Ans. b. Succinylcholine (Ref: Miller's Anesthesia 8/e p866; Morgan 4/e p210-215; Lee 13/e p181-191)Succinylcholine is a short acting depolarizing muscle relaxant, which causes initial fasciculations during induction. It can cause muscle soreness and post-op muscle pain.Succinylcholine (Scoline, Suxamethonium or Diacetylcholine)Suxamethonium chloride, a dicholine ester of acetyl cholineA clear, colorless aqueous solution of pH 3.0-5.0 with a shelf life of 2 yearsQStored at 4degCQSpontaneous hydrolysis occurs in alkaline or warm conditionsQ.Metabolism:Sch is the only depolarizing (non-competitive) muscle relaxantQ in clinical use.It is the only neuromuscular blocker with a rapid onset of action (30-60 seconds) and ultra short (shortest) duration of actionQ (3-5 min; typically < 10 min).Its rapid onset effect is mainly due to its low lipid solubilityQ and relatively overdose that is administered.The short duration of action is due to rapid hydrolysis by butyrylcholinesterase (plasma cholinesterase or pseudocholinesteraseQ).Dibucaine number indicates the percentage of inhibition of pseudocholinesteraseQ (butyrylcholinesterase) enzyme activity by local anesthetic dibucaine and it is a measure of qualitative activity of pseudocholinesterase.The dibucaine number indicates the genetic make up of an individual with respect to butyrylcholinesterase. it does not measure the concentration of enzyme in plasma, nor does it indicate the efficiency of enzyme in hydrolysing substrate succinylcholine or mivacuriumQ.Dibucaine number is proportional to enzyme function (quality) and independent of amount of enzyme (i.e. quantity)Q.Prolonged paralysis from succinylcholine caused by atypical (abnormal) pseudochoiinesterase should be treated with continued mechanical ventilation until muscle fasciculation returns to normalQ. Anticholinesterases neostigmine and pyridostigmine are avoidedQ, as these may prolong the effect of Sch.Side Effects:Sch is a relatively safe drug but because of risk of hyperkalemia, rhabdomyolysis and cardiac arrest (profound bradycardia) in children with undiagnosed myopathies, Sch is considered contraindicated in routine management of children and adolescent.Side effects of Succinylcholine include an increase in* Muscle tone (masseter spasm)Q* Muscle fasciculations (signal onset of paralysis)Q* Muscle pains or myalgia (MC complication)Q* Hyperkalemia leading to diastolic cardiac arrest refractory to CPRQ* Introcutar, intracranial, intra abdominal, intragastric pressure and opening pressure of lower esophageal sphincter (all increased)* Malignant hyperthermiaQManagement of Side-effects:Sinus bradycardias, nodal (junctional rhythms and ventricular dysrhythmiasQ occur. Children are particularly susceptible to profound bradycardia. Intravenous atropine is prophylactically, given to children prior to first dose and always before a 2nd dose.Side effects especially myalgia and fasciculation can be prevented by precurarization, self-taming with IV scoline, IV lignocaine and faster infusion. But pretreatment with small doses of nondeplarizing relaxant (e.g. rocuronium) remain the most commonly used methodQMalignant Hyperpyrexia:Autosomal dominantPredisposing conditions: Duchene muscular dystrophyQ, HalothaneQ and Succinyl cholineQTreatment: DantroleneQ, bromocriptine and external cooling