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neuromuscularBlockUpdateMay06

neuromuscularBlockUpdateMay06 - Update on Neuromuscular...

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Unformatted text preview: Update on Neuromuscular Relaxants Charles E. Smith, MD Professor of Anesthesia Case Western Reserve University Director, Cardiothoracic Anesthesia MetroHealth Medical Center Cleveland, Ohio Objectives • Mechanism of action • Monitoring • Pharmacology – non-depolarizers – depolarizers • Reversal Historical • 1942: dTC, long-acting, histamine • 1952: sux • 1954: 6 fold ↑ in mortality with dTC • 1967: panc, long acting, CV stimulation • 1986: interm acting relaxants: – vec: no CV effects – atrac: Hoffman elimination, histamine • 1990 to present: newer agents to fill specific niche – roc, cis, miv, pip, dox; rap: withdrawn from market Drachman, NEJM Classical Mechanism of Action • Non-depolarizers : – competitive block – prevent binding of Ach to receptor • Depolarizers- – mimic action of Ach – excitation followed by block Taylor: Anesthesiology 1985;63:1-3 Postjunctional Nicotinic AchR Standaert FG: 1984 Margin of Safety • Wide margin of safety of neuromuscular transmission – 70% receptor occupancy before twitch depression • Receptor alterations – burns, MG, quadra- +hemiplegia Viby-Mogensen, 1984 TOF Monitoring • TOF: – 4 supramaximal stimuli at 2 Hz, every 0.5 sec – observe ratio of 4rth twitch to first • Loss of all 4 twitches: – profound block • Return of 1-2 twitches: – sufficient for most surgeries • Return of all 4 twitches: – easily “reversible” A-Nondepolarizing. B- Sux. Viby-Mogensen: BJA 1982;54:209 Onset + Recovery of NM Block Terminology • Efficacy : ability of drug to produce a desired effect • Potency : quantity of drug to produce maximum effect • Biologic variability : individual variation in response to identical dose of drug • DRC : – measure efficacy and potency – compare drugs, disease states Concept of “Effective Dose” • ED 90 : dose that produces 90% block (+ SD) in average patient at standard muscle group • Usually adductor pollicis- ulnar nerve • Derived from dose-response studies • Intubating dose: 2- 3 x ED 90 • Repeat doses: < ED 90 DRC- show differences in potency, slope, efficacy + individual respo Donati F: Semin Anesth 2002;21:120; Donati F: Anesthesiology 198...
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neuromuscularBlockUpdateMay06 - Update on Neuromuscular...

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