Bowel obstruction is a common reason for admission or complication of patients under the surgical team, but doctors don’t frequently get that much exposure to it in medical school. It is a condition in which the normal passage of intestinal products is impaired. It can affect both large and small bowel.

Bowel obstruction can be mechanical (which could be partial or complete) or functional such as paralytic ileus.

Mechanical
This can be subdivided into affecting the small (SBO) or large bowel (LBO). The most common cause of SBO is post-operative adhesions and for LBO it is colorectal cancer. Other causes of mechanical obstruction include incarcerated hernias, IBD, diverticulitis, gallstone ileus and volvulus.

Paralytic ileus:
Common causes can be post-operative, electrolyte imbalance (mostly hypokalaemia), endocrine abnormalities, medications (commonly opiates), pelvic/spinal cord injury and inflammatory conditions (peritonitis/appendicitis). A helpful mnemonic can be 4Ps (peritonitis/post-operative/potassium/pelvic or spinal injuries)

Presentation
They share the same symptoms and signs for the most part

• Constipation (or diarrhoea)
• Nausea & vomiting
• Lack of flatulence
• Abdominal distension (more characteristic of LBO)

History:
Key questions include a background of their medical & surgical history to identify risk factors that would increase the risk of obstruction. The aim is to determine the type of obstruction & rule out possible differentials causing an acute abdomen.

• What is the nature of your abdominal pain, is it intermittent/continuous/colicky?
• Does the pain come after eating food?
• What is the colour and content of the vomit? When did it come on relative to your other symptoms?
• Are you experiencing diarrhoea/constipation? When did it come on relative to your other symptoms?
• Have you noticed any blood in your stools?
• Have you noticed passing any flatulence?

Examination:
Focus on findings to confirm bowel obstruction & an assessment of severity particularly looking for signs of peritonism to suggest perforation.

Investigations:
Perform routine pre-operative blood tests (FBC, U&Es, CRP, LFTs, group & save, clotting) and include a VBG for a lactate. A high lactate is a surgical emergency which could suggest ischaemic bowel from severe obstruction.

It is important for FY1s to understand why CT imaging is necessary for bowel obstruction as they usually do the requests and liaise with radiology. Radiopaedia has an excellent page on imaging in bowel obstruction.

AXR: Small bowel has the presence of folds which run the full width of the bowel, these are called valvular conniventes. The large bowel features pouches which run a partial width across the bowel, these are called haustra. The accepted upper limit of the intestinal tract are 3 cm for small bowel, 6 cm for colon and 9 cm for caecum. This is commonly referred to as the 3/6/9 rule.

CXR: An erect CXR should also be performed to assess for pneumoperitoneum. Causes for pneumoperitoneum include perforated bowel or recent abdominal surgery/procedure.

CT Scan: the investigation of choice for bowel obstruction. In mechanical obstructions, it is used to look for the transition point (sudden narrowing of bowel lumen), mesenteric fat stranding (sign of inflammation), signs of bowel ischaemia and structural abnormalities. In paralytic ileus, it would see dilated bowel loops with no mechanical/structural cause or transition point.

Management:
A stepwise ABCDE approach should be taken initially. It is not uncommon that patients present septic and hypotensive having had a perforation. The patient should be resuscitated and sepsis 6 initiated.

It is important to escalate to a senior if a bowel obstruction is suspected. Ultimately, further imaging and treatment options would have to be discussed with your seniors. As an FY1, a full workup of the patient as well as preparation to take the patient to theatre if needed is expected. This involves keeping the patient nil by mouth, a coagulation screen and a group & save.

Whilst awaiting a senior review for consideration of whether surgical management is necessary, start with conservative management:

• Keep the patient nil by mouth 
• Intravenous fluids
• Review their drug chart: convert oral medication to IV & stop any prokinetics (such as metoclopramide)
• Antiemetics for symptom control (ondansetron or cyclizine tends to be preferred in mechanical obstruction)
• NG tube for drainage (this is the wide bore one & nurses can place this) classically in mechanical bowel obstruction
• Analgesia