Optimum end-tidal concentration of sevoflurane to facilitate supraglottic airway device insertion with propofol at induction allowing spontaneous respiration in obese patients: A prospective observational study

Abstract

Obese patients are more likely to encounter with difficult airway management, and supraglottic airway device has been adopted to facilitate tracheal intubation. The optimum anesthetic concentration for obese patients to insert a supraglottic airway device with spontaneous respiration has not been investigated. This study was designed to determine the end-tidal concentration of sevoflurane that would provide acceptable condition for supraglottic airway device insertion with propofol at induction in obese patients without using neuromuscular blockade.Thirty elective obese patients [body mass index (BMI) 30-50 kg/m] scheduled for bariatric surgery were enrolled in this study. Sevoflurane was inhaled at a concentration of 5% after infusion of 1 mg/kg propofol (within 1 minute) according to lean body weight. The target concentration of sevoflurane was initiated at 2.5% with 0.5% as a step size using a modified Dixon up-and-down method. Five minutes after target concentration achieved, the insertion of supraglottic airway device was attempted.The minimum alveolar concentration of sevoflurane for successful insertion of supraglottic airway device calculated using up-and-down method were 2.25 (0.53) % for obese patients. The values of the effective concentration of sevoflurane for successful supraglottic airway device insertion in 50% (EC50) and 95% (EC95) of the obese patients obtained by probit regression analysis were 2.09% (95% confidence interval 1.48-2.68) and 3.31% (95% confidence interval 2.70-8.12), respectively.We conclude that sevoflurane at a minimum alveolar concentration of 2.25% can provide optimal conditions for insertion of supraglottic airway device with spontaneous respiration in obese patients with 1 mg/kg propofol at induction.

Figure 1

Flow diagram of obese patient recruitment.

Figure 2

Responses of obese patients with a modified Dixon up-and-down method. Responses of 30 consecutive obese patients induced with sevoflurane combined with propofol to supraglottic airway device insertion and the end-tidal concentrations of sevoflurane in oxygen with a modified Dixon up-and-down method. Arrows indicate the mid-point dose of all independent pairs of participants who manifested cross-over from “movement” (○) to “no-movement” (●) response.

Figure 3

Dose–response curves of sevoflurane for supraglottic airway device insertion in obese patients. The curves plotted from probit regression analysis of individual end-tidal concentration of sevoflurane and the reactions to supraglottic airway device insertion in obese patients. The end-tidal concentrations at which there were 50% and 95% probabilities of successful supraglottic airway device insertion were 2.09% (95% CI 1.48–2.68) and 3.31% (95% CI 2.70–8.12), respectively.