Optimum dose of pentazocine when combined with propofol for gastroscopy in elderly patients

Objective To determine the optimum dose of pentazocine when combined with propofol for gastroscopy in elderly patients.Methods One hundred and forty ASA physical status Ⅰ or Ⅱ patients,aged 6575 yr,scheduled for elective gastroscopy under general anesthesia,were randomly assigned into Ⅰ-Ⅳ groups (n =35 each) using a random number table.Before insertion of the gastroscope,pentazocine 0.2,0.4 and 0.8 mg/kg were injected intravenously in Ⅱ-Ⅳ groups,respectively,while the equal volume of normal saline was given in Ⅰ group.Propofol was then administered by target-controlled infusion (TCI).The half-effective concentration (EC50 of propofol was determined by up-and-down sequential trial.The target plasma concentration (Cp) was set at 3.5 μg/ml in the first patient.Gastroscopy was performed at 5 min after the target effect-site and plasma concentrations were balanced.The response to gastroscopy was defined as positive when body movement and/or bucking occurred during gastroscopy.Each time the Cp increased/decreased by 0.3 μg/ml in the next patient depending on whether or not the response to gastroscopy was positive.EC50 and 95 ％ confidence interval of propofol TCI inhibiting the response to gastroscopy were calculated using Probit analysis.The development of respiratory depression and hypotension was observed.Results EC50 (95 ％ confidence interval) of propofol TCI inhibiting the response to gastroscopy was 2.82 (2.63-3.02) μg/ml,2.78 (2.58-2.97) μg/ml,2.16 (2.00-2.32) μg/ml and 2.03 (1.88-2.19) μg/ml in Ⅰ-Ⅳ groups,respectively.Compared with group Ⅰ,EC50 was significantly decreased in Ⅲ and Ⅳ groups,and the incidence of respiratory depression was increased in Ⅳ group (P ＜ 0.05).Conclusion The optimum dose of pentazocine when combined with propofol is 0.4 mg/kg for gastroscopy in elderly patients. Key words: Pentazocine;  Propofol;  Gastroscopy ;  Dose-response relationship,drug;  Aged