Acute and chronic diarrhoea in surgical practice

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

Acute diarrhoea in surgical practice may be infectious, drug related, feed related or overflow around impaction. Chronic diarrhoea lasting more than four weeks broadens the investigation toward inflammatory bowel disease, microscopic colitis, coeliac disease, bile-acid diarrhoea and pancreatic or surgical malabsorption.

After intestinal resection, measured output and anatomy drive care. Ileal loss impairs bile-acid and vitamin B12 handling; extensive small-bowel loss reduces absorptive surface and can produce sodium, water and magnesium depletion. Distension, vomiting, peritonism or toxic dilatation changes the task from symptom control to emergency assessment.

Key points

Measure stool or stoma volume, fluid intake, urine output and weight; frequency alone does not quantify loss.
Resuscitate hypotension, oliguria and acute kidney injury while replacing sodium, potassium and magnesium deficits.
Use recent antibiotics, healthcare contact, travel and immune status to choose targeted stool tests and isolation.
Check surgical anatomy: ileal loss, shortened bowel and stoma configuration predict fluid and nutrient consequences.
Exclude overflow, partial obstruction, toxic dilatation, collection and anastomotic complication before antimotility treatment.
Investigate symptoms beyond four weeks for inflammation, coeliac disease, bile-acid loss, microscopic colitis and malabsorption.

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

Acute triggers

Infection, antibiotics, laxatives, enteral feed and postoperative inflammation commonly produce short-duration diarrhoea during admission or early recovery.

Chronic mechanisms

Inflammatory bowel disease, microscopic colitis, coeliac disease, pancreatic insufficiency, bile-acid diarrhoea and altered surgical anatomy cause persistent symptoms.

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

1
Secretory or inflammatory loss
Active secretion and damaged mucosa reduce water absorption, producing high-volume stool and electrolyte depletion faster than oral intake replaces them.
2
Osmotic retention
Poorly absorbed solute retains luminal water and often improves during fasting, depending on the cause but the pattern varies with the substrate.
3
Reduced absorptive surface
Small-bowel resection shortens contact time and surface area, while ileal loss disrupts bile-acid recycling and may accelerate small-bowel transit.

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

Duration and likely cause

Acute diarrhoea lasting days is commonly infectious or drug-related; symptoms persisting beyond four weeks require a structured chronic-diarrhoea assessment.

Healthcare-associated infection

Recent antibiotics, healthcare contact and immunosuppression increase concern for Clostridioides difficile and determine isolation and stool-testing decisions.

Post-resection anatomy

After bowel resection, stool volume depends on the segment and length removed, continuity, stoma anatomy and adaptation; label the anatomy before prescribing symptomatic treatment.

Overflow around loading

Small-volume frequent liquid stool with rectal loading may be overflow rather than high intestinal output, especially in frail patients receiving opioids.

Organic warning features

Nocturnal symptoms, weight loss, blood, fever, anaemia and raised inflammatory markers favour organic disease over a purely functional disorder.

Red flags requiring action

Hypotension, severe dehydration, peritonism, ileus, toxic dilatation, blood with systemic toxicity or high-output stoma losses require urgent assessment and cause-directed resuscitation.

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
ABCDE assessment, fluid balance and venous blood gasFirst step
Why
quantify dehydration, perfusion and acid-base consequences
Interpretation and limitations
Tachycardia, postural hypotension, oliguria, rising creatinine and metabolic acidosis indicate significant loss even before collapse.
02
Targeted stool microbiology including C difficile testing
Why
identify infection when exposure, severity or public-health context supports testing
Interpretation and limitations
Interpret toxin and organism assays using the laboratory algorithm; asymptomatic carriage and recent treatment can complicate results.
03
Full blood count, renal profile, magnesium, CRP and albumin
Why
assess inflammation, electrolyte loss, kidney injury and nutritional consequence
Interpretation and limitations
Results indicate severity but do not by themselves distinguish infection, inflammation and surgical anatomy.
04
Abdominal imaging
Why
evaluate obstruction, perforation, collection or toxic dilatation when examination or physiology raises concern
Interpretation and limitations
Do not request routine imaging for uncomplicated self-limited diarrhoea; specify the suspected surgical complication.
05
SeHCAT and colon biopsies for chronic watery diarrhoea
Why
Distinguish bile-acid diarrhoea from microscopic colitis when baseline tests and medication review do not explain persistent symptoms.
Interpretation and limitations
SeHCAT retention supports bile-acid loss where the test is available. Microscopic colitis requires histology from right and left colon because endoscopic mucosa may look normal.

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

Overflow around impaction

Small-volume liquid leakage with rectal loading and constipating medicines can mimic diarrhoea despite apparently frequent bowel movements.

Partial bowel obstruction

Hyperperistalsis and liquid passage may occur before absolute constipation; pain, distension and vomiting are warning features.

Faecal incontinence

Loss of control may be described as diarrhoea even when stool volume and consistency are normal.

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

01Worked case: applied acute and chronic diarrhoea in surgical practiceReach a specific decision and confirm it happenedFirst stepFive days after ileal resection, an adult has 2.5 litres of stoma output, thirst, oliguria and rising creatinine. The team must quantify losses, replace fluid and electrolytes, review anatomy and exclude postoperative sepsis or obstruction.

