Bowel obstruction: recognising SBO and LBO in general practice

Mechanical bowel obstruction is a same-day surgical emergency. The GP’s role is narrow but critical: recognise the triad of colicky abdominal pain, progressive abdominal distension, and obstipation (inability to pass flatus or stool); initiate nil-by-mouth and IV access; never prescribe a laxative or enema; and arrange same-day transfer to the emergency department. Small bowel obstruction (SBO) accounts for ~80% of cases, caused by adhesions in 75%; large bowel obstruction (LBO) accounts for the remaining 20%, with colorectal cancer the cause in approximately 60% of LBO. Overall mortality is 5–10% for SBO and 10–15% for LBO, rising to 20–30% with strangulation or delayed presentation.

A. Core clinical — the AU general-practice framework

Red flags for strangulation (call 000)

Strangulation — vascular compromise of the obstructed segment — is a surgical emergency. eTG complete and RACGP acute abdomen guidance identify the following as indications for immediate 000:

• Pain character shift — colicky pain becoming constant and severe.
• Peritonism — localised guarding, rigidity, rebound tenderness.
• Fever (>38.0°C) or tachycardia (>100 bpm).
• Hypotension or poor peripheral perfusion.
• Faeculent vomiting — late sign indicating prolonged obstruction or fistula.
• Suspected closed-loop obstruction — volvulus, incarcerated hernia, or adhesive band blocking bowel at two points.

In closed-loop obstruction, intraluminal pressure rises rapidly, arterial inflow is impaired, and ischaemia can progress to perforation within hours. Pre-notify the receiving emergency and surgical team during transfer.

Distinguishing SBO from LBO

Feature	SBO	LBO
Pain site	Periumbilical, colicky every 4–5 min	Lower abdominal
Vomiting	Early, bilious (faeculent late)	Late or absent
Distension	Moderate (ladder pattern on AXR)	Marked; massive in volvulus
Obstipation	Late (partial SBO may pass some gas)	Early and prominent
Bowel sounds	High-pitched tinkling → silent	Tinkling → silent

Relevant history

Identify risk factors and cause:

• Prior abdominal surgery — adhesions from appendicectomy, gynaecological, colorectal, hernia repair, or bariatric (Roux-en-Y — internal hernia risk).
• Known hernia — inguinal, femoral, incisional, umbilical; note whether recently painful or irreducible.
• Malignancy history — colorectal, ovarian, gastric, or peritoneal carcinomatosis.
• Inflammatory bowel disease — Crohn’s stricture.
• Bowel cancer screening status — National Bowel Cancer Screening Program (NBCSP) iFOBT participation.
• Change in bowel habit or rectal bleeding — raises suspicion for LBO from colorectal cancer.
• Medications — opioids, anticholinergics, antipsychotics, calcium-channel blockers (constipation / ileus precipitants).
• Residential care, cognitive impairment — faecal impaction risk.
• Remote location — sigmoid volvulus is more prevalent in some remote elderly Aboriginal and Torres Strait Islander communities; retrieval logistics need early planning.

Examination

Vital signs first — tachycardia, hypotension, and fever signal strangulation or sepsis.

• Inspection: abdominal distension; surgical scars (adhesions); visible peristalsis (proximal chronic SBO); all hernial orifices — inguinal, femoral, umbilical, incisional.
• Palpation: site and severity of tenderness; peritonism (guarding, rigidity, rebound); palpable mass (intussusception sausage, caecal mass).
• Percussion: tympany over gas-filled loops; dullness for ascites or mass.
• Auscultation: high-pitched tinkling early in mechanical obstruction → silent late; absent from the outset in ileus.
• Rectal examination (PR): faecal impaction; empty rectum (proximal mechanical obstruction); low rectal mass; blood.
• Femoral and obturator hernias in elderly women — these are commonly missed. A strangulated femoral hernia presents as vomiting and colicky pain and carries high mortality if identified late. Always examine below the inguinal ligament in elderly women with vomiting and abdominal pain.

First-line investigations

If transfer will take >30 minutes and the practice is equipped:

• IV access + blood collection: FBC (MBS 65070); UEC (66500); LFTs (66509); lipase (66518); VBG with lactate (elevated lactate indicates ischaemia or sepsis).
• Erect + supine abdominal X-ray (MBS 58300): dilated loops (small bowel >3 cm, large bowel >6 cm, caecum >9 cm), air-fluid levels, absent distal gas, free intraperitoneal gas (Rigler’s sign = perforation). Sensitivity is only 50–60% for SBO — a normal AXR does not exclude obstruction.
• CT abdomen + pelvis with IV contrast (MBS 56507) is the gold standard: sensitivity ~95%, specificity ~95%, identifies transition point, cause, and ischaemia signs (pneumatosis intestinalis, portal venous gas, mesenteric fat stranding) per WSES ASBO 2018. In practice, CT is usually requested from the ED under surgical review.

