What is the most specific and sensitive sign of malignant hyperthermia?

The most specific and sensitive sign of malignant hyperthermia is an elevation in end-tidal CO2. This increase occurs due to the hypermetabolic state of skeletal muscle, which results from an abnormal release of calcium from the sarcoplasmic reticulum. This condition leads to significantly increased carbon dioxide production as the muscles metabolize excessively.

In the context of malignant hyperthermia, elevated end-tidal CO2 is particularly telling because it can occur early in the course of the reaction, often before other signs, such as tachycardia or muscle rigidity, become pronounced. While muscle rigidity is a classic symptom of malignant hyperthermia, it may not appear immediately, and not all patients will exhibit it. Tachycardia and hypotension can be present in many other conditions, making them less specific as signs of malignant hyperthermia.

In summary, the elevation in end-tidal CO2 is a consistent indicator that is both sensitive to the hypermetabolic changes occurring in malignant hyperthermia and specific to this condition, distinguishing it from other possible causes of similar clinical presentations.