Sedative and hypnotic interaction between propofol and remifentanil by target-controlled infusion during induction of anesthesia

Objective To investigate the sedative and hypnotic interaction between remifentanil and propofol by target-controlled infusion (TCI) during induction of anesthesia.Methods Third-two ASA Ⅰ or Ⅱpatients,aged 22-63 yr,body mass index 18-25 kg/m2,scheduled for elective surgery under general anesthesia,were randomly divided into 4 groups(n=8 each).Group Ⅰ only received TCI pmpofol.GroupⅡ,Ⅲ,and Ⅳreceived a target concentration of 2,4 or 6 ng/ml remifentanil respectively.While the blood-effect site concentrations of remifentanil were equilibrated,patients received TCI of propefol,with an initial target concentration of 0.5μg/ml.After the blood-effect site concentrations of propofol were equilibrated then with 0.5μg/ml increments until the loss consciousness was achieved.The eyelash reflex and state of consciousness were assessed and radial arterial blood sample 6 ml was taken every 3 min to determine the remifentanil and propofol concentrations in blood.Propofol and remifentanil concentrations in blood were measured by reversed-phase high-performance liquid chromatography and high-performance liquid chromatography with ultraviolet detection respectively.The sedative and hypnotic interaction between propofol and remifentanil was determined with a pharmacodynamie interaction model by regression analysis and determined using the isobolographic method.Results Propofol concentrations in blood were lower in group Ⅱ,Ⅲ and Ⅳ than group Ⅰ(P<0.05).The propofol concentratopms in blood were significantly decreased in trun with the increase in the remifentanil concentrations in blood in group Ⅱ-Ⅳ(P<0.05).At loss of eyelash reflex and loss of consciousness of patients,the pharmacodynamic interaction model by curve fitting was superior to linear regression (P<0.05).At loss of eyelash reflex of patients,the curve fitting result showed EC50,prop=2.77μg/ml and EC50,rem=26.67 ng/ml,and the isobolographic method equation is ECprop/2.77+ECrem/26.67=0.69.At loss of consciousness of patients,the curve fitting result showed EC50,prop==3.76μg/ml and EC50,rem=31.56ng/ml,and the isobolographic method equation is Ecprop/3.76+Ecrem/31.56=0.65.Conclusion Remifentanil (Cp 2-6 ng/ml) and propofol by TCI shows a synergistic type of pharmacodynamic interaction on the sedative and hypnotic during induction of anesthesia. Key words: Piperidines; Propofol; Drug delivery systems; Drug interactions; Conscious sedation; Hypnosis,anesthetic