THE TOF-GUARD NEUROMUSCULAR-TRANSMISSION MONITOR - A COMPARISON WITH THE MYOGRAPH-2000

The TOF-Guard neuromuscular monitor uses an accelerometer to measure the response to nerve stimulation. In this study, we have compared it to a standard mechanomyographic monitor, the Myograph 2000, for neuromuscular monitoring in 28 subjects. A train-of-four mode of stimulation was used in both cases. The times taken for onset of block, and for the recovery of T1 (the first response in the train of four) to 25% of control, the time from recovery of T1 from 25-75% and for the recovery of the train of four ratio to 0.7 were compared with the two monitors. There was a good correlation between the two devices for both onset and recovery times. However, differences were highlighted when the data were analysed by the method of Bland and Altman. The 95% limits of agreement for the T1 recovery to 25%, as measured by the TOF-Guard, ranged from 5 min less to 8 min more than when measured by the Myograph 2000. For recovery of the train of four ratio to 0.7, the limits of agreement were approximately 6 min in either direction. The 95% limits for the TOF-Guard measured train of four ratio were from 0.47 to 0.99, at the Myograph reading of 0.7. We recommend that information from the TOF-Guard and the Myograph 2000 should not be used interchangeably. However, the TOF-Guard is likely to improve considerably on tactile evaluation of the responses to stimulation.