4: Intra-operative assessment of effects of positive end expiratory pressure compared with zero end-expiratory pressure on atelectasis during surgery under general anaesthesia using ultrasonography: A randomised controlled trial

Abstract

Background and Aims:Many clinical trials have investigated the use of intraoperative lung protective ventilation to prevent post-operative pulmonary complications. But, few have visually confirmed if protective measures led to decreased intra-operative atelectasis. This study evaluates whether protective ventilation measures reduces peri-operative atelectasis, using ultrasonography.Methods:After obtaining informed consent, 30 patients going through surgery under general anaesthesia were randomly assigned to either lung protective ventilation group (n=15) or zero end expiratory pressure (ZEEP) group (n=15). Lung protective ventilation involved a positive end expiratory pressure (PEEP) of 7cm H2O and recruitment manoeuvres (30cm H2O for 20 seconds) done every 30 minutes during the course of surgery. Lung ultrasound was performed on the patients at four different time points before and after surgery. Lung ultrasound score (LUS) at each time point was then compared between the two groups to analyse the effects of lung protective ventilation on atelectasis.Results:Prior to lung protective ventilation, the LUS was similar between the two groups. Before emergence from general anaesthesia, the mean LUS was lower among patients in the lung protective ventilation group compared to patients in ZEEP group (p<0.05). Lower mean LUS signifies better aeration in lung protective ventilation group before emergence. However, there was no significant difference in mean LUS between the two groups post operatively.Conclusion:Intra-operative lung protective ventilation reduces atelectasis compared to zero end expiratory pressure during surgery as assessed by ultrasound. However, this reduction in aeration loss does not continue in the post-operative period.