Pseudo-obstruction and acute colonic dilatation

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

Acute colonic pseudo-obstruction, often called Ogilvie syndrome, is marked colonic dilatation without a mechanical blockage. It commonly develops during another illness or after surgery, including orthopaedic procedures, and frequently affects patients with multiple comorbidities. Autonomic dysregulation is thought to impair coordinated colonic transit, with immobility, opioids, anticholinergic drugs, electrolyte disturbance and systemic illness contributing. This mechanism differs from the physical twist of volvulus or the fixed narrowing of a cancer. The distinction must be demonstrated because a drug intended to stimulate motility can be dangerous in mechanical obstruction or threatened bowel.

Acute colonic dilatation is a descriptive finding, not a final diagnosis. Ileus may affect small and large bowel more diffusely; ACPO predominantly involves the colon, but the pattern alone is insufficient. Acute inflammatory or infective colitis with systemic toxicity raises toxic megacolon, which requires its own urgent gastroenterology and surgical pathway. Ask about diarrhoea, rectal bleeding, inflammatory bowel disease, recent antibiotics and infection while reviewing CT for colitis and structural obstruction. Passing stool, having bowel sounds or being recently postoperative does not reliably settle these distinctions. A diagnosis of ACPO must remain open to revision when the patient deteriorates or the expected response does not occur.

Key points

ACPO is a diagnosis of exclusion: CT must exclude a structural obstruction, and acute colitis with systemic toxicity requires a separate toxic-megacolon assessment.
Correct precipitants, review opioids and anticholinergics, restore fluids and electrolytes, and reassess repeatedly; conservative care is appropriate only while the patient remains uncomplicated and stable.
New tenderness, peritonitis, fever or physiological deterioration overrides a planned observation period or reassuring diameter and requires urgent surgical reassessment.
Persistent uncomplicated ACPO may require specialist neostigmine in a monitored setting or colonoscopic decompression; choose according to contraindications, response and available expertise.
The South East London formulary provides one local off-label adult option of neostigmine 2 mg IV over 40–60 minutes once; preparation and monitoring must be verified by the administering service.
After decompression, demonstrate sustained clinical improvement and address the precipitant; a bowel movement alone does not end observation or exclude recurrence.

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

Acute illness and surgery

ACPO often accompanies major medical illness, trauma or surgery remote from the bowel. These contexts can disturb autonomic control and reduce effective colonic motility.

Medicines and metabolic disturbance

Opioids, anticholinergics and abnormalities of potassium or other electrolytes can contribute. Several factors commonly coexist, so identifying one precipitant does not complete the assessment.

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

1
Disordered colonic propulsion
Autonomic and enteric dysfunction is thought to reduce coordinated colonic transit without a fixed luminal blockage. The precise mechanism is incompletely established and may differ between patients.
2
Progressive caecal distension
Gas and fluid accumulate as transit slows, often enlarging the proximal colon substantially. Increasing radius and sustained pressure raise concern for impaired perfusion and wall failure.
3
Transition to complicated disease
Persistent or rapidly increasing dilatation can progress to ischaemia or perforation. At that point the problem extends beyond reversible dysmotility and may require operative source control.

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

The typical context

A hospitalised patient develops progressive distension during recovery from trauma, major surgery or a medical illness. Review the timing of new medicines, immobility and electrolyte abnormalities. These associations support suspicion but do not establish ACPO in the presence of an unexcluded mechanical lesion.

Conservative-care eligibility

Observation with active supportive treatment requires clinical stability and absence of peritonitis, concerning focal tenderness or evidence of bowel compromise. A caecum below 12 cm is part of this assessment, not a guarantee of safety. Fever, rising inflammatory markers or increasing pain should prompt reconsideration.

A changing danger patternRed flag

New caecal tenderness, guarding, systemic deterioration or rapidly increasing distension suggests threatened viability or perforation. Obtain urgent surgical review even if the caecum has not crossed a memorised size threshold or fewer than 48 hours have elapsed.

