A Train-of-Four Count Should Be a Train-of-Four Count, Independently of the Method It Was Determined With

To the Editor: 

We read with interest the article from Murphy et al.  entitled “Intraoperative Acceleromyography Monitoring Reduces Symptoms of Muscle Weakness and Improves Quality of Recovery in the Early Postoperative Period.”1 

Indeed, the authors confirmed previous findings that objective acceleromyographic neuromuscular monitoring may improve perioperative neuromuscular management.2In the current study this improved perioperative management led to a better spontaneous recovery at the time of neostigmine administration: 61 of 76 patients in the acceleromyographic group compared with 41 of 74 patients in the control group had a train-of-four (TOF) count of 4 when neostigmine was given: P = 0.014. However, it is well known that the degree of spontaneous recovery at the time of neostigmine administration may have a major effect on neostigmine‘s efficacy. In this context Kirkegaard et al.  3reported that 20 min after the administration of neostigmine 70 μg/kg⁻¹at a TOF count of 4 the incidence of residual paralysis (defined as a TOF ratio less than 0.9) was 25%. This incidence increased to 56% when neostigmine was given at a TOF count of 2 instead of 4 without changing any of the other parameters.3Unfortunately, the timing of neostigmine administration was hardly controlled in the trial by Murphy et al.  2and therefore some points seem quite unclear to us: first, according to the Methods section neostigmine should be given when a TOF count of at least 3 was present. In the Results section, however, the TOF count at the time of neostigmine administration ranged from a TOFcount between 0 and 4. Second, and as mentioned previously, the number of patients who had a TOF count of 4 at this time was increased by 30% in the acceleromyographic group versus  control. Murphy et al. found a significant difference in repeat doses of rocuronium between the two groups during the last 45 min of the surgical procedure, a finding that is supposed to explain the effect in the acceleromyographic group. As stated in the Methods section, participating anesthesiologists were allowed to use “TOF ratio data to guide neuromuscular blocking agents dosing when surgical relaxation was not longer required.” The authors are requested to provide some information about the management of neuromuscular blocking agents dosing in the control group during this period. Third, most patients (102 of 150) had 4 TOF responses at the moment of neostigmine administration. It is not obvious whether these patients all had a simple TOF count of 4 (4 responses present with the first response less than 20%; the TOF-Watch SX®[Bluestar Enterprises, Omaha, NE] display shows the TOF count) or whether recovery was even more advanced in some patients (still 4 responses present but the first response more than 20%; the TOF-Watch SX® calculates and shows the TOF ratio). Further, it should be reported if and how this distinction was made in the control group. Finally, it would be interesting to know if all patients received a standard dose of 50 μg/kg⁻¹neostigmine, even in case of a deeper residual block with less than three twitch responses. Some information about the real doses of neostigmine that have been used could be helpful in this context.

Based on the information provided, we must conclude that the difference in symptoms of muscle weakness and improved quality of recovery observed in this study could simply be the consequence of the dose or the timing of the administration of neostigmine rather than the direct consequences of intraoperative acceleromyographic monitoring as supposed by Murphy et al. 

We suggest that the authors should complete the missing information and report the incidence of residual blockade and associated unpleasant symptoms of muscle weakness separately according to the patients' individual TOF count at the time of neostigmine administration to clarify this key issue. In our opinion, these data are essential for the reader to allow a correct interpretation of the results and, thus, to improve patient's safety. Moreover, it would be very instructive to see whether there were any significant differences in unpleasant symptoms if neostigmine was given at TOF count of 4 independently from the technique of determination (acceleromyographic or conventional qualitative monitoring, respectively), as supposed by Murphy et al.  Currently, we are in doubt about this issue.

In addition, the number of included patients reported in the “What This Article Tells Us That Is New” section is probably incorrect and should be 155 instead of 115.