## **Core Concept**
Abdominal distension in intestinal obstruction is primarily caused by the accumulation of gas and fluid within the bowel lumen. This condition leads to increased intraluminal pressure, which can compromise blood flow and lead to ischemia of the bowel wall. Understanding the pathophysiology of intestinal obstruction and its effects on bowel dynamics is crucial.

## **Why the Correct Answer is Right**
The correct answer, **C. Gas**, is right because gas accumulation is the most significant contributor to abdominal distension in intestinal obstruction. The gas is primarily composed of swallowed air (nitrogen, oxygen) and gas produced by bacterial fermentation. In the setting of an obstruction, the normal propulsion of intestinal contents is impaired, leading to accumulation of gas and fluid proximal to the obstruction. This accumulation of gas is what primarily causes the abdominal distension.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Fluid accumulation does contribute to abdominal distension but is not the most important cause compared to gas. Fluid can accumulate due to secretion and transudation, but its volume is generally less than that of gas.
- **Option B:** While both fluid and gas accumulate, this option is vague and does not specify the most important cause.
- **Option D:** Faeces can contribute to a lesser extent but are not the primary cause of acute abdominal distension in intestinal obstruction.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that abdominal distension due to intestinal obstruction can lead to significant complications, including respiratory compromise and bowel ischemia. Early recognition and intervention are critical. A classic clinical correlation is that a closed-loop obstruction (where both ends of a bowel segment are obstructed) can lead to more rapid distension and severe consequences.

## **Correct Answer:** C. Gas.