What is a characteristic of Malignant Hyperthermia (MH)?

Malignant Hyperthermia Characteristics

Malignant hyperthermia is associated with an intraoperative rise of end-tidal CO2, which is the earliest and most specific sign of this condition. 1

Pathophysiology and Clinical Presentation

• Malignant hyperthermia (MH) is a progressive life-threatening hypermetabolic reaction that occurs during general anesthesia in genetically susceptible individuals 2
• MH is triggered specifically by exposure to potent inhalational anesthetics or suxamethonium, not merely by the stress of surgery or anesthesia 2
• The condition results from excessive release of calcium from the sarcoplasmic reticulum in skeletal muscle cells, leading to uncontrolled muscle contraction and hypermetabolism 3
• Increased intermediary metabolism leads to increased oxygen consumption and carbon dioxide production, which manifests as increased ETCO2 in mechanically ventilated patients 1

Key Diagnostic Features

• Increased end-tidal CO2 (ETCO2) is the cardinal clinical feature and appears before temperature elevation in the typical progression of MH 1
• The increased CO2 production is resistant to control by increasing minute ventilation during an MH reaction 1
• Tachycardia accompanies increased carbon dioxide production due to sympathetic nervous system activation 2
• Hyperthermia typically develops after the rise in ETCO2 and heart rate 1
• Other clinical features include muscle rigidity, acidosis, hyperkalaemia, and rhabdomyolysis 2, 4

Management and Prevention

• Immediate treatment is essential when MH is suspected, as delay in commencing treatment is associated with increased mortality and complications 1
• Dantrolene sodium is a specific antagonist for MH and should be administered at an initial dose of 2-3 mg/kg with further doses of 1 mg/kg every 5 minutes until treatment goals are reached 2
• Treatment should continue until ETCO2 is <6 kPa with normal minute ventilation and core temperature is <38.5°C 2
• Patients at increased risk of developing malignant hyperthermia must not be exposed to potent inhalation anesthetics or suxamethonium in future anesthetics 2
• Calcium channel blockers are not recommended for prevention of MH and may actually be dangerous when used in conjunction with dantrolene due to potential synergistic effects on cardiac function 3

Clinical Importance and Epidemiology

• MH is rare, occurring in approximately 1:100,000 to 1:250,000 general anesthetics in the UK 2
• Despite the availability of dantrolene, deaths from MH still occur with a mortality rate of approximately 4% in the UK 2
• The highest reported incidence of MH occurs in pediatric populations and there is a consistently higher incidence in males compared to females 2
• A history of uneventful previous anesthesia does not exclude the possibility of MH susceptibility 2

Common Pitfalls and Caveats

• Delayed diagnosis is a major pitfall, as early recognition and treatment are critical for survival 1
• Assuming a patient is not at risk due to previous uneventful anesthetics is dangerous, as patients can have multiple uneventful exposures before developing a reaction 2
• Failure to have dantrolene immediately available wherever general anesthesia is administered can lead to preventable mortality 2
• Misinterpreting early signs like increased ETCO2 and tachycardia as due to other causes can delay life-saving treatment 1

In conclusion, malignant hyperthermia is characterized by an intraoperative rise in end-tidal CO2, is triggered specifically by anesthetic agents rather than surgical stress alone, requires avoidance of triggering agents in future anesthetics, and cannot be prevented by calcium channel blockers.