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Proposed Models Need Validation
- Mohamed Naguib, Aaron F. Kopman and Joe E. Ensor (11 July 2007)
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Mathematics of the mind, risks and hermeneutics may help the understanding of the neuromuscular moni
- Rogerio L R Videira (29 June 2007)
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Neuromuscular monitoring and postoperative residual curarisation: a response
- Mohamed Naguib, [Aaron F. Kopman] and [Joe E. Ensor] (11 May 2007)
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Neuromuscular monitoring and postoperative residual curarisation
- Jørgen Viby-Mogensen, Casper C. Kjær, Lars I. Eriksson (1 May 2007)
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Mohamed Naguib, Professor Department of Anesthesiology and Pain Medicine, University of Texas M.D. Anderson Cancer Center, USA, Aaron F. Kopman and Joe E. Ensor
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To the Editor: In rephrasing a comment that appeared in our response to Viby- Mogensen et al., Dr. Videira and colleagues have incorrectly represented our point of view. Our comment was: "What makes the difference in the incidence of PORC is not the monitor but the anesthesiologist behind the monitor." Dr. Videira and colleagues write, We proposed that Dr. Viby-Mogensen’s view complements Dr. Naguib’s point of view. The missed link between these apparently different views is that even for the objective monitoring to be useful there has to be an educated human mind using it.... Rewriting a phrase from Dr. Naguib’s letter we propose that “What makes the difference in the incidence of postoperative residual curarisation is the monitor AND the anaesthesiologist behind the monitor.” In fact, we did not conclude that the monitor matters(1). We did acknowledge, "While we believe that the proper application of neuromuscular monitoring should reduce the incidence of PORC, proving this hypothesis has proved difficult." In other words, "common sense" may suggest that the incidence of PORC should be lower with the use of neuromuscular monitoring, but the data do not lend themselves to such a conclusion. Dr. Videira and colleagues present a risk model that they have developed: SR = (DeAwR x ID x DC x TSCouBRD x BoBePhP)/(ARTB x DetR x RevD x RevRF x TSLagSinLKD x GProcDespR) where sense of risk (SR) varies directly with the degree of awareness of the risk (DeAwR), the incidence of the damage related to the risk (ID), the damage costs (DC), the time-space coupling between risk and damage (TSCouBRD), and the psychological bond between physician and patient (BoBePhP). The factors that vary inversely to SR are autonomy of risk- taking behaviour (ARTB), detectability of the risk (DetR), reversibility of the damage (RevD), reversibility of the risk factor (RevRF), time-space lag since last known damage (TSLagSinLKD), and gains by proceeding despite the risk (GProcDespR). We have several questions about this model: (1) Has it been validated? (2) What is the decision rule associated with this risk model—i.e., once a sense of risk is calculated, how does one know what action to take? (3) How and on what scales are these variables measured? For example, is there a validated instrument (e.g., survey) with which "awareness of risk" is measured? If so, what are the possible values of this variable? We believe it is critically important that the model be accompanied by documentation of its validation and guidelines for its use and interpretation. Reference: 1. Naguib M, Kopman AF, Ensor JF. Neuromuscular monitoring and postoperative residual curarisation: a meta-analysis. Br J Anaesth 2007;98:302-316. Conflict of Interest:None declared |
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Rogerio L R Videira, consultant anesthesiologist University of Sao Paulo
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By the end of May 2007 we had the honour of having Dr. Viby-Mogensen as a lecturer at the Sao Paulo Congress of Anaesthesiology. At that meeting we had the opportunity of talking about the controversy regarding the usefulness of neuromuscular junction (NMJ) monitoring. We proposed that Dr. Viby-Mogensen’s view(1) complements Dr. Naguib’s point of view.(2) The missed link between these apparently different views is that even for the objective monitoring to be useful there has to be an educated human mind using it, according to an efficient mental model that may allow fair predictions about the future clinical situation and, by doing this, would implement decisions in the present that would modify the future condition of the patient. Rewriting a phrase from Dr. Naguib’s letter we propose that “What makes the difference in the incidence of postoperative residual curarisation is the monitor AND the anaesthesiologist behind the monitor” Central to this problem is that the understanding of the proposal of Ali, Utting and Gray in 1971 of T4/T1 Train-of-four (TOF) ratio (3) has evolved, but it is still poorly understood by clinicians. The resulting number of the TOF monitoring is interpreted by our minds as absent (zero) to normal (100 %) NMJ activity. However this interpretation is physiopathologically incongruent, as it is currently supposed that the TOF result is mainly due to a presynaptic action of nondepolarizing neuromuscular blockers on neural nicotinic acetylcholine receptors and that this variation from 0 to 100 usually corresponds to a postsynaptic acetylcholine receptor occupancy ratio by nondepolarizing neuromuscular blockers from 90% to 75 %, which is a very narrow window of only 15% of the possible range.