Ventilation with high positive end-expiratory pressure improves oxygenation after cardiac surgery independently of the mode of ventilation and of the use of nitric oxide

Introduction

Postoperative pulmonary dysfunction in patients undergoing cardiac surgery with cardiopulmonary bypass is a significant clinical problem and has long been recognized. Postoperative hypoxemia carries high morbidity leading to prolonged postoperative recovery and hospital stays. We hypothesized that adding high positive end-expiratory pressure (PEEP) would be effective for treatment of postoperative hypoxemia after cardiac surgery with cardiopulmonary bypass, independently of the mode of ventilation or the use of nitric oxide.

Methods

During 2 years, 210 patients undergoing coronary artery bypass with pump surgery after diagnosis of hypoxemia (PO₂/FiO₂ <200) were randomized into six groups after operation (35 in each group): pressure-controlled ventilation (PCV) with inhaled nitric oxide and ideal PEEP (group 1), PCV without inhaled nitric oxide and ideal PEEP (group 2), PCV without inhaled nitric oxide and PEEP 5 cmH₂O (group 3), volume-controlled ventilation (VCV) with inhaled nitric oxide and ideal PEEP (group 4), VCV without inhaled nitric oxide and ideal PEEP (group 5) and VCV without inhaled nitric oxide and PEEP 5 cmH₂O (group 6). Arterial and mixed venous blood were drawn and analyzed before the interventions, 1, 2, 4 and 6 hours after the interventions in the ICU to determine the PaO₂/FiO₂ ratio. Hemodynamic measurements were analyzed. The time to extubation was compared among groups, accordingly to the ICU weaning protocol.

Results

There was no significant difference among the groups regarding hemodynamic measurements (mean arterial blood pressure, heart rate, central venous pressure and SVO₂). Oxygenation was higher in both high-PEEP groups (groups 1, 2, 4 and 5) than in the PEEP 5 groups (groups 3 and 6) during the mechanical ventilation period (P < 0.01). Also, the time to extubation was significantly lower in high PEEP groups than in the PEEP 5 groups (220 min vs. 428 min, P < 0.03).

Conclusion

Ventilation with high PEEP after cardiac surgery is associated with improvement of oxygenation and less time of mechanical ventilation independently of the mode of ventilation and of the use of nitric oxide.