Comparison of train-of-four count by anesthesia providers versus TOF-Watch® SX: a prospective cohort study

Qualitative monitoring of neuromuscular blockade using the train-of-four (TOF) count is widely used to determine the timing and dose of reversal agents for neuromuscular blockade. We compared TOF count measured manually by anesthesia providers with that determined by TOF-Watch® SX.

This prospective observational cohort study included patients who were American Society of Anesthesiologists physical status III or less and undergoing elective surgery. During recovery from an intubating dose of rocuronium or vecuronium, the TOF count was measured every 15 sec using TOF-Watch SX. Anesthesia providers assessed the TOF count twice at each level of TOF-count, 15 sec after the TOF-Watch SX count increased to the next level and then two to five minutes later.

In 75 patients, 687 observations were collected. There was agreement between the TOF-Watch SX and the subjective assessment by the provider in 386 (56%) of these observations. The agreement was 87% at TOF counts of 0 and 4. In the 409 observations at TOF counts 1, 2, and 3, the agreement was 36%. Among the 264 observations with disagreement at these TOF counts, providers assessed a higher TOF count in 254 (96%) observations and a lower count in 10 (4%) observations compared with the TOF-Watch SX.

Anesthesia providers report higher values of TOF count compared with the TOF-Watch SX, especially at intermediate levels of neuromuscular blockade. Since the dosing guidelines for the timing and dose of reversal agents are based on the TOF count derived from the TOF-Watch SX, a manually assessed TOF count may lead to inadequate dosing and/or premature administration of reversal agents.