Constipation and faecal impaction

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Constipation reflects stool consistency, transit and evacuation. Clarify onset and chronicity, Bristol stool form, frequency, straining, incomplete emptying, blockage, digitisation, pain, bloating and overflow. Ask whether the urge is absent, stool is hard or a soft stool cannot be expelled, because these suggest different mechanisms. Diet and fluid matter, but immobility, inaccessible toilets, cognitive impairment, pain and loss of privacy are equally important. Medication review is often the highest-yield intervention. Secondary causes include hypothyroidism, hypercalcaemia, diabetes, neurological disease, depression, eating disorder, colorectal obstruction and pelvic-floor dysfunction.

Faecal loading is retained stool in the rectum or colon; impaction is a more severe mass that cannot be passed spontaneously. Rectal pressure can cause paradoxical overflow and faecal incontinence, while bladder compression or shared neural dysfunction causes urinary symptoms. Frail patients may present with delirium or reduced appetite rather than bowel complaint. Examine hydration, nutrition, abdomen, hernias and neurological status. Rectal examination requires consent, a chaperone and a purpose: describe stool consistency and amount, mass, blood, anal tone and whether attempted bearing down relaxes or paradoxically contracts the sphincter.

Management separates clearance from prevention. If impaction is confirmed and obstruction excluded, use the NICE CKS and current BNF oral macrogol escalation or a rectal approach chosen from stool location, tolerance and swallowing. Hard distal stool may need suppository, enema or carefully analgesed manual removal by trained staff. Once cleared, start maintenance immediately, address medicines and toileting and monitor stool rather than waiting for recurrence. Refractory constipation after adequate trials needs phenotype testing: colonic transit for slow transit, anorectal manometry and balloon expulsion for evacuation disorder, and defecography for selected structural questions. Specialist medicines or surgery require confirmed mechanism and multidisciplinary review.

Key points

Constipation is not only infrequent stool: ask about hard form, straining, incomplete evacuation, blockage sensation, manual manoeuvres, pain and the patient's baseline.
New constipation with rectal bleeding, iron-deficiency anaemia, weight loss, abdominal or rectal mass, or persistent change in bowel habit needs the current colorectal cancer pathway.
Faecal impaction can present with overflow liquid stool, faecal incontinence, urinary retention, anorexia, delirium or apparent diarrhoea, particularly in frailty and neurological disease.
Review opioids, anticholinergics, iron, calcium, verapamil, antipsychotics and anti-Parkinson medicines, and assess hydration, mobility, toileting privacy and access.
Digital rectal examination should answer whether rectal stool, mass, bleeding or evacuation dysfunction is present; a loaded proximal colon can coexist with an empty rectum.
Exclude obstruction before escalating oral laxatives. A plain abdominal radiograph is not routinely required for uncomplicated constipation but can help selected acute or uncertain cases.
For routine chronic constipation, adequate soluble fibre and fluid, regular toileting and an osmotic laxative are common first steps; stimulant treatment is added or substituted according to stool response.
Impaction needs a disimpaction regimen followed immediately by maintenance treatment and correction of the cause, otherwise rapid recurrence is predictable.
Symptoms of outlet obstruction despite soft stool may need anorectal physiology and pelvic-floor biofeedback rather than simply stronger laxatives.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Lifestyle and medicines

Low intake, immobility, disrupted toileting and opioids, anticholinergics, iron or calcium commonly reduce stool frequency or increase hardness.

Neurological and metabolic disease

Parkinson disease, spinal or autonomic disorders, hypothyroidism, hypercalcaemia and diabetes can slow transit or impair evacuation.

Structural and pelvic-floor causes

Colorectal cancer, stricture, prolapse, rectocele and dyssynergic defaecation cause outlet resistance or incomplete emptying and require targeted evaluation.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Slow colonic transit
Prolonged passage permits excessive water absorption, producing hard stool, reduced urge and progressive colonic loading and difficult evacuation.
2
Evacuation failure
Poor pelvic-floor relaxation, weak propulsion or structural outlet obstruction leaves stool in the rectum despite straining and urge.
3
Impaction and overflow
Retained stool becomes desiccated and obstructive; liquid content passes around it, creating apparent diarrhoea or faecal incontinence.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Mechanical large-bowel obstructionRed flag

Progressive distension, colicky then constant pain, vomiting, absolute constipation, weight loss or a mass raises tumour, volvulus or stricture. Peritonism, fever or shock suggests ischaemia or perforation and precludes routine laxative escalation.

Rectal faecal impaction

Hard stool palpable in the rectum with overflow soiling, tenesmus, urinary symptoms or inability to pass an effective stool supports distal impaction. Pain, fissure and haemorrhoids can perpetuate retention.

Proximal faecal loading

A distended tender colon, reduced intake and overflow can occur with an empty rectal vault when stool lies proximally. Examination and selected imaging must be integrated rather than using one negative rectal examination to exclude loading.

