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Chapter: Medicine Study Notes : Gastro-Intestinal


Infrequent bowel action (ie > 3 days) or difficult/painful defecation



·        = Infrequent bowel action (ie > 3 days) or difficult/painful defecation


·        Affects 3% in young adults ® 20% in elderly

·        Physiology:


o  Muscular movements: segmentation mixes bowel contents. Peristalsis moves it along. Mass movements occur once or twice a day (usually after a meal)


o  Faecal mass in rectum ® internal anal sphincter opens by reflex. External sphincter remains contracted voluntarily, but will tire quickly ® leakage


o  Defaecation requires relaxation of external sphincter, pelvic floor muscles and abdominal straining


o  Motility affected by sympathetic (®­segmentation) and parasympathetic (® ­peristaltic and mass movement) system, hormones, fibre, acid pH, lactobacilli


o  Age related changes: mucosal atrophy (®¯mucus), muscular atrophy, etc

·        Assessment:


o   History: What do they mean? Frequency, stool consistency, presence of blood/mucus, ease of evacuation, onset of symptoms, and drug history.


o   In elderly screen for risk factors: ¯fibre following changed diet or false teeth, can‟t shop or prepare food, ¯physical activity ® ¯transit time, dehydration, neurological disease (eg diabetic neuropathy)

o   Exam: systemic disease, abdominal exam and perianal sensation


o   Investigations: Usual, plus blood tests to exclude anaemia, hypothyroidism and electrolyte abnormality


·        Management:

o   Review medication, eg:

§  Opioids

§  Anticholinergics (eg antihistamine, antiemetics)


§  Serotonin antagonists

§  Phenothiazines

§  Tricyclic antidepressants


o   Bowel retraining. Try during high motility periods – first thing in the morning and after meals. Exercise to improve abdominal muscles


o   Adequate fibre and fluid

o   Laxatives:


§  Hydrophilic bulk forming agents, eg Normacol, Metamucil. Must also take adequate water. Not useful in palliative care (patients are too sick to eat it)


§  Osmotic agents, eg lactulose or sorbitol ® not broken down in small bowel ® ­osmotic gradient ® ­water content. Take 1 to 2 days to act. Safest agent in the long term


§  Stool softeners and lubricants. Take 1 to 3 days to act. Act as detergents top increase water penetration and thus softening of the stool. Eg docusate agents, Coloxyl (a detergent effect ® breaks up stool, may be hepatotoxic) and lubricants. Oil based lubricants (eg paraffin) can affect vitamin and drug absorption and be aspirated


§  Stimulants and irritants ® ­peristalsis and net fluid secretion. Eg Senna. Take 6 to 12 hours to act. Stimulates the myenteric plexuses to produce peristalsis. Avoid irritant laxatives unless impaction, severe muscle weakness. Long term use of laxatives causes constipation by damaging the nerve supply of the gut


§  Locally acting agents eg glycerol suppository at peak motility time. Can have osmotic and irritant agents

§  Investigational agents such as cisapride (prokinetic agent)

o   Rectal Laxatives:

§  For faecal impaction


§  On exam will either have a loaded rectum or ballooning of the rectum (dilated distally Þ impacted further up)


§  Types:

·        Glycerine suppositories: soften stool by lubrication and osmosis

·        Bisacodyl (Dulcolax) suppositories: Causes peristalsis

·        Sodium Phosphate enemas

·        Oil Enemas




·        Dietary Fibre: the undigested and unabsorbed polysaccharide (cereal, fruit, vegetable) that remains at the end of the small bowel. Contains cellulose and non-cellulose polysaccharides, lignin, gums and waxes 

·        Worth a trial in constipation, IBS (esp. with constipation) and non-ulcer dyspepsia of dysmotility type

·        Get good 24 hour dietary history 

·        Intake from cereal source is 4 or 5 times greater than fruit or vegetables. It is also less fermented in large bowel

·        Ideal level = 30g/24 hours.  Usual NZ adult approx. 15 g/24 hours

·        20 g of fibre in 6 tablespoons of bran, 2 Weetbix or 4 large thick slices of whole meal bread

·        Suggestions for use: 

o   Increase SLOWLY (i.e. aim for a full bowl of All bran in 2-3 months): otherwise bloating, distension, gas

·        Take fibre every day

·        Necessary amount is not a weight – but the amount necessary to keep stools soft

·        Drink lots of water (2 L per day is recommended)

·        Will increase gas (fibre promotes bacterial growth): take stairs not lift!


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Medicine Study Notes : Gastro-Intestinal : Constipation |

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