Which finding is NOT consistent with malignant hyperthermia?

Which finding is NOT consistent with malignant hyperthermia?

• A. PaCO2 150 mm Hg
• B. MVO2 50 mm Hg
• C. pH 6.9
• D. Arterial oxygen saturation 85% on 100% FIO2

Answer: (B)

Malignant hyperthermia drives a sudden, extreme increase in skeletal muscle metabolism due to calcium release, so the body's oxygen use and carbon dioxide production soar. That hypermetabolic state causes tissues to extract more oxygen, raise CO2 levels, and generate lactic acid, leading to severe acidosis and hypercapnia. Even with high inspired oxygen, the combination of high O2 demand and ventilation–perfusion mismatch can keep arterial oxygen saturation low. In this context, a very high PaCO2 (such as 150 mm Hg) and a profoundly low pH (6.9) fit, reflecting massive CO2 production and lactic acidosis. Arterial O2 saturation remaining only at 85% on 100% FiO2 also fits the picture of overwhelming oxygen demand and V/Q mismatch. The value described as mixed venous O2 tension being 50 mm Hg, however, would not align with MH: the muscles are extracting more O2, so the mixed venous O2 tension tends to fall rather than stay relatively high. Thus that finding is not consistent with malignant hyperthermia.

Malignant hyperthermia drives a sudden, extreme increase in skeletal muscle metabolism due to calcium release, so the body's oxygen use and carbon dioxide production soar. That hypermetabolic state causes tissues to extract more oxygen, raise CO2 levels, and generate lactic acid, leading to severe acidosis and hypercapnia. Even with high inspired oxygen, the combination of high O2 demand and ventilation–perfusion mismatch can keep arterial oxygen saturation low.

In this context, a very high PaCO2 (such as 150 mm Hg) and a profoundly low pH (6.9) fit, reflecting massive CO2 production and lactic acidosis. Arterial O2 saturation remaining only at 85% on 100% FiO2 also fits the picture of overwhelming oxygen demand and V/Q mismatch. The value described as mixed venous O2 tension being 50 mm Hg, however, would not align with MH: the muscles are extracting more O2, so the mixed venous O2 tension tends to fall rather than stay relatively high. Thus that finding is not consistent with malignant hyperthermia.