Intestinal Obstruction and Colorectal Disease

Surgery — Intestinal Obstruction and Colorectal Disease, NMC MBBS licence examination syllabus (Nepal Medical Council).

Intestinal Obstruction and Colorectal Disease

Four features make the diagnosis. One further question — is the bowel still alive — decides whether the patient can wait until morning.

Obstruction is among the commonest surgical emergencies and the classic long case, because almost everything about it can be reasoned out from one idea: gut is a tube, something is blocking it, and the consequences depend on where.

The four cardinal features

Colicky pain — the gut contracting against a blockage, coming in waves with pain-free intervals. Vomiting. Distension. And absolute constipation, which means no flatus and not merely no stool: a patient still passing flatus has something getting through.

The single most useful question is which feature came first, because that locates the obstruction. Vomiting early with little distension means the block is high; distension first with vomiting late means it is low. One variable — how much gut sits above the block — generates the whole difference.

High and low obstruction

In high obstruction there is a short column of bowel above the block. It fills quickly and empties upwards, so vomiting is early and profuse, distension is slight, and dehydration develops fast.

In low obstruction the column is long. It takes time to fill, so distension is marked and vomiting is late — and by then bacteria have acted on stagnant contents, which is why it becomes faeculent. That smell is a sign of duration, not of perforation.

The question that decides the timing

A simple obstruction blocks the lumen while the blood supply remains intact. A strangulated one has compromised the blood supply, and the bowel is dying.

The features that suggest it: pain that becomes constant instead of colicky, tenderness and guarding, fever, and tachycardia. The change in the character of the pain matters more than its severity — colic is gut contracting, and constant pain is gut ischaemic.

🩺 This distinction, rather than the underlying cause, decides urgency. A simple adhesional obstruction may settle with conservative management over a day or two. A strangulated one will not settle, and every hour of delay costs bowel that would have been viable. A candidate who can articulate that difference has answered the examiner's real question.

The common causes, by likelihood

🔍 What is blocking it

AdhesionsThe commonest cause in anyone who has had abdominal surgery. Always ask, and always look for scars.

HerniaThe commonest cause in someone who has NOT. Examine the hernial orifices in every obstructed patient — see NMCSU04.

TumourParticularly in the left colon, and particularly in an older patient with a changed bowel habit.

VolvulusA loop twisting on its mesentery, which obstructs and strangulates together.

💡 Examining the hernial orifices is the step most often skipped and the one most likely to give the answer at the bedside. An obstructed hernia is diagnosed by looking, needs no imaging, and is treatable — while the alternative is a patient investigated for hours for a lump nobody examined.

Initial management

Nothing by mouth, and decompress the stomach. This stops the column above the block growing and protects an obstructed patient from aspirating.

Fluid resuscitation, because these patients are far drier than they look. Litres are lost into the bowel lumen — fluid that is inside the body but no longer in the circulation — as well as through vomiting. NMCPY03 covers the assessment.

Then decide. Observation is reasonable for a simple obstruction with a likely adhesional cause. Suspected strangulation, or an obstructed hernia, goes to theatre.

Colorectal cancer: how it announces itself

Which side the tumour sits on changes the presentation completely, and the reason is mechanical.

The right colon is wide and its contents are liquid, so a tumour grows large before it obstructs anything. It bleeds slowly and invisibly, so the patient presents late with iron-deficiency anaemia, weight loss and tiredness.

The left colon is narrower and the stool is formed. A much smaller tumour narrows it enough to matter, so the presentation is a change in bowel habit, visible blood, or obstruction.

The rule worth carrying out of this chapter: iron-deficiency anaemia in an older patient is a colonic lesion until proven otherwise. Treating the anaemia with iron and not investigating the cause is a recognised way to miss a curable cancer for a year — and NMCMD10 makes the same point from the medical side.

Clinical reasoning: four presentations

Colicky pain, early profuse vomiting, minimal distension, previous appendicectomy. High small bowel obstruction, likely adhesional. Decompress, resuscitate, observe — and watch for the pain changing character.

Gross distension, absolute constipation, vomiting starting on day three, no previous surgery. Low obstruction. Examine the hernial orifices, and consider a left colonic tumour in an older patient.

An obstructed patient whose colic becomes constant, with guarding and a rising pulse. Strangulation until proven otherwise. This patient needs theatre, not another period of observation.

A 68-year-old with iron-deficiency anaemia and no obvious bleeding. Investigate the colon. Iron alone treats the number and leaves the cause.

Commonly confused

Constipation and absolute constipation. The second means no flatus either, and that is what makes it obstruction rather than a slow bowel.

Faeculent vomiting and faecal vomiting. Faeculent means stagnant small bowel contents acted on by bacteria, which indicates duration. It is not stool.

Simple and strangulated. The distinction is the blood supply, not the severity of the pain — and it decides the timing of everything.

Right and left colonic cancer. Anaemia and weight loss on the right; changed habit, bleeding and obstruction on the left.

Rapid revision

Colic, vomiting, distension, absolute constipation — and which came first tells you the level.

High: early vomiting, little distension. Low: marked distension, late faeculent vomiting.

Constant pain, guarding, fever, tachycardia — suspect strangulation and stop observing.

Adhesions if they have had surgery, hernia if they have not. Examine the orifices.

Nothing by mouth, decompress, resuscitate, then decide.

Iron-deficiency anaemia in an older patient means investigate the colon.

Syllabus points

The four cardinal features: colicky pain, vomiting, distension, absolute constipation
Absolute constipation meaning no flatus, not merely no stool
Which feature came first as the clue to the level
High obstruction: early profuse vomiting, little distension, rapid dehydration
Low obstruction: marked distension, late and faeculent vomiting
Why faeculent vomiting indicates duration rather than perforation
Simple obstruction versus strangulation as the decision that sets urgency
Pain becoming constant rather than colicky as a sign of ischaemia
Peritoneal signs, fever and tachycardia in strangulation
Adhesions as the commonest cause after abdominal surgery
Hernia as the commonest cause without previous surgery, and examining the orifices
Tumour and volvulus as further causes
Nothing by mouth and gastric decompression, and why
Fluid resuscitation and the losses into the bowel lumen
Right colonic cancer presenting late with iron-deficiency anaemia
Left colonic cancer presenting with changed bowel habit, bleeding or obstruction
Iron-deficiency anaemia in an older patient as a colonic lesion until excluded

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