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Deadly Heat

2014; Lippincott Williams & Wilkins; Volume: 119; Issue: 6 Linguagem: Inglês

10.1213/ane.0000000000000487

1526-7598

Steven L. Shafer, Franklin Dexter, Sorin J. Brull,

Thermoregulation and physiological responses

Every contemporary anesthesiologist knows the signs of malignant hyperthermia (MH). Every facility where anesthetic drugs are used has been advised to have supplies of dantrolene, a specific and effective antidote.a American Society of Anesthesiologists guidelines call for temperature monitoring for “every patient receiving anesthesia … when clinically significant changes in body temperature are intended, anticipated or suspected.”b Given this, you would expect that any patient with an MH episode would be rapidly diagnosed and quickly treated. You would expect that the risk of dying from an MH episode would be small. You would expect that, as uniform standards are adopted for ambulatory facilities, office-based facilities, and remote locations where anesthetics are administered, the risk of dying from an MH episode would be decreasing. You would be wrong. As demonstrated by Larach and colleagues1 in this issue of Anesthesia & Analgesia, the risk of dying from an MH episode has increased approximately 7-fold (lower confidence interval 2-fold) over the past 6 years when compared to a previous cohort. The authors analyzed the outcome from MH episodes reported to the North American Malignant Hyperthermia Registry of the Malignant Hyperthermia Association of the United States. They found that the risk of dying from an MH episode was about 10%, a risk greater than the 1.3% in their previous analysis of deaths prior to 2007. Why? We don’t know. What we do know from the authors’ analysis is that (1) MH patients die because they get hot and (2) temperature monitoring makes a big difference in survival. When temperature was not monitored, 30% of the patients with an MH episode died. If skin temperature was monitored, the mortality risk was reduced to 21%. Both are unacceptably high. If core monitoring was used, the risk was reduced to 2% (P = 0.0012). The clinical implication seems simple and obvious. If you monitor core temperature, you pick up MH early, you start treatment earlier, and you save the patient’s life. Starting dantrolene at the first sign of trouble, a rise in temperature (also shown by the authors), improves the chance of your patient surviving. If you don’t start dantrolene quickly, the patient overheats and dies. Monitoring core temperature requires an electronic temperature probe. Why is it that 12% of the patients in the Malignant Hyperthermia Association of the United States registry had no temperature monitoring, and 23% had just skin temperature monitoring? We suspect that this is partly because the clinical implications for the individual patient are clear, but the economic implications are not. The economics of MH is well understood because of studies related to the availability of succinylcholine and dantrolene.2–4 Let’s do some “back of the envelope” calculations. We focus on outpatient surgery because continuous temperature monitoring is commonly used for neurological, cardiac, transplantation, and other major inpatient surgical procedures. The incidence of MH is approximately 3.1 per million anesthetics.4,5 Presumably, only patients undergoing general anesthesia are at risk of MH. Since general anesthesia accounts for 53% of outpatient anesthetics,6 the incidence is 5.85 cases per million general anesthetics, or 1 in every 170,698 general anesthetics. Larach and colleagues1 demonstrate that the absolute increase in the risk of death due to absence of use of core temperature monitoring is approximately 25%. Thus, if electronic temperature monitoring were routinely employed, it would result in the saving of ¼ of a life in every 170,698 general anesthetics ([3.1 MH cases/1 million total anesthetics] × [1 anesthetic/0.53 general anesthetics] = 5.85 MH cases/1 million general anesthetics = 170,968 general anesthetics/MH case). That means we would save 1 life in every 683,871 general anesthetics. Disposable electronic temperature probes cost approximately $6 each.c The “cost” of each saved life would be $4,103,226. Of course, it is silly to calculate the numbers to such precision, given the uncertainty in the underlying estimates. We have done so to help the reader reproduce the algebra on a spreadsheet. Calculating to the dollar also emphasizes that the calculation produces a dollar estimate of the cost of saving a life. The societal value of a life saved ranges between $3 and $10 million.7,8 Multiple United States federal agencies use a figure of around $6 million.9,d Based on a cold cash calculation, there is a very clear conclusion. Based solely on the risk of dying from MH, we should use continuous electronic core temperature monitoring during general anesthesia. Cost utility analyses are useful from a societal perspective, in part because they have built in the public perception about the economic value of life.7–9 Ford Motor Company was widely condemned for failing to install a safer gas tank in the Ford Pinto that would have prevented the car from exploding in rear end collisions.e The cost benefit analysis prepared by Ford appears in Table 1. They projected that a redesigned fuel tank would prevent 180 burn deaths, valued at $200,000 per death, 180 