Short Quiz of 10 Questions on NEET PG Exam Pattern Questions with complete Discussion For More Such Short Quiz Please Visit www.medicoapps.org

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Anesthesia Important Concepts: Neuromuscular Blockade
(For NEET PG, USMLE, PLAB, FMGE /MCI Screening Entrance Exams)
Classificationofnondepolarizing( Competitive) neuromuscular blockingagents:
 Long acting : d Tubocurarine,Doxacurium,PancuroniumandPipecuronium.
 Intermediate acting: Vecuronium,Atracurium, Cisatracurium, RocuroniumandRapacuronium.
 Short acting : Mivacurium.
Classificationofdepolarizingneuromuscularblockers:
 Succinylcholine andDecamethonium
Train offour fade
Muscle responsestodifferentpatternsof nerve stimulationusedinmonitoringskeletal muscle
relaxation.The fade associatedwithNon -depolarizingblockhelpsin quantitative assessmentof the
non-depolarizingblock.
Train ofFour Count:
 Observe andcountthe sequential disappearance of twitches.
 Disappearance of 4th twitchimplies75% block.
 Disappearance of 3rd twitchimplies80% block.
 Disappearance of 2ndtwitch implies90% block.
Train ofFour Ratio:
 Thisis the ratioof amplitude of the 4thresponse tothat of the firstexpressedasthe percentage.
 It providesanestimationof the degreeof non-depolarizingneuromuscularblockage.
Vecuroniumisa nondepolarizingneuromuscularblocker.Itiswidelyusedbecauseof itsintermediate
durationof actionand lack of cardiovasculareffects.
80% of the drug is clearedbyhepaticmetabolismandbiliaryexcretion.Active metabolitesof
vecuroniumare clearedbykidney.
Succinylcholine depolatizationfeatures:
 Neuromuscularblockingactionof succinylcholine isprecededbymuscle fasiculations.Itstartsinthe
eye andfacial muscles,thenitpropagatestothe extremities,neckandtrunkmuscles.
 Aftersuccinyl choline the ratioof the fourthandfirsttwitchi.e the TOF rationalwaysequals1,
regardlessof the extentof muscle relaxation.ThismakesTOFratioill suitedforevaluating
neuromuscularrecoveryaftersuccinylcholine.
 No posttitanicpotentiationoccur aftersuccinylcholine induceddepolarizationblock.

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 Continuousorrepeatedadministrationof succinylcholinecanleadtophase II block,characterizedby
fadingafterrepeatedstimulation.Posttetanicpotentiationcanoccur.A phase IIblockis similartoa
nondepolarizingblock.Actionof succinylcholine cannotbe reversedbycholinesterase inhibitors.
Fentanyl isa syntheticfatsoluble opioid,usedwidelytoprovide rapidshortlivedpainrelief during
surgery.Inveryhighdosesitcan be usedas opioidanesthesia.Highdose of fentanyl canresultinmuscle
hypertonus.Severe chestwall rigiditywhichoccur,caninterfere withventilation.Thisisincreasedin
presence of nitrousoxide andcanbe preventedortreatedwithsedative hypnoticsorlow dose muscle
relaxants.
Respiratory depressionisthe majorcomplicationof fentanyl evenatappropriate doses.Respiratory
depressioncanlastupto30minutes.Mostpatientswhohypoventillate canbe arousedbyverbal or
physical stimulationandwill breathe deeplyoncommand.
Pancuronium isthe longestactingnondepolarizingneuromuscularblocker.Ithasmodesthistamine
releasingpropertiesandvagolyticeffectsthatmaycause tachycardiaand hypotension.
Elimination –50% is excretedunchanged,of which 80% appearsinthe urine.Of it,40% is deacetylated
inthe liverto3-hydroxy,17-hydroxyand3,17-dihydroxyderivativeswhichare eliminatedinthe bile.
Antibioticswhich has synergeticaction with competitive neuromuscularblockersare:
 Aminoglycosides
 Tetracyclines
 Polypeptide antibiotics
 Clindamycin
 Lincomycin
Questions and Solutions
1.Which one of the following muscle relaxant has the maximum duration of action?
a. Atracurium
b. Vecuronium
c. Rocuronium
d. Doxacurium
Solution :
Doxacuriumisthe longestactingmuscle relaxantamongstthe optionsprovidedinthe question. So, it
is suitable for long duration surgeries.
Other long acting muscle relaxants are Tubocurarine, Pancuronium and Pipecuronium.

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2. At the end of a balanced anaesthesia technique with non-depolarizing muscle relaxant, a patient
recovered spontaneously from the effect of muscle relaxant without any reversal. Which is the most
probable relaxant the patient had received?
a. Pancuronium
b. Gallamine
c. Atracurium
d. Vecuronium
Solution :
This patienthasreceivedanon depolarizing muscle relaxant and has recovered spontaneously from
its effect without any reversal, so he would have received atracurium. Atracurium is a short acting
muscle relaxant.
It is inactivated spontaneously by nonenzymatic degradation (Hofmann elimination) in addition to
that by cholinesterase. So reversal is mostly not required when it is used.
Hofmann elimination is the spontaneous fragmentation of atracurium at the bond between the
quaternary nitrogen and the central chain.
3.Which one of the following antibacterials should not be used with d-tubocurarine?
a. Norfloxacin
b. Doxycycline
c. Cefotaxime
d. Streptomycin
Solution :
Use of Streptomycin along with competitive non depolarizing blockers like d-tubocurarine can
potentiate itsactionandproduce prolongedapnea.Itactsby reducingthe release of acetylcholine from
the prejunctional nerveendingsbycompetingwithcalcium. Therefore streptomycinshould not be used
with d-tubocurarine.