(4) The clinical meaning of the number provided by the TOF monitoring has to be adequately comprehended and Dr. Viby-Mogensen group took an important step when they suggested the TOF ratio as a quantifier of risk of developing pulmonary complications in the postoperative period rather than a binary monitor of muscle strength.(5) However the clinical use of risk factors as individual prognostic tools has its own problems and complexities (6) that would be lengthy to be discussed here. In the last couple of years we have been developing a study about the appropriateness of the anaesthesiologist’s decision to administer neostigmine at the end of a surgical procedure. The quantitative part of this study consisted of an audit of this decision compared to acceleromyography, assuming this method of monitoring as a gold standard. The patients at risk, defined as those with a TOF < 0.9, were 77 %, but after the clinical decision still 50 % of the patients remained at risk. The most impressive attitude was that 43 % of the patients were extubated even after the anaesthesiologists had been informed that the TOF ratio was less than 0.9. (7) How such a decision can be consciously made in the year of 2007? What is risk and how it may be sensed by our minds? Accepting the complexities of the social and historical construct of risk (8), we think that a synthetic semantic description of risk-sensing may improve the understanding about it and its use in our clinical decisions. The formula we propose, through a cognitive psychological point of view, developed with some suggestions from Peter Dieckmann, an organizational psychologist that participate in the Safety Committee of the European Society of Anaesthesiologists, is: SR = ______DeAwR x ID x DC x TSCouBRD x BoBePhP_____ ARTB x DetR x RevD x RevRF x TSLagSinLKD x GProcDespR where sense of risk (SR) varies directly with the degree of awareness of the risk (DeAwR), the incidence of the damage related to the risk (ID), the damage costs (DC), the time-space coupling between risk and damage (TSCouBRD), and the psychological bond between physician and patient (BoBePhP). The factors that vary inversely to SR are autonomy of risk- taking behaviour (ARTB), detectability of the risk (DetR), reversibility of the damage (RevD), reversibility of the risk factor (RevRF), time-space lag since last known damage (TSLagSinLKD), and gains by proceeding despite the risk (GProcDespR). We speculate that the “discounting” effect, the process by which people are less concerned with damages that are not immediate (represented by factor TSCouBRD in the formula), is the main explanation for a neglecting attitude, as respiratory complications will more commonly be seen hours to days after the patient was exposed to the TOF < 0.9 risk factor.(9) Recommending the routine use of reversal agents is equivalent to trying to correct the error of not monitoring by the subsequent error of using unnecessary reversal drugs that may be associated with higher costs (usually a characteristic of newer drugs) or higher incidence of adverse effects (usually a characteristic of older drugs).(10) Anaesthesiologists need to have a historical consciousness of the need for a better monitoring of the neuromuscular junction. Maybe a strict scientific approach through randomized controlled trials could be considered inadequate for the analysis of this problem, just as it has not been, in the recent past, to establish the utility of monitors, such as the pulse oximetry, widely used nowadays.(11) What really should not be lost from our view is that, with the introduction of the new cyclodextrin concept of reversal, we are on the verge of a deep change in our practice of using and reversing neuromuscular blocking agents. Through modern hermeneutics, that tries to integrate understanding, interpretation and application as interdependent activities, we may consciously change our concepts from a mechanistically determined “mean and standard deviation” point of view to a fully and radically individualized approach to our practice.(12) And this task calls for both monitoring and deep understanding of what the patient is telling us through the monitored numbers. Otherwise we will keep on repeating the same old mistakes with technologically newer drugs. We need to use the evidence-based medicine ladder to reach the individual patient, not only to accept the individual sometimes as a deviant from the mean but always in his/her uniqueness. And to reach this point we need to make a fusion of horizons from apparently controversial views, combining wisely meta-analysis with decision analysis, reducing the gap between research and practice, and collectively constructing a safer practice in the present that will allow us to walk ahead toward a safer horizon of our clinical practice in our future. We would like to hear from Dr. Cecil-Gray and his group what they think about it. But we also wonder what a first-year resident of anaesthesiology will think while reading this letter in the year of 2043. Rogerio L R Videira, MD (rovid@uol.com.br) Joaquim E Vieira, MD, Anthropologist Division of Anesthesiology, University of Sao Paulo References 1- Viby-Mogensen J, Kjaer CC, Eriksson LI. Neuromuscular monitoring and postoperative residual curarisation. BJA e-letter 1 May 2007 2- Naguib M, Kopman AF, Ensor JF. Neuromuscular monitoring and postoperative residual curarisation: a meta-analysis. Br J Anaesth 2007;98:302-316. 