Correspondence  |   April 2009
Conventional Neuromuscular Monitoring versus  Acceleromyography: It's Not the Monitor but the Anesthetist
Author Affiliations & Notes
  • Glenn S. Murphy, M.D.
  • *Evanston Northwestern Healthcare, Evanston, Illinois.
Article Information
Correspondence   |   April 2009
Conventional Neuromuscular Monitoring versus  Acceleromyography: It's Not the Monitor but the Anesthetist
Anesthesiology 4 2009, Vol.110, 949-950. doi:10.1097/ALN.0b013e31819c6c22
Anesthesiology 4 2009, Vol.110, 949-950. doi:10.1097/ALN.0b013e31819c6c22
In Reply:—
We thank Dr. Horowitz for his comments on our study.1 We welcome the opportunity to address his criticisms of the methodology used in our investigation and of our conclusions related to the effect of acceleromyography monitoring on residual neuromuscular blockade and adverse postoperative respiratory events.
First, we agree with the statement that nuances in neuromuscular management protocols may affect outcomes. Practices related to dosing, monitoring, and reversal of neuromuscular blocking agents may vary widely between institutions. The protocol used in our control group (conventional qualitative train-of-four [TOF] monitoring) was designed to reflect “optimal” neuromuscular management, as defined by Kopman et al.  (use of intermediate-acting muscle relaxants, avoidance of total twitch suppression, anticholinesterase reversal of blockade at a TOF count of 3–4).2 These techniques, which may reduce the incidence of residual paresis in the postanesthesia care unit, are routinely used at our institution in surgical patients requiring muscle relaxation. Dr. Horowitz suggests that the methodology of neuromuscular monitoring used in the conventional TOF group was flawed, because use of visual evaluation of TOF responses may result in an underestimation of the level of the blockade and an overestimation of neuromuscular recovery. Available evidence does not support this hypothesis. Two studies specifically comparing visual versus  tactile assessment of fade concluded that the ability of both techniques to detect fade was comparable at TOF ratios below 0.4 and between 0.4–0.7.3,4 The sensitivity in detecting fade was poor with both methods at all TOF ratios > 0.4, and no statistically or clinically significant differences were observed when either visual or tactile assessments were evaluated.3,4 Therefore, we do not believe that using tactile instead of visual evaluations of TOF responses would have influenced our findings in the conventional TOF group. In addition, there are no clinical studies demonstrating that the use of tactile assessments of TOF responses results in a reduced incidence of postoperative residual blockade when compared to visual evaluations.
Second, Dr. Horowitz questions our use of interoperative acceleromyography monitoring in our study group. We agree that quantitative neuromuscular monitoring does not provide any additional information over standard peripheral nerve monitoring during moderate levels of neuromuscular blockade (TOF count of 2–3) required for surgical relaxation. As described in our article, the value of acceleromyography monitoring is primarily during neuromuscular recovery. Our data suggests that acceleromyography monitoring allows for more rational and precise neuromuscular management during the last 45–60 minutes of the anesthetic.
Third, Dr. Horowitz states that we “did not follow common practices of neuromuscular monitoring and management of extubation when using a conventional monitor.” Dr. Horowitz does not define what these “common practices” are. Current evidence suggests that “common practices of neuromuscular monitoring” are not evidence-based, and techniques proven to reduce the incidence of residual neuromuscular blockade are infrequently applied by clinicians. Surveys from Germany, Denmark, France, and Great Britain all indicate that quantitative and qualitative monitoring is rarely used in daily clinical practice.5–7 In addition, knowledge about appropriate neuromuscular and clinical criteria required to exclude residual paresis before tracheal extubation is lacking.5–7 Although we did not follow “common practices of neuromuscular management” (which would have increased the incidence of residual neuromuscular blockade in the conventional TOF group), we believe that our neuromuscular management protocol represented the best available evidence. In fact, the two previous randomized acceleromyography trials compared a group of patients monitored with acceleromyography with a control group receiving no neuromuscular monitoring (the more “common clinical practice of neuromuscular monitoring” referred to by Dr. Horowitz).8,9 Of interest, the incidence of residual paresis was significantly reduced by acceleromyography monitoring in all three randomized trials. Furthermore, neuromuscular blockade was reversed at a mean visual TOF count of 4 in both groups, which represents good “evidence-based” practice.
Methods proven to reduce the incidence of postoperative residual blockade (use of intermediate-acting neuromuscular blocking agents, avoidance of total twitch suppression, anticholinesterase reversal of blockade at a TOF count of 3–4) should be adopted by clinicians. However, current data does not support the belief expressed by Dr. Horowitz that use of tactile assessment of TOF responses is superior to visual evaluation in reducing the risk of residual neuromuscular blockade and adverse postoperative outcomes. At the present time, “evidence-based standards for conventional monitoring” as described by Dr. Horowitz do not exist. Such guidelines would likely result in increased routine use of neuromuscular monitoring and anticholinesterase agents, and reduced complications related to incomplete neuromuscular recovery in the postoperative period.
*Evanston Northwestern Healthcare, Evanston, Illinois.
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