The fraction of nitrous oxide in oxygen for facilitating lung collapse during one-lung ventilation with double lumen tube

BACKGROUND: The ideal fraction of nitrous oxide (N(2)O) in oxygen (O(2)) for rapid lung collapse remains unclear. Accordingly, this prospective trial aimed to determine the 50% effective concentration (EC(50)) and 95% effective concentration (EC(95)) of N(2)O in O(2) for rapid lung collapse. METHODS: This study included 38 consecutive patients undergoing video-assisted thoracoscopic surgery (VATS). The lung collapse score (LCS) of each patient during one-lung ventilation was evaluated by the same surgeon. The first patient received 30% N(2)O in O(2), and the subsequent N(2)O fraction in O(2) was determined by the LCS of the previous patient using the Dixon up-and-down method. The testing interval was set at 10%, and the lowest concentration was 10% (10, 20, 30, 40%, or 50%). The EC(50) and EC(95) of N(2)O in O(2) for rapid lung collapse were analyzed using a probit test. RESULTS: According to the up-and-down method, the N(2)O fraction in O(2) at which all patients exhibited successful lung collapse was 50%. The EC(50) and EC(95) of N(2)O in O(2) for rapid lung collapse were 27.7% (95% confidence interval 19.9–35.7%) and 48.7% (95% confidence interval 39.0–96.3%), respectively. CONCLUSIONS: In patients undergoing VATS, the EC(50) and EC(95) of N(2)O in O(2) for rapid lung collapse were 27.7 and 48.7%, respectively. TRIAL REGISTRATION: http://www.chictr.org/cn/ Identifier ChiCTR19 00021474, registered on 22 February 2019.