الفهرس 
ANATOMY RELEVANT TO SUBARACHNOID ANDOnly 14 pages are availabe for public view
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Abstract
Alpha 2 adrenoceptor agonists are being increasingly used in anesthesia and critical care as they not only decrease sympathetic tone and attenuate the stress responses to anesthesia and surgery; but also cause sedation and analgesia. They are also used as adjuvant during regional anesthesia. Clonidine, which was initially introduced as antihypertensive, is the most commonly used α 2 agonist by anesthesiologists. Dexmedetomidine is the most recent agent in this group approved by FDA in 1999 for use in humans for analgesia and sedation.
The aim of this study was to compare the effect of Dexmedetomidine 5μg versus fentanyl 25 μg on intraoperative analgesia, the onset and duration of sensory&motor block, side effects as well as hemodynamic variables when added to 10 mg intrathecal bupivacaine in patients undergoing lower limb orthopedic surgery.
Present results in this study showed that the supplementation of spinal bupivacaine with 5μg Dex significantly prolonged both sensory and motor block compared with intrathecal 25μg fentanyl and bupivacaine in lower limb orthopedic surgery.
Intrathecal Dex when combined with spinal bupivacaine prolongs the sensory block by depressing the release of C-fibers transmitters and by hyperpolarization of pos-synaptic dorsal horn neurons.