Malignant hyperthermia, sometimes called malignant hyperpyrexia (MH), is a life-threatening inherited autosomal dominant condition. It may be triggered by volatile anaesthetic agents and succinylcholine, but not necessarily at the first exposure.
The common clinical features are increasing end tidal CO2, tachycardia and increased oxygen consumption. Hyperthermia is not an early sign.
Although masseter muscle spasm and generalized muscle rigidity after succinylcholine indicate a high risk of susceptibility to MH, they rarely progress to full-blown MH and are usually transient.
If MH is suspected, it is imperative that you summon help.
Treatment involves:
- Removing the suspected triggering agent
- Ventilating with a high minute volume in a high FIO2
- Administering dantrolene at 2 mg/kg up to 10 mg/kg
- Active cooling
Intensive care is required in the postoperative period, because symptoms may return.
Dantrolene
This uncouples the action potential from the contractile process within skeletal muscle by binding to the ryanodine receptor. This receptor is responsible for the release of calcium from the sarcoplasmic reticulum.
However, genetically abnormal receptors are unable to switch off, leading to a high concentration of calcium within the cell. The body's response is to try to reverse this and in doing so it consumes large amounts of energy and oxygen and produces large amounts of CO2 and heat.
Dantrolene is presented in a glass vial containing only 20 mg. For an average man of 80 kg, 2 mg/kg requires 160 mg (= 8 vials). Mannitol is in the vial to increase its solubility.