1Recognise high-output dehydration from 2.5 litres of ileostomy loss, thirst, oliguria and rising creatinine; obtain intravenous access and give balanced isotonic crystalloid boluses with frequent reassessment while replacing measured ongoing loss.
2Confirm the remaining small-bowel and ileal length, stoma type, oral intake and medicines, and examine for obstruction, intra-abdominal sepsis and active enteritis before any antimotility drug.
3Measure stoma and urine output, weight, venous gas, creatinine, sodium, potassium and magnesium; send targeted stool microbiology only when the exposure and syndrome warrant it.
4After perfusion improves and obstruction or sepsis is excluded, replace hypotonic drinks with a prescribed glucose-saline solution. One litre of St Mark’s solution contains 20 g glucose, 3.5 g sodium chloride and 2.5 g sodium bicarbonate and supplies at least 90 mmol/L sodium.
5Verify increasing urine output, falling creatinine and lower measured stoma loss, correct magnesium and nutrition, and arrange stoma, dietetic and surgical follow-up before discharge.

02Chronic watery-diarrhoea pathwayUse discriminating tests rather than an empirical labelA 57-year-old has six months of watery nocturnal diarrhoea, normal colonoscopy appearance, mild weight loss and no previous bowel resection.

1Review medicines, coeliac serology, blood count, CRP, thyroid tests and stool infection studies according to history; nocturnal symptoms and weight loss argue against a purely functional diagnosis.
2Request right- and left-colon biopsies despite normal mucosal appearance to detect microscopic colitis, and use SeHCAT or the locally available validated pathway to assess bile-acid diarrhoea.
3Verify histology and bile-acid results before long-term treatment; if tests are negative, reassess pancreatic insufficiency, small-bowel disease and factitious or endocrine causes according to phenotype.

03Toxic or obstructive diarrhoea pathwayTreat the dangerous abdomen before slowing stoolA postoperative patient has small-volume liquid stool, progressive distension, vomiting, fever, guarding and reduced urine output.

1Stop laxatives and withhold antimotility treatment, begin ABCDE care, keep nil by mouth, obtain access and correct fluid and electrolyte deficits.
2Perform rectal examination for impaction and urgent contrast CT for obstruction, leak, abscess or toxic dilatation; isolate and test for C difficile when healthcare-associated colitis is plausible.
3Involve colorectal surgery and microbiology or gastroenterology according to the result and verify source control, decompression, renal recovery and infection precautions.

Key medicines and prescribing safety1 treatment · regimens, roles and cautions

Provides at least 90 mmol/L sodium to promote coupled sodium and water absorption in a high-output ileostomy or short-bowel state after immediate hypovolaemia has been corrected.

St Mark’s oral rehydration solution

Dissolve 20 g glucose, 3.5 g sodium chloride and 2.5 g sodium bicarbonate in water to a final volume of 1 litre, prepare fresh daily and sip the prescribed volume through the day after specialist assessment.

Monitor renal function, sodium, potassium, magnesium, weight, urine and stoma output. This is not a substitute for intravenous resuscitation in shock, and fluid restriction or antimotility medicines require individual specialist instruction after obstruction and sepsis are excluded.

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

Dehydration and kidney injury

Ongoing water and sodium loss causes thirst, hypotension, oliguria and acute kidney injury when replacement does not match measured output.

Electrolyte depletion

Potassium, magnesium and bicarbonate loss can produce weakness, arrhythmia and metabolic acidosis during continuing high-volume intestinal losses.

Malnutrition

Persistent inflammatory or short-bowel diarrhoea impairs energy, protein and micronutrient status and compromises recovery and can delay wound healing or surgery.

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

Record stool or stoma frequency and measured volume, fluid intake, urine output, weight and renal indices until losses are controlled.
Review microbiology promptly and narrow, stop or start treatment according to the actual result and clinical syndrome.
After resection or high-output stoma, monitor sodium, potassium, magnesium, nutrition and renal function with specialist dietetic and stoma input.
Persistent or recurrent diarrhoea after negative initial tests needs planned gastroenterology review rather than repeated non-specific antidiarrhoeal prescriptions.

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

Volume matters more than labels

Measured output connects symptoms to replacement needs and distinguishes a dangerous high-output state from frequent small evacuations.

Postoperative diarrhoea may signal obstruction

Liquid overflow can pass around partial obstruction or impaction, so distension and vomiting change the interpretation.

Anatomy predicts physiology

Loss of terminal ileum can cause bile-acid diarrhoea and vitamin B12 risk, while extensive small-bowel loss drives fluid and nutrient failure.

Sampling should answer a question

Stool tests are most useful when timing, exposures and the requested organisms match the clinical syndrome.

11Common pitfallsFrequent interpretation and management errors.

01
Giving antimotility treatment before excluding ileus, severe colitis or C difficile infection can worsen an unsafe situation.
02
Writing diarrhoea without documenting volume, duration and surgical anatomy prevents rational replacement and investigation.
03
Assuming every postoperative loose stool is antibiotic-associated can miss an anastomotic leak, abscess or partial obstruction.
04
Failing to isolate a patient with plausible healthcare-associated infectious diarrhoea exposes other patients while results are pending.

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