GP management before transfer

1. Nil by mouth immediately.
2. IV access — large-bore peripheral cannula; blood collection as above.
3. IV fluid resuscitation — Hartmann’s or 0.9% NaCl 1 L over 1 hour; cautious in known cardiac or renal disease.
4. Nasogastric tube if vomiting is severe and transfer is prolonged — large-bore NG to free drainage reduces aspiration risk.
5. Analgesia — paracetamol 1 g IV or PO is safe. Avoid opioids pre-arrival where possible (masks signs, worsens ileus), but do not withhold if pain is severe.
6. Do NOT prescribe laxatives, enemas, or prokinetics — in mechanical obstruction, these increase intraluminal pressure and risk perforation of a strangulated or closed-loop segment.
7. Document prior surgery and hernia history, medications (especially opioids and anticholinergics), fasting time, allergies, and vital-sign trend.
8. Transfer Cat-1 (call 000) for peritonism, haemodynamic instability, fever, severe constant pain, or suspected strangulation. Otherwise same-day ED referral.

B. Evidence: Gastrografin, SEMS, and the 48–72-hour trial

Gastrografin challenge in adhesive SBO

Branco et al. (World J Emerg Surg 2017) pooled data from multiple randomised controlled trials and showed that water-soluble contrast (Gastrografin, 100 mL via NG) has a dual role in stable adhesive SBO without peritonism:

• Predictive: contrast reaching the colon within 24 hours on plain X-ray predicts non-operative resolution with sensitivity ~96% and specificity ~98%.
• Therapeutic: its hyperosmolarity draws fluid into the bowel lumen, accelerating resolution and reducing operative rates.

Abbas et al. (Cochrane 2007) confirmed these findings in an earlier systematic review, showing Gastrografin reduces both the operative rate and total hospital length of stay.

The WSES Bologna ASBO 2018 guidelines recommend a time-limited conservative trial of 48–72 hours — NG decompression, IV fluid, electrolyte correction, and Gastrografin with close monitoring — for stable adhesive SBO without signs of strangulation or peritonism. Approximately 60–80% of cases resolve without surgery within this window. Beyond 72 hours, mortality and complication rates rise sharply, and surgery is indicated.

Self-expanding metal stent for malignant LBO

For obstructing left-sided colorectal cancer, Pirlet et al. (Surg Endosc 2011) and Sloothaak et al. (Lancet Oncol 2014) showed that endoscopic self-expanding metal stent (SEMS) placement can serve as a bridge to elective resection (avoiding emergency colostomy and allowing pre-operative staging) or as definitive palliation in patients unfit for surgery. Both trials demonstrated reduced stoma rates and non-inferior short-term oncological outcomes. Long-term oncological signal regarding perforation and tumour seeding continues to be studied. Current NICE NG151 guidance supports selective use — strongest evidence for palliation in incurable obstructing CRC, and as a bridge-to-surgery in carefully selected candidates per multidisciplinary team (MDT) decision. SEMS is not available in all Australian centres; the treating colorectal team makes this decision.

Sigmoid volvulus: endoscopy first

Flexible sigmoidoscopy with flatus tube placement achieves decompression in approximately 80% of sigmoid volvulus cases and avoids emergency surgery with its associated morbidity in frail elderly patients. Recurrence rates without subsequent resection are 40–60%, so semi-elective sigmoid colectomy is recommended after recovery. Caecal volvulus does not respond reliably to endoscopic reduction and requires right hemicolectomy.

