Malignant Hyperthermia

Malignant Hyperthermia
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Malignant hyperthermia is an autosomal dominant condition that can affect 50% of offspring (Figure 1). This disorder can be lethal.

Dantrolene is used to help treat malignant hyperthermia. Dantrolene is a lifesaving drug that stops the release of calcium from the sarcoplasmic reticulum into the cell. Dantrolene blocks the calcium and decreases the intracellular calcium and stabilizes the sarcoplasmic reticulum (Figure 2).

Other treatment methods can be utilized such as cooling and hydrating the patient and balancing electrolytes (Figure 3).

The patient will get succinylcholine, halothane, or other inhalation agents that will trigger the initiation of malignant hyperthermia (Figure 4). Anesthetic agents (such as succinylcholine and halothane) impair the function of the sarcoplasmic reticulum and calcium hemostasis.

The conditions associated with MH are usually central core diseases like Duchenne Muscular Dystrophy (DMD) (Figure 5), Arthrogryposis, or Osteogenesis Imperfecta (OI).

Malignant hyperthermia is usually diagnosed during anesthesia or by family history. There is no special, simple test for MH, but a muscle biopsy and other testing is occasionally done in select facilities. Because there is a problem in the ryanodine receptor, there will be uncontrolled release of calcium (Figure 6). You will get sustained muscle contraction, rigidity, spasms, muscle damage, myoglobinuria, rhabdomyolysis, and acute renal failure. Because of all the hypermetabolic activity, you will get the classic hyperthermia, that’s why they call it malignant hyperthermia (classic findings).

You can also find metabolic acidosis and hyperkalemia, which may give the patient dysrhythmia or a marked CO2 production. If the CO2 production increases, you will have increased end-tidal CO2 (ETCO2), which can’t be explained, but it is the earliest sign and probably the most specific and sensitive finding (Figure 7). A rise in the end-tidal CO2 concentration is probably the earliest indication that the patient may have malignant hyperthermia.

How does this condition of malignant hyperthermia occur? What is going on? What is the physiology of malignant hyperthermia?

For diagnosis of malignant hyperthermia, you will probably need to know three things sarcolemma, which is in the membrane of the cell, T-tubule which is like a divot into the cell or a cliff, and the sarcoplasmic reticulum is storage for calcium (Figure 8). The sarcoplasmic reticulum is a container for calcium when the muscle is relaxed. Larger protein is embedded into the wall that serves as a calcium release channel. After the muscle contracts, the calcium is taken up by the sarcoplasmic reticulum (storage site).

When there is decirculation of this process because the ryanodine receptor is defective, then ryanodine triggers the release of calcium to the inside of the cell in large quantities than normal. The intracellular concentration of calcium increases substantially and will have a sustained contracture of these muscles, which is how you get malignant hyperthermia.

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