Exertional Heat Illness Linked to Rare Anesthesia Complication

Newswise — Physically fit military recruits occasionally develop an “exertional heat illness” (EHI), which can cause them to collapse during training, or even on the battlefield. Emerging research evidence suggests a potentially important link between EHI and malignant hyperthermia—a rare but feared complication of anesthesia, according to an article in the October issue of Anesthesia & Analgesia, official journal of the International Anesthesia Research Society (IARS).

Drs. John F. Capacchione and Shelia M. Muldoon of the Uniformed Services University of Health Sciences, Bethesda, Md., review recent research suggesting that EHI—along with a related disorder called “exertional rhabdomyolysis," in which muscles break down with intense exercise—has some key similarities to malignant hyperthermia. The review appears in a special update on malignant hyperthermia assembled by Dr. Peter J. Davis, Chief of Anesthesiology at the Children’s Hospital of Pittsburgh.

Malignant hyperthermia is a serious but rare genetic disorder familiar to anesthesiologists. In this condition, previously healthy patients develop a sudden and rapid increase in body temperature after receiving certain anesthetic drugs. The raging fever is a result of hypermetabolism of skeletal muscles triggered by the anesthetic drug. The muscle fibers start to break down, releasing their contents into the bloodstream. This can result in kidney failure, multi-organ failure, and death. Fortunately, effective antidotes for malignant hyperthermia are available in every operating room, and anesthesiologists are trained to handle this emergency. Additionally, new genetic tests may help identify susceptible patients, so the anesthesiologist can choose an anesthesia technique that will not cause malignant hyperthermia.

Link to Heat Illness May Help in Recognizing Malignant Hyperthermia

In their article, Drs. Capacchione and Muldoon review recent research evidence suggesting some important areas of overlap between EHI and malignant hyperthermia. Studies have described apparently full-blown episodes of malignant hyperthermia—some of them fatal—in susceptible individuals, without exposure to anesthetic drugs.

In these cases, patients have collapsed during exercise or military training, sometimes (but not always) in hot, humid weather. Subsequent tests of these patients have identified the same gene abnormality that causes malignant hyperthermia. Sometimes, the abnormal gene has been found in other family members as well.

Although incomplete, the new evidence offers anesthesiologists some intriguing clues as to the possible relationships among EHI, exertional rhabdomyolysis, and malignant hyperthermia. Further study will be needed to clarify these links, according to Drs. Capacchione and Muldoon. For example, there is some evidence that patients who have had episodes of malignant hyperthermia are more likely to have problems with heat or exercise intolerance. However, it is unknown whether people with heat/exercise intolerance are at increased risk of malignant hyperthermia when receiving anesthesia.

Meanwhile, from the perspective of military physicians, the associations “may have implications for some malignant hyperthermia-susceptible patients and their capacity to exercise, as well as for clinicians treating and anesthetizing patients with histories of unexplained exertional heat and exercise illness,” Drs. Capacchione and Muldoon write.

Dr. Davis adds, "The message is that any individual who has experienced a greatly elevated body temperature (104° F or higher) or severe muscle pain and red urine after exercise—signs of exertional rhabdomyolysis—should share this information with their anesthesiologist and their military recruiter."

Read the full study in Anesthesia & Analgesia

About the IARSThe International Anesthesia Research Society is a nonpolitical, not-for-profit medical society founded in 1922 to encourage, stimulate, and fund ongoing anesthesia-related research and projects that will enhance and advance the anesthesiology specialty. The IARS has a worldwide membership of 15,000 physicians, physician residents, and others with doctoral degrees, as well as health professionals in anesthesia-related practice. In addition to publishing the monthly scientific journal Anesthesia & Analgesia, the IARS sponsors an annual clinical and scientific meeting, funds anesthesia-related research, and sponsors the SAFEKIDS research initiative in conjunction with the FDA. Additional information about the society and the journal may be found at www.iars.org and www.anesthesia-analgesia.org.

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