Gastroenterology - Disorders of the colon and rectum Flashcards
What is the main function of the large intestine?
The main role of the colon is absorption of water and electrolytes and propulsion of contents from the ceacum to the anorectal region. About 9000ml of water containing electrolytes enters the GIT each day; the majority from gastrointestinal secretions (stomach, pancreas, bile, intestinal secretion) and only a small amount from the diet. Most is absorbed in the small intestine and only about 1500ml passes through the ileocaecal valve into the colon, of which about 1350ml is normally absorbed.
What is constipation?
This is a consistent difficulty in defecation. It is common in the elderly (associated with immobility and poor diet) and in young women (associated with slow transit or post partum pelvic floor abnormalities).
Specific definitions are infrequent passage of stools (<3/week - Rome criteria), straining, passage of hard stools, incomplete evacuation and sensation of anorectal blockage. In many patients it is part of IBS.
In the elderly, constipation can present as:
- confusion
- overflow diarrhoea
- abdominal pain
- urinary incontinence
What is functional constipation?
This is chronic constipation without a known cause. It is also known as primary constipation or idiopathic constipation.
What is secondary constipation?
This is constipation caused by drugs or other medical conditions. It is also known as “organic constipation”.
What is faecal loading, or impaction?
This is retention of faeces to the point that spotaneous evacuation is unlikely. Retained faeces are usually palpable on abdominal examination, and may be felt on internal rectal examination.
What is meant by the term overflow incontinence?
This is the leakage of loose stools around impacted faeces. Small quantities of stool are passed frequently and without sensation. It is also known as “bypass soiling”
What is a normal frequency of bowel movements in adults?
Bowel movements occurring less than 3 times per week is one of the Rome criteria for constipation
What causes of secondary constipation should I consider in adults?
Drugs
Predisposing factors
Organic causes
What drugs are associated with constipation?
Many drugs are constipating, some of the most common are: Aluminium antacids Antimuscarinics (e.g. procyclidine) Antidepressants (most commonly TCAs) Some antiepileptics (e.g. carbamazepine, gabapentin) Sedating antihistamines Antipsychotics Diuretics Iron supplements Opioids Verapamil
What factors predispose to constipation in adults?
Physical factors:
- mild pyrexia, dehydration, immobility
- position for defecation
Psychological factors:
- anxiety
- depression
- somatisation
- eating disorders
Social factors:
- low fibre diet
- lack of exercise or reduced mobility
What organic causes of secondary constipation should I consider in adults?
In adults with no drug causes for their constipation, consider:
1) Endocrine and metabolic - diabetes, hypercalcaemia, hypokalaemia, uraemia, hyperparathyroidism
2) Myopathic conditions - amyloidosis, myotonic dystrophy
3) Neurological disease - autonomic neuropathy, CVA, MS, Hirschsprungs disease, PD
4) Structural problems - anal fissures, strictures, haemorrhoids, colonic strictures (following diverticulitis surgery), cancer, IBD
How do I know my patient has constipation?
Constipation is diagnosed in adults when defecation is unsatisfactory because of infrequent stools, difficult stool passage, or seemingly incomplete defecation.
In the elderly constipation may present as confusion, overflow diarrhoea, abdominal pain, urinary retention.
Functional constipation is diagnosed by ruling out drug or organic causes of constipation.
How is faecal loading/ impaction diagnosed?
On history. The person reports:
- passing hard, lumpy stools, either large and infrequent (for example every 7–10 days), or small and relatively frequent (for example every 2–3 days).
- having to use manual methods to extract faeces.
- overflow faecal incontinence, or loose stool
On examination:
- faecal masses are palpable abdominally or peri-anally, or on internal rectal examination
What investigations should I make to diagnose constipation?
Initial evaluation is with history and examination, include DRE during which the patient should be asked to strain. A patient with a defecatory disorder has paradoxical contraction rather than normal relaxation of the puborectalis and external anal sphincter during straining, which may prevent defecation.
