[Study of the effects on the heart function when different positive end expiratory pressure levels were used on patients treated with mechanical ventilation]

Abstract

Objective: To study the effects on the hemodynamics and the heart function when different positive end-expiratory pressure (PEEP) levels were used on patients treated with mechanical ventilation.

Methods: Thirty-nine critical patients with respiratory failure and treated with mechanical ventilation, and hemodynamics was monitored, were divided into two groups according to the cardiac index (CI). Hemodynamics was measured with non-invasive cardiac output (NICO) continuously. The changes in hemodynamic parameters [including cardiac output (CO), CI, pulmonary capillary blood flow (PCBF), central venous pressure (CVP), systemic vascular resistance (SVR)], lung mechanical parameters [intrinsic positive end expiratory pressure (PEEPi), peak inspiratory pressure (PIP), mean of airway pressure (Pmean)], pulse saturation of oxygen (SpO(2)), blood pressure (BP) and heart rate (HR)] were determined with different selected PEEP levels of 0, 5, 7, 10 and 13 cm H(2)O (1 cm H(2)O=0.133 kPa) under the bi-phasic positive airway pressure (BIPAP) mode in normal cardiac function group (CI > or =2.0 L x min(-1) x m(-2), n=18) and poor cardiac function group (CI<2.0 L x min(-1) x m(-2), n=18).

Results: In the normal cardiac function group, the increase in PEEP led to an increase of CVP, but it had no significant effects on CO, CI, PCBF and SVR; in the poor cardiac function group, the increase of PEEP led to an increase of CVP and SVR, a decrease of PCBF, CO, CI, and the latter two variables showed a curvilinear change. In both groups, PIP, Pmean, PEEPi increased and the resistance of airway (R) fell with the increase of PEEP.

Conclusion: Under the condition of mechanical ventilation, when the lung volume was relatively constant, change in PEEP levels (0-13 cm H(2)O) had no obvious effects on the normal cardiac function group, but can significantly decrease right ventricular preload, PCBF and left ventricular preload. Optimal PEEP may improve the cardiac function. The change in the airway pressure is not consistent with the changes in cardiac function.