Defaecatory disorder

Prolonged straining, blockage sensation, vaginal or perineal pressure, manual assistance and failure to pass soft stool suggest impaired pelvic-floor coordination or structural outlet disease, which may respond to biofeedback.

Slow-transit phenotype

Infrequent urge and bowel movement with diffuse bloating despite adequate evacuation technique can reflect slow colonic transit. Medicines, metabolic and neurological causes must be addressed before specialist labelling.

Acute neurological bowel dysfunctionRed flag

New constipation or retention with saddle sensory change, severe back pain, bilateral weakness, altered anal tone or urinary dysfunction raises cauda equina or spinal compression and requires emergency neurological imaging and referral.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Digital rectal examinationFirst step
Why
Detect distal stool, rectal mass, blood, anal tone and a possible evacuation coordination problem.
Interpretation and limitations
Describe findings rather than recording only 'DRE done'. An empty rectum does not exclude proximal loading or obstruction, and a mass or blood activates the relevant urgent pathway.
02
Full blood count, calcium and thyroid testing
Why
Identify anaemia, hypercalcaemia or hypothyroidism when history, examination or new persistent symptoms support secondary constipation.
Interpretation and limitations
Testing should be targeted rather than routine for every mild case. Iron-deficiency anaemia requires cause investigation; correcting a metabolic disorder does not remove cancer warning features.
03
Quantitative FIT and colorectal assessment
Why
Guide suspected colorectal cancer referral for eligible new bowel symptoms under the current NICE pathway.
Interpretation and limitations
A low FIT does not override an abdominal or rectal mass, unexplained iron-deficiency anaemia or continuing high clinical concern. Endoscopic or CT colon assessment follows the pathway and patient suitability.
04
Abdominal radiography or CT
Why
Assess selected suspected obstruction, megacolon, volvulus, perforation or uncertain proximal faecal loading rather than routine uncomplicated constipation.
Interpretation and limitations
Plain radiography can show dilatation and stool burden but is imperfect; CT better defines transition and cause. Imaging must not delay surgical review in peritonism or shock.
05
Colonic transit study
Why
Distinguish slow-transit constipation from normal transit after secondary causes and adequate medical treatment have been addressed.
Interpretation and limitations
Medicine withholding and method follow the physiology unit. Delayed markers throughout the colon support slow transit; distal clustering may suggest evacuation dysfunction requiring anorectal assessment.
06
Anorectal manometry and balloon expulsion
Why
Assess sphincter pressure, rectoanal coordination, sensation and practical evacuation in suspected defaecatory disorder.
Interpretation and limitations
No single metric defines the disorder. Concordant symptoms, examination and physiology guide pelvic-floor biofeedback; discordance may require defecography or specialist review.
07
Defecography
Why
Visualise selected structural and functional evacuation problems such as rectocele, intussusception or prolapse when the result will change intervention.
Interpretation and limitations
Anatomical abnormalities are common and not always causal. Interpret evacuation, symptoms and physiology together before considering surgery.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Mechanical bowel obstruction

Progressive distension, colicky pain, vomiting and obstipation with a CT transition point require urgent surgical assessment rather than routine laxative escalation.

Colorectal cancer

New persistent change, bleeding, iron-deficiency anaemia, weight loss or abdominal or rectal mass triggers the current suspected-cancer pathway.

IBS with constipation

Recurrent abdominal pain linked to defaecation and altered stool form without alarm features supports IBS-C rather than isolated transit failure.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Acute triageExclude obstruction and neurologyFirst stepConstipation is new, severe or associated with pain, vomiting, distension or urinary symptoms.

1Assess physiology, hydration, abdomen, hernias and stool or flatus passage, and ask about cancer, postoperative and medicine risks.
2Seek peritonism, absolute obstipation and neurological warning features, performing rectal and focused lower-limb examination when clinically indicated.
3EscalationEscalate suspected mechanical obstruction or cauda equina urgently and avoid oral disimpaction until the dangerous mechanism is excluded.
4Use imaging and blood tests to answer the specific obstruction, perforation, metabolic or neurological question with senior input.

02ImpactionClear then prevent recurrenceRectal or proximal faecal loading is clinically established without obstruction.

1Identify stool location and consistency, hydration, swallowing ability, pain and cause, and explain the staged disimpaction plan to the patient or carer.
2EscalationUse the NICE CKS oral macrogol escalation when suitable or choose suppository, enema or trained manual removal for distal stool according to local policy and patient tolerance.
3Monitor pain, stool output, overflow, hydration and electrolyte risk, stopping and reassessing if vomiting, severe pain or distension develops.
4Begin a maintenance bowel regimen immediately after clearance and address medicines, mobility, fluid, fibre, toileting routine and follow-up.

03Chronic managementMatch treatment to stool and transitPersistent constipation has no emergency or cancer warning feature.

