Effect of low dose fentanyl on target plasma concentration of propofol that prevents response to proseal laryngeal mask insertion in 50% of patients

Objective To evaluate the effect of low dose fentanyl on target plasma concentration (CP) of propofol (P) given by target controlled infusion (TCI) required to prevent response to proseal laryngeal mask insertion in 50% of patients (EC50). Methods Forty-six ASA Ⅰor Ⅱ patients aged 20-50 yr with body mass index ≤ 30 kg/m2 undergoing elective gynecological laparoscopy were randomly divided into 2 groups (n=23each):propofol group (P) and propofol-fentanyl group (PF). Anesthesia was induced with TCI of propofol. The initial Cp of propofol TCI was set at 2.5 μg/ml in group PF and 4 μg/ml in group P. Following equilibration between plasma and effect site concentration of propofol, fentanyl 1 μg/kg (in group PF) or normal saline (in group P) was injected iv. Laryngeal mask airway (LMA) was inserted at 3.5 min after fentanyl administration. EC50 was determined by up-and-down sequential trial. The ratio of Cp between the two consecutive patients was 1.2 in group P and 1.1 in group PF. LMA insertion response was defined as nausea, bucking and/or body movement during insertion. Probit method was used to calculate the Echo and 95 % confidence interval required to prevent LMA insertion response. Results The EC50 and 95 % confidence interval of propofol given by TCI required to prevent LMA insertion response was 4.68 (4.20-5.21)μg/ml in group P and 2.63 (2.45-2.83) μg/ml in group PF. There was significant difference between the 2 groups. Conclusion Fentanyl 1 μg/kg iv can significantly reduce the Cp of propofol TCI required to prevent LMA insertion response. Key words: Fentanyl;  Propofol;  Dose-response relationship, drug;  Laryngeal masks;  Drug delivery systems