Dexmedetomidine reduces sevoflurane EC50 for supraglottic airway device insertion in spontaneously breathing morbidly obese patients

Abstract

Purpose: This study aimed to assess the effect of intravenous dexmedetomidine (DEX) on sevoflurane EC₅₀ for supraglottic airway device (SAD) insertion in spontaneously breathing morbidly obese patients. Patients and methods: Thirty-eight morbidly obese patients with a body mass index 40-57 kg/m² who were scheduled for bariatric surgery under general anesthesia requiring tracheal intubation were randomly allocated to two groups receiving the different treatments: group S, saline was given intravenously, and group D, a bolus dose of DEX 1 μg/kg was administered intravenously over 10 mins, followed by intravenous DEX infusion at a rate of 0.5 μg/kg/h. Five percent sevoflurane was initially inhaled for anesthesia induction and then end-tidal expiratory sevoflurane concentration (ET_sev) was adjusted to a target value as to the modified Dixon's up-and-down method. Patients' response to SAD insertion was classified as "movement" or "no movement". The average of the midpoints of all crossover points was defined as calculated sevoflurane EC₅₀ for successful SAD insertion. Furthermore, the probit regression analysis was used to determine sevoflurane end-tidal concentrations where 50% (EC₅₀) and 95% (EC₉₅) insertions of SAD were successful. After the observation was completed, flexible bronchoscope-guided intubation was performed through the SAD. Results: The calculated sevoflurane EC₅₀ for successful SAD insertion was significantly lower in group D than in group S (1.75±0.32% vs 2.92±0.26%, p<0.001). By the probit regression analysis, EC₅₀ and EC₉₅ of sevoflurane for successful SAD insertion were 1.59% (95% CI, 1.22-1.90%) and 2.15% (95% CI, 1.86-3.84%) in group D, respectively, and 2.81% (95% CI, 2.35-3.29%) and 3.32% (3.02-6.74%) in group S. Conclusion: When sevoflurane inhalational induction is performed in spontaneous breathing morbidly obese patients, intravenous DEX can reduce sevoflurane EC₅₀ for successful SAD insertion by about 40%. Chinese Clinical Trial Registry: No. ChiCTR1800016868.

Keywords: dexmedetomidine; inhalational induction; obesity; sevoflurane; supraglottic airway device.

Figure 1

Flow diagram of morbidly obese patients’ recruitment. Notes: Group S, saline was given intravenously; group D, a bolus dose of DEX 1 μg/kg was administered intravenously over 10 mins, followed by intravenous DEX infusion at a rate of 0.5 μg/kg/h.

Figure 2

Responses of morbidly obese patients in the two groups with the modified Dixon’s up-and-down method. Responses of 16 (group S) and 22 (group D) consecutive morbidly obese patients to BlockBuster^TM SAD insertion and their ET_sev with a modified Dixon’s up-and-down method are shown. Arrows indicate the mid-point dose of all independent pairs of patients who manifested cross-over from “movement” (○) to “no movement” (●) response. Notes: Group S, saline was given intravenously; group D, a bolus dose of DEX 1 μg/kg was administered intravenously over 10 mins, followed by intravenous DEX infusion at a rate of 0.5 μg/kg/h. Abbreviations: D, dexmedetomidine; S, saline; SAD, supraglottic airway device.

Figure 3

Dose–response curves of sevoflurane for successful insertion of BlockBuster^TM SAD in the two groups. The curves plotted from probit regression analysis of individual ET_sev and the responses to BlockBuster^TM SAD insertion in the morbidly obese patients were shown. Notes: Group S, saline was given intravenously; group D, a bolus dose of DEX 1 μg/kg was administered intravenously over 10 mins, followed by intravenous DEX infusion at a rate of 0.5 μg/kg/h. Abbreviations: D, dexmedetomidine; S, saline; SAD, supraglottic airway device.