3- Ali HH, Utting JE, Gray C. Quantitative assessment of residual neuromuscular antidepolarizing block (part II). Br J Anaesth 1971;43:478- 485. 4- Johnson M, Gurley D, Dabrowski M, et al. Distinct pharmacologic properties of neuromuscular blocking agents on human neuronal nicotinic acetylcholine receptors. Anesthesiology 2006;105:521-533. 5- Berg H, Viby-Mogensen J, Roed J, et al. Residual neuromuscular block is a risk factor for postoperative pulmonary complications. Acta Anaesthesiol Scand 1997;41:1095-1103. 6- Ware JH. Statistics and medicine: the limitations of risk factors as prognostic tools. (Perspective) N Engl J Med 2006;325(25):2615-2617. 7- Videira R, Oda F, Biazotto C, Vieira J, Carmona M. Neostigmine use: audit of the clinical decision compared to acceleromyography. (abstract) Eur J Anaesthesiol 2007;24(S39):125. 8- Ayres JRCM. Sobre o risco – para compreender a epidemiologia (About risk – in order to comprehend epidemiology) 2nd ed. Editora Hucitec, São Paulo 2002. (in Portuguese) 9- Naimark D, Krahn MD, Naglie G, et al. Primer on medical decision analysis: part 5 – working with Markov processes. Med Decis Making 1997;17:152-159. 10- Sprung J, Warner ME, Contreras MG, et al. Predictors of survival following cardiac arrest in patients undergoing noncardiac surgery: a study of 518,294 patients at a tertiary referral center. Anesthesiology 2003;99:259-269. 11- Orkin FK, Cohen MM, Duncan PG. The quest for meaningful outcome. (editorial) Anesthesiology 1993;78:417-422. 12- Bernstein RJ. Beyond objectivism and relativism: science, hermeneutics, and praxis. University of Pennsylvania Press. Philadelphia, Pennsylvania, 1983. Conflict of Interest:None declared |
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Mohamed Naguib, Professor Department of Anesthesiology and Pain Medicine, University of Texas M.D. Anderson Cancer Center, [Aaron F. Kopman] and [Joe E. Ensor]
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We would like to thank Drs. Viby-Mogensen, Kjær, 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 postoperative residual curarization (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 endpoints. While we believe that the proper application neuromuscular monitoring should reduce the incidence of PORC, proving this hypothesis has proved difficult. In response to Dr. Viby-Mogensen’s letter, we performed additional analysis and compared monitored and non-monitored conventional groups and also monitored and non-monitored quantitative groups by using weighted t- tests on the transformed data. None of the comparisons was statistically significant View Image. The only comparison that was close to being significant was based on only 2 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. 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 anesthesiologists are willing to delay extubation in the operating room and keep their patients asleep until adequate recovery occurs (2). 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 anesthesiologist 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 (3). In addition, as Horlocker and Brown (4) stated: “Clinical questions pertinent to the practice of anesthesiology 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 the randomized studies, we also graded each randomized study according to the criteria of the Jadad 5- 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. Kopman AF, Sinha N. Acceleromyography as a guide to anesthetic management: a case report. J Clin Anesth 2003; 15: 145-8 3. 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 4. Horlocker TT, Brown DR. Evidence-Based Medicine: Haute Couture or the Emperor's New Clothes? Anesth Analg 2005; 100: 1807-10 Conflict of Interest:None declared |
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Jørgen Viby-Mogensen, Professor Copenhagen University Hospital, Rigshospitalet, Casper C. Kjær, Lars I. Eriksson
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Editor - In their meta-analysis of neuromuscular monitoring and postoperative residual curarisation (PORC) Naguib, Kopman and Ensor (1) 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 upon 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: 1) Does non-objective neuromuscular monitoring decrease the incidence of PORC? 2) Does objective neuromuscular monitoring decrease the incidence of PORC? Secondly; it is well known that meta-analyses are never better than the studies on which they are based. As stressed by the authors themselves, the included studies are very heterogeneous and of varying qualities. Therefore, it seems that the authors would have been better of if they had chosen to use generally accepted standards for evidence based medicine, for instance as outlined by Eccles and colleagues (2) and Pedersen and Møller (3). If the authors had applied these principles (please see table) on exactly the same studies the following two conclusions would have emerged. View Image 1) There is insufficient evidence to confirm or deny that subjective neuromuscular monitoring decreases the incidence of PORC. 2) There is good evidence that objective neuromuscular monitoring with i.e. 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.” 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. BMJ 1998; 316: 1232-5. 3. Pedersen T, Moller AM. How to use evidence-based medicine in anaesthesiology. Acta Anaesthesiol Scand 2001; 45: 267-74. Conflict of Interest:None declared |
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