Comparison of the TOF-Scan™ acceleromyograph to TOF-Watch SX™: Influence of calibration

Quantitative neuromuscular monitoring is now widely recommended during anesthesia using neuromuscular blocking agents to prevent postoperative residual paralysis and its related complications. We compared the TOF-Watch SX™ accelerometer requiring initial calibration to the TOF-Scan™, a new accelerometer with a preset stimulation intensity of 50mA not necessitating calibration.

This pilot, prospective, observational study included adults undergoing general anesthesia with endotracheal intubation and muscle relaxation, having both arms free during surgery. Accelerometers were set up randomly on each arm. Anesthesia was started with remifentanil and propofol before an intubation dose of atracurium or rocuronium. Train of four stimulation was performed every 15s. Differences between measures were tested using Student's t-test and agreement assessed by Bland and Altman analysis.

Thirty-two patients were included. During onset, a mean bias of -26seconds with a limit of agreement from -172 to +119seconds was observed between TOF-Watch SX™ and TOF-Scan™ to obtain 0 response to TOF. During recovery, TOF-Scan™ showed a significantly later recovery from 1 response to T4/T1>10%, but a bias of 0minute and limits of agreement from -4 to +4minutes for T4/T1>90% (NS).

These results suggest a poor agreement between the calibrated TOF-Watch SX™ and the fix intensity TOF-Scan™ for onset and early recovery of relaxation (i.e. deep neuromuscular blockade) but a good agreement for recovery to TOF 90%. Data are not interchangeable between the devices, but both can be useful to detect residual paralysis.