During emergence from anesthesia after a neuromuscular blocking agent, does the diaphragm recover before the laryngeal muscles?

Diaphragm Recovers First During Neuromuscular Blockade Reversal

The diaphragm and laryngeal muscles recover before peripheral muscles like the adductor pollicis, with the diaphragm and larynx showing similar recovery times that are significantly faster than peripheral muscle recovery. 1, 2

Recovery Pattern of Respiratory Muscles

Differential Recovery Times

• The larynx and diaphragm recover to 90% function in approximately 7-8 minutes after succinylcholine, compared to 9 minutes at the adductor pollicis 1
• After rocuronium, the diaphragm recovers to 90% in 30.4 minutes and the larynx in 34.9 minutes, while the adductor pollicis requires 49.1 minutes 1
• Both the larynx and diaphragm show similar recovery kinetics, with no statistically significant difference between them, but both recover substantially faster than peripheral muscles 1, 2

Clinical Implications for Airway Safety

The key clinical point is that peripheral muscle monitoring (adductor pollicis) underestimates respiratory muscle recovery, meaning patients may have adequate diaphragmatic and laryngeal function even when peripheral monitoring shows incomplete recovery 3, 1

• Recovery of neuromuscular function at the end of any procedure is best reflected at the adductor pollicis muscle where neuromuscular transmission is last restored 3
• This creates a safety margin: when the adductor pollicis reaches adequate recovery (TOF ratio ≥0.9), the respiratory muscles have already recovered more completely 3

Monitoring Considerations

Optimal Monitoring Sites

• The corrugator supercilii muscle better reflects the time course of neuromuscular blockade at the larynx than the adductor pollicis and is better suited to monitor onset for intubation 3
• However, for assessing adequate recovery before extubation, the adductor pollicis remains the gold standard because it is the last muscle to recover, providing the most conservative assessment 3

Sugammadex Reversal Dynamics

• With sugammadex 16 mg/kg for immediate reversal, laryngeal muscles recover in 70 seconds, while the adductor pollicis TOF ratio reaches 0.9 in 118 seconds 4
• This confirms that even with pharmacological reversal, respiratory muscles recover faster than peripheral muscles 4

Critical Clinical Pitfalls

Common Monitoring Errors

• Assuming that awakening implies disappearance of effects on laryngeal muscles is dangerous—propofol effects on laryngeal muscles remain measurable at concentrations as low as 0.7 mg/mL even after consciousness returns 5
• Extubating based solely on consciousness without objective neuromuscular monitoring risks residual weakness of both respiratory and peripheral muscles 5

Safe Extubation Criteria

• Quantitative neuromuscular monitoring showing TOF ratio ≥0.9 at the adductor pollicis ensures that all muscle groups, including respiratory muscles, have adequately recovered 6
• Post-reversal monitoring should continue in the recovery area, as recurarization can occur even after initial adequate reversal 6

Physiological Basis

The larynx and diaphragm are more resistant to neuromuscular blocking agents than peripheral muscles, showing less intense blockade (94-97% maximum block vs 99-100% at adductor pollicis) and faster recovery 1, 2

• This resistance pattern is consistent across different neuromuscular blocking agents including succinylcholine, rocuronium, and mivacurium 1, 2
• The clinical duration (time to 25% recovery) at the larynx and diaphragm after mivacurium is approximately half that of peripheral muscles (10-11 minutes vs 20 minutes) 2