The concentration of desflurane preventing spectral entropy change during surgical stimulation: A prospective randomized trial.

STUDY OBJECTIVE: To determine the concentration of desflurane necessary to blunt changes in spectral entropy during surgical incision when two different target-controlled effect-site concentrations of remifentanil (1 and 3ng/ml) were infused.

DESIGN: Prospective, randomized controlled study.

SETTING: Operating room of a university hospital.

INTERVENTIONS: Forty-two patients undergoing general anesthesia for elective surgery were enrolled and randomly allocated to the R1 (1ng/ml of remifentanil, n=21) or R3 (3ng/ml of remifentanil, n=21) group. After at least a 10-min administration of target-controlled remifentanil concentration and predetermined end-tidal desflurane following endotracheal intubation, changes in spectral entropy in response to surgical incision were evaluated.

MEASUREMENTS: Concentration of desflurane necessary to blunt changes in spectral entropy during surgical incision for each group was determined using Dixon's up-and-down method. Hemodynamic variables including mean arterial pressure (MAP) and heart rate (HR) were measured.

MAIN RESULTS: Concentration of desflurane necessary to blunt changes in spectral entropy during surgical incision in 50% of patients (EC50 ) was 4.1% (95% CI: 3.5-4.7%) for the R1 group and 3.4% (95% CI: 3.0-3.8%) for the R3 group (P=0.033). Additionally, the calculated EC95 values using the logistic regression analysis for the R1 and R3 groups were 5.8% (95% CI: 5.0-10.8%) and 5.1% (95% CI: 4.3-10.6%), respectively. MAPs and HRs were significantly higher in the R1 than in the R3 group after surgical incision.

CONCLUSIONS: Desflurane 4.1% with remifentanil 1ng/ml and desflurane 3.4% with remifentanil 3ng/ml significantly blunt the change in spectral entropy after surgical incision in 50% of patients.