Which monitoring method is used to assess neuromuscular blockade during mechanical ventilation?

• A. Pulse oximetry
• B. Train-of-four
• C. Capnography
• D. Chest radiograph

Answer: (B)

To gauge how deeply a patient is neuromuscularly blocked during mechanical ventilation, train-of-four stimulation is used. This involves delivering four quick electrical stimuli to a peripheral nerve (commonly the ulnar nerve at the wrist) and observing the resulting muscle responses, usually in the thumb (adductor pollicis) or another monitored muscle. The blockade reduces the size of each twitch, and by comparing the fourth twitch to the first, you get a train-of-four ratio. A low ratio means deeper blockade; as the blockade wears off, the ratio rises toward 1.0, indicating recovery. This approach lets clinicians titrate neuromuscular blocking agents to maintain adequate relaxation for ventilation while avoiding excessive blockade and lingering weakness. Other monitoring methods like pulse oximetry, capnography, or chest radiographs measure oxygenation, ventilation efficiency, or anatomy, but they don’t assess neuromuscular transmission, so they aren’t used for this purpose.