Malignant Hyperthermia

Malignant Hyperthermia

Welcome Back and Happy New Year, Everyone! 

I know, I know. We really left you hanging for a long time. But now we're back, we gave you lots of tragedy to start up the new year, and now we've got an amazing second half of the season for you. With LOTS of heart-pounding (and hopefully a few will be a little bit more uplifting) medical cases in store.

But first, let's discuss the heart-pounding-ness of Michael from Episode 810 "Suddenly." What the heck happened in his surgery? Didn't he just have an injury to his liver from the car accident?

Michael did suffer a grade 4 liver laceration, which Meredith and Bailey had begun to repair successfully, but then his vitals started to go completely awry. His temperature inexplicably skyrocketed, his heart rate rapidly increased, and his carbon dioxide levels soared. If it wasn't for Ben's quick diagnosis of malignant hyperthermia, Michael may not have been one of the surviving members of his family.

Malignant hyperthermia is quite different than the hyperthermia one associates with heat stroke or infection.

Malignant hyperthermia is a life-threatening condition that can be triggered by exposure to certain drugs used in general anesthesia. In patients at risk for malignant hyperthermia (MH), these drugs can induce a severe crisis by causing muscle rigidity, a breakdown in muscle fibers, a high temperature (it may exceed 110 degrees F), increased acid levels in the blood and other tissues, and a rapid heart rate.

If not diagnosed and treated promptly, MH may lead to cardiac arrest, brain damage, internal bleeding, organ failure, and even death.

But the good news… It can be treated! If non-emergent, the surgery will be temporarily halted, and the anesthesiologist will discontinue the use of volatile agents and succinylcholine. The anesthesiologist will also administer intravenous medications such as dantrolene, lidocaine, and even a beta-blocker drug to help with heart arrhythmias. The health care team may also wrap the patient in cooling blankets and pack with ice to reduce the high temperature.

Is susceptibility to MH common?

The exact incidence of the disease is unknown because a patient may not experience symptoms until he or she undergoes medical treatment (or is given anesthesia before surgery). However, the Malignant Hyperthermia Association of the United States estimates the rate of occurrence to be as frequent as one in 5,000 or as rare as one in 65,000 administrations of general anesthesia with triggering agents.

In the past years, research has found that MH susceptibility is inherited in an autosomal dominant pattern, usually meaning that an affected patient receives the altered gene from a parent who is also at risk for the disorder.

Patients at risk for MH can still undergo surgery safely.

If a family history of MH exists (or if a family member suffered an unexplained death during anesthesia), tests may be run to determine whether a patient may be susceptible to a reaction. These tests include:

- Chem-20 blood test.
- Genetic testing to identify any defects in the RYR1 gene.
- Muscle biopsy.
- Urine myoglobin (muscle protein) determination.
Then, depending on the patient's results, doctors can prepare the safest anesthesia plan possible. The team would avoid using the following "trigger" medications: the paralyzing agent succinylcholine, or the inhalation agents such as sevoflurane, desflurane, isoflurane, halothane, enflurane, and methoxyflurane.

Non-"trigger" anesthetic agents/drugs include: propofol, barbituates, narcotics, ketamine, benzodiazepines, etomidate, nitrous oxide (not a potent inhalation anesthetic), local/regional anesthetics, and monitored anesthesia care (local anesthesia plus sedation).

In rare cases, an MH crisis can occur outside of surgery.

Most cases are triggered in the operating room while under general anesthesia. However, the one-hour period directly AFTER surgery (the recovery period) also should be noted as an extremely critical time for a possible crisis. Other places that an MH crisis can be expected are any location in which general anesthesia drugs may be used, which includes procedures that take place in emergency rooms, dental surgeries, and intensive care units.

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