A patient receiving vecuronium has a train-of-four (TOF) ratio of 0.4 on peripheral nerve stimulator with a supramaximal stimulus. What does this indicate about residual neuromuscular blockade?
- A Complete reversal — the patient is safe for extubation
- B Deep block — post-tetanic count monitoring is required
- C Moderate residual block; approximately 80% of receptors are still occupied ✓
- D Profound block — a TOF count cannot be elicited
Correct answer: C. Moderate residual block; approximately 80% of receptors are still occupied
Explanation
A TOF ratio of 0.4 represents approximately 80% receptor occupancy by the non-depolarising agent. While a TOF count of 4 twitches is present (indicating <75% receptor block for eliciting twitches), the ratio of T4:T1 of 0.4 is well below the 0.9–1.0 threshold required for safe extubation. At a ratio <0.9, clinically significant residual paralysis is present with risk of aspiration, airway obstruction, and hypoxia. Reversal with neostigmine or sugammadex (for rocuronium/vecuronium) is required before extubation.
Reference: Morgan & Mikhail's Clinical Anesthesiology, 6th ed.
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