Small and Large Bowel Obstruction

Bowel obstruction is a mechanical block to the passage of intestinal content, and at the CST management and clinical station the answer is a CCrISP sequence: resuscitate, decompress, image with CT, and decide. According to the WSES Bologna guideline, non-operative management is the treatment of choice for adhesive small bowel obstruction unless there is peritonitis, strangulation or ischaemia. NCEPOD's 2020 report Delay in Transit found delays at every step of that pathway, and the panel is listening for a candidate who removes them.

Key takeaways

NCEPOD recommends a prompt CT with intravenous contrast as the definitive imaging for suspected acute bowel obstruction, with time to CT reporting audited locally
NCEPOD also asks for a consultant review at the latest within 14 hours of admission, and a consultant discussion within an hour for high-risk patients
The WSES Bologna guideline permits a trial of non-operative management for up to 72 hours in adhesive small bowel obstruction without peritonitis, strangulation or ischaemia
Water-soluble contrast that has not reached the colon on a radiograph at 24 hours is highly indicative of failed non-operative management
Physical examination detects strangulation in only 48% of cases, which is why CT, lactate and repeated review matter
In NCEPOD's review only 163 of 686 patients (23.8%) had their hydration status recorded, so say the fluid balance out loud

How do I assess a patient with suspected bowel obstruction?

Assess suspected bowel obstruction with the CCrISP three stages: immediate ABCDE management, then a full assessment of chart, history, examination and results, then decide and plan.

In the immediate stage, obstruction is a fluid problem first. Vomiting and third-space losses produce hypovolaemia and electrolyte disturbance, so secure access, send bloods including lactate, and start crystalloid resuscitation with reassessment.

In the full assessment, ask about previous laparotomy, hernias, weight loss and change in bowel habit, because adhesions, hernias and cancer are the three causes the panel expects you to name. Examine every hernial orifice and any scar.

What are the key investigations in bowel obstruction?

The key investigation in bowel obstruction is a CT of the abdomen and pelvis with intravenous contrast, requested promptly rather than after a plain film.

According to the WSES Bologna guideline, plain radiographs have only limited value and are not recommended in the work-up of small bowel obstruction, while CT has approximately 90% accuracy in predicting strangulation and the need for urgent surgery.

NCEPOD's review found delays in imaging in 57 of 276 cases (20.7%), and a delay in imaging led to a delay in diagnosis in 35 of those 57 (61.4%). Bloods should include a full blood count, urea and electrolytes, a venous gas with lactate, and a group and save.

How do I decide between small and large bowel obstruction?

Distinguish small from large bowel obstruction on CT, supported by the history: early vomiting and central colic point to small bowel, and distension with absolute constipation and a change in habit point to large bowel.

The distinction matters because the causes differ. Adhesions and hernias dominate small bowel obstruction, whereas a large bowel obstruction is malignant until proven otherwise, with volvulus and diverticular stricture behind it.

A competent caecum is the trap to name in large bowel obstruction. A closed loop between an obstructing tumour and an intact ileocaecal valve perforates at the caecum, so tenderness there is an operative sign.

What is the initial management of bowel obstruction?

The initial management of bowel obstruction is nil by mouth, a nasogastric tube on free drainage, intravenous fluid with electrolyte replacement, analgesia, a urinary catheter and a fluid balance chart.

The WSES Bologna guideline lists exactly these principles for non-operative treatment: nil per os, nasogastric or long-tube decompression, and intravenous supplementation with fluids and electrolytes.

Say that you would record the hydration status and the electrolytes, because NCEPOD found these were often not assessed and named dehydration with kidney injury as a common complication of the condition.

When is non-operative management safe, and for how long?

Non-operative management is safe for adhesive small bowel obstruction without peritonitis, strangulation or ischaemia, and the WSES Bologna guideline states a trial can be continued safely for 72 hours.

That 72-hour figure is the number the panel wants. The guideline notes evidence for the optimal duration is absent, but most authors and the panel consider a 72-hour period safe and appropriate.

A water-soluble contrast study sharpens the decision. If contrast has not reached the colon on an abdominal radiograph taken 24 hours after administration, the guideline calls this highly indicative of failed non-operative management.

