1687-7934 © 2014 Department of Anesthesiology, Intensive Care and Pain Management, Faculty of Medicine, Ain-Shams University, Cairo, Egypt DOI: 10.4103/1687-7934.133442 Original article 205 Introduction Dexmedetomidine is a highly selective a2-adrenoceptor agonist recently introduced to anesthesia. It produces dose-dependent sedation and analgesia without respiratory depression [1,2]. It was primarily used for intravenous sedation [3]. Dexmedetomidine, an imidazole compound, is the pharmacologically active dextroisomer of medetomidine that displays speciic and selective a2-adrenoceptor agonism. Activation of the receptors in the brain and spinal cord [4] presynaptically and postsynaptically [5] inhibits neuronal iring causing hypotension, bradycardia, sedation, and analgesia. he molecular mechanisms of the analgesic action of a2-agonists are through activation of inwardly rectifying G1-protein-gated potassium channels, resulting in membrane hyperpolarization thus decreasing the iring rate of excitable cells in the central nervous system. In addition, a2-agonists inhibit neurotransmitter release through reduction in calcium conduction into the cell [6]. hese two mechanisms represent two very diferent ways of afecting analgesia: irst, by preventing the nerve from iring and second, by inhibiting propagation of the signal to its neighbor. Administration of a2-agonists through the intrathecal route by acting as an adjuvant drug to local anesthetics Effect of intravenous versus intrathecal low-dose dexmedetomidine on spinal block in lower limb orthopedic surgery Ahmed M.S. Hamed, Sahar M. Talaat Objectives The aim of this study was to investigate the effect of dexmedetomidine administered intravenously or intrathecally in prolonging spinal anesthesia using bupivacaine in patients undergoing lower limb orthopedic surgery. Patients and methods Sixty adult patients classiied as ASA I or II and scheduled for lower limb orthopedic surgery under spinal anesthesia were enrolled in this study. Patients were randomly assigned into one of the three groups. Group B (n = 20) was injected with 10 ml isotonic saline intravenously over 5 min immediately after patient has received intrathecal hyperbaric bupivacaine 12.5 mg; group IV (n = 20) was injected with dexmedetomidine 0.5 μg/kg intravenously diluted in 10 ml isotonic saline over 5 min immediately after patient has received intrathecal hyperbaric bupivacaine 12.5 mg; and group IT (n = 20) was injected with 10 ml isotonic saline over 5 min immediately after patient has received intrathecal hyperbaric bupivacaine 12.5 mg and dexmedetomidine 3 μg. The onset time, maximum block level, time to maximum sensory and Bromage 3 motor block, duration of sensory and motor anesthesia, time to irst analgesic request, and total analgesic consumption in the irst 24 h were recorded. Hemodynamics, side effects, and sedation scores were assessed. Results Patients in groups IV and IT had a highly signiicantly longer sensory and motor block duration than patients in group B. Both durations were signiicantly longer in the IT group than in the IV group. The time to reach Bromage 3 motor block was signiicantly shorter in the IV and IT groups than in the B group, with no statistically signiicant difference between each other. The systolic and diastolic blood pressures were comparable in the three groups intraoperatively and postoperatively. Mean heart rate values were signiicantly decreased at 20–60 min in the IV group in comparison with the other two groups. The time to irst analgesic needed was signiicantly prolonged in groups IV and IT in comparison with group B. The mean total consumption of intravenous tramadol postoperatively in the irst 24 h was signiicantly decreased in groups IV and IT in comparison with group B. Conclusion In bupivacaine spinal block, dexmedetomidine whether administered intravenously at a dose of 0.5 μg/kg or intrathecally in addition to bupivacaine at a dose of 3 μg produced a signiicant prolongation in the durations of the motor and sensory block, but that administered intrathecally produced more signiicant prolongation of effect than that administered intravenously, with preserved hemodynamic stability and lack of sedation. Keywords: bupivacaine, dexmedetomidine, intrathecal, intravenous, spinal anesthesia Ain-Shams J Anesthesiol 07:205–210 © 2014 Department of Anesthesiology, Intensive Care and Pain Management, Faculty of Medicine, Ain-Shams University, Cairo, Egypt 1687-7934 Department of Anesthesiology, Faculty of Medicine, Ain Shams University, Cairo, Egypt Correspondence to Ahmed M.S. Hamed, MD, Department of Anesthesiology, Faculty of Medicine, Ain Shams University, 14 th Hammoda Muhmoud st., 8 th district, Nasr City, Cairo 11471, Egypt. Mobile no.: +201006616765; e-mail: drshaikahmed@yahoo.com Received 11 August 2013 Accepted 28 August 2013 Ain-Shams Journal of Anesthesiology 2014, 07:205–210 [Downloaded free from http://www.asja.eg.net on Tuesday, September 12, 2017, IP: 112.110.104.154]