Measurement of right ventricular performance during apnea in patients with acute lung injury

Mechanical ventilation resulted in increased, decreased or unchanged end-diastolic volumes together with either profoundly decreased or unchanged right ventricular ejection fraction (RVEF). The goal of our study was, therefore, to evaluate the effects of positive end-expiratory pressure on measurements of RVEF performed during apneic periods with different levels of positive end-expiratory pressure.

Fifteen consecutive patients suffering from acute lung injury after major surgery or trauma were included. Measurements were performed during 15 seconds of apnea at airway pressure levels of 0 (baseline), 10, 20, and 30 cm H2O. Cardiac output and RVEF were determined using the thermodilution technique.

Lung inflation to an airway pressure of 30 cm H2O caused a 22 +/- 14% decrease of cardiac output resulting from a 20 +/- 14% decrease of stroke volume index. The decrease of stroke volume index was induced by a 17 +/- 11% decrease of right ventricular end-diastolic volume index, while RVEF remained virtually unchanged (0.49 +/- 0.10 vs. 0.47 +/- 0.12 at 0 and 30 cm H2O, respectively). Relative changes of cardiac output were closely correlated with changes of right ventricular end-diastolic volume index (p < 0.05, r2 = 0.78).

Right ventricular systolic function was well maintained despite substantially decreased end-diastolic volumes. In our study, during apneic conditions, higher levels of positive end-expiratory pressure did not worsen RVEF in patients with acute lung injury. The proposed technique of apneic lung inflation may serve as an alternative approach to obtain comparable measurements of RV function in patients with acute lung injury.