The train-of-four (TOF) ratio at the adductor pollicis is used to assess neuromuscular recovery. A TOF ratio of 0.9 is considered the threshold for safe extubation. However, even at TOF ratio ≥0.9, residual neuromuscular blockade may be demonstrated at the:

• A Diaphragm, which recovers last
• B Intercostal muscles causing paradoxical chest wall movement
• C Orbicularis oculi used for facial nerve monitoring
• D Pharyngeal and upper oesophageal muscles ✓

Explanation

The pharyngeal dilator muscles and upper oesophageal sphincter are exquisitely sensitive to non-depolarising neuromuscular blocking agents and are the last to fully recover. Even at a peripheral TOF ratio of 0.9 measured at the adductor pollicis, pharyngeal dysfunction may persist, impairing swallowing, laryngeal reflexes, and cough, which substantially increases aspiration risk. The adductor pollicis recovers more slowly than the diaphragm; the diaphragm is the most resistant muscle to blockade and recovers first (central pattern).

Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.