What are trigger substances?
The trigger substances of malignant hyperthermia, i.e. substances that can trigger this functional disorder, are Inhalation anesthetics, succinylcholine and also caffeine. Inhalation anesthetics, such as sevoflurane, are used to induce and maintain anesthesia. An exception is nitrous oxide, which is a safe substance and not a trigger for malignant hyperthermia.
Succinylcholine is a depolarizing muscle relaxant used in some cases during anesthesia and is the main trigger substance. Stress can also be a trigger. Neostigmine is a cholinesterase inhibitor.
It prevents the breakdown of acetylcholine in the synaptic cleft by the enzyme acetylcholinesterase. This effect makes it suitable as an antagonist of nondepolarizing muscle relaxants used in the induction and maintenance of anesthesia. Neostigmine is used, for example, in the removal of anesthesia or to counteract muscle weakness myasthenia gravis. Since nondepolarizing muscle relaxants, unlike depolarizing agents such as succinylcholine, are not trigger substances of malignant hyperthermia, neostigmine is not used here.
Symptoms of malignant hyperthermia
Early, but unspecific signs of incipient malignant hyperthermia are cardiac arrhythmias under anesthesia. An increased carbon dioxide content can be measured in the exhaled air of the patient, and in the course of the disease muscle stiffness (rigor) occurs throughout the body. The blood pressure drops with increasing heart rate, the patients’ circulation destabilizes. Only relatively late does a strong increase in body temperature occur.In the further course of malignant hyperthermia, the cell death in the crisis-ridden muscles leads to potassium overload of the blood, which can lead to cardiac arrhythmia, the oxygen debt in the body and inadequate respiration lead to acidosis. Complications can include kidney failure, respiratory insufficiency, cardiovascular failure or brain swelling.
Diagnostics
Patients under anesthesia are extensively instrumental monitored (“monitoring“), anesthesiologists are very attentive to malignant hyperthermia. An early sign of malignant hyperthermia is the increasing carbon dioxide content in the exhaled air, signs of hyperacidity can be detected in blood gas analysis. In case of suspicion of the development of a malignant hyperthermia crisis, immediate action and diagnostics are essential. In order to clarify the presence of a predisposition to malignant hyperthermia in the run-up to an operation, the only specific possibility currently exists to examine a muscle sample taken in the laboratory. However, since this requires a minor operation (muscle biopsy), this procedure is not suitable for comprehensive testing diagnostics.