Toxic dilatation clues

Bloody diarrhoea, known severe colitis, recent antibiotic exposure or features of enteric infection accompanied by systemic toxicity demand a separate assessment. Do not give neostigmine simply because CT lacks a focal tumour: absence of mechanical obstruction does not by itself establish uncomplicated ACPO.

Suitability for neostigmine

Check allergies, baseline pulse and ECG, asthma or active bronchospasm, recent coronary disease, renal function and recent intestinal anastomosis. Mechanical gastrointestinal or urinary obstruction, peritonitis and doubtful bowel viability are product exclusions. Availability of continuous monitoring and immediate resuscitation is part of eligibility.

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
Contrast-enhanced CT abdomen and pelvisFirst step
Why
Exclude a mechanical lesion and assess the dilated colon and its wall.
Interpretation and limitations
Look for tumour, volvulus, an obstructing transition, inflammation, impaired enhancement and perforation. A functional calibre change can occur without a causative structural lesion. Review uncertain images with radiology before concluding that the patient is suitable for conservative ACPO treatment or neostigmine.
02
Serial abdominal assessment and radiographs
Why
Follow the trajectory of caecal dilatation after the initial structural diagnosis.
Interpretation and limitations
Record both diameter and change over time, together with pain and tenderness. Larger and more prolonged dilatation increases risk, but deterioration can occur below 12 cm. A stable measurement should not overrule worsening perfusion or new peritoneal signs.
03
Renal function, potassium, magnesium and calcium
Why
Identify reversible contributors and establish a safe basis for replacement and prescribing.
Interpretation and limitations
Correct abnormalities with attention to renal function and ongoing losses. Electrolyte recovery supports motility but may not be sufficient to resolve established ACPO. Repeat testing according to the disturbance and treatment, rather than assuming one replacement prescription completes the task.
04
Blood count, inflammatory markers and targeted infection testing
Why
Assess concurrent illness and distinguish uncomplicated ACPO from a toxic or septic process.
Interpretation and limitations
New leukocytosis, fever or increasing inflammatory response needs clinical interpretation. If diarrhoea or colitis suggests infection, obtain appropriate stool testing, including a C. difficile assessment when indicated, while urgent specialist evaluation proceeds. Do not wait for a stool result to act on peritonitis.
05
Baseline ECG and cardiopulmonary review
Why
Assess whether pharmacological decompression can be delivered safely.
Interpretation and limitations
Identify bradycardia or conduction disease and review recent cardiac ischaemia, bronchospasm and interacting medicines. The selected neostigmine regimen requires specialist oversight, continuous ECG and immediate support for bradycardia or bronchospasm; an unmonitored bed is not an equivalent setting.

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

Mechanical large-bowel obstruction

Cancer or volvulus can mimic ACPO and must be excluded by appropriate structural assessment. Prokinetic treatment is unsafe when a true mechanical obstruction or doubtful viability remains.

Toxic megacolon

Acute colitis with systemic toxicity and colonic dilatation is a separate emergency. Infection and inflammatory bowel disease are relevant contexts, and absence of a tumour does not establish uncomplicated ACPO.

Postoperative ileus

Diffuse impairment of small- and large-bowel motility can follow surgery or severe illness. Imaging, distribution and clinical context help distinguish this from predominant acute colonic dilatation.

Faecal impaction

Accumulated stool can cause distension and altered passage, sometimes with overflow diarrhoea. Rectal and radiological assessment should establish whether impaction or a structural complication is actually present.

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

01Initial active supportConservative care with defined limitsFirst stepCT and clinical review establish uncomplicated ACPO without a mechanical or toxic cause.

