Determination of the Pharmacodynamic Interaction of Propofol and Remifentanil during Esophagogastroduodenoscopy in Children

BACKGROUND: Propofol is commonly used to anesthetize children undergoing esophagogastroduodenoscopy. Opioids are often used in combination with propofol to provide total intravenous anesthesia. Because both propofol and remifentanil are associated with rapid onset and offset, the combination of these two drugs may be particularly useful for procedures of short duration, including esophagogastroduodenoscopy. The authors previously demonstrated that the median effective concentration (C50) of propofol during esophagogastroduodenoscopy in children is 3.55 microg/ml. The purpose of this study was to describe the pharmacodynamic interaction of remifentanil and propofol when used in combination for esophagogastroduodenoscopy in pediatric patients. METHODS: The authors studied 32 children aged between 3 and 10 yr who were scheduled to undergo esophagogastroduodenoscopy. Propofol was administered via a target-controlled infusion system using the STANPUMP software based on a pediatric pharmacokinetic model. Remifentanil was administered as a constant rate infusion of 25, 50, and 100 ng.kg(-1).min(-1) to each of three study groups, respectively. A sigmoid Emax model was developed to describe the interaction of remifentanil and propofol. RESULTS: There was a positive interaction between remifentanil and propofol when used in combination. The concentration of propofol alone associated with 50% probability of no response was 3.7 microg/ml (SE, 0.4 microg/ml), and this was decreased to 2.8 microg/ml (SE, 0.1 microg/ml) when used in combination with remifentanil. CONCLUSION: A remifentanil infusion of 25 ng.kg(-1).min(-1) reduces the concentration of propofol required for adequate anesthesia for esophagogastroduodenoscopy from 3.7 to 2.8 microg/ml. Increasing the remifentanil infusion yields minimal additional decrease in propofol concentration and may increase the risk of side effects.