Malignant bowel obstruction

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

Malignant bowel obstruction is failure of forward gastrointestinal transit caused by cancer or its treatment. A colorectal tumour may create one intraluminal narrowing, whereas ovarian or gastrointestinal carcinomatosis often fixes several small-bowel loops. Previous surgery adds adhesions and anastomotic stricture; pelvic radiotherapy adds fibrosis; opioids, anticholinergics, sepsis and electrolyte disturbance can superimpose functional ileus. Defining whether disease is single-level, multifocal, mechanically correctable or predominantly dysmotile is more useful than treating every presentation as terminal carcinomatosis.

Obstruction traps swallowed air and ongoing gastric, biliary, pancreatic and intestinal secretion. Distension initially impairs venous and lymphatic drainage, causing wall oedema and further secretion. In a closed loop or progressive high pressure, arterial supply fails and bowel becomes necrotic or perforates. Vomiting and third-space loss cause kidney injury and electrolyte disturbance that worsen motility. High obstruction produces early frequent vomiting with limited distension; distal obstruction produces greater distension and later faeculent vomiting. Passage of stool or diarrhoea can persist in partial obstruction and does not rule it out.

Contrast-enhanced CT abdomen and pelvis is the key first-line anatomical examination. It locates transition points, distinguishes small from large bowel, identifies closed loop, wall enhancement, free fluid or gas, maps peritoneal burden and shows whether a stent, stoma, resection, bypass or venting gastrostomy is technically plausible. Plain radiography may demonstrate dilated loops but lacks enough information for definitive malignant planning. Blood tests assess dehydration, renal and electrolyte injury, inflammation, lactate, cytopenia and operative risk but cannot exclude bowel ischaemia.

Management starts with physiology and symptom relief, then a realistic procedural decision. Nil by mouth, intravenous fluid, potassium and magnesium correction, analgesia, antiemetic and temporary nasogastric decompression stabilise the patient. Emergency surgery is considered for perforation or ischaemia. Elective palliative surgery or colonic stenting offers most benefit when there is a single target, acceptable performance and a meaningful interval of expected function; multifocal disease, ascites and poor reserve reduce benefit. Medical care uses antisecretory and antispasmodic therapy, corticosteroid in selected oedematous obstruction and venting gastrostomy for recurrent vomiting, while hydration and nutrition decisions follow prognosis and patient goals.

Key points

Malignant bowel obstruction may be a single intraluminal stricture, external compression, multifocal peritoneal encasement or diffuse functional ileus; treatment depends on the mechanism.
Colicky pain, vomiting, distension and reduced flatus or stool are typical, but partial obstruction can still pass stool and high small-bowel obstruction can vomit before marked distension.
First-line definitive imaging is contrast-enhanced CT abdomen and pelvis, which identifies level, transition, multiplicity, tumour burden, closed loop, ischaemia and potential stent or surgical target.
Initial care is nil by mouth, reassessed intravenous fluid and electrolyte replacement, antiemetic and analgesia, with nasogastric decompression for persistent vomiting or major gastric distension.
Peritonism, continuous severe pain, shock, rising lactate, closed loop or poor bowel-wall enhancement requires immediate senior surgical assessment regardless of cancer prognosis.
A single operable obstruction in a fit patient may benefit from resection, bypass or stoma; selected left-sided malignant colonic obstruction may be treated with an endoscopic self-expanding metal stent.
When surgery or stent will not provide worthwhile benefit, octreotide reduces gastrointestinal secretion, anticholinergic therapy reduces colic and a venting gastrostomy can replace prolonged nasogastric drainage.
Use metoclopramide only in selected partial obstruction without colic; avoid prokinetic treatment in complete mechanical obstruction because it can worsen painful contractions and risk.

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

Intraluminal or mural tumour

Colorectal and other primary or recurrent cancers narrow the bowel wall directly, creating a fixed transition point and proximal dilatation.

Extrinsic peritoneal disease

Ovarian, colorectal, gastric and other peritoneal metastases encase or tether several bowel loops, often producing multifocal small-bowel obstruction.

Post-treatment structural disease

Adhesions, radiation fibrosis, anastomotic stricture and recurrent tumour can coexist after abdominal or pelvic cancer surgery and radiotherapy.

