The term bowel obstruction usually refers to the mechanical blockage of the bowel – where a structural pathology (e.g obstructing cancer) blocks the normal passage of intestinal contents. Around 15% of acute abdomen cases are found to have a bowel obstruction.
When the bowel is not mechanically blocked but does not work properly, for example because of inflammation, electrolyte derangement or recent surgery, this is known as paralytic ileus or pseudo-obstruction.
In this article, we shall look at the causes, clinical features and management of bowel obstruction.
The most common causes of bowel obstruction depend on location:
- Small bowel – adhesions (either congenital or post-operative) and hernias.
- Large bowel – malignancy (a large bowel obstruction should be considered to be caused by a GI cancer until proved otherwise), diverticular disease, and volvulus.
The full list of causes of bowel obstruction can otherwise be divided into extrinsic, intramural and intraluminal causes, as described in Table 1.
|Table 1: Causes of Bowel Obstruction|
|Intraluminal||Gallstone ileus, ingested foreign body, faecal impaction|
|Mural||Carcinoma, inflammatory strictures (especially in CD patients), intussusception (most common in children), diverticular strictures, Meckel’s diverticulum, lymphoma|
|Extramural||Hernias, adhesions, peritoneal metastasis, volvulus|
Once the bowel segment has become occluded, there is gross dilatation of the proximal limb of bowel, which in turn results in increased peristalsis of the bowel. This leads to secretion of large volumes of electrolyte rich fluid into the bowel (sometimes termed ‘third spacing’).
If there is a 2nd obstruction proximally (as occurs if the obstruction is due to a twist in the bowel or in large bowel obstruction if the ileocaecal valve is competent) this is termed a “closed-loop” obstruction. This is a surgical emergency as the bowel will continue to distend, stretching the bowel wall until it becomes ischaemic and ultimately perforates.
The cardinal features of bowel obstruction are:
- Abdominal pain – colicky in nature, secondary to the bowel peristalsis. Any pain originally colicky that is now constant in nature or worse on movement should be a “red flag” that ischaemia may be developing.
- Vomiting – initially of gastric contents, before becoming bilious and then eventually faeculent (a dark-brown, bitter, foul-smelling vomitus).
- Abdominal distension
- ‘Absolute’ constipation – failure to pass flatus and faeces.
It is important to remember that patients may not display all of these features at once. For example, in a closed-loop obstruction, vomiting will be absent whilst in patients with very distal obstructions it will develop late, if at all. Likewise, the more proximal the obstruction, the later constipation will develop.
On examination, patients may show evidence of the underlying cause (e.g. surgical scars, cachexia from malignancy, or obvious hernia) and of abdominal distension. Assess for any clinical signs of dehydration or sepsis.
Palpate for focal tenderness (including guarding and rebound tenderness on palpation). Percussion may reveal a tympanic sound and auscultation may reveal ‘tinkling’ bowel sounds, both signs characteristic of bowel obstruction.
Note – Focal tenderness indicates ischaemia and is a key warning sign. Patients with bowel obstruction may be uncomfortable on palpation due to the discomfort from pressing on a distended abdomen, but there should be no focal tenderness, guarding, or rebound tenderness unless ischaemia is developing.
The differential diagnoses for bowel obstruction include:
- Paralytic (functional) Ileus
- Toxic megacolon (dilation of bowel without mechanical obstruction)
- Intestinal pseudo-obstruction (inability of the bowel smooth muscle to contract sufficiently for peristalsis)
All patients with suspected bowel obstruction require FBC, CRP, U&Es (hypokalaemia and high urea may be present), and a Group and Save or Crossmatch (if patient is taken to theatre).
An arterial blood gas can be useful to evaluate the signs of ischaemia (high lactate) or for the immediate assessment of any metabolic derangement (secondary to dehydration or excessive vomiting).
A plain abdominal X-ray (AXR) is typically the first line investigation for bowel obstruction. The AXR findings seen in a patient with bowel obstruction are:
- Small bowel obstruction:
- Dilated bowel (>3cm)
- Central abdominal location
- Valvulae conniventes visible (lines completely crossing the bowel)
- Large bowel obstruction:
- Dilated bowel (>6cm, or >9cm if at the caecum)
- Peripheral location
- Haustral lines visible (lines not completely crossing the bowel, ‘indents that go Halfway are Haustra’)
An incompetent ileocaecal valve in a large bowel obstruction may show concurrent large and small bowel dilatation on AXR. An erect chest x-ray may also be requested to assess for free air under the diaphragm if clinical features suggest a bowel perforation.
CT scans are more useful than AXRs as they are (1) more sensitive for bowel obstruction; (2) can differentiate between mechanical obstruction and pseudo-obstruction; (3) can demonstrate the site and cause of obstruction (hence extremely useful for operative planning; and (4) may demonstrate the presence of metastases if caused by a malignancy (which is likewise extremely useful in operative planning).
Contrast fluoroscopy has been advocated in adhesional small bowel obstruction. It has been shown to predict quite reliably whether or not the obstruction will settle and some studies have shown a therapeutic benefit of the contrast itself, although this is controversial. However, they can be more difficult to obtain than CT scans and their use is less wide-spread.
The definitive management of bowel obstruction is dependent on the aetiology and whether it has been complicated by bowel ischaemia, perforation, and/or peritonism.
In the absence of signs of ischemia or strangulation, initial management is essentially conservative and is often referred to as a ‘drip and suck’ management:
- Make the patient nil-by-mouth (NBM) and insert a nasogastric tube to decompress the bowel (‘suck’)
- Start IV fluids and correct any electrolyte disturbances (‘drip’).
- These patients are often significantly dehydrated, so adequate fluid replacement is essential (up to 4 litres may be required in the first 24 hours).
- Urinary catheter and fluid balance.
- Analgesia as required with anti-emetics.
Adhesional small bowel obstruction resulting from previous surgery is treated conservatively in the first instance (unless there is evidence of strangulation / ischaemia), with a success rate of around 80%.
Large bowel obstruction or small bowel obstruction in a patient who has not had previous surgery (and therefore is said to have a “virgin abdomen”) rarely settles without surgery.
Surgical intervention is indicated in patients with:
- Suspicion of intestinal ischaemia or with a closed loop bowel obstruction
- Small bowel obstruction in a patient with a virgin abdomen
- A cause that requires surgical correction (e.g. a strangulated hernia or obstructing tumour)
- If patients fail to improve with conservative measures (≥48 hours)
The nature of surgical management will depend on the underlying cause but generally involves a laparotomy.
If resection of bowel is required, the re-joining of obstructed bowel is often not possible and a stoma is necessary.
The complications of bowel obstruction include:
- Bowel ischaemia
- Bowel perforation, leading to faecal peritonitis (high mortality)
- Intra-abdominal abscess from anastomotic leakage post-op
- Any pain originally colicky in a suspected case of bowel obstruction that is now constant in nature or worse on movement should be a “red flag” that ischaemia may be developing
- Focal tenderness indicates ischaemia and is a key warning sign. Patients with bowel obstruction may be uncomfortable on palpation due to the discomfort from pressing on a distended abdomen, but there should be no focal tenderness, guarding, or rebound tenderness.
- A closed loop bowel obstruction is a surgical emergency
- Early recognition of those patients with impending strangulation and ischaemia is essential as early surgery will prevent the need for bowel resection.