Anaesthetics

Question 1

What is the aetiology of Malignant Hyperthermia?

Answer 1

Malignant hyperthermia (MH) is a subclinical myopathy in which general anaesthesia triggers an uncontrollable contraction of skeletal muscle that leads to a life-threatening hypercatabolic state and increase in body temperature.

The disease is primarily autosomal dominant; mutations in receptors (especially ryanodine receptor type 1) predispose to volatile anesthetic agents or succinylcholine causing excessive release of Ca2+ from the sarcoplasmic reticulum of skeletal muscle. Smooth muscle and cardiac muscle remain unaffected.

Causative agents:

• Volatile anaesthetic agents such as halothane
• Suxamethonium

Question 2

What are the clinical features of Malignant Hyperthermia?

Answer 2

Early signs:

• Tachycardia
• Tachypnea
• Cyanosis
• Rigidity

Late signs:

• Elevated body temperature (up to 45ºC/113°F)
• Signs of secondary organ damage
  
  • Complex arrhythmias
  • Oliguria (acute kidney injury)
  • Seizures
  • Bleeding and/or thrombosis (disseminated intravascular coagulation)
  • Myoglobinuria , muscle pain, swelling, and weakness of the affected muscles (rhabdomyolysis)

Question 3

Describe the diagnosis of Malignant Hyperthermia

Answer 3

Malignant hyperthermia is a clinical diagnosis characterised by a rise in body temperature and signs of muscle breakdown including:

• Lactic acidosis
• Electrolyte abnormalities such as hyperkalaemia
• CK raised

Question 4

Describe the management of Malignant Hyperthermia

Answer 4

Immediate administration of dantrolene - prevents Ca2+ release from the sarcoplasmic reticulum. Also immediate cessation of potential triggering agents.