Abstract
BACKGROUND AND AIMS: Inadequate antinociception during skull pin fixation can destabilise haemodynamics in patients undergoing intracranial surgery. However, the concentration of remifentanil required to achieve sufficient antinociception and maintain stable haemodynamics under surgical pleth index (SPI) monitoring remains unestablished. We aimed to determine the 95% effective concentration (EC95) of remifentanil for skull pin fixation using haemodynamic and SPI monitoring. METHODS: Nineteen patients undergoing intracranial surgery were enroled. Anaesthesia was administered via target-controlled infusion (TCI) of remifentanil and propofol and monitored using the SPI and bispectral index (BIS). Skull pin fixation was conducted at varying remifentanil effect-site concentrations, determined using Dixon's up-and-down method with a 0.5-ng/mL step size while maintaining a BIS of 40-60. Severe pain was defined as SPI >80, haemodynamic change >20% from baseline, heart rate (HR) >100 bpm, or blood pressure >180/100 mmHg and classified as a failure. Success was defined as SPI ≤80 and haemodynamic stability (haemodynamic changes < 20% from baseline, HR ≤100 bpm, and arterial blood pressure ≤180/100 mmHg occurring simultaneously). Statistical tests were conducted using SPSS Statistics (Version 27.0; IBM, Armonk, NY) for Windows. RESULTS: Probit analysis of seven pairs of failure-success outcomes revealed that the EC95 of remifentanil for skull pin fixation, providing adequate antinociception and haemodynamic stability, was 4.23 ng/mL. CONCLUSION: Skull pin fixation can be performed in 95% of patients without triggering noxious stimulation-induced cardiovascular responses by setting remifentanil to 4.23 ng/mL, utilising remifentanil/propofol TCI with SPI and BIS monitoring.