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Normalization to detect Residual paralysis?
- Thomas Fuchs-Buder (10 May 2006)
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Thomas Fuchs-Buder, Staff Anaesthesiologist CHU Nancy/Brabois, department of Anaesthesia and Critical care
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Suzuki et al proposed normalization of acceleromyographic train-of- four ratio, i.e. dividing the TOF-ratio noted on the acceleromyographic monitor display screen by the baseline value obtained before injection of the neuromuscular blocking agent, for detecting residual neuromuscular block1. Whilst the concept of normalization is supported by the author of this letter to the editor2, the study of Suzuki et al deserves some comments: The major problem of that study is the fact that the authors did not make simultaneous mechanomyographic or electromyographic measurements, this would have allowed to validate their concept of normalization. Moreover, they used the first generation of portable acceleromyographs (TOF-Guard®, Organon, Oss, The Netherlands) and the limits of agreement of this device with mechanomyographically measured neuromuscular recovery seems to be particularly wide, an increase in T1 up to 192% compared to initial value and a TOF ratio up to 1.47 as reported by Suzuki et al. confirmed this limitation of the first generation of AMG. With the current generation of AMG devices, i.e. TOF Watch® significantly less increase in both, T1 and TOF ratio are reported2,3. Nevertheless, there is no doubt that AMG slightly overestimates the degree of neuromuscular recovery. To detect with AMG residual paralysis reliably, several different concepts have been proposed: use of adequate preload, initial calibration and continuous neuromuscular monitoring and recovery of TOFR to unity detects even slight degrees of residual paralysis2. Normalization may also be performing, however, calculation of the normalized values by the physician in charge of the patient is rather unpractical and limits the wide spread application of the concept. In addition, in current clinical practice AMG is often, if not most often, used punctually at the end of surgery and thus, without possibility of baseline registration and subsequent normalization. Thus, TOF normalization would appear to have little relevance to the average clinican. References 1 Suzuki T, Fukano N, Kitajima O, Saeki S, Ogawa S. Normalization of acceleromyographic train-of-four baseline value for detecting residual neuromuscular block. British Journal of Anaesthesia 2006; 96: 44-7 2 Capron F, Alla F, Hottier C, Meistelman C, Fuchs-Buder T. Can acceleromyography detect low levels of residual paralysis? A probability approach to detect a mechanomyographic train-of-four ratio of 0.9 Anesthesiology 2004; 100:1119-24 3 Samet A, Capron F, Alla F, Meistelman C, Fuchs-Buder T. Single accelerometric train-of-four, 100 Hz tetanus or double-burst stimulation: which test performs better to detect residual paralysis. Anesthesiology 2005; 102:51-6 Conflict of Interest:None declared |
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