1Review the patient with the surgical team, institute bowel rest and correct dehydration and electrolyte disturbances. Stop or reduce contributory opioids and anticholinergics where feasible, treat the precipitating illness and support mobilisation or regular position changes.
2Use nasogastric decompression when vomiting or upper gastrointestinal distension warrants it and consider a suitable rectal decompression tube. Avoid routine stimulant or osmotic laxatives during active marked dilatation because they may worsen gas and distension.
3EscalationContinue close examinations and serial calibre assessment. ACPGBI allows an initial 48–72-hour conservative period only while the patient remains stable without caecal tenderness or peritonism and the caecum remains below 12 cm; a worsening trajectory requires earlier escalation.
4If the uncomplicated dilatation persists despite support, discuss monitored neostigmine or colonoscopic decompression. Any evidence of ischaemia or perforation moves the decision toward urgent surgery, rather than simply another round of conservative treatment.

02Worked casePersistent ACPO responds to monitored treatmentA 72-year-old develops colonic distension after hip surgery while receiving opioids.

1CT excludes a tumour, volvulus and colitis, showing a caecum of 10.8 cm. He is afebrile, stable and without focal tenderness; potassium is 2.9 mmol/L. The team diagnoses uncomplicated ACPO after reviewing the clinical and radiological differential.
2Opioids are reduced, hydration and potassium are corrected, oral intake is held temporarily and supported mobilisation begins. At 48 hours potassium is 3.8 mmol/L, but the abdomen remains distended and the caecum has increased to 11.8 cm. Persistent failure to improve prompts decompression planning.
3The specialist reviews a pulse of 78, an ECG without conduction abnormality, preserved renal function and no asthma, drug hypersensitivity, mechanical urinary obstruction or recent intestinal anastomosis. A monitored setting with atropine and resuscitation support is available. The team selects the local South East London off-label option described below.
4After the administering service verifies the compatible local preparation, plain neostigmine 2 mg is given intravenously over 60 minutes as a single dose. Continuous ECG and cardiopulmonary observations detect no bradycardia, hypotension or bronchospasm; the patient passes flatus and stool and the abdomen softens.
5Repeat examination and next-day imaging confirm sustained improvement, with the caecum reduced to 7.8 cm. Diet and mobility recover, no further dose is given, and the opioid and constipation plan is revised after the acute dilatation has resolved. Recurrent distension would trigger reassessment rather than an automatic repeat prescription.

03Escalation and rescueWhen pharmacological decompression is unsuitable or failsEscalationACPO persists or the risk-benefit assessment does not favour neostigmine.

1If mechanical obstruction, peritonitis or doubtful viability is present, do not administer neostigmine; reassess for urgent operative treatment. Marked bradycardia, active bronchospasm or inability to provide appropriate monitoring requires another decompression plan rather than casual administration on the ward.
2For persistent uncomplicated ACPO with neostigmine contraindicated or ineffective, arrange experienced colonoscopic decompression with minimal insufflation and consideration of a decompression tube. Explain the risk of perforation and the possibility that further intervention will be needed.
3If nonoperative measures fail, or ischaemia or perforation occurs, discuss surgery promptly with anaesthesia and the patient or appropriate decision makers. The operation and postoperative support depend on the involved bowel, physiological reserve and agreed goals; deterioration should not wait for completion of a nominal treatment ladder.

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

Increase colonic activity in a selected patient after mechanical obstruction, toxic dilatation and threatened bowel have been excluded; subsequent intervention follows reassessment of the actual response.

Neostigmine methylsulfate: plain 2.5 mg/mL injection

For confirmed adult ACPO after failed supportive care, the South East London Joint Medicines Formulary lists a local off-label option of 2 mg intravenously over 40–60 minutes once, with specialist supervision. In the selected 2.5 mg/mL stock, 2 mg corresponds to 0.8 mL before preparation; this is stock-dose arithmetic, not the prepared administration volume. The administering service must verify its compatible local preparation and delivery method.