serious burn injuries, valued at $67,000 per death, and 2100 burned vehicles, valued at $700 each. The total benefit from a redesigned fuel tank would be $49.5 million. However, to achieve this benefit would entail an $11 cost per vehicle. Distributed across 12.5 million vehicles, the total cost would have been $137 million. Ford decided it wasn’t worthwhile to pay $137 million to save 180 lives and prevent 180 serious burns, not to mention the 2100 burned vehicles!Table 1: Benefits and Costs Relating to Fuel Leakage Associated with the Static Rollover Test Portoin of FMVSS 208The argument seems crazy, and Ford was pilloried in the press for the coldhearted calculation. Plaintiffs, or their survivors, were awarded huge punitive damages by juries. In the court of law and the court of public opinion, Ford could not defend refusing to spend $11 per car to save a life. The injured victim, or the bereaved family, would have gladly paid $11 more for the car. It seemed heartless to compare the cost of dying from an exploding gas tank to the cost of a simple fix. However, such calculations are essential to allocate limited resources. Ford’s mistake was not in making the calculation, but in valuing the life of a driver at merely $200,000, dramatically less than appropriate. 7–9 Therefore, the rational choice for continuous temperature monitoring in strictly economic terms is to adopt the recommendations by Larach and colleagues.1 Still, a less rational, but entirely understandable response, is for anesthesiologists and nurse anesthetists to spend the extra dollars, and provide continuous temperature monitoring for every patient undergoing general anesthesia, simply to avoid the fate that befell Ford Motor Company. Imagine having to tell parents that their child died because you decided to not spend $6 for continuous temperature monitoring? Like the lottery, it probably won’t happen to you. But if it does, your life changes forever. Temperature monitoring is the standard of care for good reason. Quoting Daniel Sessler’s 2008 review in Anesthesiology: “Hypothermia-induced complications include morbid myocardial outcomes secondary to sympathetic nervous system activation, surgical wound infection, coagulopathy, increased allogeneic transfusions, negative nitrogen balance, delayed wound healing, delayed postanesthetic recovery, prolonged hospitalization, shivering, and patient discomfort.”11 You don’t have to defend temperature monitoring because it reduces the risk of dying from an MH episode. That statement is true, but it is nearly irrelevant in the overall risk-benefit assessment. Continuous, high-fidelity temperature monitoring should be routine because of the many tangible benefits that apply to nearly every patient.11 The relevance of Larach et al.’s paper1 is that it shows an additional reason, economically justifiable in its own right, for continuous temperature monitoring during general anesthesia. Perhaps part of the blame for the lack of universal temperature monitoring resides with us. A cursory review of several anesthesia textbooks, and the top 10 Google hits to the search, “temperature as a sign of malignant hyperthermia” all listed temperature elevation “as a late sign of MH.” Perhaps clinicians believe they can diagnose MH by clinical signs other than an increase in their patient’s temperature. Larach et al.’s analysis1 shows that peak temperature best predicts which patients will die. Heat kills. If you don’t monitor core temperature routinely, start today. Do it right, with a continuous electronic measurement of core temperature. Tell risk management at your facility that every patient deserves the benefits of continuous core temperature monitoring, and that the economic risks of not monitoring are easily outweighed by the economic benefit in lives saved. This is better than explaining to patients, parents, or the next of kin, why you chose to save $6. DISCLOSURES Name: Steven L. Shafer, MD. Contribution: This author helped write the manuscript. Attestation: Steven L. Shafer approved the final manuscript. Conflicts of Interest: The author declares no conflicts of interest. Name: Franklin Dexter, MD, PhD. Contribution: This author helped write the manuscript. Attestation: Franklin Dexter approved the final manuscript. Conflicts of Interest: The University of Iowa, Department of Anesthesia, Division of Management Consulting, performs analyses for organizations, including the Malignant Hyperthermia Association of the United States. Dr. Dexter has tenure and receives no funds personally, including honoraria, other than his salary and allowable expense reimbursements from the University of Iowa. Income from the Division’s consulting work is used to fund research. Name: Sorin J. Brull, MD, FCARCSI (Hon). Contribution: This author helped write the manuscript. Attestation: Sorin J. Brull approved the final manuscript. Conflicts of Interest: The author declares no conflicts of interest. RECUSE NOTE Dr. Steven L. Shafer is the Editor-in-Chief for Anesthesia & Analgesia. Dr. Franklin Dexter is the Statistical Editor and Section Editor for Economics, Education, and Policy for Anesthesia & Analgesia. Dr. Sorin J. Brull is the Section Editor for Patient Safety for the Journal. This manuscript was handled by Dr. James G. Bovill, Guest Editor-in-Chief, and Drs. Shafer, Dexter, and Brull were not involved in any way with the editorial process or decision.