 cm H2O pressure control ventilation during 2 minutes between the second and third EELV measurement in half of the patients. Forty one patients were enrolled and 21 of them received the recruitment maneuver (RM).

Measured EELV corresponded to 52% of the predicted value. It remained stable during the whole study period. EELV correlated well with the PaO2/FiO2 ratio (r2 = 0.40, p <0.0001) and with compliance of the respiratory system (r2 = 0.525, p < 0.0001). EELV was inversely correlated to the body mass index (r2 = 0.165, p = 0.008). RM did not significantly improve EELV.

EELV is profoundly reduced after cardiac surgery. Measuring EELV is a new tool that is now available during mechanical ventilation. It seems to bring some new robust and possibly useful information. Recruitment maneuvers using sighs does not modify this volume.