Post-Operative Constipation

Constipation is a common post-operative complaint and is one that all doctors across all specialities should assess for regularly.

In the post-operative setting, most cases of constipation are caused by paralytic ileus. However, it is always important to exclude other significant causes.

In this article, we shall look at the aetiology, clinical features and management of post-operative constipation.


Aetiology

The main causes of constipation that are seen on the surgical ward include:

  • Post-operative ileus – the most common cause in the post-operative setting
  • Physiological – due to factors such as a low fibre diet or poor fluid intake
  • Iatrogenic – medications such as opioid analgesia, anticonvulsants, or antihistamines
  • Functional – mainly painful defecation (such as anal fissures)
  • Pathological – such as bowel obstruction, hypercalcaemia, or hypothyroidism)

Risk Factors

The risk factors for developing post-operative constipation include:

  • Intra-operative factors (e.g. excessive bowel handling)
  • Poor diet or reduced fluid intake
  • Reduced mobility
  • Age
  • Medication (as above)

Clinical Features

Constipation will normally be reported by the patient or observed from the patient’s stool charts. However, in worsening cases, patients may also present with abdominal distension, nausea and vomiting, anorexia, or even abdominal pain.

Fig 1 - The Bristol stool chart, used in the UK to monitor bowel habit.

Figure 1 – The Bristol stool chart, used in the UK to assess stool type

Most patients will have no clinical signs on examination; only severe cases are likely to have abdominal distension or tenderness (both secondary to faecal impaction).

A Digital Rectal Examination (DRE) is essential for any patient with post-operative constipation (despite rarely actually being routinely performed in clinical practice), to assess the degree of faecal impaction.

Whilst most cases of post-operative constipation will be benign, a small proportion may have a serious underlying pathology present. Ensure to assess for signs of bowel obstruction  or peritonism with any assessment of constipation.


Investigations

Most cases of post-operative constipation are benign in nature and can be made as a clinical diagnosis, with no further investigations required.

If no cause can obviously be identified or it is severe/resistant to treatment, routine bloods (TFTs, serum Ca2+) may be requested.

Abdominal radiograph or CT scans are generally not indicated unless a pathological cause of the post-operative constipation is suspected. Any imaging may show faecal impaction (yet this is not an indication for the image request).

Fig 2 - X-ray image of constipation in a child. The faecal matter is opaque white, surrounded by black bowel gas.

Figure 2 – X-ray image of constipation in a child. The faecal matter is opaque white, surrounded by black bowel gas.


Management

In the vast majority of cases, post-operative constipation can be treated via conservative measures alone. These include ensuring adequate hydration, ensuring sufficient dietary fibre, and early mobilisation.

Assuming any pathological cause of constipation has been ruled out, most patients should have their bowels monitored, and eventually they should return to normal function.

Pharmacological

Laxatives can be used if the patient remains constipated; the choice of laxative depends on suspected underlying cause and stool consistency on PR examination. The major types of laxatives are:

  • Osmotic laxatives – increase the amount of fluid in the bowel thereby softening stool. e.g. lactulose, movicol
  • Stimulant laxatives – stimulate the bowel to contract thus expelling faeces. e.g. senna, picosulphate
  • Bulk forming laxatives – help stool to retain water thereby softening stool. e.g. ispaghula husk
  • Rectal medications – glycerin suppository (stimulant), phosphate enema (stimulant)

Patients with a hard stool and chronic constipation issues will benefit from a stool-softening laxative, such as movicol or lactulose, but may require glycerine suppositories to help soften the rectal stool initially.

Patients with post-operative ileus, opioid-induced constipation, or a soft stool will benefit from a stimulant laxative, such as senna or picosulphate.

In resistant cases, additional therapy can be given via manual evacuation or an enema.


Prophylaxis

Opioid analgesia should be avoided where possible and other opioid-sparing agents used. Prophylactic stimulant laxatives, such as senna, should be used for patients on opioid analgesia, especially in the elderly.

Key Points

  • Constipation is a common post-operative complaint and in the post-operative setting the most common cause is paralytic ileus
  • Most cases are multi-factorial and all should be addressed to ensure optimal management
  • Ensure to perform a digital rectal examination on all cases of constipation
  • Most cases can be treated conservatively, with use of laxatives as required, tailored to the underlying cause of the constipation

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