Bowel Obstruction
A mechanical block or a paralysed bowel both stop luminal contents moving forward, so gas and fluid accumulate proximally, and the cardinal features (distension, vomiting, absolute constipation) follow directly from where along the gut that stoppage sits.
In a nutshell
Bowel obstruction is mechanical (a physical block driving colic) or functional (ileus, no colic), and whichever it is, gas and fluid build up proximal to the stoppage, producing distension, vomiting and absolute constipation. Strangulation converts colicky pain into constant, severe pain and is a surgical emergency.
Classic presentation
Colicky central abdominal pain, distension, vomiting and absolute constipation of faeces and flatus, often in a patient with previous abdominal surgery (adhesions) or a hernia.
Key points
- Mechanical obstruction causes colic because bowel contracts against a physical block; ileus does not, because there is nothing to contract against.
- High (small bowel) obstruction vomits early with modest distension; low (large bowel) obstruction distends grossly with vomiting a later, faeculent feature; both follow from how much bowel lies upstream.
- Strangulation (pain becoming constant, fever, tachycardia, peritonism, rising lactate) is a surgical emergency requiring urgent operation, not a trial of conservative management.
- "Drip and suck" (NBM, NG decompression, IV fluids) is first-line for simple obstruction, but a hernia-related or closed-loop obstruction should prompt earlier surgical review.
- CT is the investigation of choice to define the level, cause and viability of the obstructed bowel.
First-line investigation
Erect chest and abdominal X-ray to screen for perforation and gauge the level of obstruction, followed by contrast CT abdomen/pelvis for a definitive diagnosis.
First-line management
Nil by mouth, nasogastric decompression and IV fluid resuscitation ("drip and suck"), with urgent surgery if strangulation, a closed loop or an irreducible hernia is present.
Exam traps
- Absence of colic does not exclude obstruction: it points towards ileus rather than a mechanical cause.
- A hernia found on examination in a patient with obstruction should prompt urgent surgical assessment; do not assume conservative management is appropriate.
- Faeculent vomiting suggests a distal (large bowel or very late small bowel) obstruction, not necessarily infection or unrelated pathology.
- A patient whose colicky pain suddenly becomes constant and severe should be reassessed immediately for strangulation, not reassured that things are settling.
Educational content pending clinical review. Not medical advice.