Patients at Risk
Identifying patients with increased risk of developing MH
There are no overt clinical features that are specific for the patient with susceptibility to malignant hyperthermia. Clues that a patient may have an increased risk are:
- a history of an adverse reaction to general anaesthesia
- a family history of problems with anaesthesia
- a family history of proven malignant hyperthermia.
It is vital that all anaesthetists understand that a history of apparently uneventful general anaesthesia does not exclude underlying malignant hyperthermia susceptibility. This is because malignant hyperthermia susceptible patients do not trigger upon every exposure to the triggering general anaesthetics. For this reason, establishing a negative family history is a compulsory part of preoperative anaesthetic assessment in every case.
Patients with a family history, or previous reactions to anaesthesia
It is imperative that the anaesthetist attempts to establish the likelihood that the history is indicative of malignant hyperthermia, within the time constraints imposed by the urgency of the proposed surgery.
For elective surgical procedures it is our advice that an increased risk of MH susceptibility is excluded prior to proceeding with the case, unless the usual anaesthetic management for the case would not include MH triggering drugs.
A more pragmatic approach is required for urgent or emergency surgery. Here, when an increased risk of malignant hyperthermia susceptibility cannot be excluded, anaesthesia should proceed on the assumption that the risk is present.
Patients with congenital myopathies
Some rare congenital myopathies are associated with an increased risk of malignant hyperthermia susceptibility. In these cases specialist advice is recommended. In the current era of molecular genetic diagnosis of neuromuscular conditions, a knowledge of the underlying genetic variant responsible for a neuromuscular condition is more informative than a presumptive clinical or even histopathological diagnosis.
In recent years the association between susceptibility to MH and exertional rhabdomyolysis has been established. Patients with a history of recurrent rhabdomyolysis or those in whom rhabdomyolysis has occurred in response to an apparently innocuous stimulus should be considered for further investigation of MH susceptibility.
Exertional heat illness
The association between exertional heat illness and MH susceptibility is less clear than that between rhabdomyolysis and MH susceptibility. Patients giving a history of multiple incidents of exertional heat illness or exertional heat illness developing in a temperate climate may be worth investigating for malignant hyperthermia susceptibility prior to elective surgery.