When does bowel obstruction need an operation?

Bowel obstruction needs an operation when there is peritonitis, strangulation or bowel ischaemia, when a hernia is irreducible, when a closed loop or a competent caecum is at risk, or when non-operative management fails.

The WSES Bologna guideline names peritonitis, strangulation and ischaemia as the contraindications to non-operative treatment. Clinically that is peritonism, a rising lactate, fever, tachycardia or pain out of keeping with the distension.

For large bowel obstruction, NCEPOD asked for improved access to stenting for those patients who require it, so mention a colonic stent as an option to be discussed with the consultant and the colorectal team rather than as your own decision.

Who do I escalate a bowel obstruction to, and when?

Escalate every bowel obstruction to the surgical registrar on diagnosis and ensure a consultant review at the latest within 14 hours of admission, or a consultant discussion within an hour if the patient is high risk.

NCEPOD defines high risk as a predicted mortality greater than 10%, or a patient who is unstable and not responding to treatment as expected. Say the definition, because it shows you know when the clock is running.

Escalate earlier for a rising lactate, new peritonism, a closed loop on CT, an irreducible hernia, or a patient who has failed 72 hours of conservative care. Involve anaesthetics and critical care early, because NCEPOD found surgery delayed by theatre and anaesthetist availability.

What is the interviewer listening for in a bowel obstruction scenario?

The interviewer is listening for the CCrISP structure said aloud, a prompt CT with contrast, the 72-hour non-operative limit, the indications for surgery, and a named consultant escalation with a time.

Resuscitation and nasogastric decompression before imaging, with fluid balance and electrolytes stated
CT with intravenous contrast requested promptly, and the reason a plain film is not enough
The three contraindications to conservative care named in one breath
Water-soluble contrast used as a decision tool, with the 24-hour reading explained
Recognition that a large bowel obstruction is cancer until proven otherwise and that a competent caecum perforates

How this comes up at the CST interview

Bowel obstruction usually arrives as a ward or emergency department call: a patient with distension and vomiting and a previous laparotomy. The panel then pushes on one axis, typically the failed conservative trial or the rising lactate.

Follow-up questions include what you would do if the CT showed a closed loop, how a colonic stent fits in, and how you would hand the patient over at the end of the night.

The coresurgeryinterview question bank has a scored bowel obstruction scenario among its 299 questions, with AI-marked spoken practice for the answer structure: /Question-Bank/Sample-Questions.

FAQ

How long can adhesive small bowel obstruction be managed conservatively?

The WSES Bologna guideline states a trial of non-operative management can be continued safely for 72 hours, provided there is no peritonitis, strangulation or ischaemia. Persistent high nasogastric output beyond 72 hours without deterioration remains a matter of debate.

Is a plain abdominal radiograph enough to diagnose bowel obstruction?

No. The WSES Bologna guideline says plain films have limited value and are not recommended, and NCEPOD recommends a prompt CT with intravenous contrast as the definitive imaging. CT also predicts strangulation with approximately 90% accuracy.

What does a water-soluble contrast study tell you?

If contrast has not reached the colon on a radiograph 24 hours after administration, that is highly indicative of failed non-operative management. Contrast in the colon predicts resolution, and studies show it shortens hospital stay.

When must a bowel obstruction patient be seen by a consultant?

NCEPOD's Delay in Transit recommends a consultant review as soon as clinically indicated and at the latest within 14 hours of admission, with a consultant discussion within an hour for high-risk patients, defined as predicted mortality above 10% or an unstable patient.

Why is a competent ileocaecal valve dangerous in large bowel obstruction?

It creates a closed loop between the obstructing lesion and the valve, so pressure rises with nowhere to decompress. The caecum has the thinnest wall and largest diameter, so it perforates first, which makes caecal tenderness an operative sign.

What are the indications for surgery in bowel obstruction?

Peritonitis, strangulation or ischaemia, which the WSES Bologna guideline names as contraindications to conservative care, plus an irreducible hernia, a closed loop, and failure of non-operative management within the 72-hour window.