Bowel obstruction refers to complete or partial disruption of the normal flow of gastrointestinal content.
It may occur in the small or large intestines, and is secondary to mechanical obstruction and/or peristaltic failure (non-mechanical).
Classifying bowel obstruction depends on the location, segments of intestines involved, underlying aetiology and whether blood flow is compromised, which could lead to ischaemia and perforation.
Mechanical (or dynamic) bowel obstruction refers to physical obstruction to normal flow of bowel contents.
The most common cause of mechanical small bowel obstruction within the western world is post-operative adhesions. These refer to strands of fibrous tissue that form following surgery and can lead to the abnormal adhesion between intra-abdominal tissue.
Another major cause of mechanical small bowel obstruction are hernias (e.g. inguinal hernias). Loops of bowel can become trapped within the hernial sac leading to obstruction and potentially strangulation and infarction if not managed urgently.
Other causes of small bowel obstruction are listed below:
It is estimated that 60% of patients with mechanical large bowel obstruction occurs secondary to colorectal malignancy.
Other causes of mechanical large bowel obstruction are listed below:
Non-mechanical (or adynamic) bowel obstruction refers to a dilatation of the bowel in the abscence of mechanical blockage through failure of normal peristalsis.
Non-mechanical bowel obstruction is caused by impairment of the muscles or nerves responsible for peristalsis. It may be divided into a number of clinically distinct conditions.
Terminology varies widely here and some texts would only consider paralytic ileus here. We will also discuss acute colonic pseudo-obstruction and toxic megacolon.
Paralytic ileus is the general slow-down of the intestines and affects the entire intestinal tract (small and large bowel).
Its aetiology is poorly understood though it is commonly seen post-operatively. Other triggers include abnormal electrolytes and systemic upset.
Also termed Ogilvie syndrome, ACPO refers to the dilations of the colon in the absence of mechanical obstruction. Its aetiology is poorly understood and likely multifactorial. A combination of systemic illness, medications and biochemical abnormalities are implicated.
The condition is also often seen in the post-partum setting, particularly following caesarian section.
The classical features of bowel obstruction include abdominal pain, distension, vomiting & obstipation.
It is important to remember that each patient presents uniquely and no one feature is diagnostic. If the overall picture fits with a diagnosis of bowel obstruction arrange surgical review and consider imaging options.
Signs of systemic upset may be present if significant dehydration or a complication (e.g. perforation, ischaemia) has occured.
Biochemical abnormalities frequently seen in bowel obstruction include a raised lactate and inflammatory markers.
As bowel obstruction typically presents with acute abdominal pain it is important to investigate other potential causes. Furthermore, bowel obstruction can cause significant dehydration, electrolyte derangements and complications such as perforation. Therefore, investigations are essential to help exclude and treat these potential issues.
NOTE: Lactate is a key biochemical marker in bowel obstruction, acting as an indicator for ischaemia. DO NOT however be deceived by a normal lactate which can be found despite significant ischaemia having occurred. As always it must be interpreted in the wider clinical context.
In todays NHS, CT is (normally) a readily available investigation that can be arranged and completed in a relatively short period of time.
At a basic level, being able to differentiate between dilatation of the small or large bowel is essential for all medical practitioners.
It is important to note that if bowel obstruction is still suspected in patients with an equivocal X-ray, they may require further imaging in the form of computed tomography (CT).
CT imaging of the abdomen provides a more comprehensive assessment of the specific site, severity, underlying aetiology and complications in bowel obstruction.
The additional benefit of CT imaging is that it helps to differentiate from the many other causes of acute abdominal pain, which present through the emergency department.
The finer details of CT imaging in patients with bowel obstruction is beyond the scope of these notes.
NOTE: Patients undergoing emergency laparotomies based on CT findings should, where possible, have these reported by a consultant radiologist.
The P-POSSUM provides an estimate of morbidity and mortality in patients undergoing surgical management
The management of bowel obstruction largely depends on the underlying aetiology and whether there is any evidence of complications (e.g. ischaemia, perforation).
Surgical management is dependent on numerous factors including the underlying aetiology, patient factors and the presence of complications. It should be noted emergency surgery for bowel obstruction carries significant morbidity and mortality which must be conveyed to the patient and next of kin.
Supportive therapy should be employed in all patients presenting with bowel obstruction, which involves bowel decompression and fluid resuscitation.
‘Drip and suck’: Dilatation of the proximal part of the GI tract is associated with excessive secretion and accumulation of gas leading to distention and vomiting. The use of a nasogastric tube (with regular aspirations) helps decompress the stomach and prevent aspiration. Fluid resuscitation is essential due to the large amount of third spacing that occurs in bowel obstruction because of compression of lymphatic and vascular beds leading to excessive bowel wall oedema.
Other essential aspects in the management of patients with bowel obstruction include:
Reversible causes should be considered and treated. Any electrolyte abnormality should be corrected and adequate IVF administered. NG tube decompression is often indicated. Exacerbating agents such as opiate analgesia should be reviewed.
Commonly seen in the post-operative setting, it tends to settle with conservative management.
The treatment of ACPO involves identification and treatment of any underlying cause.
Neostigmine, a cholinesterase inhibitor, may be given to encourage motility. Endoscopic colonic decompression can be used in those failing to respond.
Those at increasing risk of or who have developed complications (e.g. necrosis, perforation) will typically need surgical management if they are appropriate candidates.
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