Effects of prone position on pulmonary gas exchange during mechanical ventilation under general anesthesia

Objective To evaluate the effects of the prone position on pulmonary gas exchange during mechanical ventilation under general anesthesia. Methods Thirty patients scheduled for elective spine surgery in the prone position under general anesthesia (group prone, n=30), 30 patients scheduled for elective spine surgery in the supine position under general anesthesia (group supine, n=30), aged 30-64 yr, with body mass index of 19-30 kg/m2, of ASA physical status Ⅰ or Ⅱ, were enrolled in the study.After induction of general anesthesia, the patients were mechanically ventilated.Anesthesia was maintained with total intravenous anesthesia.At 10 min before pre-oxygenation (T0), 10 min after intubation (immediately after the patients were moved from the supine to the prone position) (T1), 45 and 90 min after intubation (T2, 3), 5 min before extubation (immediately before supine position to the prone position) (T4), and 15 min after extubation (T5), arterial blood samples were taken for blood gas analysis, and PaO2 and PaCO2 were recorded.Alveolar-arterial oxygen difference (A-aDO2) was calculated.Digital radiography was performed and the changes of the lung were observed. Results Compared with supine group, PaO2 was significantly increased and A-aDO2 was decreased at T1-4 in prone group.There was no significant difference in PaCO2, and PaO2 and A-aDO2 at T0 and T5 between the two groups.The results of digital radiography showed no atelectasis at different time points in either group. Conclusion Pulmonary gas exchange in the prone position is superior to that in the supine position during mechanical ventilationunder general anesthesia. Key words: Prone position; Respiratory function tests; Atelectasis; Anesthetsia, general