EC50 of sevoflurane for classic laryngeal mask airway insertion in children at different time points: A randomized blind trial

Background and Aims: Literature documents EC50(End-tidal) of sevoflurane for CLMA (Classic Laryngeal Mask airway) insertion between 1.5 and 2% and most of these studies suggest maintaining the required end-tidal sevoflurane concentration for 10-25 minutes before LMA insertion. Waiting for this long interval for blood brain sevoflurane equilibration may not be feasible in children especially during failed ventilation. We aimed to estimate EC50 of sevoflurane for CLMA insertion at equilibration time points of 2.5 min and 5.0 min. Material and Methods: In this randomized trial, children aged 2_8 years of either sex having American Society of Anesthesiologists status I undergoing elective cataract surgery were included. After inhalational induction of general anesthesia with 8% sevoflurane and 100% oxygen, intravenous cannulation was secured. The sevoflurane vaporizer was finely adjusted to maintain an end-tidal sevoflurane concentration at 2% for 2.5 min for first child in group 2.5 and 5 min in group 5.0. This was followed by LMA insertion which was considered to be unsuccessful if there was “movement” and successful if “no movement” occurred. End-tidal concentration was increased/decreased (step-size 0.2%) using Dixon and Massey up and down method in the next patient depending upon the previous patient's response. Results: EC50 of sevoflurane for insertion of classic LMA in children aged 2-8 yrs in 100% oxygen was 1.1% (0.9-1.2) at 2.5 min and 1.6% (1.5-1.7) at 5.0 min. Derived EC95 (95% CI) at 2.5 min was 1.8% (1.5-9.2) and at 5.0 min was 1.8% (1.4-8.8) respectively. Conclusion: We suggest maintaining end-tidal sevoflurane of 1.6% for 2.5 min and 1.8% for 5 min for successful CLMA insertion.