Routine blood tests, radiography and endoscopy are not usually indicated in the evaluation of patients with constipation without alarm symptoms: these include
- rectal bleeding
- anaemia
- recent onset constipation in middle aged (>55), esp if associated with sense of incomplete evacuation
How should I manage short term constipation in adults?
Adjust any constipation causing medication
Dietary advice about increasing fibre and adequate fluid intake
Oral laxatives if dietary measures are ineffective:
- start treatment with bulk forming laxative (adequate hydration is necessary)
- if stools remain hard, switch to osmotic laxative
- if stools are soft but patient still finds it hard to pass, add a stimulant laxative
If a person has opioid induced constipation:
- avoid bulk forming laxatives
- use an osmotic laxative and a stimulant laxative
Advise the patient that laxatives can be stopped once stools become soft and are easily passed.
How should I manage chronic constipation in adults?
Laxatives are indicated if:
- lifestyle measures are insufficient
- for people taking a constipating drug that cannot be stopped
- for people with secondary causes of constipation
- as “rescue” medications in patients with faecal loading
Start treatment with a bulk forming laxative (maintain hydration).
If stools remain hard, switch to osmotic laxative, macrogol is first line, lactulose second.
If stools are soft but the person is still finding them difficult to pass, then add a stimulant laxative.
The dose of laxative can be up or down titrated to achieve 1-2 soft stools per day.
What agent can be considered If at least two laxatives (from different classes) have been tried at the highest tolerated recommended doses for at least 6 months?
Prucalopride (women only)
- invasive methods should be considered
- reassess if no result after 4 weeks
Lubiprostone
- invasive methods should be considered
- reassess if no result after 2 weeks
Both have NICE prescribing criteria.
How should I manage faecal loading/ impaction in adults?
For hard stools consider using high doses of oral macrogols.
For soft stools or hard stools that persist after a few days of macrogol therapy, consider adding a stimulant laxative.
If response to oral agents is insufficient, consider:
- a suppository - e.g. bisacodyl
- a mini enema - e.g. docusate
If response is still insufficient consider using an enema (sodium phosphate), needs to be repeated multiple times
When and how should I stop treatment for chronic constipation in adults?
Laxatives can be slowly withdrawn when regular bowel movements occur without difficulty (for example, 2–4 weeks after defecation has become comfortable and a regular bowel pattern with soft, formed stools has been established).
The rate at which doses are reduced should be guided by the frequency and consistency of the stools. Weaning should be gradual in order to minimize the risk of requiring ‘rescue therapy’ for recurrent faecal loading. Laxative medication should not be suddenly stopped.
If a combination of laxatives has been used, reduce and stop one laxative at a time. Begin by reducing stimulant laxatives first, if possible. However, it may be necessary to also adjust the dose of the osmotic laxative to compensate.
What is faecal incontinence?
This is recurrent, uncontrolled passage of stool or flatus. continence depends on a number of factors, including mental function, stool volume, and consistency, structural and functional integrity of the anal sphincters, puborectalis muscle, pudendal nerve function, and anorectal sensation.
Faecal impaction is a common cause of faecal incontinence in the elderly. Anal sphincter tears or trauma to the pudendal nerve can occur after childbirth or anal surgery (e.g. for haemorrhoids). Impaired rectal sensation occurs with diabetes mellitus, multiple sclerosis, dementia and spinal cord injuries.
Detailed investigations are needed to confirm the underlying cause.
What is diverticular disease?
Pouches of mucosa extrude through the colonic muscular wall via weakened areas near blood vessels to form diverticula. The term diverticulosis means the presence of diverticula. Diverticular disease is a condition where diverticula cause intermittent lower abdominal pain, without inflammation and infection. Diverticulitis refers to inflammation, which occurs when faeces obstruct the neck of the diverticulum. Diverticula are common, affecting 50% of the population over 50 years of age.
