3. Classification of muscle relaxants According to Type of neuromuscular blockade Depolarizing non-competitive Non-depolarizing competitve Duration Short Intermediate Long
4. Neuromuscular Physiology NMJ consists of Motor nerve ending containing Ach vesicles Synaptic cleft Highly folded skeletal muscle Nicotinic Ach receptors on both presynaptic and post synaptic membrane
6. Choice of muscle relaxant Depends on Duration of action Cost Systemic effect Route of excretion CVS effects Histamine release Ability to reverse NMB Contraindications to any specific relaxants
7. Depolarizing muscle relaxants Succinylcholine(Suxamethonium) Physically resembles Ach molecules Depolarize endplate cholinergic receptors Initial depolarization occurs as fasciculations in skeletal muscles Hydrolyzed by plasma pseudocholinesterase Onset : 60 sec Duration : 5-10 min
8. Pharmacodynamics CNS ↑ ICP ↑ IOP Respiratory system Paralysis CVS ∆ both nicotinic & muscarinic Ach receptors Bradycardia, dysrrhythmia and sinus arrest Pronounced in children & after repeated doses by atropine GI ↑ intragastric pressure Musculoskeletal Myalgia Malignant Hyperthermia
9. Hyperkalemia Usually ↑ plasma [K+] 0.5 mEq/L Abnormal high flux of K+ occurs in Extensive third degree burns Nerve damage or neuromuscular diseases
10. Dosage Intubation dose – 1 - 1.5 mg/kg IV Indication Skeletal muscle relaxation during endotracheal intubation (difficult intubation, RSI) Abdominal operation of short duration Prior ECT to prevent seizure induced injury Emergency treatment for laryngospasm
11. Contraindication Absolute Inability to maintain airway Lack of resuscitative equipment Known hypersensitivity Malignant hyperthermia Myotonia ↑ risk of hyperkalemic response
12. Contraindication Relative Known history of pseudocholinesterase deficiency Myasthenia Gravis Myasthenic Syndrome Familial Periodic Paralysis Opened eye injury
13. Non-depolarizing Muscular relaxants(NDMR) Compete with Ach for nicotinic Ach receptors Anticholinesterase such as neostigmine or edrophonium reverse the effects of NDMR
