**Core Concept**
Intra-arterial injection of thiopentone is a clinical scenario that tests the understanding of the toxic effects of barbiturates when introduced into the arterial circulation. Thiopentone is a barbiturate that acts as a central nervous system depressant by enhancing the activity of inhibitory neurotransmitters, such as GABA.

**Why the Correct Answer is Right**
When thiopentone is injected intra-arterially, it can cause severe damage to the affected limb due to its potent vasodilatory effects. Thiopentone binds to the sulfhydryl groups of proteins, leading to an imbalance in the sulfhydryl/disulfide ratio, which disrupts the normal functioning of proteins and enzymes. This results in the denaturation of proteins, leading to cellular damage and necrosis. The affected limb may exhibit signs of ischemia, including pallor, pulselessness, paresthesia, and poikilothermia (coldness).

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not applicable, as the correct answer is not provided.

**Option B:** This option is incorrect because intra-arterial injection of thiopentone does not cause a decrease in blood pressure. Instead, it can lead to a reflex increase in heart rate and blood pressure due to the release of catecholamines.

**Option C:** This option is incorrect because intra-arterial injection of thiopentone does not cause a decrease in cardiac output. The vasodilatory effects of thiopentone can lead to a decrease in peripheral resistance, but this is not the primary effect.

**Clinical Pearl / High-Yield Fact**
Intra-arterial injection of thiopentone is a medical emergency that requires immediate attention. The affected limb should be elevated, and the patient should be administered analgesics and anti-inflammatory agents to alleviate pain and reduce swelling.

**Correct Answer: B. Localized tissue damage and necrosis.**