What are the key clinical signs and symptoms that indicate a patient may be experiencing malignant hyperthermia during or after anaesthesia?

Key clinical signs and symptoms indicating malignant hyperthermia (MH) during or after anaesthesia include a rapid and unexplained rise in end-tidal carbon dioxide (ETCO2) despite increased ventilation, muscle rigidity (especially masseter muscle rigidity), tachycardia, hyperthermia (a rapid increase in body temperature), acidosis, and hyperkalemia. These signs often develop shortly after exposure to triggering agents such as volatile anaesthetics or depolarizing muscle relaxants. Early signs typically include unexplained tachycardia and increased ETCO2, which may precede the rise in body temperature. Muscle rigidity, particularly of the jaw, is a hallmark sign that may be observed during induction or maintenance of anaesthesia. Hyperthermia may develop later but can escalate rapidly and is a critical warning sign. Other symptoms can include arrhythmias, cyanosis, sweating, and a mottled or flushed skin appearance. Laboratory findings often reveal metabolic and respiratory acidosis, elevated creatine kinase, and hyperkalemia due to muscle breakdown.

Recognition of these signs requires high clinical suspicion during or immediately after anaesthesia, as early intervention is crucial to reduce morbidity and mortality. The UK Association of Anaesthetists’ guideline emphasizes the importance of monitoring ETCO2 and muscle tone closely in at-risk patients and responding promptly to these clinical indicators ¹. Recent literature corroborates these findings and highlights that while hyperthermia is a key feature, it may be a late sign; thus, early detection relies heavily on observing rising ETCO2 and muscle rigidity (Hopkins et al., 2021; Klincová et al., 2022; Pinyavat et al., 2024).