Hemodynamic effects of pressure support ventilation in cardiac surgery patients

Hemodynamic consequences of pressure support ventilation (PSV) were compared with intermittent mandatory ventilation (IMV) in 20 patients following aortocoronary bypass. On the morning following surgery, all patients were weaned by IMV to a rate of eight breaths per minute, tidal volume of 12 ml/kg and inspired oxygen concentration of 40 per cent. With patients awake and able to breath spontaneously, PSV was begun at 20 cm of water. In patients with static lung compliance, less than 0.06 l/cm H2O, 30 cm H2O of PSV was used. Subsequently, all patients were weaned to PSV 10 cm of water, continuous positive airway pressure (CPAP) at 5 cm water and extubated. Hemodynamic data including oxygen transport were obtained at each level of PSV and at IMV prior to weaning. Analysis using ANOVA showed comparable hemodynamic and oxygen transport parameters for PSV of 30 cm H2O in comparison with IMV. PSV at levels of 20 and 10 cm H2O produced statistically significant increases in heart rate, mean arterial pressure, central venous pressure, and pulmonary capillary wedge pressure. Cardiac output was stable, and these increases were not clinically significant. In awake patients following cardiac surgery, PSV up to 30 cm H2O can be safely applied without hemodynamic embarrassment in patients with good left ventricular ejection fractions.