**Core Concept**
The sudden onset of increased heart rate, arrhythmia, high fever, metabolic and respiratory acidosis, and elevation of end tidal CO2 in a child undergoing squint surgery suggests a malignant hyperthermia (MH) crisis, a life-threatening condition triggered by exposure to certain volatile anesthetics or depolarizing muscle relaxants.

**Why the Correct Answer is Right**
Malignant hyperthermia crisis is characterized by an uncontrolled increase in skeletal muscle metabolism, leading to a rise in body temperature, lactic acid production, and a significant drop in pH. The primary goal in managing MH is to stop the anesthetic trigger, provide supportive care, and administer dantrolene, a specific antidote that acts by inhibiting calcium release from the sarcoplasmic reticulum, thereby decreasing muscle contraction and heat production.

**Why Each Wrong Option is Incorrect**
* **Option A:** Succinylcholine is a depolarizing muscle relaxant that can trigger MH, making it an inappropriate choice in this scenario.
* **Option B:** Naloxone is an opioid antagonist used to reverse opioid-induced respiratory depression, which is not the primary concern in MH.
* **Option C:** Fentanyl is an opioid analgesic that can be used to manage pain, but it is not the first-line treatment for MH.

**Clinical Pearl / High-Yield Fact**
Malignant hyperthermia is a medical emergency that requires immediate recognition and treatment. The key to successful management is the prompt administration of dantrolene, which can be life-saving.

**Correct Answer:** C. Dantrolene.