Neuromuscular monitoring and postoperative residual curarization
Copenhagen, Denmark
* E-mail: viby{at}rh.dk
Editor—In their meta-analysis of neuromuscular monitoring and postoperative residual curarization (PORC), Naguib and colleagues1 conclude that they ‘... could not demonstrate that the use of an intraoperative neuromuscular function monitor decreased the incidence of PORC’. We agree that given their hypothesis (that intraoperative neuromuscular monitoring, including both objective and non-objective methods, would reduce the incidence of PORC) and the chosen methodology (a meta-analysis based on both comparative and non-comparative studies), this conclusion on their work is correct. However, we do question the relevance of both the hypothesis and the use of a meta-analysis—and accordingly also their conclusion. In fact, the authors themselves also doubt the conclusion reached, based on ‘...a more detailed analysis of the studies ...’.
First of all, from all points of view, be it clinical experience, available literature or common sense, it is to be expected that the effect of neuromuscular monitoring on the incidence of PORC will depend on whether or not the monitoring method used is subjective (visual or manual evaluation) or objective (i.e. using acceleromyography). It is, therefore, not reasonable or scientifically justifiable to include both objective and non-objective methods in one hypothesis. It would make more sense to pose two questions.
- Does non-objective neuromuscular monitoring decrease the incidence of PORC?
- Does objective neuromuscular monitoring decrease the incidence of PORC?
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- There is insufficient evidence to confirm or deny that subjective neuromuscular monitoring decreases the incidence of PORC.
- There is good evidence that objective neuromuscular monitoring with acceleromyography decreases the incidence of PORC.
These conclusions certainly are different from the main conclusion in the abstract: ‘That it was not possible to demonstrate that intraoperative neuromuscular function monitoring decrease the incidence of PORC’.
Houston, USA
* E-mail: naguib{at}mdanderson.org
Editor—We would like to thank Drs Viby-Mogensen, Claudius, and Eriksson for their interest in our paper.1 We were interested in finding out from the published literature whether the use of an intraoperative neuromuscular monitor (conventional or quantitative) would decrease the incidence of PORC. Viby-Mogensen and colleagues appear to have two concerns about our investigation. First, they propose that we were incorrect in combining studies using conventional methods of monitoring neuromuscular block with others in which objective or quantitative monitors were employed. This objection appears to be based in large part on ‘common sense’. They suggest it is ‘obvious’ that the incidence of PORC should be lower with the use of the quantitative than with the use of conventional neuromuscular monitoring. Perhaps, but the same reasoning would suggest it is ‘apparent’ that monitoring neuromuscular function with conventional peripheral nerve stimulators should clearly result in a lower incidence of PORC than when purely clinical signs are the only available end-points. Although we believe that the proper application of neuromuscular monitoring should reduce the incidence of PORC, proving this hypothesis has proved difficult.
In response to this letter, we performed additional analysis and compared monitored and non-monitored conventional groups and also monitored and non-monitored quantitative groups using weighted t-tests on the transformed data. None of the comparisons was statistically significant (Table 2). The only comparison that was close to being significant was based on only two studies for the monitored quantitative group for long-acting neuromuscular blockers. Therefore, there is currently no evidence to support the hypothesis that the use of quantitative neuromuscular function monitors is superior to conventional monitors in reducing the incidence of PORC. Hence, the assumption made by Viby-Mogensen and colleagues is unfounded.
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Studies using quantitative neuromuscular monitoring which demonstrate a lower incidence of PORC used very strict criteria for extubation, which may not reflect the actual clinical practice. Quantitative monitors will only produce superior results if anaesthetists are willing to delay extubation in the operating room and keep their patients asleep until adequate recovery occurs.4 The issue is not which type of monitor (conventional or quantitative) is used, but appears to be who is using the monitor. What makes the difference in the incidence of PORC is not the monitor but the anaesthetist behind the monitor.
Viby-Mogensen and colleagues also question our use of meta-analysis and suggest using ‘generally accepted standards for evidence-based medicine’. However, using very narrow inclusion criteria would result in more homogenous data at the cost of excluding valuable studies, introducing bias, and making the data less generalizable.5 In addition, as Horlocker and Brown6 stated: ‘Clinical questions pertinent to the practice of anaesthesiology frequently do not meet criteria for high-level evidence as judged by evidence-based medicine advocates’. To avoid the problems associated with using narrow inclusion criteria, we included 13 randomized and 11 observational studies in the meta-analysis. To provide a measure of the quality of the results of the randomized studies, we also graded each randomized study according to the criteria of the Jadad five-point scale and provided the Jadad scores.
In meta-analysis, after pooling of the results, the next step is to determine the heterogeneity of the data. We do not know how heterogeneity can be determined if not through meta-analysis. Dr Viby-Mogensen's suggested approach misses another advantage of meta-analysis. A random-effects model is able to consider both the size of the study and the heterogeneity of the study results. Without meta-analysis, heterogeneity and weight cannot be determined, and definitely neither can be determined by simple categorization and data description.
As we had stated in our paper, ‘We believe that evidence based reviews must be read with some prior knowledge of the subject’, and ‘...systematic evidence based reviews are limited by the quality of the individual trials analysed and reviewed. Nuances in protocol and apparently "minor" variations in methodology may markedly affect outcome. Widely cited studies are often poorly designed to detect any advantages conferred by monitoring that might exist’.
We stand by the validity of our hypothesis and our decision to use meta-analysis to assess the published studies.
References
1 Naguib M, Kopman AF, Ensor JE. Neuromuscular monitoring and postoperative residual curarisation: a meta-analysis. Br J Anaesth (2007) 98:302–16.
2 Eccles M, Freemantle N, Mason J. North of England evidence based guidelines development project: methods of developing guidelines for efficient drug use in primary care. Br Med J (1998) 316:1232–5.
3 Pedersen T, Moller AM. How to use evidence-based medicine in anaesthesiology. Acta Anaesthesiol Scand (2001) 45:267–74.[CrossRef][Web of Science][Medline]
4 Kopman AF, Sinha N. Acceleromyography as a guide to anesthetic management: a case report. J Clin Anesth (2003) 15:145–8.[CrossRef][Web of Science][Medline]
5 Gotzsche PC. Methodology and overt and hidden bias in reports of 196 double-blind trials of nonsteroidal antiinflammatory drugs in rheumatoid arthritis. Control Clin Trials (1989) 10:31–56.[CrossRef][Web of Science][Medline]
6 Horlocker TT, Brown DR. Evidence-based medicine: haute couture or the emperor's new clothes? Anesth Analg (2005) 100:1807–10.
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