The effects of prolonged inspiratory time during one-lung ventilation: a randomised controlled trial

We evaluated the effects of a prolonged inspiratory time on gas exchange in subjects undergoing one-lung ventilation for thoracic surgery. One hundred patients were randomly assigned to Group I:E=1:2 or Group I:E=1:1. Arterial blood gas analysis and respiratory mechanics measurements were performed 10min after anaesthesia induction, 30 and 60min after initiation of one-lung ventilation, and 15min after restoration of conventional two-lung ventilation. The mean (SD) ratio of the partial pressure of arterial oxygen to fraction of inspired oxygen after 60min of one-lung ventilation was significantly lower in Group I:E=1:2 compared with Group I:E=1:1 (27.7 (13.2) kPa vs 35.2 (22.1) kPa, respectively, p=0.043). Mean (SD) physiological dead space-to-tidal volume ratio after 60min of one-lung ventilation was significantly higher in Group I:E=1:2 compared with Group I:E=1:1 (0.46 (0.04) vs 0.43 (0.04), respectively, p=0.008). Median (IQR [range]) peak inspiratory pressure was higher in Group I:E=1:2 compared with Group I:E=1:1 after 60min of one-lung ventilation (23 (22-25 [18-29]) cmH(2)O vs 20 (18-21 [16-27]) cmH(2)O, respectively, p<0.001) and median (IQR [range]) mean airway pressure was lower in Group I:E=1:2 compared with Group I:E=1:1 (10 (8-11 [5-15]) cmH(2)O vs 11 (10-13 [5-16]) cmH(2)O, respectively, p<0.001). We conclude that, compared with an I:E ratio of 1:2, an I:E ratio of 1:1 resulted in a modest improvement in oxygenation and decreased shunt fraction during one-lung ventilation.