What is the first sign of malignant hyperthermia?

The first sign of malignant hyperthermia is often masseter muscle rigidity. This condition typically presents initially with sustained rigidity of the jaw muscles, followed by a rapid progression of symptoms that can include tachycardia, elevated temperature, and respiratory distress. While tachycardia is an important sign of malignant hyperthermia and indicates the body's response to stress and increased metabolic demand, it is not the earliest manifesting sign.

Masseter muscle rigidity can occur soon after the exposure to triggering agents (such as certain anesthetic drugs) and should prompt immediate investigation for malignant hyperthermia. Early identification and response to this sign are critical in managing the condition effectively before it escalates into more severe symptoms such as elevated body temperature and respiratory compromise. It’s essential to recognize that while tachycardia can be a prominent feature in the clinical presentation of malignant hyperthermia, masseter muscle rigidity is a more specific and immediate indicator that necessitates prompt action.