Clinical Applications and Monitoring
Train-of-four monitoring, disease-altered sensitivity, and reversal decision guide
Neuromuscular Monitoring
Train-of-Four — Key Thresholds
  • Four equal twitches = no block
  • Fade (4th < 1st) = nondepolarizing block pattern
  • No fade, uniform depression = depolarizing block pattern
  • Train-of-four ratio < 0.9 = residual block — do not extubate
  • Train-of-four ratio ≥ 0.9 required before extubation
  • Subjective assessment alone is unreliable at the margin
Drug Interactions
Agents That Potentiate Block
  • Aminoglycosides — pre- and postsynaptic; calcium partially reverses
  • Volatile anesthetics — postsynaptic sensitization; dose-dependent
  • Magnesium — reduces acetylcholine release; important in pre-eclampsia
  • Calcium channel blockers — mild presynaptic effect
Myasthenia Gravis Lambert-Eaton Myasthenic Syndrome
Defect site Postsynaptic — nicotinic receptor loss Presynaptic — voltage-gated calcium channel antibodies
Nondepolarizing agents Exquisitely sensitive — use minimal doses Sensitive — reduced acetylcholine release
Succinylcholine Relatively resistant — fewer receptors to depolarize Sensitive — receptors underactivated at baseline
Association Thymoma Small cell lung cancer
Reversal Decision Guide
Use Neostigmine + Antimuscarinic when…

Any nondepolarizing agent was used AND at least 1–2 train-of-four twitches are present. Pair with atropine or glycopyrrolate. Confirm train-of-four ratio ≥ 0.9 before extubation.

Use Sugammadex when…

Rocuronium or vecuronium was used. Block is deep (zero or few twitches), reversal is urgent, or neostigmine is inadequate or contraindicated. No antimuscarinic needed.