Non-Depolarising Muscle Relaxants Flashcards Preview

Anesthetics > Non-Depolarising Muscle Relaxants > Flashcards

Flashcards in Non-Depolarising Muscle Relaxants Deck (16)
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1
Q

Classification (chemical structure)

A

Aminosteroid:

  • Pancuronium
  • Vecuronium
  • Rocuronium

Benzylisoquinolium:

  • Atracurium
  • Cisatracurium
  • Mivacurium
2
Q

Classification (duration of action)

A

Long acting

  • Pancuronium

Intermediate acting

  • Atracurium
  • Cisatracurium
  • Rocuronium
  • Vecuronium

Short acting

  • Mivacurium
3
Q

Mechanism of action

A
  • Occupation of one or both of the ACh receptor sites
  • Prevents ACh from binding to both sites (i.e. they compete with ACh)
  • These agents do not produce the conformational change necessary for channel opening. The ion channel therefore remains closed, ions do not flow and depolarisation does not occur
  • Nondepolarising muscle relaxants are competitive antagonists at the AChR
4
Q

Side effects

A

Autonomic effects:

  • d- tubocurarine may block autonomic ganglia, causing hypotension
  • Pancuronium blocks vagal muscarinic receptors in the SA node, causing a tachycardia
  • Atracurium, cisatracurium, mivacurium, vecuronium, and rocuronium do not have significant autonomic side effects

Histamine release:

  • Benzylisoquinolones - precipitate bronchospasm, hypotension and skin flushing
  • Cisatracurium has no direct histaminergic effects, nor do any of the aminosteroids
5
Q

Metabolism

A

Hepatic clearance:

  • Vecuronium (significantly metabolised by the liver)
  • Rocuronium (lesser extent of metabolism)

Renal excretion

  • Pancuronium
  • Rocuronium

Plasma pseudocholinesterase

  • Mivacurium
  • Atriacurium (lesser extent)

Hoffman degradation

  • Atracurium
  • Cisatracurium
6
Q

Drug interactions

A

Volatiles decrease requirements by 15% (Desflurane > sevoflurane >isoflurane >halothane >N2O)

The following may potentiate neuromuscular blockade:

  • antibiotics
  • antiarrhythmics
  • antihypertensives
  • dantrolene
  • furosemide (<10µg/kg)
  • ketamine
  • magnesium sulphate

The following may cause resistance to neuromuscular blockade

  • anticonvulsants
  • cholinesterase inhibitors
  • furosemide (1-4 mg/kg)
7
Q

Factors affecting neuromuscular blockade

A
  • Hypothermia - decreases metabolism or delays excretion, prolonging duration of action
  • Respiratory acidosis potentiates block and antagonizes reversal
  • Electrolytes: hypokalaemia, hypocalcaemia and hypermagnesaemia potentiate block
  • Age: neonates are more sensitive, but have an increased volume of distribution; therefore the dose is not necessarily changed
  • Hypersensitivity to relaxants e.g. amyotrophic lateral sclerosis, autoimmune disorders, familial periodic paralysis, Guillian-Barré syndrome, muscular dystrophy, myasthenia gravis, myotonia
  • Resistance may occur with other conditions e.g. burns, cerebral palsy, severe chronic infections (tetanus, botulism)
  • Muscle groups: diaphragm, laryngeal and orbicularis occuli muscles are paralysed faster and recover faster
8
Q

Pancuronium

A
  • Dose: 0.08-0.12mg/kg
  • Onset: 3.5-4 minutes
  • Duration: 70-120 minutes
  • Metabolism & excretion:
    • Metabolised by the liver to a small degree
    • Primarily renally excreted
    • About 10% excreted in the bile
  • Side effects:
    • Hypertension & tachycardia due to vagal block & release of catecholamines from adrenergic nerve endings
    • Ventricular arrhythmias secondary to increased AV conduction and catecholamine release
    • Allergic reactions in those sensitive to bromides
9
Q

Atracurium

A
  • Dose: 0.5mg/kg
  • Onset: 3-4 minutes
  • Duration: 50-60 minutes
  • Metabolism & excretion
    • Independent of renal & hepatic function - metabolised by 2 processes
    • Hoffman elimination, a spontaneous nonenzymatic chemical breakdown which produces laudanosine
    • Ester hydrolysis by nonspecific esterases
  • Side effects
    • Histamine release (bronchospasm) - may be decreased by slow injection
    • Cardiovascular effects unusual at normal doses
    • Laudanosine has been associated with CNS excitation and seizures in animal studies
    • Hypothermia and acidosis prolong the duration of action
  • Contraindications - avoid in asthmatics
10
Q

Cisatracurium

A
  • Dose: 0.15mg/kg
  • Onset: 4-5 minutes
  • Duration: 70-80 minutes
  • Metabolism & excretion - Hoffman elimination
  • Side effects:
    • Does not release histamine
    • No cardiovascular effects, even at high doses
11
Q

Vecuronium

A
  • Dose: 0.08-0.12mg/kg
  • Onset: 3 minutes
  • Duration: 50-60 minutes
  • Metabolism & excretion:
    • Hepatic metabolism
    • Primarily excreted in bile
    • About 20% renal excretion
  • Side effects:
    • Devoid of cardiovascular effects
    • Does not release histamine
    • Females more sensitive than males
12
Q

Rocuronium

A
  • Dose: 0.6-1.2mg/kg
  • Onset: 1-1.5 minutes
  • Duration: 60-70 minutes
  • Metabolism & excretion: -
    • Not metabolised
    • Eliminated primarily by the liver
    • Minimal renal excretion
  • Side effects:
    • At dose of 0.9-1.2mg/kg has onset similar to succinylcholine, but much longer duration
    • Slight vagolytic tendencies
    • No histamine release
13
Q

Agents used in reversal

A
  • Ach esterase inhibitors - reversal
    • neostigmine
    • pyridostigmine
    • edrophonium

*Neostigmine may prolong the effect of mivacurium through inhibition of pseudocholinesterase

Muscarinic receptor antagonists - symptomatic treatment

  • atropine
  • glycopyrrolate
14
Q

Muscarinic effects

A
  • Diarrhoea
  • Urinary incontinence
  • Miosis
  • Bronchoconstriction, bradycardia
  • Emesis
  • Lacrimation
  • Salivation
15
Q

Monitoring reversal

A
  • Nerve stimulator
    • Single twitch
    • Train of 4
    • Double burst stimulation
    • Tetanic stimulation & posttetanic count
  • Clinically
    • 5 second head lift, 5 second leg lift
    • Effective swallowing
    • Patent airway without jaw lift
    • Glottic closure against valsalva to oesophageal pressure of +30cm H2O
    • Vital capacity >30% of control
16
Q

Train of Four

A

T4 - 70-75% receptor occupancy

T3 - 85%

T2 - 85-90%

T1 - 90-98%

Reversal given if

  • 1 response present (short-acting agents)
  • 1-2 responses for intermediate acting
  • 2-3 responses for long acting