Faecal Impaction

Faecal impaction is a large, hard, dry mass of stool in the rectum (and sometimes the sigmoid colon) that cannot be passed spontaneously, usually from chronic constipation. Liquid stool from above the mass may leak around it, causing overflow diarrhoea and faecal incontinence, which is often mistaken for diarrhoea.

• It affects up to 40% of older adults in care homes and hospitals, and is common in children with chronic constipation (up to 30 to 40% of those with chronic constipation present with impaction), in neurologically impaired and immobile patients, and in patients taking opioids.
• Risk factors: older age, immobility, low fibre and fluid intake, dementia, stroke, spinal cord injury, Parkinson disease, multiple sclerosis, diabetes, hypothyroidism, hypercalcaemia, hypokalaemia, depression, psychiatric illness, behavioural withholding (children, after painful defecation), pelvic floor dysfunction, anorectal disease (fissure, haemorrhoids, stricture), previous bowel surgery, and medicines (opioids, anticholinergics, antihistamines, tricyclic antidepressants, antipsychotics, calcium channel blockers (verapamil), iron, aluminium and calcium antacids, ondansetron, clozapine, and diuretics).
• Mechanism: prolonged stool retention leads to water absorption and harder stool, rectal distension and loss of the sensation of fullness (reduced rectal sensation), and impaired rectal emptying, which perpetuates impaction. The internal anal sphincter relaxes reflexly with a large mass, leading to leakage.
• Complications: urinary retention and urinary tract infection, delirium, abdominal pain and distension, bowel obstruction, stercoral ulceration with bleeding or perforation (a surgical emergency), haemorrhoids and anal fissure, faecal incontinence, rectal prolapse, aspiration from vomiting, and rarely sepsis and death.

• Chronic constipation with infrequent hard stools (fewer than 3 per week), straining, a feeling of incomplete evacuation, and rectal fullness, with a sudden onset of liquid or semi-formed leakage, urgent loose stools, or smearing of underwear (overflow) in the setting of constipation. Many patients and carers report "diarrhoea".
• Abdominal pain and cramps, bloating, distension, nausea, vomiting, loss of appetite, and a palpable faecal mass in the lower abdomen (left iliac fossa and suprapubic).
• Confusion, agitation or delirium in older adults, urinary symptoms (retention, frequency, incontinence), and back pain.
• Examination: abdominal distension and tenderness, a palpable hard mass that is indentable, bowel sounds that are normal or hyperactive, and, on digital rectal examination, a rectum filled with hard or putty like stool, or an empty rectum with a high impaction. Check for fissures, haemorrhoids, masses, and anal tone.
• Differential diagnosis: bowel obstruction, colorectal cancer, infectious or inflammatory diarrhoea, inflammatory bowel disease, ischaemic colitis, volvulus, diverticular disease, megacolon (Hirschsprung disease in children, Chagas disease, acquired megacolon), urinary retention, ovarian or other abdominal masses, and pregnancy.
• Red flags: severe abdominal pain, vomiting and absolute constipation (obstruction), fever, peritonism or rigidity (perforation), rectal bleeding, weight loss, anaemia, a family history of colorectal cancer, new constipation after age 50, a rectal mass, hypotension and tachycardia, and acute kidney injury.

• Clinical, with digital rectal examination as the key test (after explaining the procedure, with consent, a chaperone, and privacy). If the rectum is empty but impaction is suspected, a high faecal mass may be palpable abdominally.
• Abdominal X-ray (plain film) can show faecal loading and exclude obstruction, megacolon, or perforation, particularly when the examination is inconclusive or in a patient with severe pain. Use CT in suspected perforation, stercoral colitis, or obstruction.
• Blood tests for secondary causes and complications: full blood count, urea, creatinine and electrolytes (including calcium, potassium), glucose, thyroid function tests, and, if unwell, C-reactive protein and lactate.
• Urinalysis for urinary tract infection in confused or retaining patients, and bladder scan for residual volume.
• Review all medicines, and screen for depression, dementia and eating habits. Carry out colonoscopy or CT colonography for red flags (age above 50 years with change in bowel habit, bleeding, weight loss, anaemia).
• Specialist anorectal tests (manometry, balloon expulsion, defecography) for refractory constipation after impaction is cleared, and a colonic transit study when slow transit is suspected.

