The EC(50) of remifentanil to minimize the cardiovascular changes during head holder pinning in neurosurgery

BACKGROUND: 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% (EC(50)). METHODS: 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 EC(50) of remifentanil. RESULTS: The EC(50) of remifentanil was 2.19 ± 0.76 ng/ml by the turning point estimate (TPE). In probit analysis, EC(50) was 2.42 ng/ml (95% CI : -0.62-4.66) and EC(95) was 5.70 ng/ml (95% CI : 4.02-67.53). The EC(50) estimator comes from isotonic regression is 2.90 ng/ml (95% CI : 1.78-3.65). The EC(95) estimator comes from isotonic regression is 4.28 ng/ml (95% CI : 3.85-4.41). CONCLUSIONS: This study showed that EC(50) of remifentanil was 2.19 ± 0.76 ng/ml by TPE. EC(50) was 2.42 ng/ml (95% CI -0.62-4.66) in probit analysis, as back up analysis. The EC(50) estimator comes from isotonic regression is 2.90 ng/ml (95% CI : 1.78-3.65).