Monitoring Neuromuscular Blockade
CA-1 · draft
CA-1 Bootcamp day 8. Authored from cited abstracts; every claim carries a PMID.
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until you approve it. Read every point and its source first — they were drafted
from search results, not from clinical judgement.
Before induction
Residual paralysis means a train-of-four ratio below 0.9, it is common rather than rare — 26% of adults in a multicentre acceleromyographic study had a ratio below 0.9 on arrival in recovery, and incomplete recovery was more frequent among the patients who had been given a reversal agent — and you cannot see it, because patients who developed critical respiratory events in recovery averaged a train-of-four ratio of 0.62 against 0.98 in matched controls.
The 2023 American Society of Anesthesiologists practice guidelines for monitoring and antagonism of neuromuscular blockade exist because monitoring and reversal are the two levers that move this problem, and a single-centre study found that no patient who received both intraoperative neuromuscular monitoring and sugammadex had residual block, while the absence of monitoring and the use of neostigmine were identified risk factors for it.
Where you put the electrodes changes the answer you get: measured simultaneously in the same patients after mivacurium, the adducting laryngeal muscles and the diaphragm were blocked and recovered fastest, while the adductor pollicis was the slowest of the five muscles studied and lagged the corrugator supercilii and orbicularis oculi by several minutes to 90% twitch recovery — so a reassuring twitch beside the eyebrow is reporting on a muscle that recovers early, not on the muscles that will hold her airway open.
Electrode placement is not a detail you can wave at: when an independent observer checked electromyographic electrode positions before and after a teaching intervention, ideal positioning over the ulnar nerve groove rose from 74.5% to 95% and ideal distal placement within 2 cm of the wrist crease rose from 61.8% to 96.7%, and correct placement tracked directly with whether clinicians believed the number the monitor gave them.
Direct muscle stimulation is the classic explanation for a twitch that lies, but it is easier to invoke than to demonstrate — when electrodes were deliberately placed over the hand between the first and second metacarpals instead of over the ulnar nerve at the wrist, the train-of-four ratios agreed with wrist stimulation (bias 0.5%) rather than exceeding them, so a suspicious twitch is a reason to go back and check where your electrodes are sitting rather than proof of anything by itself.
Quantitative and qualitative monitoring are not two grades of the same measurement: a qualitative twitch monitor gives you no ratio at all, only twitches you count and fade you guess at, while even a quantitative acceleromyograph needs care, because baseline train-of-four ratios before any relaxant ranged from 0.95 to 1.47 in one series and a displayed 0.9 therefore does not always represent real recovery unless it is normalised to that patient's own starting value.
Questions in the room
Show me your electrodes. Which nerve are you stimulating, and how do you know it is that nerve and not the muscle underneath?
Four twitches with no visible fade — what range of train-of-four ratios is that compatible with?
You are reading the eyebrow. Which muscle recovers first, the eyebrow or the hand, and which one guards her airway?
What is the actual number you need before extubation, and is your monitor capable of producing it?
Oral boards stem
A 74-year-old is finishing a laparoscopic cholecystectomy. She has had two doses of rocuronium, the last one about 35 minutes ago. The surgeon is closing, the patient is grimacing and taking shallow breaths, and the nerve stimulator — with its electrodes on the forehead, beside the eyebrow — shows four strong twitches with no fade that you can see. The examiner asks whether this patient is reversed, where you would rather the electrodes had been, and what number, measured how, you actually need before that tube comes out.
Sources
Esteves et al., Eur J Anaesthesiol 2013
PMID 23344123
Murphy et al., Anesth Analg 2008
PMID 18635478
Raval et al., J Clin Anesth 2020
PMID 32585565
Thilen et al., Anesthesiology 2023
PMID 36520073
Özbey et al., Turk J Med Sci 2022
PMID 36422506
Hemmerling et al., Br J Anaesth 2000
PMID 11732519
Ebert et al., J Clin Monit Comput 2025
PMID 39433701
Nepveu et al., Anesth Analg 2005
PMID 15616069
Suzuki et al., Br J Anaesth 2006
PMID 16299046
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