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

The earliest and most sensitive sign of malignant hyperthermia is an increase in end-tidal carbon dioxide (ETCO2). This response occurs due to an increase in metabolic activity and carbon dioxide production resulting from abnormal calcium release in muscle cells during episodes of malignant hyperthermia, typically triggered by certain anesthetics or succinylcholine.

As the muscles become hypermetabolic, they require more oxygen and produce more carbon dioxide, leading to a sharp rise in ETCO2 levels. This rise is detectable even before significant increases in body temperature or other clinical manifestations occur, making it a key early indicator.

Other signs, such as increased heart rate, increased blood pressure, and increased body temperature, may follow but are not as immediate or sensitive as the rise in ETCO2. These later signs can reflect a more advanced or severe state of malignant hyperthermia but do not serve as the initial alert in the same way that elevated ETCO2 does. Therefore, recognizing increased ETCO2 is crucial for early intervention and management of malignant hyperthermia.