Depolarising Muscle Relaxants MCQs

Cisatracurium This R-Cis, R-Cis enantiomer of atracurium is nearly 4 times more potent , slower in onset (Option A ruled out), but similar in duration of action .(Option C ruled out) Like atracurium it undergoes Hofmann elimination (Option D ruled out), but in contrast to the racemate, it is not hydrolysed by plasma cholinesterase and hepatic metabolism is limited, so that less of the toxic metabolite is formed. Most importantly, it does not provoke histamine release and side effects are fewer. Currently, cisatracurium is one of the preferred muscle relaxants, especially for liver/kidney disease patients and for the elderly.

Atropine, a tertiary amine, is an anticholinergic drug which is used along with anticholinesterases like neostigmine to minimize the muscarinic adverse effects of anticholinesterases ( Option C is CORRECT ) It has no effect on the reversal of neuromuscular blockade produced by the nicotinic effect of anticholinesterases (Option A, B & D) It counteracts the cardiovascular effects of anticholinesterases like bradycardia and other bradyarrhythmia Glycopyrrolate , a quaternary amine, is another anticholinergic which can be used with the anticholinesterases It has slower onset than atropine but does not cause central effects as it does not cross blood brain barrier unlike atropine Reference: Morgan and mikhail's clinical anaesthesiology 6th edition

Neonates, infants, and young children have relatively greater alveolar ventilation and reduced FRC compared with older children and adults This greater minute ventilation-to-FRC ratio with relatively greater blood flow to vessel-rich organs contributes to a rapid increase in alveolar anaesthetic concentration and speeds inhalation induction Furthermore, the blood/gas coefficients of volatile anaesthetics are reduced in neonates compared with adults, resulting in even faster induction times and potentially increasing the risk of accidental overdosage Reference: E Book Morgan and Mikhail’s 6th Edition Chapter 42 Page No 1532.

The introduction of short- and intermediate- acting agents has resulted in the greater use of priming doses Theoretically, giving 10% to 15% of the usual intubating dose (Option A) 5 min before induction will occupy enough receptors so that paralysis will quickly follow when the balance of relaxant is administered A priming dose does not usually lead to clinically significant paralysis, which requires that 75% to 80% of the receptors be blocked (a neuromuscular margin of safety) Priming can additionally cause measurable deterioration in respiratory function (e.g., decreased forced vital capacity) and may lead to oxygen desaturation in patients with marginal pulmonary reserve These negative side effects are more common in older, sicker patients Reference: Morgan and mikhail's clinical anaesthesiology 6th edition

The benzylisoquinolinium class of drugs comprises atracurium, 51W89, doxacurium, rocuronium, tubocurarine and vecuronium and mivacurium The administration of benzylisoquinolinium neuromuscular blocking drugs ( except for cisatracurium ) is associated with → histamine release, which may result in →increased airway resistance and bronchospasm in patients with hyperactive airway disease Reference: Morgan and mikhail's clinical anaesthesiology 6th edition

In patients with significant burns (>20% TBSA), injury and disruption of neuromuscular end plates occurs, followed by up regulation of acetylcholine receptors. Beyond 15-48 h after significant burn injury, succinylcholine can produce lethal hyperkalemia. This risk for succinylcholine-induced hyperkalemia persists for up to 2 years following burn injury. Reference: Morgan and Mikhail’s clinical anesthesiology 6th edition pg 837.

Succinylcholine has been associated with severe hyperkalaemia in patients with Burn Severe abdominal infections Severe metabolic acidosis Closed head injury Conditions associated with upregulation of extra junctional acetylcholine receptors (e.g., hemiplegia or paraplegia, muscular dystrophies, Guillain-Barre syndrome, and burn) Because of the risk of massive rhabdomyolysis , hyperkalaemia, and death in children with undiagnosed muscle disease, succinylcholine is not recommended for use in children except for emergency tracheal intubation Patients with renal failure are no more susceptible to an exaggerated hyperkalaemia response to succinylcholine than are patients with normal renal function ( Option A ) Reference: Morgan and mikhail's clinical anaesthesiology 6th edition

All the other given agents can provide for ideal intubation condition following induction rapidly. Atracurium besylate. Non-depolarizing neuromuscular blocking drug, first used in 1980. A bis-quaternary nitrogenous plant derivative. Initial dose: 0.3–0.6 mg/kg. Intubation is possible approximately 90 s after a dose of 0.5 mg/kg. Effects last 20–30 min. Supplementary dose: 0.1–0.2 mg/kg. May cause histamine release, usually mild, but severe reactions have been reported at body temperature and pH, undergoes spontaneous Hofmann elimination to laudanosine. Up to 50% ester hydrolysis also occurs. Often considered the drug of choice in renal or hepatic impairment. Its cardio stability, low risk of accumulation and spontaneous reversal are also advantages. Stored at 2–8°C; at room temperature. Reference: FRCA A TO Z, page no 56