Do not use with hypersensitivity to neostigmine or excipients, mechanical gastrointestinal or urinary obstruction, peritonitis, doubtful bowel viability or concurrent suxamethonium. Review bradycardia, conduction disease, recent coronary ischaemia, asthma, renal function and any intestinal anastomosis. Administer with continuous ECG and cardiopulmonary assessment, atropine and resuscitation support immediately available; stop and treat significant bradycardia, hypotension or bronchospasm. Use the plain product, not a fixed glycopyrronium combination, and do not infer a repeat, dilution or rescue-dose schedule from this single-dose example.

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

Caecal infarction

Sustained wall stress and impaired perfusion can produce nonviable bowel. Increasing pain or tenderness may be more informative than a single diameter measurement.

Perforation and sepsis

Failure of the dilated colon releases intestinal contents into the abdomen. The resulting contamination requires urgent surgical consideration in parallel with treatment of systemic deterioration.

Recurrent dilatation

Initial decompression can be followed by recurrence if the precipitant persists or motility remains impaired. Continued assessment and a post-resolution medication and bowel-care plan are necessary.

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

Track symptoms, focal tenderness, abdominal size, caecal calibre and physiological observations together. Rising pain with an unchanged film is a clinical change requiring assessment, not evidence of safe stability.
During specialist neostigmine administration, monitor the cardiac rhythm and cardiopulmonary state and have immediate treatment available for cholinergic adverse effects. Stop administration and manage clinically significant bradycardia, hypotension or bronchospasm.
After a response, reassess the abdomen and bowel function and confirm that improvement persists. The local service determines the observation arrangements; a transient stool does not prove that the colon has remained decompressed.
Continue to address the precipitating illness, drug burden, mobility and electrolyte balance. After resolution, a constipation-prevention plan may include appropriate laxative treatment, but this is distinct from giving laxatives into an acutely dilated colon.
Document any decision against intervention in the context of frailty, prognosis and the patient’s preferences. Provide an active comfort and escalation plan, and communicate which further measures would be appropriate if the patient worsens.

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

Diameter is a risk signal

A caecum above approximately 12 cm, a rapidly increasing diameter or prolonged dilatation increases concern for perforation. The cited thresholds derive largely from observational evidence and are not hard biological boundaries. Clinical stability, tenderness, perfusion and the rate of change determine whether further observation is safe.

The local dose is not universal

The South East London formulary permits a single 2 mg IV dose over 40–60 minutes for this off-label indication. ACPGBI discusses a different, faster regimen from its evidence base. These timings must not be blended into an invented protocol; the actual administering service must use a verified compatible preparation and its own approved delivery arrangements.

Product and indication must match

Plain neostigmine injection is different from a fixed neostigmine–glycopyrronium product used in anaesthesia. The hameln product lists paralytic ileus dosing by intramuscular or subcutaneous routes; the intravenous ACPO example is off-label. Reversal-of-neuromuscular-blockade dosing and routine coadministration rules cannot simply be imported into ACPO treatment.

Access is part of timely care

A patient who needs decompression should not drift through repeated days of supportive care because the required monitored bed or endoscopist is difficult to obtain. Escalate the service problem with the responsible consultant while reassessing clinical risk. Choice between neostigmine and endoscopy depends on eligibility, expertise and response, with surgery for complications or refractory disease.

11Common pitfallsFrequent interpretation and management errors.

01
Diagnosing ACPO from postoperative timing or a single enlarged caecal measurement can conceal cancer, volvulus or colitis that needs a different treatment pathway.
02
Waiting for exactly 72 hours or a caecum larger than 12 cm despite new tenderness ignores the clinical exclusions that make conservative care acceptable.
03
Using the whole 1 mL ampoule when 2 mg is prescribed delivers 2.5 mg with the selected product; stock concentration and prepared administration volume are separate checks.
04
Giving neostigmine without appropriate monitoring and immediate rescue capability omits an essential part of the treatment’s safety, even when the numerical dose is correct.

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