Comparison of the systolic pressure variation between Controlled Mandatory Ventilation (CMV) and Biphasic Positive Airway Pressure (BIPAP) after cardiac surgery

The purpose of the present study was to investigate the changes of the left ventricular preload using the systolic pressure variation during Biphagic Positive Airway Pressure (BIPAP) compared to those in controlled mandatory ventilation (CMV) after cardiac surgery. Twenty patients who had undergone off-pump coronary artery bypass grafting without pulmonary disease. All patients were mechanically ventilated under sedation with midazolam 0.1 mg kg ^-1 h^-1. The ventilator setting was changed from CMV (Phase 1) to BIPAP (Phase 2) and then return to CMV (Phase 3) with 15minutes intervals. We measured heart rate (HR), mean blood pressure (mBP), mean pulmonary artery pressure (mPA), central venous pressure (CVP), the peak airway pressure (Ppeak), the inspiratory plateau pressure (Pplat), the inspiratory pressure (Pins), arterial blood pH (pH), arterial oxygen tension (Pa _O2), arterial carbon dioxide tension (Pa_CO2) and systolic pressure variation at each period. There were no significant changes in HR, mBP, mPA, CVP, pH, Pa_O2 and Pa_CO2 during the study. The Ppeaks in Phase 1 and 3 were significantly higher than the Pplat in Phase 1 and the Pins in Phase 2. The systolic pressure variation in Phase 1 (9 ± 2 mmHg) was similar to that in Phase 2 (7 ± 2 mmHg). Considered from the systolic pressure variation, Left ventricular preload was not different between BIPAP and CMV in the sedated patients after cardiac patients.