Small bowel obstruction is more common (80%) than large bowel obstruction.

Obstruction results in a build up of gas and faecal matter proximal to the obstruction = back-pressure = vomiting and dilatation of the intestines proximal to the obstruction.

Bowel obstruction is a surgical emergency.

SBO ➡️  Hypovolaemia ➡️  shock:

The gastrointestinal tract secretes fluid that is later absorbed in the colon. When there is an obstruction, and fluid cannot reach the colon, it cannot be reabsorbed. As a result, there is fluid loss from the intravascular space into the gastrointestinal tract. This leads to hypovolaemia and shock. This abnormal loss of fluid is referred to as third-spacing. The higher up the intestine the obstruction, the greater the fluid losses as there is less bowel over which the fluid can be reabsorbed.

Causes

The “big three” causes account for around 90% of cases:

• Adhesions (small bowel) - Most common cause of SBO
• Hernias (small bowel)
• Malignancy (large bowel) - Most common cause of LBO

Other causes include:

• Volvulus (large bowel)
• Diverticular disease - second most common cause of LBO
• Strictures (e.g., secondary to Crohn’s disease)
• Intussusception (in young children aged 6 months to 2 years)

Closed-Loop Obstruction:

Closed-loop obstruction describes a situation where there are two points of obstruction along the bowel; meaning that there is a middle section sandwiched between two points of obstruction. This might happen with:

• Adhesions that compress two areas of bowel