During neuroanesthesia, head holder pinning commonly results in sympathetic stimulation manifested by hemodynamic changes, such as increased heart rate and arterial blood pressure. Remifentanil has been used successfully to control acute autonomic responses during neurosurgical procedures. The objective of this study was to determine effect-site concentration of remifentanil for suppressing the hemodynamic response to head holder pinning with the probability of 50% (EC₅₀).

Forty-one ASA physical status I or II patients, between the ages of 20-70, who were scheduled for neurosurgery were recruited into this study. After arrival in the operating room, standard monitoring was applied throughout the study, which included a bispectral index monitor. Both propofol and remifentanil were administered by Target-control infusion device. The Dixon "up-and-down" sequential allocation method was used to determine the EC₅₀ of remifentanil.

The EC₅₀ of remifentanil was 2.19 ± 0.76 ng/ml by the turning point estimate (TPE). In probit analysis, EC₅₀ was 2.42 ng/ml (95% CI : -0.62-4.66) and EC₉₅ was 5.70 ng/ml (95% CI : 4.02-67.53). The EC₅₀ estimator comes from isotonic regression is 2.90 ng/ml (95% CI : 1.78-3.65). The EC₉₅ estimator comes from isotonic regression is 4.28 ng/ml (95% CI : 3.85-4.41).

This study showed that EC₅₀ of remifentanil was 2.19 ± 0.76 ng/ml by TPE. EC₅₀ was 2.42 ng/ml (95% CI -0.62-4.66) in probit analysis, as back up analysis. The EC₅₀ estimator comes from isotonic regression is 2.90 ng/ml (95% CI : 1.78-3.65).