C. Special situations in general practice

Palliative malignant bowel obstruction

When bowel obstruction arises in a patient with advanced incurable malignancy — particularly peritoneal carcinomatosis from ovarian, colorectal, or gastric cancer — the goals of care shift from curative intent to comfort and symptom control. Obita et al. (Cochrane 2016) supports the following symptom-focused approach in inoperable malignant bowel obstruction:

• Goals-of-care discussion — essential early; involve the patient, family, and palliative care team.
• Venting nasogastric tube or percutaneous gastrostomy — for chronic high-level obstruction where surgery is not appropriate.
• Octreotide 100–600 µg/day SC (PBS Authority Required for palliative bowel obstruction) — reduces intestinal secretions and vomiting frequency.
• Dexamethasone 8–16 mg/day — reduces peri-tumour oedema and acts as an anti-emetic.
• Anti-emetics — haloperidol, cyclizine, or levomepromazine SC via syringe driver.
• Avoid prokinetics (metoclopramide, domperidone) in complete mechanical obstruction — they worsen colic without relieving the block.
• SEMS for selected partial obstruction; surgery reserved for fit patients with an isolated, technically amenable lesion.

Advance care planning — including the patient’s preferences regarding future surgery, NG tube insertion, and hospital admission — is best established proactively during a GP consultation rather than in an acute emergency setting.

Elderly faecal impaction

Faecal impaction in elderly, institutionalised, cognitively impaired, or opioid-treated patients can present with abdominal pain, distension, and vomiting that resembles mechanical obstruction. PR examination confirming a loaded rectum, combined with AXR showing diffuse faecal loading without a clear transition point, supports the diagnosis. Management is gentle manual disimpaction followed by tap-water enemas and an osmotic laxative (Macrogol; PBS General Schedule for chronic constipation, not for acute obstruction). Crucially, faecal impaction in an older person warrants interval colonoscopy 4–8 weeks after resolution to exclude underlying colorectal cancer.

Ogilvie pseudo-obstruction

Ogilvie syndrome — acute colonic pseudo-obstruction without mechanical cause — occurs in hospitalised, post-operative, trauma, or acutely unwell patients. Caecal diameter >12 cm risks perforation (Laplace’s law). Management: correct electrolytes; cease opioids and anticholinergics; neostigmine 2 mg IV (with cardiac monitoring) if caecal diameter >12 cm or the condition persists >48 hours; colonoscopic decompression if neostigmine is contraindicated or fails.

Paediatric intussusception

Ileocolic intussusception in infants aged 3–9 months presents with episodic colic, drawing up of the legs, red-currant-jelly stool, and a sausage-shaped abdominal mass. Ultrasound confirms the target sign. Air or water-soluble contrast enema reduction is first-line (success ~80%); surgery is required for failed reduction, perforation, or peritonism. Adult intussusception is uncommon and has an underlying lead point in ~90% of cases (lipoma, tumour, Meckel’s diverticulum), requiring surgical management.

D. Australian operations

MBS billing for GP-led care

Item	Descriptor
23 / 36 / 44	Level B / C / D consultation
597–600	Urgent after-hours attendance
965 / 967	GP Chronic Condition Management Plan (post-CRC survivorship, recurrent SBO)
2715 / 2717	Mental Health Treatment Plan (stoma adjustment, post-operative anxiety)
715	ATSI annual health assessment
705	Health assessment for people aged ≥75 years
92024	ACAT assessment for elderly patients transitioning to aged care after bowel obstruction

PBS items relevant to bowel obstruction management

• Octreotide (Sandostatin) — Authority Required (palliative malignant bowel obstruction is an accepted indication, alongside neuroendocrine tumours and acromegaly).
• Macrogol (Movicol, OsmoLax) — General Schedule for chronic constipation (not for acute obstruction).
• Opioid analgesia — General + Authority depending on formulation; SafeScript / RTPM monitoring applies in Victoria and other participating states.
• Gastrografin — not PBS-listed; supplied via hospital pharmacy under contrast media budget.
• Broad-spectrum antibiotics (piperacillin-tazobactam, ceftriaxone, metronidazole) — hospital supply for surgical or septic obstruction.

Referral pathway

Scenario	Referral	Urgency
Suspected mechanical obstruction (any)	ED (000 if peritonism or instability)	Same-day
Strangulation / closed-loop / peritonism	000 + surgical pre-alert	Immediate
Stable malignant LBO	ED → colorectal MDT	Same-day
Sigmoid volvulus, no peritonism	ED → endoscopic decompression	Same-day
Elderly faecal impaction, no obstruction signs	GP disimpaction; ED if failed / red flags	Routine to soon
Recurrent adhesive SBO (outpatient)	Colorectal surgeon	Routine
Palliative malignant bowel obstruction	Palliative care + colorectal MDT	Soon
Post-operative GP review	GP + stoma nurse + dietitian	Within 1–2 weeks

Guideline alignment

AU primary: eTG complete — Bowel obstruction · RACGP AJGP acute abdomen · RACS general surgery · Cancer Council OCP for Colorectal Cancer · ACSQHC Acute Deterioration Standard.

