To investigate the effect of positive end expiratory pressure (PEEP) on hemodynamics in patients with hypovolemic tendency undergoing mechanical ventilation.

Totally 20 patients with hypovolemic tendency undergoing mechanical ventilation were enrolled in this study. All patients were given PEEP of 0, 5, 10, and 15 cmH₂O in the basal breathing mode for about 30 min each time. The hemodynamic indexes of heart rate, mean arterial pressure (MAP), pulmonary arterial wedge pressure (PAWP), stroke volume index (SVI), cardiac output (CO), cardiac index and systemic vascular resistance index (SVRI), venous reflux gradient indexes of central venous pressure (CVP), common iliac venous pressure (CIVP) and ΔCVP, and respiratory mechanics indexes of peak inspiratory pressure(PIP), airway resistance (RAW), platform pressure (Pplat), mean airway pressure (Pmean) and pulmonary vascular resistance index (PVRI) were detected and compared among different PEEP levels.

As the level of PEEP went up, the heart rate, PAWP and SVRI increased significantly, the MAP, CO, cardiac index and SVI decreased gradually (F = 20.311, 15.100, 32.915, 15.100, 198.635, 435.100, 17.000; all P < 0.001), and the CO level in the PEEP of 5 cmH₂O was much lower than that in the PEEP of 0 cmH₂O [(5.31 ± 0.11) L / min vs. (5.46 ± 0.24) L / min]. The levels of CVP and CIVP increased gradually, and ΔCVP decreased (F = 47.879, 27.578, 21.393; all P < 0.001). Meanwhile, the levels of PIP, Pplat, Pmean and PVRI increased gradually, and peaked at the PEEP of 15 cmH₂O (F = 67.152, 74.025, 818.208, 31.141; all P < 0.001). However, there was no significant difference in RAW among different PEEP levels (F = 2.082, P = 0.131).

When PEEP is no less than 5 cmH₂O, CO significantly decreases in patients with hypovolemic tendency undergoing mechanical ventilation, so the minimal PEEP should be used for therapeutic purposes.