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4.A patientwithbilirubinvalue of 8mg/dl andserumcreatinine of 1.9mg/dl isplannedforsurgery.What
is the muscle relaxant of choice in this patient?
a. Vecuronium
b. Pancuronium
c. Atracurium
d. Rocuronium
Solution:
Atracuriumisthe muscle relaxantof choice inpatientswithliverandrenal failure becausethese drugs
undergo extensive plasma degradation.
Atracurium undergoes esterase degradation and spontaneous breakdown at physiologic pH and
temperature called Hoffman elimination. Metabolism of atracurim yields a metabolite called
laudanosine, a renally cleared excitatory amine that can induce seizures.
Atracurium,cisatracuriumandmivacurium are nondepolarizingneuromuscularblockerswhichcanbe
used in patients with hepatic and renal failure.
5.Which of the following is the muscle relaxant of choice in renal failure?
a. Rapacurium
b. Pancuronium
c. Atracurium
d. Rocuronium
Solution:
Muscle relaxantof choice inrenal failure isatracurium, since itisnot eliminatedthroughthe kidney.It
is inactivated in the plasma by spontaneous non enzymatic degradation (Hofmann elimination) in
addition to that by cholinesterase.
Question 6
1. Fastest acting non depolarising blocker is Rocuronium
2. Longest acting neuromuscular blocker is Pancuronium

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3. Vagal stimulation is caused by succinylcholine
4. Most potent skeletal muscle relaxant is Doxacurium
5. Shortest acting non depolarising neuromuscular blocker is Mivacurium
a. 1, 2, 3 - True & 4, 5 - False
b. 1, 2, 3, 5 - True & 4 - False
c. 1, 2 - True & 3, 4, 5 - False
d. 1, 2, 3, 4, 5 - True
Solution :
Amongthe non depolarisingneuromuscular blockers Rocuronium has the fastest onset of action ( 90
seconds). Mivacurium is a short acting non depolarising muscle relaxant that is rapidly hydrolysed by
plasma pseudocholinesterase.
Pancuronium is a potent long acting neuromuscular blocking drug with both vagolytic and
butyrylcholinesterase inhibitng properties.
Doxacurium is 2.5 to 3 times more potent than pancuronium another long acting non depolarizing
agent.
7. Train of four fade is a characteristic feature of:
a. Depolarizing block
b. Non depolarizing block
c. Both depolarizing and non-depolarizing block
d. Malignant hyperthermia
Solution:
Train of four fade isa characteristicof a non-depolarizingblock.The Train-of-fourstimulationdenotes
the administration of four successive 200-ps stimuli in 2 seconds (2 Hz) and a series of patterns are
producedandthese patternsdifferinadepolarizingblockdiffersfromthat of a non-depolarizing block.
In a non-depolarizing block there is progressive depression of height with each twitch (fade) and in a
depolarizing block there is equal depression of all four twitches (No fade).

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8.All of the followingstatements about neuromuscular blockage produced by succinylcholine are true,
except:
a. No fade on Train of four stimulation
b. Fade on tetanic stimulation
c. No post tetanic facilitation
d. Train of four ratio > 0.4
Solution :
Succinylcholine isa depolarizing neuromuscular blocker. With succinylcholine no fading is observed
after train of four or tetanic stimulation. All four stimulatory responses after TOF stimulation are
suppressed to the same extent.
9.A 25 year oldoverweightfemale wasgivenfentanyl-pancuroniumanesthesiaforsurgery.Aftersurgery
and extubation she was observed to have limited movement of the upper body and chest wall in the
recovery room. She was conscious and alert but voluntary respiratory effort was limited. Her blood
pressure and heart rate were normal. The likely diagnosis is:
a. Incomplete reversal of pancuronium
b. Pulmonary embolism
c. Fentanyl induced chest wall rigidity
d. Respiratory depression
Solution :
Patientwithlimitedmovement of the upper body and chest wall and limited respiratory effort after
receivingalongactingmuscle relaxantpancuroniumisshowingfeaturesof incomplete reversal fromthe
effects of muscle relaxant drug.
Factors affecting rate of recovery of neuromuscular activity after reversal depend upon:
1. Intensity of block – greater the intensity of block at the time or reversal longer the recovery of
neuromuscular activity.
2. Dose.
3. Choice of neuromuscular blocking agent – Overall recovery of intermediate acting agents
(atracuium,vecuronium, mivacurium, rocuronium) following same dose of anticholinesterase is more
rapid and more complete than after pancuronium.

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4. Age – recoveryoccur more rapidlywithsmallerdosesof anticholinesterasesin infants and children
than adults.
5. Drug interactions
6. Renal failure.
10.Post anaesthetic myalgia is commonest with which of the following drugs?
a. Suxamethonium
b. Pancuronium
c. Vecuronium
d. Atracurium
Solution :
Post anaesthetic myalgia is seen after administration of depolarising skeletal muscle relaxants. It is
reduced by administration of non polarising skeletal muscle relaxants.