Hypotension and pulmonary atelectasis during general anaesthesia: a randomised crossover laboratory study

Background Atelectasis is common during general anaesthesia and contributes to postoperative pulmonary complications. Despite preventive strategies targeting established underlying mechanisms, extensive atelectasis still often occurs, suggesting that additional factors may be involved. We tested the hypothesis that hypotension contributes to atelectasis formation during anaesthesia. Methods We conducted a randomised, evaluator-blinded crossover study in 12 anaesthetised, mechanically ventilated pigs under conditions simulating anaesthesia induction, in which preoxygenation was followed by either normotension or profound hypotension induced with nitroprusside. The primary outcome was total atelectasis volume, measured by computed tomography. Pulmonary blood flow distribution was assessed using [ 15 O]-water positron emission tomography. Results Atelectasis volume was greater during induced hypotension (median MAP 46 mmHg [interquartile range: 43–49]), compared with normotension (median MAP 85 mmHg [81–93]) in 11 of 12 pigs (median difference 20 ml [95% CI 9–38]; P