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Study Objective To investigate whether the type of anesthetic agent administered affects the antitussive effect of remifentanil. Design Prospective randomized study. Setting Operating room of a university hospital. Patients 78 ASA physical status 1 and 2 women, aged 20 to 65 years, who were scheduled to undergo a thyroidectomy. Interventions Patients were randomly assigned to three groups to receive anesthesia with propofol (Group P), sevoflurane (Group S), or desflurane (Group D). The main anesthetics were titrated to maintain a target Bispectral Index for hypnosis of 40 to 60. Remifentanil was administered via effect-site target-controlled infusion (TCI). To determine the effective remifentanil effect-site concentration (Ce) to suppress coughing in each group, the up-and-down sequential allocation design was used. Measurements The half maximal effective concentration (EC 50 ) values of remifentanil for preventing coughing in the groups were estimated using isotonic regression and compared among the groups. Main Results The EC 50 of remifentanil for cough suppression in Group P [1.60 ng/mL (98.3% CI, 0.92 - 1.75 ng/mL)] was statistically lower than in Group D [1.96 ng/mL (98.3% CI, 1.81 - 2.50 ng/mL)]. The EC 50 in Group S was 1.75 ng/mL (98.3% CI, 1.39 - 2.13 ng/mL), which was higher than in Group P and lower than in Group D, but did not differ significantly from either group. Conclusions Remifentanil administration for cough suppression during emergence should be customized to the anesthetic agent.

Background The administration of short-acting opioids can be a reliable and safe method to prevent coughing during emergence from anaesthesia but the proper dose or effect site concentration of remifentanil for this purpose has not been reported. We therefore investigated the effect site concentration (Ce) of remifentanil for preventing cough during emergence from anaesthesia with propofol–remifentanil target-controlled infusion. Methods Twenty-three ASA I–II grade female patients, aged 23–66 yr undergoing elective thyroidectomy were enrolled in this study. EC50 and EC95 of remifentanil for preventing cough were determined using Dixon's up-and-down method and probit analysis. Propofol effect site concentration at extubation, mean arterial pressure, and heart rate (HR) were compared in patients with smooth emergence and without smooth emergence. Results Three out of 11 patients with remifentanil Ce of 1.5 ng ml−1 and all seven patients with Ce of 2.0 ng ml−1 did not cough during emergence; the EC50 of remifentanil that suppressed coughing was 1.46 ng ml−1 by Dixon's up-and-down method, and EC95 was 2.14 ng ml−1 by probit analysis. Effect site concentration of propofol at awakening was similar in patients with a smooth emergence and those without smooth emergence, but HR and arterial pressure were higher in those who coughed during emergence. Clinically significant hypoventilation was not seen in any patient. Conclusions We found that the EC95 of effect site concentration of remifentanil to suppress coughing at emergence from anaesthesia was 2.14 ng ml−1. Maintaining an established Ce of remifentanil is a reliable method of abolishing cough and thereby targeting smooth emergence from anaesthesia.