Positive end-expiratory pressure following coronary artery bypass grafting.

BACKGROUND Cardiac surgery-related pulmonary complications include alterations in lung mechanics and anomalies in gas exchange. Higher levels of positive end-expiratory pressure (PEEP) have been suggested to benefit cardiac surgical patients. We compared respiratory compliance, arterial oxygenation and time till tracheal extubation in 2 cohorts of patients weaned from mechanical ventilation with different levels of PEEP after elective and uncomplicated coronary artery bypass grafting (CABG). We hypothesized that higher PEEP levels improve pulmonary compliance and gas exchange in the first hours of weaning from mechanical ventilation, but not to shorten time till tracheal extubation. METHODS Secondary retrospective analysis of 2 randomized controlled trials: in the first trial patients were weaned with PEEP levels of 10 cmH2O for the first 4 hours followed by PEEP levels of 5 cmH2O until tracheal extubation (high PEEP, HP); and the second trial patients were weaned with PEEP levels of 5 cmH2O during the entire weaning phase (low PEEP, LP). The primary endpoint was pulmonary compliance. Secondary endpoints included arterial oxygenation, duration of mechanical ventilation and postoperative pulmonary complications. RESULTS The analysis included 121 patients; 60 HP patients and 61 LP patients. Baseline characteristics were similar. Compared to LP patients, HP patients had a better pulmonary compliance, 47.2±14.1 versus 42.7±10.2 ml/cmH2O (P<0.05), and higher levels of PaO2, 18.5±6.6 (138.75±49.5) versus 16.7±5.4 (125.25±40.5) kPa (mmHg) (P<0.05). Patients in the HP group were less frequent in need of supplementary oxygen after ICU discharge. These differences remained present during the entire weaning phase, even after reduction of PEEP. However, HP patients had a longer time till tracheal extubation, 16.9±6.1 versus 10.5±5.0 hours (P<0.001). HP patients had longer durations of postoperative infusion of propofol, 4.9 (2.6-7.4) versus 3.5 (1.8-5.8) hours (P<0.05). There were no differences in use of inotropes. Cumulative fluid balances were slightly higher in HP patients. CONCLUSION Use of higher PEEP levels after elective uncomplicated CABG improves pulmonary compliance and oxygenation but seems to be associated with a delay in tracheal extubation.