Median Effective Infusion Dose (ED50) of Alfentanil for Monitored Anesthesia Care of Percutaneous Vertebroplasty of Osteoporotic Fractures

Percutaneous vertebroplasty (PVP) consists of injecting small quantities of orthopedic cement to consolidate pathologic vertebral bodies. The procedure is brief but painful during vertebral puncture and cement injection requiring either general anesthesia or monitored anesthesia care with opioids. The optimal dose of alfentanil in this setting is unknown. Therefore, we sought to determine its median effective dose (ED50, or analgesic efficacy in 50% of patients) during PVP in none intubated, spontaneously breathing patients. After approval and informed consent of the Institutional Review Board, 50 patients (American Society of Anesthesiologists II-III, age 50 to 80, weight: 53 to 82 kg) with osteoporotic vertebral fractures were enrolled. The patients were premedicated with oral hydroxyzine 100 mg and had skin infiltration with 50 mg lidocaine before vertebral puncture. The prone position was adopted and oxygen was provided via a facemask. Noninvasive cardiorespiratory variables were monitored. Pain was evaluated by a numerical pain scale (NPS) where 0 represents no pain and 10 the worst tolerable pain. Alfentanil infusion was started 30 minutes before vertebral puncture. The initial dose was 2.0 mg/h. Thereafter, a 0.05 mg/h decrease or increase was applied to the next patient if analgesia was effective (NPS: 3 or less) or not (NPS>3) according to the Dixon method. The bootstrap resampling technique was used to calculate the ED50 and its 95% confidence limits. The latter was 1.05 mg/h (95% confidence interval, 1.0-1.2). Transient apnea (n=2) and nausea/vomiting (n=3) were observed. Given the median body weight of the patients (65 kg), we conclude that 0.27 μg kg/min of alfentanil provides effective analgesia for PVP under monitored anesthesia care. Summary Statement: PVP consists of injecting small quantities of orthopedic cement to consolidate pathologic vertebral bodies. The median effective dose (ED50) for pain relief during vertebral puncture and cement injection is 1.05 (95% confidence interval, 1.0-1.2) mg/h when infusion is started 30 minutes before the procedure. Given the median body weight of our study population (65 kg), this dose corresponds to 0.27 μg kg/min.