Neuromuscular Blockers Bernie Miller, MD Medical Student Lecture Series

Content Outline Indications for Neuromuscular Blockade Neuromuscular Junction Classes of Neuromuscular Blockers Metabolism of Neuromuscular Blockers Monitoring Neuromuscular Blockade Antagonism (Reversal) of Neuromuscular Blockers

Indications for Neuromuscular Blockade Intubation Optimize Surgical Conditions Optimize Ventilation in ICU

Neuromuscular Junction

Classes of Neuromuscular Blockers Depolarizing- Bind to and activate cholinergic receptors Succinylcholine Non Depolarizing- Competitively inhibit Ach binding at post-junctional receptors Short Acting Medium Acting Long Acting

Succinylcholine Depolarizing neuromuscular blocker Dose: 0.5-1.5mg/kg Onset: 30-60seconds Duration: 5-10 Minutes Metabolism: Hydrolysis by plasma cholinesterase

Succinylcholine Phase 1: Membrane is depolarized by opening AChR channels- Brief fasciculation of muscles Phase II: End-plate repolarizes, but is desensitized to acetylcholine

Succinylcholine-Adverse Side Effects Cardiac Dysrhythmia Fasciculations Hyperkalemia Myalgias Myoglobinuria Increased Intraocular Pressure Increased Intracranial Pressure Increased Intragastric Pressure Trismus Malignant Hyperthermia Trigger

Contraindications to Succinylcholine Burn injury Muscle Crush Injury Stroke Spinal Cord Injury History of Malignant Hyperthermia Neuromuscular Disorders Relative Contraindications: Eye Trauma, Increased ICP

Non Depolarizing Muscle Relaxants (NDMR) Structure Aminosteroids Pancuronium Pipercuronium Vecuronium Rocuronium Benzylisoquinolinium Atracurium Cisatracurium

Long Acting- NDMR Pancuronium Dosage: Onset: 3-5 Minutes Duration: 60-90 Minutes Metabolism: Renal (80-90%), Hepatic (10%) Side Effects: 10-15% Increase in HR, MAP, CO Selective blockade of cardiac muscarinic receptors in the sinoatrial node

Intermediate Acting - NDMR Vecuronium Intubating Dose: 0.1mg/kg Onset: 3-5 Minutes Duration: 20-35 Minutes Metabolism: Renal 15-20%, Hepatic 20-30%, Biliary 40% Side Effects: Minimal Rocuronium Intubating Dose: 0.5-1mg/kg Onset: 2-3 Minutes Renal 10-20%, Hepatic 10-20%, Biliary 50% Cisatricurium Intubating Dose: 0.1mg/kg Onset: 2-5 Minutes Duration: 20-35 Minutes Metabolism: Hoffman Elimination Side Effects: Minimal

Short Acting- NDMR Mivacurium Intubating Dose: 0.25mg/kg Onset: 2-3 Minutes Duration: 12-20 Minutes Metabolism: Plasma Cholinesterase NOT AVAILABLE IN USA

Train of Four Monitoring TOF 4 total stimuli, 1 every 0.5 secs Level of block correlates to “number of twitches” Can still have 70% of receptors blocked with 4 twitches

Neuromuscular Blockade Reversal May reverse blockade of non depolarizing muscle relaxants after patient has > 1 twitch Anticholinesterases Inhibit acetylcholinesterase and increase acetylcholine at neuromuscular junction Neostigmine, Pyridostigmine, Physostigmine Edrophonium Side Effects (Cholinergic): Bradycardia, salivation, bronchial secretions, diarrhea, increases gut motility Pair with anticholinergic agents: Atropine, Glycopyrrolate

Evaluating Neuromuscular Function Tidal Volume: > 5ml/kg TOF: No Fade Sustained Tetanus Head Lift: > 180 for 5 seconds

Sugammadex Newly developed reversal agent- Antagonizes steroidal neuromuscular blockers by encapsulating Not approved in USA

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