Muscle relaxants are used as part of the triad of anesthesia to induce muscle relaxation. They are classified based on their type of neuromuscular blockade and duration of action. The choice of muscle relaxant depends on factors like duration of action, cost, side effects, and route of excretion. Succinylcholine is a depolarizing muscle relaxant that acts quickly but has a short duration, while non-depolarizing muscle relaxants like vecuronium and atracurium have intermediate durations and are commonly used. Contraindications for muscle relaxants include inability to maintain an airway and prior conditions affecting neuromuscular function or potassium levels.

1. Muscle Relaxants

2. Triad of AnaesthesiaTriad of anaesthesiaAmnesiaMuscle relaxationAnalgesia

3. Classification of muscle relaxantsAccording toType of neuromuscular blockadeDepolarizing non-competitiveNon-depolarizing competitveDurationShortIntermediateLong

4. Neuromuscular PhysiologyNMJ consists ofMotor nerve ending containing Ach vesiclesSynaptic cleftHighly folded skeletal muscleNicotinic Ach receptors on both presynaptic and post synaptic membrane

5. Source: http://www.frca.co.uk/Page.aspx?id=60

6. Choice of muscle relaxantDepends onDuration of actionCostSystemic effect Route of excretionCVS effectsHistamine releaseAbility to reverse NMBContraindications to any specific relaxants

7. Depolarizing muscle relaxantsSuccinylcholine(Suxamethonium)Physically resembles Ach moleculesDepolarize endplate cholinergic receptorsInitial depolarization occurs as fasciculations in skeletal musclesHydrolyzed by plasma pseudocholinesteraseOnset : 60 secDuration : 5-10 min

8. PharmacodynamicsCNS↑ ICP↑ IOPRespiratory systemParalysisCVS∆ both nicotinic & muscarinic Ach receptorsBradycardia, dysrrhythmia and sinus arrestPronounced in children & after repeated doses by atropineGI ↑ intragastric pressureMusculoskeletalMyalgiaMalignant Hyperthermia

9. HyperkalemiaUsually ↑ plasma [K+] 0.5 mEq/LAbnormal high flux of K+ occurs in Extensive third degree burnsNerve damage or neuromuscular diseases

10. DosageIntubation dose – 1 - 1.5 mg/kg IVIndicationSkeletal muscle relaxation during endotracheal intubation (difficult intubation, RSI)Abdominal operation of short durationPrior ECT to prevent seizure induced injuryEmergency treatment for laryngospasm

11. ContraindicationAbsoluteInability to maintain airwayLack of resuscitative equipmentKnown hypersensitivityMalignant hyperthermiaMyotonia↑ risk of hyperkalemic response

12. ContraindicationRelativeKnown history of pseudocholinesterase deficiencyMyasthenia GravisMyasthenic SyndromeFamilial Periodic ParalysisOpened eye injury

13. Non-depolarizing Muscular relaxants(NDMR)Compete with Ach for nicotinic Ach receptorsAnticholinesterase such as neostigmine or edrophonium reverse the effects of NDMR

14. NDMRPancuroniumDuration long (60 – 75 min)CVS - ↑ HR,↑BP, ↑COExcretion – 40% renalNo histamine releaseCost

15. NDMRVecuroniumDuration – intermediate (45 – 60 min)CVS stableExcretion Mainly biliary25% renalSmall extent - liverNo histamine releaseCost

16. NDMRAtracuriumDuration – intermediate (20 -60 min)CVS - ↓BP due to histamine releaseExcretion – half elimination and ester hydrolysisCost

17. NDMROthersCisatracuriumd-tubocurareMivacuriumRocuroniumPriming DoseAwareness