**Core Concept**
The management of a patient undergoing percutaneous coronary intervention (P.C.I) who develops hypotension due to excessive nitroglycerin (GTN) administration involves understanding the pharmacodynamics of GTN and the pathophysiology of its effects on the cardiovascular system. GTN is a vasodilator that causes smooth muscle relaxation in blood vessels, leading to decreased peripheral resistance and a subsequent drop in blood pressure.

**Why the Correct Answer is Right**
In this scenario, the patient's hypotension is likely due to the excessive GTN administration, causing a significant drop in blood pressure. The correct management plan involves administering a vasopressor to increase blood pressure and ensure adequate perfusion of vital organs. Norepinephrine is a potent vasopressor that can be used in this situation to increase blood pressure and maintain cardiac output. It acts by stimulating alpha-1 and beta-1 adrenergic receptors, causing vasoconstriction and increased cardiac contractility.

**Why Each Wrong Option is Incorrect**
**Option A:** Administering a fluid bolus may help to increase blood pressure in the short term, but it does not address the underlying cause of the hypotension, which is excessive GTN administration. Additionally, fluids may not be sufficient to maintain adequate perfusion of vital organs.

**Option B:** Increasing the dose of GTN would exacerbate the hypotension and worsen the patient's condition.

**Option C:** Administering a beta-blocker would be counterproductive in this situation, as it would further decrease cardiac output and worsen the hypotension.

**Option D:** Administering a diuretic would also be inappropriate, as it would increase urine output and worsen the hypotension.

**Clinical Pearl / High-Yield Fact**
In patients undergoing P.C.I, excessive GTN administration can lead to severe hypotension. It is essential to be aware of the potential for this complication and to have a plan in place to manage it promptly.

**Correct Answer:** C. Administering a vasopressor, such as norepinephrine, is the most appropriate management plan at this stage to increase blood pressure and maintain cardiac output.