dr.bobby muscle relaxant

8/18/2019 Dr.bobby Muscle Relaxant

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MuscleRelaxants


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Muscle Relaxants

• What are they used for? –

Facilitate intubation of thetrachea – Facilitate mechanical

ventilation – Optimized surgical working

conditions


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Muscle Relaxants• ow skeletal muscle relaxation

can be achieved? – igh doses of volatile anesthetics – Regional anesthesia – !dministration of neuromuscular

blocking agents• "roper patient positioning on the

operating table


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Muscle Relaxants

• Muscle relaxants must not begiven without ade#uate dosageof analgesic and hypnotic drugs

• $nappropriately given % a patientis paralyzed but notanesthetized


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Muscle Relaxants

• ow do they work? – &euromuscular 'unction

•

Nerve terminal• Motor endplate of a muscle• Synaptic cleft

– &erve stimulation – Release of !cetylcholine (!ch) – "ostsynaptic events


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&euromuscular *unction(&M*)


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+inding of !ch to receptors on muscle end,plate


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Muscle Relaxants• -epolarizing muscle relaxant

– Succinylcholine•

&ondepolarizing musclerelaxants – Short acting – Intermediate acting – Long acting


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-epolarizing MuscleRelaxant

• .uccinylcholine• What is the mechanism of action?

– Physically resemble Ach – Act as acetylcholine receptor agonist – Not metabolized locally at NMJ – Metabolized by pseudocholinesterase in

plasma – Depolarizing action persists Ach – !ontinuous end"plate depolarization causes

muscle rela#ation


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• .uccinylcholine• What is the clinical use of

succinylcholine? – Most often used to facilitate intubation

• What is intubating dose ofsuccinylcholine?

– /,/01 mg2kg – Onset 34,54 seconds6 duration 1,/4

minutes


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• .uccinylcholine – What is phase $ neuromuscular

blockade?

– What is phase $$ neuromuscularblockade?

• $esemble bloc%ade produced bynondepolarizing muscle rela#ant• Succinylcholine infusion or dose &"'

mg(%g


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• .uccinylcholine – -oes it has side e7ects?

• 8ardiovascular•

Fasciculation• Muscle pain• $ncrease intraocular pressure• $ncrease intragastric pressure•

$ncrease intracranial pressure• yperkalemia• Malignant hyperthermia


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&ondepolarizing Muscle

Relaxants• What is the mechanism ofaction?

– !ompete )ith Ach at the binding sites – Do not depolarized the motor endplate – Act as competitive antagonist – *#cessive concentration causing

channel bloc%ade – Act at presynaptic sites+ prevent

movement of Ach to release sites


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&ondepolarizing MuscleRelaxants

• 9ong acting – Pancuronium

• $ntermediate acting –

Atracurium – ,ecuronium – $ocuronium – !isatracurium

• .hort acting – Mivacurium


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• "ancuronium – Aminosteroid compound – -nset &"' minutes+ duration ./"0/

minutes – Intubating dose /1/2"/134 mg(%g – *limination mainly by %idney 52'67+

liver 53'67 – Side e8ects 9 hypertension+ tachycrdia+

dysrhythmia+


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&ondepolarizing Muscle

Relaxants• :ecuronium – Analogue of pancuronium – much less vagolytic e8ect and shorter

duration than pancuronium – -nset &"' minutes duration 4/"&'

minutes – Intubating dose /1/2"/134 mg(%g –

*limination :/6 by %idney+ ./6 by liver


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• !tracurium – Metabolized by

• *ster hydrolysis• ;ofmann elimination

– -nset &"' minutes+ duration 4'"&'minutes

– Intubating dose /1' mg(%g – Side e8ects 9

•

histamine release causing hypotension+tachycardia+ bronchospasm• Laudanosine to#icity


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• 8isatracurium – Isomer of atracurium – Metabolized by ;ofmann elimination – -nset &"' minutes+ duration 4/"&'

minutes – Intubating dose /13"/14 mg(%g – Minimal cardiovascular side e8ects – Much less laudanosine produced


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• Rocuronium – Analogue of vecuronium – $apid onset 3"4 minutes+ duration 4/"&'

minutes – -nset of action similar to that of

succinylcholine – Intubating dose /1. mg(%g – *limination primarily by liver+ slightly by

%idney


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!lteration of responses• ;emperature• !cid,base balance•


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!lteration of responses• 8oncurrent diseases

– Neurologic diseases – Muscular diseases

• Myasthenia gravis• Myasthenic syndrome 5*aton"Lambert

synrome7 –

Liver diseases –


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!lteration of responses• -rug interactions

– Inhalation agents – Intravenous anesthetics – Local anesthetics – Neuromuscular loc%ing drugs – Antibiotics –

Anticonvulsants – Magnesium


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Monitoring &euromuscularFunction

•

What are the purposes ofmonitoring? – !dminister additional relaxant as

indicated – -emonstrate recovery


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ow to monitor?• !linical signs• =se of nerve stimulator


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• 8linical signs – Signs of ade>uate recovery

• Sustained head lift for ' seconds• Lift the leg 5child7• Ability to generate negative inspiratory

pressure at least 4' cm; 2 -+ able to s)allo)and maintain a patent air)ay

• -ther crude tests 9 tongue protrusion+ armlift+ hand grip strength


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• =se of nerve stimulator – Single t)itch 9 single pulse /14 msec – ?etanic stimulation – ?rain"of"four 9 series of : t)itch+ /14

msec long+ 4 ;z fre>uency+ administerevery 3/"3' seconds

– Double burst stimulation – Post tetanic count


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ierarchy of &euromuscular +lockade

Fraction of receptoroccupied by

nondepolarizingmuscle relaxant

Response to nervestimulator

Whole body signs

00"3// &o response Flaccid6 extremerelaxation0' "osttetanic facilitationpresent

-iaphragm moves6hiccough possible

0/ One of four twitch of;OF present

!bdominal relaxationade#uate for most

prcedure

@' Four twitch of ;OFpresent6 ;OF ratio 40>;idal volume and vitalcapacity normal

'/ /44, z tetanussustained"asses inspiratorypressure test

&/44, z tetanus

sustainedead lift and hand,grip

sustained


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!ntagonism of&euromuscular +lockade

*8ectiveness of anticholinesterases dependson the degree of recovery present )henthey are administered

• !nticholinesterases – Neostigmine

• -nset &"' minutes+ elimination hal ife @@minutes

• Dose /1/:"/1/@ mg(%g – Pyridostigmine – *drophonium


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• What is the mechanism of action? – Inhibiting activity of acetylcholineesterase – More Ach available at NMJ+ compete for

sites on nicotinic cholinergic receptors – Action at muscarinic cholinergic receptor

• Bradycardia• ;ypersecretion• Increased intestinal tone


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• Muscarinic side e8ects are minimizedby anticholinergic agents

– Atropine• Dose /1/3"/1/4 mg(%g

– Scopolamine – glycopyrrolate


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dr.bobby muscle relaxant

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