**Question:** Earliest and most pathognomic feature of malignant hyperthermia is

A. Increased muscle tone
B. Hyperventilation
C. Delayed respiratory depression
D. Delayed cardiac arrhythmias

**Core Concept:**
Malignant hyperthermia (MH) is a rare, potentially life-threatening, iatrogenic complication of general anaesthesia. It is triggered by specific volatile anaesthetics, succinylcholine, or other medications that activate the MH-sensitive ryanodine receptors in the sarcoplasmic reticulum of skeletal muscle cells, leading to excessive calcium release and uncontrolled muscle contraction.

**Why the Correct Answer is Right:**
The correct answer is B. Hyperventilation. This is because the early respiratory rate increases due to the hypermetabolic state and the hyperkalemic response to the release of potassium ions from the damaged skeletal muscle cells during a MH episode. This hyperventilation is caused by the excessive calcium release from the sarcoplasmic reticulum, leading to the activation of the diaphragm and intercostal muscles.

**Why Each Wrong Option is Incorrect:**
A. Increased muscle tone (Option A) is not the earliest feature, as hyperventilation occurs earlier.
C. Delayed respiratory depression (Option C) is not the earliest feature, as hyperventilation occurs earlier.
D. Delayed cardiac arrhythmias (Option D) may occur later in the MH episode, after other symptoms have manifested.

**Clinical Pearl:**
Malignant hyperthermia is a clinical emergency requiring immediate intervention, including discontinuation of triggering agents, administration of dantrolene (a calcium-chelating agent), and ensuring optimal airway management and fluid resuscitation. Awareness of MH risk in susceptible patients and rapid recognition of its symptoms are essential for timely management and prevention of severe complications.