Neuromuscular blockers overview

What neuromuscular blockers (NMBs) do

• NMBs cause skeletal muscle paralysis by blocking transmission at the neuromuscular junction (they do NOT provide unconsciousness or pain relief).
• Used to: facilitate tracheal intubation, improve surgical conditions, enable controlled ventilation, reduce patient movement.
• Always pair with: adequate anaesthesia (hypnosis) and analgesia as appropriate.
• Key safety idea: paralysis can hide inadequate anaesthesia—monitor depth/clinical signs and ensure appropriate anaesthetic dosing.

Types and examples

• Non-depolarising NMBs (most common): rocuronium, vecuronium, atracurium, cisatracurium.
• Depolarising NMB: suxamethonium (succinylcholine).
• Non-depolarising drugs are usually reversed at the end of surgery (neostigmine or sugammadex depending on agent and depth of block).
• Suxamethonium typically wears off by metabolism (plasma cholinesterase); reversal is not used.

Onset, duration, and when you might choose what

• Rapid sequence induction (RSI): commonly suxamethonium or high-dose rocuronium (local policy-dependent).
• Longer cases/infusions: rocuronium is common; atracurium/cisatracurium useful when organ failure is a concern.
• Atracurium/cisatracurium undergo Hofmann elimination (temperature/pH dependent) and ester hydrolysis—less reliance on liver/kidney.
• Rocuronium/vecuronium rely more on hepatic/biliary (and some renal) clearance—effects can be prolonged in organ dysfunction.

How to monitor neuromuscular block (must-know basics)

• Use a peripheral nerve stimulator; aim for objective monitoring (quantitative TOF ratio) where available.
• Train-of-four (TOF): 4 stimuli; the number/strength of twitches falls with increasing block (fade suggests non-depolarising block).
• TOF ratio (T4/T1): recovery is considered safe for extubation when TOF ratio is at least 0.9 (ideally measured quantitatively).
• Common sites: ulnar nerve (adductor pollicis) for recovery; facial nerve (orbicularis oculi/corrugator) may reflect laryngeal conditions earlier—know what you are measuring.
• Clinical tests (head lift, hand grip) are unreliable alone—use neuromuscular monitoring.

Practical dosing and top-up strategy (new starter approach)

• Give an intubating dose, then reassess before topping up—avoid routine “blind” top-ups.
• Top-ups: use small, incremental doses guided by monitoring and surgical need.
• Be cautious near the end of surgery: allow time for spontaneous recovery and plan reversal early.
• If in doubt about residual block, do not extubate—confirm TOF ratio ≥0.9 and ensure adequate ventilation and airway reflexes.

Reversal: neostigmine vs sugammadex (core principles)

• Neostigmine (with glycopyrrolate): increases acetylcholine to compete with non-depolarising NMBs; works best for shallow/moderate block (when some twitches are present).
• Neostigmine has a ceiling effect and is slower; avoid giving it for profound block (little/no twitch response).
• Sugammadex encapsulates rocuronium (and vecuronium); can reverse deeper block more reliably and quickly (dose depends on depth of block).
• After reversal, re-check neuromuscular function (ideally quantitative TOF ratio ≥0.9) and ensure clinical recovery before extubation.

Common adverse effects and interactions

• All NMBs: risk of anaphylaxis (rare but important); rocuronium and suxamethonium are common triggers.
• Suxamethonium: can cause bradycardia (especially repeat doses), hyperkalaemia, malignant hyperthermia trigger, raised intraocular/intragastric pressure, myalgia, prolonged paralysis in pseudocholinesterase deficiency.
• Atracurium: histamine release can cause hypotension/bronchospasm (dose/rate related); cisatracurium has less histamine release.
• Potentiation: volatile anaesthetics, aminoglycosides, magnesium, lithium, and some antibiotics can increase block—expect longer duration.

First-time scenarios: what to do

• Unexpected difficult intubation after paralysis: follow local difficult airway guidelines; call for help early; consider waking the patient if appropriate and feasible; ensure oxygenation is prioritised.
• Prolonged paralysis at end of case: check monitoring, temperature, acid-base, electrolytes; consider drug interactions/organ failure; ensure adequate sedation/analgesia and ventilate until recovered/reversed.
• Suspected anaphylaxis after NMB: stop suspected trigger, call for help, follow anaphylaxis algorithm (adrenaline, fluids, airway/oxygen), and take tryptase samples per policy.
• ICU transfer with ongoing paralysis: ensure clear handover (drug, dose, time, monitoring), provide sedation/analgesia, and document paralysis plan.