• Disimpaction (clear the rectum and colon first, then start maintenance therapy):
  • Rectal therapy first when the mass is in the rectum:
    • Glycerol (glycerin) suppository 4 g (adults) inserted into the rectum, or bisacodyl suppository 10 mg once daily, to soften and stimulate. Insert beyond the stool mass, against the rectal wall.
    • Docusate sodium mini enema 120 mg in 10 mL, or sodium citrate micro enema 5 mL, once or twice daily.
    • Arachis oil enema 130 mL retained overnight, to soften hard stool, followed by a phosphate or stimulant enema in the morning (avoid in peanut allergy).
    • Sodium phosphate enema 133 mL once daily (maximum 1 dose in 24 hours, for 3 days at most), only in patients with normal renal function, no dehydration and no electrolyte disturbance. Avoid in the elderly with heart or renal disease, in children under 3 years, in bowel obstruction, and in inflammatory bowel disease, because of the risk of hyperphosphataemia, hypocalcaemia and acute kidney injury.
    • Tap water or warm saline enema (500 to 1000 mL) is a safer alternative in frail patients.
  • Oral high dose macrogol (polyethylene glycol 3350 with electrolytes): 8 sachets per day dissolved in 1 L of water (each sachet in 125 mL), taken over 6 hours or less, for up to 3 days (adults). Reduce the dose or stop if diarrhoea develops. Avoid high doses in heart failure, renal impairment and in those with swallowing difficulty or risk of aspiration, and consider nasogastric administration when necessary under supervision.
  • Add a stimulant laxative when needed: bisacodyl 10 to 20 mg orally at night, or senna 15 to 30 mg orally at night (7.5 to 15 mg in the elderly), or sodium picosulfate 10 mg orally at night.
  • Manual evacuation (digital removal) under local anaesthetic gel (lidocaine 2% gel) or sedation, after other options have failed, in severe or painful impaction, performed by trained clinicians with sensitivity and care for vagal reaction (bradycardia and syncope), and with monitoring.
  • Admit for severe abdominal pain, vomiting, signs of obstruction, perforation or stercoral colitis, haemodynamic instability, acute kidney injury, or failure of outpatient measures. Surgical review for stercoral perforation or obstruction.
  • Check response with abdominal and rectal examination after treatment, and repeat the process until the rectum is clear.
• Maintenance after disimpaction (essential to prevent recurrence, usually for months):
  • Macrogol 1 to 3 sachets daily (half to 1 sachet in frail patients), adjusted to produce a soft, formed stool daily to every other day.
  • Add or alternate with a stimulant laxative if the response is poor: senna 7.5 to 15 mg orally at night, or bisacodyl 5 to 10 mg orally at night.
  • Lactulose 15 mL orally twice daily or osmotic laxatives are alternatives, with bloating as a limitation. Magnesium hydroxide 30 to 60 mL daily is used with caution (avoid in renal impairment).
  • Avoid bulk forming laxatives (ispaghula husk) in immobile patients with low fluid intake or during impaction, because they can worsen obstruction.
  • Opioid induced constipation: continue the laxatives, and add naloxegol 25 mg orally once daily (12.5 mg in renal impairment), or methylnaltrexone 12 mg subcutaneously on alternate days (8 mg for weight 38 to 61 kg), or naldemedine 0.2 mg daily in specialist use. Avoid in suspected obstruction.
  • Prucalopride 2 mg orally once daily (1 mg daily in those over 65 years and in renal impairment) for chronic constipation in adults where laxatives fail (women in some regions), reviewing the benefit at 4 weeks.
  • Lifestyle: fluid intake of 1.5 to 2 L per day, dietary fibre of 25 to 30 g per day increased gradually (if the patient is mobile and drinking), regular meals, physical activity, a toilet routine 20 to 30 minutes after meals (using the gastrocolic reflex), a footstool for the squatting position, privacy, and timely access to the toilet.
  • Address the cause: review constipating drugs, correct hypothyroidism, hypercalcaemia and hypokalaemia, treat depression, and manage painful anal conditions.
• Special groups:
  • Children: disimpaction with macrogol 3350 (without electrolytes or with electrolytes) at 1 to 1.5 g/kg per day for 3 to 6 days (or the paediatric sachet regimen, starting with 4 sachets on day 1 for ages 2 to 11 years and increasing by 2 sachets daily to a maximum of 12), or a phosphate or sodium citrate enema in specialist care, then maintenance with macrogol 0.4 to 0.8 g/kg per day, adjusted, with behavioural therapy (regular toilet sittings 2 to 3 times daily for 5 minutes after meals, a reward system) and continued for months. Avoid forceful rectal measures. Exclude Hirschsprung disease when onset is in infancy with delayed meconium passage (over 48 hours), faltering growth, or explosive stool on rectal examination.
  • Elderly and care home residents: regular rectal examination, bowel charts, laxatives prescribed with opioids, early treatment of constipation, avoidance of dehydration, and caution with phosphate enemas and high dose macrogol.
  • Pregnancy: dietary measures, lactulose or macrogol 1 to 2 sachets daily, and bisacodyl or senna when needed. Avoid castor oil and mineral oil.
  • Neurological patients (spinal cord injury, multiple sclerosis, Parkinson disease): a structured bowel programme with timed suppositories (bisacodyl 10 mg or glycerol), digital rectal stimulation, and trans anal irrigation in specialist care.
  • Renal impairment and heart failure: avoid phosphate and magnesium preparations, and monitor electrolytes when giving large volume macrogol.
  • Palliative care: prophylactic laxatives with all opioids (senna with macrogol), and rectal measures for impaction.
• Follow up: review in 1 to 2 weeks after disimpaction to check the stool pattern and adjust the maintenance laxative, then at 4 to 6 weeks. Continue maintenance therapy for at least 6 to 12 months (and longer when opioids continue). Refer to gastroenterology or colorectal surgery for refractory impaction, suspected megacolon, anorectal disease, suspected cancer, or recurrent episodes.