Agent causing malignant h erthermia –
**Question:** Agent causing malignant hyperthermia -
A. Succinylcholine
B. Halothane
C. Isoprenaline
D. Caffeine
**Core Concept:**
Malignant hyperthermia (MH) is a rare but potentially life-threatening complication of certain anaesthetic agents, particularly those used during surgical procedures. MH is caused by a genetic predisposition in some individuals, resulting in abnormal calcium handling in skeletal muscle cells.
**Why the Correct Answer is Right:**
MH is primarily caused by the administration of volatile anesthetics like halothane, which indirectly activates the ryanodine receptor in the sarcoplasmic reticulum of skeletal muscle cells. This leads to increased calcium release from the sarcoplasmic reticulum, causing uncontrolled muscle contractions, hyperthermia, and multiorgan dysfunction.
**Why Each Wrong Option is Incorrect:**
A. Succinylcholine (a neuromuscular blocking agent) is involved in MH, but it is not the primary agent causing the syndrome. In contrast to volatile anesthetics, succinylcholine directly activates the ryanodine receptor, leading to muscle contraction and heat production without the need for volatile anesthetics.
B. Halothane is indeed a volatile anesthetic that can trigger MH, but option C and D are incorrect for different reasons:
C. Isoprenaline (a beta-adrenergic agonist) is a sympathomimetic drug and not a trigger for MH. Its effects on catecholamine release and vasoconstriction do not directly cause the MH crisis.
D. Caffeine is a central nervous system stimulant and not a trigger for MH. Unlike volatile anesthetics and succinylcholine, caffeine does not directly interact with the ryanodine receptor or cause muscle contracture, making it an incorrect trigger for MH.
**Clinical Pearl:**
To prevent MH, it is crucial to identify high-risk patients with known family history or abnormal muscle contracture response during anesthesia. In these patients, alternative anesthetic agents should be chosen, and dantrolene, an antagonist of the ryanodine receptor, is the sole medication to treat an MH crisis.