Applying positive pressure at the end of each breath during anaesthesia for the prevention of mortality and postoperative pulmonary complications

Positive end-expiratory pressure (PEEP) is a mechanical technique that is often used when ventilating an unconscious patient. The technique involves adding a quantity of pressure into the lungs at the end of each breath. The process of ventilating a patient causes a degree of deflation in the lungs; between breaths the lungs contain less air than usual. By adding positive pressure at that time, we aim to re-inflate the airways. We know that PEEP can improve respiratory function during a general anaesthetic. We do not know whether patients who receive PEEP have a lower risk of postoperative mortality or respiratory complications, such as pneumonia. In this review, we aimed to assess the postoperative benefits and harms of using PEEP during general anaesthesia. After a search of the literature, we found eight randomized clinical trials (RCTs) involving 330 patients. Four trials reported mortality as an outcome. We pooled these data and found no difference between the group of patients who received PEEP and those who did not, but because of the small number of patients, and the fact that this outcome may be rare, these results did not allow us to make a conclusion about the effect of PEEP on mortality. There were two findings that suggested some benefit of PEEP. First, oxygenation was better on the day after surgery in the PEEP group. Second, radiological imaging showed less atelectasis (areas of collapsed lung) after surgery in the PEEP group. We did calculations to predict how many more patients would be needed in order to be able to make reliable conclusions about the application of PEEP on mortality. This number was 21,200. From the studies that we found, there was no suggestion that intraoperative PEEP causes harm. This finding is reassuring but, due to the small numbers, it is inconclusive. There is currently insufficient evidence to make conclusions about how intraoperative PEEP affects postoperative mortality and respiratory complications.