Functional malignant ileus

Diffuse carcinomatosis, autonomic infiltration, opioids, anticholinergics, sepsis and electrolyte disturbance impair propulsion without one correctable mechanical point.

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

1
Proximal secretion accumulates
Swallowed air and several litres of gastrointestinal secretion collect above obstruction, causing distension, vomiting and further secretory drive.
2
Venous drainage fails
Rising intraluminal pressure first impairs venous and lymphatic outflow, producing wall oedema and reducing absorption while arterial supply initially persists.
3
Arterial supply becomes threatened
Closed-loop distension, torsion or sustained wall pressure compromises arterial flow, causing necrosis, bacterial translocation, perforation and sepsis.
4
Systemic depletion develops
Vomiting and third-space loss cause hypovolaemia, kidney injury, alkalosis or acidosis and potassium, chloride and magnesium disturbance that worsen ileus.

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

Colicky mechanical pain

Waves of cramping pain with visible or audible increased activity suggest bowel contracting against a mechanical narrowing before fatigue or ischaemia develops.

High small-bowel pattern

Early frequent bilious vomiting, rapid dehydration and relatively little initial distension points to proximal obstruction.

Distal colonic pattern

Progressive distension, lower abdominal pain and obstipation with later vomiting suggests distal large-bowel obstruction and potential caecal pressure risk.

Multifocal carcinomatosis

Intermittent symptoms, ascites, several transition points and tethered loops indicate diffuse peritoneal disease less amenable to one operation or stent.

Ischaemic conversionRed flag

Pain becoming continuous, peritonism, fever, tachycardia, acidosis or shock indicates threatened bowel and needs urgent surgical action.

Functional overlay

Diffuse dilatation without a clear transition plus opioid, sepsis or electrolyte triggers suggests ileus that may improve when reversible causes are corrected.

Red flags requiring action

Continuous rather than intermittent pain, guarding, rebound or pain out of proportion raises strangulation, ischaemia or perforation.
Fever, hypotension, oliguria, confusion, raised lactate or metabolic acidosis indicates sepsis or compromised bowel and needs urgent surgical review.
Closed-loop configuration, reduced wall enhancement, pneumatosis, portal venous gas or free intraperitoneal gas on CT requires immediate escalation.
Persistent high-volume vomiting causes aspiration, severe chloride and potassium loss and acute kidney injury even without peritonism.
Recent opioid escalation, anticholinergic medicine, electrolyte disturbance and faecal impaction can worsen functional obstruction and must be assessed alongside tumour.

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
First-line contrast CT abdomen and pelvisFirst stepFirst line
Why
Locate and characterise obstruction and identify ischaemia, perforation, multiplicity and procedural options.
Interpretation and limitations
Report transition level, bowel calibre and enhancement, closed loop, free fluid or gas, carcinomatosis, ascites and whether anatomy supports stent, surgery or venting access.
02
FBC, renal profile, magnesium and acid-base status
Why
Quantify dehydration, electrolyte loss, infection, cytopenia and treatment or operative risk.
Interpretation and limitations
Correct potassium, chloride and magnesium and trend kidney function; normal bloods do not exclude early strangulation, while neutropenia changes the inflammatory response.
03
Lactate and repeated abdominal examination
Why
Detect deteriorating perfusion and evolving peritonism while imaging and decisions proceed.
Interpretation and limitations
A rising lactate or new guarding is concerning, but early ischaemia can have a normal lactate; the trajectory and CT features matter together.
04
Digital rectal examination when safe
Why
Assess distal tumour, faecal impaction, blood and rectal emptying in an appropriate non-neutropenic patient.
Interpretation and limitations
Avoid rectal instrumentation in profound neutropenia or severe thrombocytopenia; an empty rectum is non-specific and does not establish complete obstruction.
05
Endoscopic assessment for colonic stent
Why
Confirm and traverse a suitable single malignant colonic stricture for decompression.
Interpretation and limitations
Specialist endoscopy reviews location, perforation, multifocal disease and antiangiogenic therapy; stenting is not suitable for every obstruction or perforated bowel.
06
Nutrition, hydration and performance assessment
Why
Determine likely benefit and burden of surgery, parenteral nutrition, gastrostomy and discharge support.
Interpretation and limitations
Use disease trajectory, inflammatory burden, organ function, expected survival and goals rather than albumin or age alone.

