Predicting the best fit based on the synergistic interaction of remifentanil and propofol at the corrected dose in elderly patients undergoing painless gastroscopy

To validate a response surface model for the inhibition of somatic motor response at corrected body weight (CBW) doses of remifentanil plus propofol in elderly patients and to analyze the dose-effect relationship and optimal dosing range for total intravenous anesthesia (TIVA) induction in painless gastroscopy.We designed a prospective, open-ended, randomized, parallel group study. A total of 300 elderly patients undergoing painless gastroscopy were randomized to receive remifentanil (0-0.5 μg/kg) and propofol (0.8-2.2 mg/kg) dosing based on CBW. Gastroscopy was performed at the drug's peak effect time. The somatic motor response to gastroscopic stimulation and the adverse reactions at different points were recorded. The somatic motor response was used as the basic element in the subsequent RSM analysis. Model parameters and 95% confidence intervals were fitted by MATLAB software.The CBW doses of remifentanil and propofol showed synergistic inhibitory effects on motor response to noxious stimulation and attenuated adverse reactions. The 50% effective doses of remifentanil and propofol for inhibiting the motor response were 1.754 μg/kg and 2.048 mg/kg, respectively.Remifentanil or propofol alone could not inhibit the somatic motor response at weight-adjusted doses among elderly patients. A combination of remifentanil and propofol showed a synergistic interaction in suppressing the motor response and adverse reactions in elderly patients. Preinjection of remifentanil could reduce the needed dose of propofol.