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Understanding constipation


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It may seem mundane, but successfully managing constipation can make a massive difference to the lives of families. Although it’s all about faeces; it can lead on to other issues including pain and social embarrassment. Time spent managing this can have a knock on effect on the whole family, as well as the patient.

See our other Constipation Week posts

What is normal?

Normal bowel movements vary with age:

AgeStools per dayMouth to rectum time (hrs)
<2 years<216
<3 months2 to 38.5
0-1 week4-
  • The first stool is normally passed within 36 hours of birth
  • Breast-fed infants can have a huge range of normal frequency from 10 stools per day to 1 stool every 10 days
  • Formula-fed infants tend to have more bowel actions than breast-fed infants

As stool goes round the colon and out to the rectum, water is reabsorbed. So by the end, it will be smaller and harder than it was when it was at the appendix (which is why colostomy bags initially have a watery output). Hard poo is sore to pass so children often don’t want to pass it at all. Therefore it collects, and stays in the bowel longer getting more and more impacted. If stools takes a longer time to pass through the colon, it will become harder and drier. So the treatment is based around adding water to it, and getting things moving.

There are 3 periods when children are prone to developing constipation: the introduction of solids; toilet training; and starting school. These all have the potential for defecation to be an unpleasant experience, prompting the child to consciously or subconsciously avoid repeating it.

This painful defecation can then leading to avoidance of defecation which results in stool accumulation in the rectum. The stool becomes harder and therefore more painful to pass. Chronic rectal distension leads to relaxation of the internal anal sphincter and semi-solid stool leaks or soiling. Finally, the rectum is unable to generate enough pressure to pass stool.

Causes can be split into functional and organic.

This is an umbrella term for difficult, infrequent, or incomplete defecation with no structural or biochemical cause. It accounts for 95% of constipation.

This is constipation associated with an organic condition which accounts for 5% of constipation. Organic causes are anatomic malformations; metabolic; gastrointestinal; neurological; connective tissue disorders; drugs; miscellaneous.

There are several mechanism for this:

  • Infant dyschezia – straining with soft stools in a less than 6-month-old
  • Functional constipation in infants and preschool children – pebble-like stools less than twice a week
  • Functional faecal retention – holding on, soiling, cramps for at least 12 weeks
  • Functional non-retentive faecal soiling – inappropriate soiling without retention, emotional issues

Reservoir constipation is where the stools collect in the bowel and start to get larger and larger.

This is commonly seen in 5-10 year old boys.

The history is often of passing a large diameter stool every 1-2 weeks. Often because it’s painful to pass these, children can be scared to pass stools and hold them in. This causes the rectum to stretch due to pressure on the rectum. Then the nerves in the wall of the rectum stretch causing a problem with the internal sphincter. A problem with the internal sphincter means that children may be able to hold onto their stools on the journey home (using their external sphincter) but then as soon as they relax at home they will get some soiling.

These children have a numb, toneless rectum which means that they then don’t realise when it’s time to pass stools.

Reservoir constipation can occur because children are too busy to poo, find the toilets too dirty to use (or not private enough), or are scared of pain.

There are other causes of constipation too. For example, there are some psychological causes of encopresis and also some neurological causes. Any clinical examination should be careful to look for neurological signs: check for spina bifida occulta, look for any sinuses or fissures; look for a patulous anus. 

About the authors

  • Tessa Davis is a Consultant in Paediatric Emergency Medicine at the Royal London Hospital and a Senior Lecturer at Queen Mary University of London.


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