**Core Concept**
The accidental intra-arterial injection of thiopentone is a medical emergency that requires prompt management to prevent tissue necrosis and gangrene. Thiopentone is a highly lipid-soluble barbiturate that can cause severe vascular irritation and thrombosis when injected into an artery.

**Why the Correct Answer is Right**
Intra-arterial injection of thiopentone should not be attempted to be flushed with normal saline as it can further distend the artery and worsen the thrombosis. Instead, it should be managed by immediately administering 5-10 ml of 10% sodium thiosulfate into the affected limb, which can help to reduce the toxicity and thrombosis caused by the thiopentone.

**Why Each Wrong Option is Incorrect**
**Option A:** Flushing the affected limb with normal saline is incorrect because it can further exacerbate the vascular irritation and thrombosis caused by the thiopentone.

**Option B:** Administering vasodilators, such as nitroglycerin, is incorrect because they can increase the flow of thiopentone into the affected limb, worsening the toxicity.

**Option C:** Applying heat to the affected limb is incorrect because it can increase the metabolism of thiopentone, leading to further tissue damage.

**Clinical Pearl / High-Yield Fact**
When managing accidental intra-arterial injection of thiopentone, remember that sodium thiosulfate is the antidote of choice, and normal saline should be avoided to prevent further tissue damage.

**Correct Answer: D. Administering 5-10 ml of 10% sodium thiosulfate into the affected limb.**