1Agree realistic stool goals, introduce soluble fibre gradually when appropriate, optimise fluid, activity and regular unhurried toileting with foot support.
2Use an osmotic laxative for hard stool and add or substitute a stimulant if response remains inadequate, reviewing adherence and adverse effects.
3EscalationReassess after an adequate trial for outlet symptoms, overflow and medicine causes rather than escalating several agents indefinitely.
4Refer refractory symptoms for transit and anorectal physiology, with specialist consideration of secretagogues, prokinetics, irrigation or surgery only after phenotype confirmation.

04Opioid-associatedPrevent predictable bowel failureRegular opioid treatment is started or constipation develops during therapy.

1Document baseline bowel function and prescribe a prophylactic stimulant plus softening or osmotic strategy appropriate to the patient unless contraindicated.
2Review opioid indication, dose reduction and non-opioid alternatives while checking for impaction before simply intensifying laxatives.
3Use specialist or palliative guidance for refractory opioid-induced constipation and exclude obstruction before peripheral opioid-antagonist treatment.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Retains water in stool to soften faeces and supports both disimpaction and ongoing prevention.

Macrogol osmotic laxative

Use the current BNF maintenance regimen, or the NICE CKS escalating oral disimpaction schedule when loading is confirmed and obstruction has been excluded.

Ensure adequate fluid and swallowing safety, review electrolyte and volume risk in frailty or organ failure, and stop for worsening pain, vomiting or suspected obstruction.

Increases colonic propulsion and is particularly useful in opioid-related or slow bowel patterns.

Stimulant laxative

Add or substitute a current BNF stimulant dose when stool remains infrequent despite adequate osmotic treatment, commonly timing the dose for predictable next-day effect.

Cramping and diarrhoea indicate excessive effect. Do not use to push through mechanical obstruction, and review chronic high-dose need for unrecognised impaction or evacuation disorder.

Softens or stimulates the rectum when oral treatment is unsuitable, too slow or insufficient for distal impaction.

Rectal suppository or enema

Select the locally approved preparation according to whether distal stool is hard or soft, using the BNF technique and reassessing after each planned intervention.

Avoid traumatic repeated insertion, review renal and electrolyte risk for phosphate-containing products, and use extra care with neutropenia, thrombocytopenia, fissure or recent colorectal surgery.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Faecal impaction and overflow

Rectal loading causes pain, urinary retention, delirium, pressure injury and paradoxical liquid leakage, particularly in frail or neurological patients.

Stercoral ulceration and perforation

Prolonged pressure from hard stool can cause focal colonic ischaemia, ulceration, bleeding and life-threatening perforation with peritonitis.

Anorectal injury

Repeated straining and hard stool promote fissures, haemorrhoidal bleeding, prolapse and pelvic-floor dysfunction, perpetuating painful avoidance of defaecation.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Use a stool chart recording frequency, Bristol form, straining, incomplete emptying, overflow and rescue interventions rather than relying on retrospective recall.
During disimpaction, monitor pain, distension, vomiting, hydration, stool output and continence; new obstruction features require immediate cessation and reassessment.
Review fluid balance, renal function and electrolytes when frailty, high-output treatment, kidney disease or repeated enemas creates risk.
Track weight, appetite, delirium, urinary retention, pressure injury and mobility in care-dependent patients because bowel loading affects multiple systems.
At maintenance review, document medicine adherence, toileting opportunity and whether soft stool still cannot be evacuated, prompting pelvic-floor assessment.
Ensure FIT, endoscopy, imaging and physiology results have a named clinician and that persistent warning features are not lost after temporary laxative response.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Overflow is not clearance

Liquid stool can seep around a hard faecal mass and mimic diarrhoea. Giving anti-motility medicine then worsens retention, so rectal loading must be considered in frailty and new incontinence.

Rectum may be empty

Proximal colonic loading or obstruction can occur without palpable rectal stool. A negative rectal examination answers only the distal question and must be integrated with distension and imaging.

Soft stool can obstruct

Pelvic-floor dyssynergia produces failed evacuation despite a soft consistency. Escalating osmotic laxatives may create leakage without correcting coordination, whereas biofeedback targets the mechanism.

Impaction is a systems event

Rectal loading can precipitate urinary retention, delirium, appetite loss and pressure injury. Improvement should be judged across these domains, not only by one bowel movement.

Fibre needs context

Rapidly increasing insoluble bulk in severe slow transit, impaction or inadequate fluid can worsen bloating and retention. Soluble fibre is introduced gradually after obstruction and loading are addressed.

11Common pitfallsFrequent interpretation and management errors.

01
Treating overflow faecal incontinence with loperamide before checking for impaction.
02
Giving a large oral disimpaction regimen to a patient with vomiting and suspected mechanical obstruction.
03
Assuming an empty rectal vault excludes proximal faecal loading or large-bowel obstruction.
04
Prescribing repeated enemas without reviewing phosphate, renal, mucosal and trauma risks.
05
Escalating laxatives for soft-stool outlet obstruction instead of arranging anorectal and pelvic-floor assessment.
06
Stopping after clearance without a maintenance regimen and correction of opioid, mobility or toileting causes.