The optimal concentration of remifentanil required for i-gel insertion in patients with simulated difficult airways

Abstract

Background: Because difficult airways are not commonlyencountered, simulation of a difficult airway using a cervical collarhas become a well-established technique of for modeling difficultlaryngoscopic views and evaluating interventions for use in difficultairway scenarios. In this study, we have determined the optimalremifentanil concentrations (EC50 and EC95) required for i-gelinsertion in anesthetized patients fitted with cervical collars atpropofol effect-site concentrations of 4.0 and 6.0 μg/ml (group 4.0and group 6.0). Methods: The remifentanil dosage for each propofol effect-siteconcentration group was determined by the modified Dixon’sup-and-down method using previous results. The experiment wasstarted using a 4.0 ng/ml effect-site remifentanil concentration, andthe dose was reduced by 0.5 ng/ml for the next attempt when tubeinsertion was successful; if tube insertion failed, the dose for thenext attempt was increased by 0.5 ng/ml. Results: EC50 and EC95 were respectively 2.11 ng/ml (95% CI,1.78–2.26 ng/ml) and 2.44 ng/ml (95% CI, 2.28–3.67 ng/ml) for the4.0 group, and 0.42 ng/ml (95% CI, −1.30 to 0.77 ng/ml) and 0.75ng/ml (0.56–14.3 ng/ml) for the 6.0 group. Conclusions: In this study, a cervical collar was attached andhead fixation was performed to induce a difficult airway. The optimalconcentration of remifentanil at a propofol effect-site concentrationof 4.0 μg/ml was greater than 2.44 ng/ml (95% CI, 2.28–3.67 ng/ml),and that at the propofol effect-site concentration of 6.0 μg/ml wasgreater than 0.75 ng/ml (0.56–14.3 ng/ml).