Malignant Hyperthermia and Local Anesthetic Toxicity

Malignant hyperthermia and local anesthetic systemic toxicity are two anesthesia emergencies that exams love. Both are rare, both are life-threatening and both have a specific antidote. Learning the triggers, the early signs and the first actions earns easy marks.

Malignant hyperthermia: the trigger

In susceptible patients, volatile anesthetics and the depolarizing muscle relaxant succinylcholine can trigger uncontrolled calcium release in skeletal muscle. The condition is linked to a genetic abnormality of the ryanodine receptor.

Early signs

• Rising end-tidal carbon dioxide despite adequate ventilation
• Tachycardia and arrhythmias
• Muscle rigidity, including masseter spasm
• Rapid rise in temperature, which may be a later sign
• Hyperkalemia, acidosis and rhabdomyolysis

Immediate management

Stop all triggering agents and call for help. Hyperventilate with 100 percent oxygen at high flow, switch to a non-triggering anesthetic technique and give intravenous dantrolene as early as possible, repeating until the signs settle. Cool the patient, treat hyperkalemia and arrhythmias and monitor creatine kinase, electrolytes and urine output. Patients need close monitoring afterward because the problem can recur.

Local anesthetic systemic toxicity

This happens when a large amount of local anesthetic reaches the circulation, for example after an inadvertent intravascular injection or an excessive dose. Early features include perioral numbness, a metallic taste, ringing in the ears, agitation and muscle twitching. It can progress to seizures, coma, arrhythmias and cardiovascular collapse. Bupivacaine is particularly cardiotoxic.

Management of toxicity

• Stop the injection and call for help
• Support the airway and give oxygen
• Treat seizures, usually with a benzodiazepine
• Give intravenous lipid emulsion according to protocol
• Follow modified advanced life support in cardiac arrest, with attention to drug doses

Prevention

Use the smallest effective dose, aspirate before injecting, inject slowly in small increments and use ultrasound guidance when available. Know the maximum dose of each agent.

A classic exam pattern

After an ambulatory block, a patient develops perioral tingling, agitation and then a seizure. The diagnosis is local anesthetic toxicity, and the specific treatment is lipid emulsion together with supportive care.

Study tips

• Memorize the antidote for each emergency
• Compare the early signs of the two conditions
• Review each wrong answer for the sequence you forgot

This article is for exam revision and does not replace current clinical guidelines. Practice anesthesia cases in the Namazj free trial.