Transesophageal pulsed-doppler echocardiographic evaluation of transmitral and pulmonary venous flow during ventilation with positive end-expiratory pressure

Abstract

During mechanical ventilation with high levels of positive end-expiratory pressure (PEEP) several hemodynamic changes occur, the mechanism of which has been the subject of various previous studies. The effects of increasing levels of PEEP during mechanical ventilation were measured on left atrial and left ventricular filling dynamics, as assessed by pulmonary venous and transmitral flow velocities, respectively. Using transesophageal echocardiography in 12 patients, Doppler flow velocities of pulmonary venous and transmitral flow were studied at baseline (0 cmH 2O PEEP) and at 5, 10, 15, and 20 cm H 2O with 10-minute intervals, and once more after removal of PEEP. In 2 of the 12 patients, PEEP could not be increased beyond 15 cmH 20, because cardiac index fell below 2.0 L/min/m 2. Pulmonary venous flow velocity and velocity time integral during systole significantly decreased from 48 ± 7 cm/s and 10.3 ± 2.2 cm at baseline to 35 ± 6 cm/s and 5.7 ± 2.5 cm at 20 cmH 2O PEEP, respectively ( P < 0.01). In contrast, early and late diastolic velocities and velocity time integrals did not change. In regard to transmitral flow, both early and late diastolic velocities significantly decreased from 51 ± 7 cm/s and 50 ± 9 cm/s at baseline to 38 ± 7 cm/s and 39 ± 7 cm/s at 20 cmH 2O PEEP, respectively ( P < 0.01). Early and late diastolic velocity time integrals decreased from 6.1 ± 1.8 cm and 4.7 ± 1.0 cm to 4.5 ± 1.0 cm (NS) and 3.4 ± 0.7 cm ( P < 0.05), respectively. Thus, at high levels of PEEP there is a reduction in both early and late diastolic left ventricular inflow through the mitral valve and a decrease in systolic left atrial filling through the pulmonary veins, while diastolic left atrial inflow does not change. Because systolic pulmonary venous flow is mainly affected by left atrial events, the observed change in pulmonary venous flow pattern suggests that high levels of PEEP principally influence left atrial function.