Remifentanil requirements during sevoflurane administration to block somatic and cardiovascular responses to skin incision in children and adults

Background: The authors found no studies comparing intraoperative requirements of opioids between children and adults, so they determined the infusion rate of remifentanil to block somatic (IR50) and autonomic response (ERBAR(50)) to skin incision in children and adults. Methods: Forty-one adults (aged 20-60 yr) and 24 children (aged 2-10 yr) undergoing lower abdominal surgery were studied. In adults, anesthesia induction was with sevoflurane during remifentanil infusion, whereas in children remifentanil administration was started after induction with sevoflurane. After intubation, sevoflurane was administered in 100% 02 and was adjusted to an ET% of 1 MAC-awake corrected for age at least 15 min before surgery. Patients were randomized to receive remifentanil at a rate ranging from 0.05 to 0.35 mug.kg(-1).min(-1) for at least 20 min before surgery. At the beginning of surgery, only the skin incision was performed, and the somatic and autonomic responses were observed. The somatic response was defined as positive with any gross movement of extremity, and the autonomic response was deemed positive with any increase in heart rate or mean arterial pressure equal to or more than 10% of preincision values. Using logistic regression, the IR50. and IRBAR(50) were determined in both groups of patients and compared with unpaired Student t test. A P value less than 0.05 was considered significant. Results: The IR50 +/- SD was 0.10 +/- 0.02 mug.kg(-1).min(-1) in adults and 0.22 +/- 0.03 mug.kg(-1).min(-1) in children (P < 0.001). The IRBAR50 SD was 0.11 ± 0.02 μg.kg(-1).min(-1) in adults and 0.27 ± 0.06 μg.kg(-1).min(-1) in children (P < 0.001). Conclusions: To block somatic and autonomic responses to surgery, children require a remifentanil infusion rate at least twofold higher than adults.