What is the earliest sign of malignant hyperthermia?

Malignant hyperthermia (MH) is a life-threatening condition usually triggered by certain anesthetic agents. One of the earliest signs indicative of this serious complication is a sudden rise in end-tidal carbon dioxide (ETCO2). This increase occurs due to heightened muscle metabolism resulting from increased calcium release from the sarcoplasmic reticulum in skeletal muscle, which causes increased carbon dioxide production as muscles become hypermetabolic.

The rise in ETCO2 typically precedes other signs, such as increased heart rate, muscle rigidity, or a rapid rise in core body temperature. Monitoring ETCO2 is critical because it can provide early recognition of MH even before more severe manifestations develop. Thus, in clinical practice, a sudden rise in ETCO2 is a crucial alert for anesthesiologists to take immediate action to mitigate the effects of MH.

In this scenario, while elevated core temperature, decreased oxygen saturation, and hyperkalemia can all occur as secondary manifestations during malignant hyperthermia, they do not represent the earliest sign. Instead, they follow the early increase in ETCO2, which serves as a more immediate marker for the condition's onset.