The effect of intraoperative ventilation strategies on perioperative atelectasis

Several methods of ventilation have previously been shown to reduce intraoperative atelectasis and alveolar to arterial oxygen gradient (A-a DO2) in healthy patients. This study was designed to show firstly the relative intra-operative benefit and secondly if any method had an effect on atelectasis postoperatively. Using a factorial design we randomized 24 patients to each of the four ventilatory interventions (manual inflations, large tidal volumes, PEEP, and pressure control inverse ratio ventilation (IRV)). The A-a DO2 was used as the measure of atelectasis and data collected intra- and postoperatively for 24 hours. The mean pre-induction A-a DO2 was 80 mmHg. This study demonstrated that PEEP and IRV were most effective in reducing intraoperative A-a DO2 (P < 0.05 ANCOVA). Using more than one intervention did not improve the A-a DO2. No method had any effect on postoperative A-a DO2.