Question

1. Describe the etiology, signs, and symptoms of malignant hyperthermia; the drugs associated with a high risk for that condition; and interventions to be implemented should it develop.
2. Identify the class of drugs used to reverse the effects of nondepolarizing neuromuscular blockers and describe the mechanism by which they cause that reversal. Also explain why pharmacologic reversal is not used when succinylcholine is the neuromuscular blocker.
3. Describe the signs and symptoms associated with “irreversible” cholinesterase inhibitors and the general approaches used to manage poisoning caused by these substances.
4. Describe the signs and symptoms associated with cholinesterase inhibitor overdose and the general approaches to managing it.

Answer 1

1.

malignant hyperthermia is a fatal condition which occurred due to hypermetabolism of skeletal muscles. It is an inherited disorder with an abnormal ryanodine receptor.

aetiology

• certain inhalational anaesthetic agents  
• depolarising muscle relaxants.(succinylcholine)

Abnormal ryanodine receptor interferes with the regulation of calcium in the muscle, results in massive muscle reaction

signs and symptoms

EARLY SIGNS

• muscle rigidity
• respiratory and metabolic acidosis
• increased carbon dioxide concentration
• tachycardia
• tachypnea
• hyperkalemia

LATER SIGNS

• hyperthermia
• myoglobinuria
• multiple organ failure.

drugs associated with malignant hyperthermia

volatile anaesthetic gases: halothane, sevoflurane, desflurane, isoflurane, enflurane

depolarizing muscle relaxants: suxamethonium, decamethonium.

interventions

• cool mist and fans or cooling blankets to lower temperature.
• administer cooled intravenous fluids.
• administer oxygen
• administer antihypertensive drugs
• administer dantrolene to reverse reaction

2.

the direct-acting skeletal muscle relaxant is the drug of classification of dantrolene, used as an antidote for malignant hyperthermia.

if any signs of developing malignant hyperthermia with triggering medicine, immediately stop the medicine. administer dantrolene (dantrium). it relaxes the muscle and ceases massive muscle metabolism.

succinylcholine is the depolarising agent which has a short term action of 5 minutes. no cholinergic agents are used currently to reverse the reaction other than time. use of cholinergic worsens the condition. the only management is the administration of artificial respiration and gives time to subside. if the effect is prolonging, intubation and use of ventilator till the effect subside.