Constipation

Overview

•Classic and frequently overlooked cause of acute-onset confusion in elderly patients - visceral discomfort and autonomic stress from colonic distension triggers delirium in a vulnerable brain

•Clues: palpable fullness in the left iliac fossa, mild abdominal discomfort, no fever, normal observations

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Always consider constipation before attributing new confusion to infection or dementia progression - it is one of the most common presentations in elderly inpatients.

Presentation

•Fewer than 3 bowel movements per week

•Hard/lumpy stools (Bristol Type 1-2), straining, sensation of incomplete evacuation

•Abdominal bloating and discomfort; palpable faecal mass in left iliac fossa (sigmoid colon)

•Overflow diarrhoea - liquid stool leaks around an impacted faecal mass; do not mistake for infective diarrhoea

Management

•Lifestyle (all patients): increase dietary fibre, fluid intake (at least 1.5-2 litres/day), physical activity, regular toilet routine

•Faecal impaction: oral macrogol (high-dose) first-line; if fails, rectal interventions (phosphate enema, glycerol suppositories, or manual evacuation)

Red flag features - refer urgently

•Rectal bleeding (unexplained), unintentional weight loss, new change in bowel habit in patients >50 years

•Iron-deficiency anaemia without clear cause, palpable abdominal or rectal mass

Laxative stepped approach - standard (non-opioid) constipation

First-line
1Ispaghula husk (bulk-forming) - absorbs water to increase stool bulk and stimulate peristalsis; must be taken with adequate fluid; avoid if poor fluid intake or suspected obstruction
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Second-line (if bulk-forming fails)
1Macrogol (osmotic) - draws water into bowel lumen, softens stool and stimulates peristalsis; preferred over lactulose due to less bloating
2Lactulose (osmotic) - alternative if macrogol not available/tolerated; causes more bloating and flatulence
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Third-line (add to osmotic if insufficient response)
1Senna or bisacodyl (stimulant) - stimulate myenteric plexus to increase peristalsis; can cause cramping; licensed for short-term use
2Docusate (stool softener/mild stimulant) - primarily for chronic constipation or as enema in faecal impaction
3Prucalopride (5-HT4 agonist) - prokinetic; consider if laxatives have failed and NICE prescribing criteria met

Opioid-induced constipation

•Bulk-forming laxatives are NOT effective - opioids suppress peristalsis centrally, not by reducing stool bulk

•First-line: senna (stimulant) + osmotic laxative (macrogol or lactulose)

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Prophylactic laxatives should be co-prescribed whenever opioids are started - do not wait for symptoms to develop.

Constipation in pregnancy

•First-line: ispaghula husk; lactulose is an alternative

•Senna - avoid in first trimester, use with caution thereafter; docusate and macrogol on specialist advice only

Laxative comparison

Key laxatives - class, mechanism and when to use
DrugClassWhen to use
***Ispaghula husk***Bulk-formingFirst-line, non-opioid constipation; first-line in pregnancy
***Macrogol***OsmoticSecond-line (non-opioid); first-line for faecal impaction (high dose); add to senna in opioid-induced
***Lactulose***OsmoticSecond-line if macrogol not tolerated; causes more bloating
***Senna***StimulantFirst-line for opioid-induced constipation (with osmotic); third-line non-opioid; avoid in first trimester
***Docusate***Stool softener / mild stimulantChronic constipation; enema for faecal impaction

Drug	Class	When to use
*Ispaghula husk*	Bulk-forming	First-line, non-opioid constipation; first-line in pregnancy
*Macrogol*	Osmotic	Second-line (non-opioid); first-line for faecal impaction (high dose); add to senna in opioid-induced
*Lactulose*	Osmotic	Second-line if macrogol not tolerated; causes more bloating
*Senna*	Stimulant	First-line for opioid-induced constipation (with osmotic); third-line non-opioid; avoid in first trimester
*Docusate*	Stool softener / mild stimulant	Chronic constipation; enema for faecal impaction