Non-Depolarising Neuromuscular Blockers
Non-depolarising NMBs are muscle relaxants used to:
- Facilitate laryngoscopy and tracheal intubation
- Control ICP
- Improve respiratory system compliance
- Improve patient safety on transportation
Common Features of Neuromuscular Blockers
|Route of Administration||IV/IM|
|Distribution||Small VD as they are polar and unable to cross lipid membranes|
|Elimination||Reduced urinary clearance which prolongs the mechanism of action of aminosteroids in renal failure|
|MSK||↑ Duration in hypothermia|
|Renal||↑ Duration in acidosis, ↑ duration in hypokalaemia, ↓ duration in hyperkalaemia, ↑ duration in hypermagnesaemia|
|Metabolic||Critical Illness Myopathy in patients with long-term relaxant use|
The ED95 is:
- The dose of a neuromuscular blocking drug required to produce a 95% reduction in twitch height in 50% of the population
- A commonly-used therapeutic end-point for neuromuscular blocking drugs
Typically, induction doses used are 2-5x the ED95.
Comparison of Neuromuscular Blockers
|Class||Aminosteroid||Aminosteroid||Bis-quaternary aminosteroid||Benzylisoquinolinium derivative||Benzylisoquinolinium derivative|
|Presentation||Clear, colourless solution at 10 mg.ml-1||10mg powder for reconstitution in water. Contains mannitol and NaOH.||Colourless solution at 2 mg.ml-1, which must be stored at 4°C||Colourless solution at 10mg.ml1, which should be stored at 4°C. Mixture of all ten extant diastereoisomers.||R-Cis, R'-Cis isomer of atracurium, which is 15% of atracurium by weight but provides 50% of its NMBD action.
Colourless solution at 2-5mg.ml-1, which should be stored at 4°C
|Intubating Dose||0.6-1.2 mg.kg-1||0.1 mg.kg-1||0.05-0.1 mg.kg-1||0.5 mg.kg-1||0.15-0.2mg.kg-1|
|ED95||0.3 mg.kg-1||0.05 mg.kg-1||0.07 mg.kg-1||0.25 mg.kg-1||0.05 mg.kg-1|
|Duration||~30 minutes with normal renal function, repeat doses may be more unpredictable||45-65 minutes||60-100 minutes||15-35 minutes||25-30 minutes|
|Metabolism||< 5% hepatic deacetylation to inactive metabolites||20% hepatic deacetylation with weakly active metabolites||20% hepatic deacetylation with weakly active metabolites||60% by ester hydrolysis, with remainder by Hofmann elimination.
Metabolised to laudanosine, which causes seizures in high concentrations (relevant when administered by long infusion)
|Elimination||60% biliary, 40% urinary. Prolonged duration in hepatic and renal failure||70% biliary, 30% urinary||80% biliary, 20% urinary|
|Resp||Slight risk of bronchospasm with rapid injection||Slight risk of bronchospasm with rapid injection|
|CVS||↑ HR at high doses||No ↑ HR||↑ HR and MAP due to muscarinic antagonism||Risk of ↓ BP with rapid injection||Risk of ↓ BP with rapid injection|
|Immune||Higher risk of anaphylaxis, ~6/100,000. Anaphylaxis risk associated with use of pholcodine in the previous 3 years.||Notably no anaphylaxis recorded in NAP 6||Anaphylaxis ~ 4/100,000.|
|Other||Reversible with sugammadex||Reversible with sugammadex|
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