Nitrous oxide added at the end of sevoflurane anaesthesia hastens emergence and eliminates prolonged time to extubation (SEVONATE study): A randomised controlled trial

Nitrous oxide (N₂O) has both MAC (Minimum Anaesthetic Concentration) sparing and rapid pharmacokinetic washout properties. We hypothesised that adding N₂O at the end of surgery would hasten emergence from anaesthesia, decrease variability in emergence duration and reduce the number of prolonged emergences. Adult patients, American Society of Anesthesiologists Physical Status I–III, undergoing general anaesthesia for surgery with duration of over 120 min were randomised into two groups according to carrier gas: air/30% oxygen, and the same mixture until the last 30 min of surgery when 70% N₂O in 30% oxygen was used. Anaesthesia was maintained at ~1 MAC with sevoflurane in both groups. Early and late recovery, postoperative nausea and vomiting, and pain scores and analgesic use were assessed. Time to extubation time was deemed prolonged if it lasted more than 15 min. Fifty-one patients in N₂O/O₂ and 50 in air/O₂ were enrolled. N₂O administration lasted (mean ± standard deviation) 24.8 ± 9.4 min. Time to extubation was faster with N₂O/O₂ (5.5 ± 2.6 min) than with air/O₂ (9.1 ± 4.0 min), mean difference 3.6 min; 95% confidence interval 2.3 to 4.9, p < 0.001. Ability to open eyes, follow commands and being oriented were similarly significantly faster (mean differences 3.6, 3.4 and 3.7 min, respectively, p < 0.001 in all). None of the patients with N₂O/O₂, but 6% of patients with air/O₂, had prolonged time to extubation, p < 0.001. There were no differences between the groups in postoperative pain scores, or in early and late postoperative recovery. Patients administered N₂O/O₂ received significantly less analgesics: tramadol (medians 0 vs 100 mg, p = 0.037), paracetamol (33% vs 62%, p = 0.004) and ketoprofen (16% vs 32%, p = 0.054). Adding N₂O at the end of sevoflurane-based anaesthesia hastened extubation, eye opening, following commands and orientation, and eliminated prolonged time to extubation without increasing early or late complications.