Increased requirement for minute ventilation and negative arterial to end-tidal carbon dioxide gradient may indicate malignant hyperthermia.

Characteristic signs of malignant hyperthermia (MH) include unexplained tachycardia, increased end-tidal carbon dioxide (Etco₂) concentration, metabolic and respiratory acidosis, and an increase in body temperature above 38.8°C. We present the case of a patient with highly probable MH. In addition to sinus tachycardia and metabolic and respiratory acidosis, this patient also had a negative arterial to Etco₂ gradient and an increased requirement for minute ventilation to maintain a normal Etco₂ concentration, with signs of increased CO₂ production. Despite these signs of MH, the patient's rectal temperature monitoring equipment did not show an increase in temperature, although the temperature measured in the mouth was increased. This case illustrates the unreliability of measuring rectal temperature as a means of reflecting body temperature during MH and the usefulness of increased CO₂ production signs in helping to diagnose MH.