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

Severe constipation or impaction

Rectal loading and opioid-related stool retention can mimic distal obstruction and may coexist; examination and CT determine whether proximal mechanical disease is present.

Treatment-related ileus

Opioids, anticholinergics, vinca alkaloids, immunotherapy enteritis, sepsis and electrolyte deficiency can stop motility without a fixed tumour transition.

Acute colonic pseudo-obstruction

Marked colonic dilatation without mechanical occlusion occurs in severe illness or after surgery and follows a distinct decompression and medicine pathway.

Gastrointestinal infection or inflammation

Gastroenteritis, neutropenic enterocolitis, diverticulitis and inflammatory strictures cause pain, vomiting and bowel change and may be more urgent than malignant progression.

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

01InitialResuscitate and define anatomyFirst stepA person with cancer develops vomiting, colicky pain, distension or failure to pass stool or flatus.

1Use ABCDE, keep nil by mouth, establish intravenous access, correct fluid and electrolyte loss, provide analgesia and antiemetic and decompress persistent vomiting with a nasogastric tube.
2Obtain contrast CT abdomen and pelvis promptly and repeat examination and lactate while looking for peritonism, closed loop, poor enhancement, free gas or shock.
3Call senior surgery immediately for ischaemia, perforation or sepsis and involve acute oncology and palliative care early for cancer context and symptom support.

02ProceduralSelect a durable mechanical optionImaging shows a potentially correctable single or dominant obstruction and the patient is fit enough to benefit.

1Review resection, bypass or stoma from obstruction site, cancer burden, ascites, prior surgery, nutrition, performance, expected survival and the patient's functional priorities.
2For a suitable malignant colonic stricture without perforation, discuss self-expanding metal stent as palliation or bridge to planned surgery through an experienced endoscopy service.
3Explain mortality, leak, re-obstruction, stent migration or perforation and the realistic time to eating and discharge rather than presenting an intervention as automatically beneficial.

03Medical palliationReduce secretion, colic and vomitingSurgery or stenting is unsuitable, unwanted or unlikely to provide worthwhile function.

1Stop non-essential oral medicines and use subcutaneous or parenteral routes; give antiemetic matched to obstruction type, analgesia and an antisecretory medicine such as octreotide.
2Add hyoscine butylbromide for colic and consider a short dexamethasone trial for tumour or bowel-wall oedema, reviewing benefit and stopping if ineffective.
3Avoid prokinetic metoclopramide in complete obstruction or significant colic; it may be considered only for selected partial obstruction with ongoing output and no mechanical danger.

04Recurrent vomitingReplace prolonged nasogastric drainageVomiting recurs despite medicines and long-term gastric decompression is needed.

1Discuss radiological or endoscopic venting gastrostomy, including feasibility with ascites, infection, anatomy and the person's goals for home care.
2Teach tube venting, skin care, blockage response and medicine routes and arrange community nursing and equipment before discharge.
3Review clinically assisted hydration and parenteral nutrition separately from decompression, offering them only when expected functional benefit outweighs line, infection and fluid burden.

Key medicines and prescribing safety4 treatments · regimens, roles and cautions

Reduces gastrointestinal and pancreatic secretion and motility, decreasing vomiting and nasogastric losses in inoperable malignant obstruction.

Octreotide

Start octreotide 300 micrograms by continuous subcutaneous infusion over 24 hours for persistent vomiting and high gastrointestinal secretion, titrating within the current specialist palliative-care protocol according to output and symptom response.

Monitor abdominal symptoms, glucose, heart rate and injection site; longer use can cause biliary effects. It does not reverse ischaemia or perforation and should not delay surgical reassessment when pain changes.

Reduces smooth-muscle spasm and gastrointestinal secretion when intermittent colicky pain accompanies obstruction.

Hyoscine butylbromide

Give 20 mg subcutaneously as needed for colic and, when recurrent, 60 mg by continuous subcutaneous infusion over 24 hours, titrating to the palliative-care protocol and response.

