Birgenheier et al.'s article in this issue1 describes a device that will rapidly remove a volatile agent from the breathing circuit when a patient unexpectedly develops malignant hyperthermia (MH) during an anesthetic.
In 2011, MH is a completely preventable disease. It is 100% preventable by avoiding the use of volatile anesthetic agents and succinylcholine. Although there are arguments in favor of retaining the volatile agents (cost versus IV agents, inhaled inductions in pediatrics) and succinylcholine (more rapid onset than nondepolarizing agents, short clinical effect) in our practice, the occasional occurrence of MH is one of several arguments against continuing their use.
When we use volatile agents and succinylcholine, therefore, we are making a conscious or unconscious decision that we accept the small risk that the patient will develop MH. One hopes that we are actually thinking about the risk–benefit ratio, the risk of MH and other adverse events associated with these agents versus the benefit to be gained by choosing them over IV anesthetics and nondepolarizing muscle relaxants. An anesthesiologist could eliminate the possibility of ever causing MH, simply by avoiding triggering agents. Alternatively, anesthesiologists as a group could make a decision to abandon the use of these agents.
Such a decision would be welcomed by some (families and friends of patients susceptible to MH) and not welcomed by others (companies that manufacture volatile agents and traditional anesthesia machines—and dantrolene). Anesthesia machines would become ventilators, and ventilators would become anesthesia machines!
As long as the triggering agents are used, however, the possibility of MH is always present. As noted in the article, prompt treatment is usually, but not always, effective in terminating the episode of MH and restoring the patient to health.
MH as a surprise event is an extraordinary occurrence, one that most anesthesiologists will not encounter in a lifetime of practice. In the rare event of a case of MH that develops during an anesthetic, the anesthesiologist must have an immediate plan. Today that plan generally follows the guidelines set forth by the Malignant Hyperthermia Association of the United States (MHAUS). The guidelines are not static, but evolving, and they are available on the Internet.a
In 2011, the items included in the first step of the guidelines are to get help, get dantrolene, and notify the surgeon. Succinylcholine is to be discontinued, but unless an old-fashioned technique with a succinylcholine infusion is in use, there is nothing to do in most cases. Volatile agents are to be discontinued (vaporizer shut off) and the patient's lungs are to be hyperventilated with a fresh gas flow of 10 L/min or more. As MHAUS specifies, “Don't waste time changing the circle system and CO2 absorbant [sic].”
In the past, some recommended changing the breathing circuit. This action is quick and simple, yet the absorption and subsequent release of volatile agent from the breathing circuit is minimal. Others recommended changing the carbon dioxide absorbent, but that task is difficult and time consuming, and it may result in leaks in the breathing circuit. Still others recommended changing to a specially prepared, inhaled agent-free anesthesia machine. Again this step is difficult, expensive, and time consuming.
Still another alternative is to switch ventilation to a nonrebreathing bag or a standard ventilator (intensive care ventilator, portable ventilator, or transport ventilator). Use of an open breathing circuit immediately reduces the inspired volatile agent to zero. Such a step is also time consuming, however.
The recommendation changed, however, with recognition that volatile agent persists in the patient's body for an extended time, and that removal of a tiny additional amount of agent from the inspired gas is not the antidote. The antidote is dantrolene—and fast. Anything that slows down the administration of dantrolene is undesirable.
The present manuscript1 offers a device that will rapidly remove the volatile agent from the circuit. If the device is readily available, it could be installed in a few seconds, and it need not slow down the administration of dantrolene. But several issues remain.
The first is that it is not known what amount of residual volatile agent might serve as a persistent trigger to MH. Even in the presence of dantrolene, it seems reasonable and logical to remove from the circuit and from the patient as much agent as possible, as quickly as possible. As noted above, one should not waste time in trying to take extreme measures. But an MH emergency cart should already be present in the operating suite, wherever triggering agents are used. Adding a charcoal absorbent to the cart, and placing it in the breathing circuit when MH is suspected, is a logical course of action. Certainly it is in the category of treatments that “won't hurt and might help.”
Another issue is that the great majority of patients who develop MH during an anesthetic today are being treated successfully with dantrolene and without the use of a charcoal absorbent. One may question whether the device would somehow save a patient who might not otherwise be saved today. The remaining deaths from MH likely occur from delayed or missed diagnoses, and late or no treatment. It would be impossible to conduct a clinical study to demonstrate that the charcoal absorbers improve outcome; it is more likely that the use of volatile agents and succinylcholine will be abandoned before such a study could be done.
The third issue is that there is no possibility of knowing whether the charcoal absorbent device is working or not. Anesthetic gas analyzers that measure concentrations of parts per million of agent (mass spectrometers and Raman scattering analyzers) have not been manufactured for 15 or 20 years. Today's anesthetic agent analyzers do not have the sensitivity to discern whether the agent concentration is falling more rapidly with the charcoal absorbent than it would with high fresh gas flows alone. On that basis, an anesthesiologist would be unable to distinguish a working charcoal absorbent from one with a manufacturing defect, one that was absorbing no agent at all. Another way of making the same point is to note that if the patient's heart rate, carbon dioxide production, and temperature are decreasing, one would be more likely to attribute the improvement to dantrolene than to the charcoal absorbent.
Another issue is, will the use of these charcoal absorbents be deemed the “Standard of Care”? With or without charcoal absorbents, there will continue to be a few deaths from MH. What if a charcoal absorbent is not used, and the patient dies? Will experts for the plaintiffs' bar be ready to testify that a charcoal absorbent should have been used, and that failure to use one in every suspected case of MH is malpractice? In the absence of clinical proof of their effectiveness, one hopes that they will not become “Standard of Care,” even though they fall in the “won't hurt and might help” category.
And finally, if one accepts that these charcoal absorbents are important, is there created a mandate to conduct dozens or even hundreds of studies, to test these charcoal absorbent devices in every make and model of anesthesia machine around the world, with every manufacturer's breathing circuits and breathing bags, and with every available carbon dioxide absorbent? Such studies could keep investigators busy for their entire careers! This author does not believe that multiple investigations along these lines would be valuable. Without clinical proof that lives are saved, we shall have to use these absorbents on an intuitive basis, and recognize that in one environment they may remove more, or less, agent than in another. Alternatively, the manufacturers of the anesthesia machines and accessories could take on the task of publishing data about the performance of the charcoal absorbents with their equipment. But this writer does not believe that science will be advanced by the publication of individual studies on how the charcoal absorbent performs in a certain combination of anesthesia products.
In conclusion, the authors describe a device that quickly and easily removes volatile agent from an anesthesia machine and breathing circuit. It seems reasonable to consider the use of this device whenever MH is suspected, even in the absence of proof that lives will be saved by its use. Still this writer is eagerly awaiting the passing of volatile agents and succinylcholine, so that we can worry about MH no more than we currently worry about toxicity from chloroform.
Name: Frank E. Block, Jr., MD.
Contribution: This author wrote the manuscript.
Attestation: Frank E. Block, Jr., approved the final manuscript.