From MOST to LEAST rapid, select the correct temporal sequence of neuromuscular blockade in the adductor of the thumb, the orbicularis oculi, and the diaphragm after administration of an intubating dose of vecuronium to an otherwise healthy patient.

From MOST to LEAST rapid, select the correct temporal sequence of neuromuscular blockade in the adductor of the thumb, the orbicularis oculi, and the diaphragm after administration of an intubating dose of vecuronium to an otherwise healthy patient.

• A. Diaphragm, orbicularis oculi, thumb
• B. Orbicularis oculi, diaphragm, thumb
• C. Orbicularis oculi same as diaphragm, thumb
• D. Thumb, orbicularis oculi, diaphragm

Answer: (C)

Blockade from nondepolarizing neuromuscular blockers begins in the most rapidly perfused, smallest muscles with high receptor density and then spreads to larger, less-perfused muscles. The eye muscles (orbicularis oculi) fit this pattern and show very rapid onset after an intubating dose. The diaphragm is also highly perfused and very sensitive to these agents, so its blockade occurs almost as quickly as the eye muscles. The adductor pollicis (thumb) is a larger, less-perfused muscle, so its blockade develops later. Therefore, the fastest onset is essentially the eye muscles and diaphragm together, with the thumb showing a slower onset. This is why the sequence from most to least rapid is orbicularis oculi (tied with diaphragm) followed by the thumb.

Blockade from nondepolarizing neuromuscular blockers begins in the most rapidly perfused, smallest muscles with high receptor density and then spreads to larger, less-perfused muscles. The eye muscles (orbicularis oculi) fit this pattern and show very rapid onset after an intubating dose. The diaphragm is also highly perfused and very sensitive to these agents, so its blockade occurs almost as quickly as the eye muscles. The adductor pollicis (thumb) is a larger, less-perfused muscle, so its blockade develops later.

Therefore, the fastest onset is essentially the eye muscles and diaphragm together, with the thumb showing a slower onset. This is why the sequence from most to least rapid is orbicularis oculi (tied with diaphragm) followed by the thumb.