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Dip. Software statistics- PhD ( physiology) IDRA, FICA
Dexmedetomidine Dr. S. Parthasarathy MD., DA., DNB, MD (Acu), Dip. Diab., DCA, Dip. Software statistics- PhD ( physiology) IDRA, FICA
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Eight times more specific for alpha 2 receptors than clonidine
Chemistry Dexmedetomidine hydrochloride; Dexmedetomidine HCL; 4-((S)-alpha,2,3-trimethylbenzyl)imidazole monohydrochloride Eight times more specific for alpha 2 receptors than clonidine
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Physiology Alpha 2 receptor agonist There are three types of alpha two( α2 a, α2 b, α2 c) receptors α2 a- sedation, analgesia , sympatholysis α2 b- spinal analgesia , peripheral vasoconstriction α2 c – modulation of cognition, sensory processing, mood changes
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Pictures from the net for closed academic purpose only
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How does it act ? Αlpha 2 stimulation Decreased CAMP Potassium efflux
Nerve hyper polarization Decreased calcium entry
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Alpha 2 is presynaptic and alpha 1 is post synaptic
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Pharmacokinetics Following intravenous administration, dexmedetomidine shows rapid distribution phase with a distribution half life of six minutes and a terminal elimination half life (t1/2) of approximately two hours Oral ?? But nasal and sublingual use is proved Nasal 1- 2 µg/kg has an onset of 20 minutes Cytochrome p 450 glucorinidation and hydroxylation and excreted through kidneys
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Adrenergic agonists Alpha Beta Isoprenaline Dexmed Dopamine Clonidine
Phenyleph Dobutamine Oxymetazoline Isoprenaline Noradrenaline Terbutalin norad Adrenaline Alpha Beta Alpha 1 Alpha 2 Beta 1 Beta 2 Beta 3 Ephedrine Ephedrine
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Clinical applications
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Perioperative hemodynamics
0.25 – 1 µg/kg - Blunted Pressor response to intubation Better intraop hemodynamics No reflex tachycardia as inhalational agents 0.5 µg/kg blunted extubation response also Hypotension and bradycardia are the common side effects Used for Deliberate hypotension
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Dexmedetomidine is an effective and safe agent for controlled hypotension mediated by its central and peripheral sympatholytic action.
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In cardiac Dexmedetomidine in addition to blunting the hemodynamic response to endotracheal intubation also reduces the extent of myocardial ischemia during cardiac surgery Decrease pulmonary hypertension in MVR cases
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Perioperative analgesia
0.8 µg/kg doses decreased morphine requirements by 60 % in major cases . Infusion of 0.4 µg/kg/hour decreased opioids by 66% in the 24 hour period Superior to clonidine but duration only two hours Nausea and vomiting less Why?? opioids less !!
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Perioperative analgesia (continued)
Analgesic effects of Dex were associated with more incidence of postoperative bradycardia But usually – asymptomatic Beware of combined beta blockers – increased stroke incidence Dexmed on chronic pain or hyperalgesia – not established
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Awake fiber optic intubation
Routine midaz or opioids Respiratory depression in compromised airways But dexmed – OK Loading dose with continued infusion Sympatholysis , analgesia, sedation --- yes But some decreased salivary secretion effect ?? !!
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Adjunct to GA Stress reduction equivalent to epidural in some studies
When epidural is risky ?? Decreased dosage requirement of propofol on induction and TIVA Decreased dosage – rocuronium
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Sedation is OK ?? Dexmedetomidine does not cause respiratory depression. This fact can be utilized in sedating morbidly obese patient thereby avoiding respiratory depression caused by narcotics High dose dexmedetomidine (3mcg/kg IV load over 10 minutes with an infusion of 1 mcg/kg/hour) has been used successfully for sedation of children undergoing MRI.( BRADY ?)
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On the CNS surgery side ?? Dexmedetomidine provides stable cerebral hemodynamics NO sudden increase in ICP during intubation, extubation, and head pin insertion. It attenuates neurocognitive impairment (delirium and agitation) allowing immediate postoperative neurological evaluation. Some neuroprotective effects
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Special awake craniotomy for the resection of tumors or epileptic foci in eloquent areas, the implantation of deep brain stimulators for Parkinson’s disease No interference with neuro monitoring
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Dexmeditomedine has high lipophilicity and so it passes through placenta but it disappears very fast. Cautious in pregnancy and lactation Intrathecal also – risk Vs benefit
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Loco regionals - in nerve blocks
Dexmed shortens onset Prolongs sensory and motor blockade Duration prolonged by more than 16 hours extra with 150 mic.gm of dexmed Not due to CNS effects or vasoconstriction But probably hyperpolarization is the mechanism But IV also prolongs nerve blocks !! Hypotension and bradycardia remains
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Neuraxial blockade 1 µg/kg – epidural –
prolongs sensory and motor blockade No without major side effects Caudal additive in children – good results 3 – 10 µg single dose combining with spinal local anesthetics – similar results IV dexmed can prolong sensory and mainly analgesic effects of spinal local anesthetics
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Biers block 0.3 µg/kg addition Better and prolonged analgesia
Reduced local anesthetics Possible protection from CNS and cardiac toxicity But done and proved only in upper limbs
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Postoperative period Intra articular dexmedetomidine in patients undergoing arthroscopic knee surgery improves the quality and duration of postoperative analgesia antihyperalgesic effect when administered locally after bilateral third molar surgery Preemptive local infiltration dexmed for hernia surgery !! Dexmed decreases the incidence of sevoflurane emergence delirium in pediatrics
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Some potential uses ?? used successfully in the treatment of withdrawal from benzodiazepines, opioids, alcohol, and recreational drugs Management of tetanus in ICU. As an anti shivering agent. ? preventing ethanol induced neuro degeneration
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Side effects hypotension, hypertension, bradycardia, dry mouth and nausea. fever, rigors, cyanosis, muscle weakness. Rarely arrhythmias, AV Block, cardiac arrest, T-wave inversion, tachycardia, angina pectoris, pulmonary edema, bronchospasm respiratory depression, syncope, neuropathy, paresthesia, paresis, hyperkalaemia, lactic acidosis and hyperglycaemia.
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Antagonist ?? pharmacological effects of dexmedetomidine can be reversed by α2-AR antagonist atipamezole, combination of dexmedetomidine and atipamezole can provide titratable form of sedation in the future. Upto 30 mg / subject dose in humans – no major problems
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Summary What is it ? Pharmacokinetics Receptors
uses - hemodynamics , cvs cns , regionals analgesia sedation, pediatrics etc Potential uses Antagonist
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Thank u all
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