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

ABSTRACT

BACKGROUND: Because difficult airways are not commonly encountered, simulation of a difficult airway using a cervical collar has become a well-established technique of for modeling difficult laryngoscopic views and evaluating interventions for use in difficult airway scenarios. In this study, we have determined the optimal remifentanil concentrations (EC50 and EC95) required for i-gel insertion in anesthetized patients fitted with cervical collars at propofol effect-site concentrations of 4.0 and 6.0 microg/ml (group 4.0 and group 6.0). METHODS: The remifentanil dosage for each propofol effect-site concentration group was determined by the modified Dixon's up-and-down method using previous results. The experiment was started using a 4.0 ng/ml effect-site remifentanil concentration, and the dose was reduced by 0.5 ng/ml for the next attempt when tube insertion was successful; if tube insertion failed, the dose for the next 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 the 4.0 group, and 0.42 ng/ml (95% CI, -1.30 to 0.77 ng/ml) and 0.75 ng/ml (0.56-14.3 ng/ml) for the 6.0 group. CONCLUSIONS: In this study, a cervical collar was attached and head fixation was performed to induce a difficult airway. The optimal concentration of remifentanil at a propofol effect-site concentration of 4.0 microg/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 microg/ml was greater than 0.75 ng/ml (0.56-14.3 ng/ml).