Target-Controlled Infusion of Alfentanil for Conscious Sedation

Background: Opioids are frequently used to relieve pain or to induce sedation during monitored anesthesia care and regional anesthesia. Infusion rates for alfentanil range from 0.25-0.72 /kg/min. This study was performed to define the optimal range of blood concentration of alfentanil to produce a conscious sedation without significant vital sign changes and side effects in spinal anesthesia patients. Methods: One hundred patients were administered spinal anesthesia with 0.5% hyperbaric bupivacaine 12-18 mg and then a target controlled infusion (TCI) of alfentanil using a syringe pump equiped with a stelpump program. The target concentrations of alfentanil were 20 ng/ml (n = 20, group A20), 25 ng/ml (n = 20, group A25), 30 ng/ml (n = 20, group A30), 35 ng/ml (n = 20, group A35) and 40 ng/ml (n = 20, group A40). Sedation scale, bispectral index (BIS), systolic and diastolic blood pressure, heart rate, , and anxiety score were checked during the operation and postoperatively one hour later in the recovery room. Results: The sedation scale was significantly higher in groups A30, A35, and A40 than in the other two groups (P /kg/min. Time from end of alfentanil infusion to response to a verbal command was significant delayed in groups A30, A35, and A40 than in the other two groups. Recall of operative procedure occurred in 50-65%. Intraoperative hypotension, bradycardia, and respiratory depression occurred more frequently in groups A35, and A40 than in the other three groups (P