International: WSES Bologna ASBO 2018 · NICE NG151.

E. Special populations

Aboriginal and Torres Strait Islander peoples

Remote and very remote communities face extended transport times to definitive surgical care — strangulation may be irreversible by arrival. The threshold for early retrieval via the Royal Flying Doctor Service or aeromedical transfer should be low. Sigmoid volvulus is more prevalent in some remote elderly Aboriginal communities, possibly related to chronic constipation and dietary factors. The NBCSP iFOBT should be offered opportunistically at every general practice contact. The Closing the Gap PBS co-payment applies to post-operative medications.

Post-bariatric surgery patients

Patients who have undergone Roux-en-Y gastric bypass are at risk of internal hernia — herniation through mesenteric defects created during the anastomosis. Internal hernia can cause a subtle closed-loop SBO that is difficult to detect on standard CT and may require laparoscopy for diagnosis and treatment. Any post-bariatric patient presenting with abdominal pain warrants a high index of suspicion and urgent surgical assessment.

Hereditary colorectal cancer syndromes

A patient presenting with obstructing LBO at a young age (under 50 years) or with a family history of colorectal cancer warrants referral to a Family Cancer Clinic post-acutely for Lynch syndrome and familial adenomatous polyposis (FAP) assessment. RACGP Genomics in General Practice guidance provides the referral framework.

Malignant bowel obstruction in advanced cancer

Patients with peritoneal carcinomatosis from ovarian, colorectal, or gastric cancer face ongoing risk of recurrent bowel obstruction. Advance care planning — covering preferences regarding further surgery, NG tube insertion, hospital admission, and the role of octreotide and palliative SEMS — is best undertaken proactively during a GP consultation rather than during an acute crisis. Early palliative care referral supports this process.

When to escalate

• Call 000 immediately for peritonism, haemodynamic instability, fever, or pain shifting from colicky to constant in a patient with suspected obstruction — these indicate strangulation or perforation.
• Same-day ED for all other suspected mechanical bowel obstruction. Do not manage at home or in the practice pending imaging.
• Seek senior GP or specialist telephone advice if uncertain between obstruction, severe constipation, and ileus — the safe default is same-day ED referral.
• Palliative care team early in any patient with advanced malignancy and recurrent obstruction, to establish goals of care before the next acute episode.

What this article is and is not

This article summarises current Australian and international guideline recommendations for bowel obstruction, written to support GP-level recognition and transfer decisions. It is not a substitute for clinical judgement, specialist assessment, or the full eTG and WSES guideline text. Decisions about Gastrografin challenge, SEMS, surgical technique, and palliative management are made by the treating surgical and palliative care teams, not in general practice.

This article does not constitute individual medical advice. Patients with abdominal pain, distension, or vomiting should seek assessment from their GP or, if symptoms are severe or rapidly worsening, call 000 or present to the nearest emergency department.

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Sources cited

1. RACGP — Acute abdomen: GP assessment (AJGP)
2. eTG complete — Bowel obstruction and acute abdomen
3. RACS — General surgery resources
4. ACSQHC — Recognising and Responding to Acute Deterioration Standard
5. Cancer Council Australia — Optimal Care Pathway for People with Colorectal Cancer
6. WSES Bologna Guidelines — Adhesive Small Bowel Obstruction (ASBO) 2018
7. NICE NG151 — Colorectal cancer (acute presentation)
8. Branco BC et al. Systematic review and meta-analysis of Gastrografin in adhesive SBO. World J Emerg Surg 2017
9. Abbas SM et al. Oral water-soluble contrast for adhesive SBO — Cochrane 2007
10. Pirlet IA et al. Emergency stent placement vs surgery in obstructing left-sided colon cancer. Surg Endosc 2011
11. Sloothaak DAM et al. Optimal interval between stent placement and surgery for malignant LBO. Lancet Oncol 2014
12. Obita GP et al. Somatostatin analogues for malignant bowel obstruction — Cochrane 2016
13. MBS Online — items 23, 36, 44, 56507, 58300, 65070, 66500, 66509, 66518, 66830, 69300, 705, 715, 965, 967, 2715, 2717, 92024, 597–600
14. Pharmaceutical Benefits Scheme — octreotide (Authority — palliative MBO), Macrogol (General — chronic constipation), opioids (General + Authority + SafeScript)