Recovery Profile Following Isoflurane-based Low-flow Anaesthesia with Nitrous Oxide and without Nitrous Oxide: An Observational Cohort study

Although nitrous oxide (N 2 O) is widely used during low-flow anaesthesia for its volatile-sparing effect, its impact on the trend of minimum alveolar concentration (MAC) decline and recovery remains uncertain.

This study aimed to compare the rate of decline in MAC during isoflurane-based low-flow anaesthesia with and without N 2 O.

This observational study included 70 patients of either sex, aged 18-65 years, with American Society of Anesthesiologists physical status I-III, undergoing endotracheal intubation for general anaesthesia. Patients were categorised to one of two groups: Group N received N 2 O, isoflurane and oxygen, whereas Group A received isoflurane, oxygen, and air. The rate of MAC decline during extubation was recorded. Extubation time, time to eye opening, response to verbal commands and orientation were compared between the two groups. Data were analysed using the Chi-square test and Student's t -test, with a P < 0.05 considered statistically significant.

Patients in both groups had similar demographics. After discontinuation of isoflurane, MAC decreased more quickly with N 2 O than with air, with an estimated half-life of 5.2 min (Group N) compared to 7.7 min (Group A). N 2 O use was also associated with an approximately 4-min reduction in recovery endpoints, including shorter times to extubation, eye opening, response to verbal commands and orientation, compared with air (all P < 0.05).

Compared with isoflurane-air-oxygen anaesthesia, N 2 O-isoflurane-oxygen low-flow anaesthesia was associated with a more rapid decline in MAC after discontinuation and earlier recovery endpoints, including extubation, eye opening, response to verbal commands and orientation.