Can worsen dry mouth, urinary retention, glaucoma and delirium and may oppose a desired prokinetic strategy; continuous severe pain requires renewed ischaemia assessment rather than more antispasmodic alone.

May reduce peritumour and bowel-wall oedema and improve transit in selected malignant obstruction while other decisions are made.

Dexamethasone short trial

Use dexamethasone 6 to 16 mg subcutaneously or intravenously once daily for a time-limited specialist trial, commonly three to five days, then stop if ineffective or taper promptly when benefit permits.

Monitor glucose, infection, delirium, dyspepsia and proximal weakness; benefit is uncertain and prolonged exposure without an objective response adds harm.

Promotes coordinated upper gastrointestinal transit and treats nausea in a carefully selected incomplete functional or mechanical obstruction.

Metoclopramide in selected partial obstruction

When obstruction is partial, flatus or stool continues and colic is absent, use the specialist palliative-care oral or subcutaneous regimen, commonly 30 mg by continuous subcutaneous infusion over 24 hours, with daily review.

Avoid in complete obstruction, colicky pain, perforation or gastrointestinal haemorrhage because stronger contractions can worsen pain or risk; monitor dystonia, akathisia and Parkinsonism.

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

Bowel ischaemia and perforation

Pressure and vascular compromise cause transmural necrosis, free contamination, septic shock and need for emergency surgery or drainage.

Aspiration pneumonia

Recurrent vomiting, gastric stasis, reduced consciousness and nasogastric procedures increase aspiration and hypoxaemic respiratory failure risk.

Renal and electrolyte failure

Large fluid and chloride losses plus poor intake cause acute kidney injury, potassium and magnesium depletion and acid-base disturbance.

Recurrent obstructive symptoms

Multifocal peritoneal disease commonly re-obstructs after initial improvement, requiring anticipatory decompression, medicine and personalised goals planning.

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

During initial care, measure observations, pain pattern, abdominal signs, vomiting and nasogastric output, urine, fluid balance, creatinine, potassium, chloride and magnesium.
Repeat surgical examination immediately if pain becomes continuous, guarding appears, lactate rises or physiological support increases, even after a palliative plan was agreed.
Review every antisecretory, antispasmodic, antiemetic and corticosteroid at least daily for symptom response, adverse effects and route feasibility.
After stent or surgery, monitor perforation, leak, sepsis, recurrent obstruction, stoma function, oral intake and the expected rehabilitation and discharge trajectory.
For a venting gastrostomy, monitor output, blockage, leakage, skin, ascites and patient or carer ability to manage the device at home.
Revisit hydration, nutrition and future intervention decisions as cancer and function change, documenting who to contact for recurrent vomiting or new continuous pain.

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

Stool passage does not exclude

Distal contents and liquid can pass during partial or early obstruction, so continuing stool does not overrule the symptom and CT pattern.

One obstruction is different

A single colonic transition may be stented or bypassed, while multifocal tethered small bowel often cannot be corrected by one procedure.

Pain pattern can change urgency

Intermittent colic reflects contractions; conversion to constant severe pain suggests ischaemia, perforation or tumour pain needing reassessment.

Octreotide reduces the upstream load

Antisecretory treatment can relieve vomiting even when luminal patency cannot be restored, improving comfort and facilitating home care.

Nutrition is a separate decision

Venting the stomach and providing parenteral nutrition answer different goals and should not be bundled into one automatic intervention.

11Common pitfallsFrequent interpretation and management errors.

01
Ruling out obstruction because the patient passed stool or has diarrhoea.
02
Using plain abdominal radiography as the definitive malignant-anatomy study when CT is feasible.
03
Calling continuous severe pain ordinary colic and missing ischaemia or perforation.
04
Offering surgery without considering multifocal disease, ascites, performance, recovery time and patient goals.
05
Using metoclopramide in complete mechanical obstruction or painful colic.
06
Leaving a nasogastric tube indefinitely without considering medication optimisation or venting gastrostomy.
07
Starting parenteral nutrition automatically without an expected functional benefit and line-risk discussion.