Malignant hyperthermia: Clinical sciences

Malignant hyperthermia is a serious anesthetic complication that must be emergently recognized and treated. It can develop in susceptible individuals who have a genetic mutation in their dihydropyridine or ryanodine receptors, which normally regulate skeletal muscle contraction by controlling calcium release from the sarcoplasmic reticulum. When these individuals are exposed to a volatile anesthetic like isoflurane or sevoflurane, or less commonly, to the neuromuscular blocking agent succinylcholine, there is an unregulated calcium release in the muscle cells. As a result, intracellular calcium overload causes sustained muscle contraction and breakdown, leading to a hypermetabolic state called malignant hyperthermia.

Alright, malignant hyperthermia typically develops while a patient is getting anesthesia, or less commonly within one hour of stopping the anesthetic. The first step in approaching someone suspected to have malignant hyperthermia is to assess their ventilatory status and vitals. To assess the ventilatory status, check the respiratory rate and see if it matches the ventilator settings. Next, look for hypercarbia, which is the most common presenting sign of malignant hyperthermia. Hypercarbia is an unexplained increase in exhaled CO2 caused by widespread muscle contraction and hypermetabolism despite adequate ventilation. Additionally, be sure to rule out other causes of hypercarbia, such as hypoventilation, rebreathing, or gas absorption during laparoscopy. Finally, check the vital signs for tachypnea, tachycardia, and hyperthermia, which might occur later in the course of malignant hyperthermia.

After checking the vitals, you should obtain a brief physical examination. A physical exam might show signs of hyperthermia, such as warmth and sweating. Individuals might also exhibit generalized muscle rigidity due to widespread skeletal muscle contraction. Less often, this rigidity is confined to the masseter muscles, leading to jaw tightness and airway compromise if the airway has not been secured.

Finally, after a brief physical examination, you should obtain a 12-lead ECG. When it comes to ECG, it usually shows sinus tachycardia. However, as muscle cells break down, they may release intracellular contents like potassium, and the patient might develop hyperkalemia. So, be on the lookout for ECG changes related to hyperkalemia, such as peaked T waves, wide QRS complexes, and ventricular arrhythmias.

If signs point to malignant hyperthermia, check the history for any risk factors. Since malignant hyperthermia usually occurs during anesthesia, the patient is already sedated, so you’ll have to obtain the history from other members of the clinical team or the patient’s health record. You should determine whether the patient received any volatile anesthetics or succinylcholine; and then, determine when the medication was administered.

Now, here are some high-yield facts to keep in mind! A major risk factor for malignant hyperthermia is any family history of known malignant hyperthermia or poor reactions to anesthesia, since the condition is genetic. However, most people who develop malignant hyperthermia will have no known family history of this condition, so even a negative family history can’t rule it out. In addition, keep in mind that some medications can mask the signs and symptoms of malignant hyperthermia. For instance, beta blockers can mask tachycardia, sedatives block respiratory drive and tachypnea, while neuromuscular blocking agents prevent being able to see the rigidity. Thus, if the patient is on one of these medications, a high index of suspicion is important to not miss malignant hyperthermia.

Alright, if there are signs of hypermetabolism in a patient who received one of the common triggering medications, you can suspect malignant hyperthermia. Due to the severity and rapid progression of this condition, you should start acute management right away. First, administer dantrolene intravenously as soon as it’s available. This is the only known antidote for malignant hyperthermia, acting on ryanodine receptors to inhibit calcium release and muscle contraction. Next, stop the offending agent, or if it’s necessary to continue the procedure, switch to a non-triggering anesthetic. This should involve a discussion with the intraoperative team, but in general, elective procedures should be safely terminated, while non-elective procedures should be completed as quickly as possible.

Then, hyperventilate the patient to remove excess CO2, and increase the oxygen flow rate and the fraction of inspired oxygen, or FiO2. If not already present, place an endotracheal tube to secure the airway, as well as an arterial line and a Foley catheter. If the person’s core temperature exceeds 39 degrees celsius, initiate cooling with the goal of normothermia, meaning 38 degrees or less. Lastly, if the person has an arrhythmia, follow ACLS resuscitation protocols, but be sure to avoid calcium channel blockers, which can be harmful in malignant hyperthermia. Because of the high risk of hyperkalemia, you should stabilize related arrhythmias by administering calcium gluconate or calcium chloride, as well as insulin plus glucose, and sodium bicarbonate.