On-Call Decision Making: Four Common Emergencies

Not what the condition is — what you actually decide at 2am.

You know the pathology. What erodes with time away from the on-call rota is decision speed: who needs CT tonight, who can wait until the morning, who goes to theatre now, and when you pick up the phone to the consultant.

This is written as the decision, not the textbook.

Last reviewed: August 2026. Reflects NICE, ACPGBI, ESGE and AUGIS positions current at that date. Local pathways vary — check your trust protocol. Educational resource; not a substitute for senior clinical advice.

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Before Any Of It — The Universal First Five Minutes

Whatever the referral, the same sequence:

1. Are they sick? — NEWS2, lactate, urine output. A NEWS2 of 7 changes your timeline regardless of diagnosis.
2. Do they have peritonitis? — this is the single question that most often determines theatre tonight vs imaging first.
3. Resuscitate while you think. Two cannulae, bloods including lactate and VBG, group and save, fluids, catheter, analgesia. Do not wait for the diagnosis to start.
4. Analgesia does not mask peritonism in any clinically meaningful way. Give it.
5. What's the anaesthetic risk? — ASA, frailty, anticoagulation, functional status. This shapes the plan as much as the diagnosis does.

Three things that should raise your threshold to act immediately, regardless of how well the patient looks:

• On steroids or immunosuppressed — peritonism is blunted, and the abdomen can be soft with frank contamination inside it.
• Elderly and frail — physiology is preserved until it collapses. A normal blood pressure in an 85-year-old on beta-blockers means very little.
• Rising lactate on serial gases — a single normal lactate reassures far less than a trend.

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1. ACUTE DIVERTICULITIS

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The call

"LIF pain, tender, CRP 180, known diverticular disease."

What you need to establish

• Systemically well or unwell? This is the branch point for antibiotics.
• Localised or generalised peritonism?
• Immunocompetent? Steroids, biologics, chemotherapy, transplant — changes everything.
• First episode or recurrent?
• Any red flags for cancer? Weight loss, altered bowel habit, iron deficiency anaemia, no previous diagnosis.

Antibiotics — the change most people haven't absorbed

NICE NG147: do not routinely give antibiotics to patients with uncomplicated acute diverticulitis who are systemically well and immunocompetent. The evidence (AVOD, DIABOLO) shows no difference in recovery time, complications or recurrence.

Give antibiotics if:

• Systemically unwell (fever, tachycardia, raised inflammatory markers with clinical toxicity)
• Immunosuppressed
• Significant comorbidity
• Complicated disease on CT (abscess, perforation, fistula, obstruction)
• Sepsis — follow the sepsis pathway

Duration: review IV antibiotics at 48 hours or after the CT, whichever is sooner. Switch to oral where possible. Up to 14 days for a CT-confirmed abscess. Abscesses under 3 cm can usually be managed with antibiotics alone and an oral switch.

Audits consistently show antibiotic overuse here — this is one of the easiest closed-loop audits available if you need one for a portfolio.

Who gets a CT tonight

CT abdomen-pelvis with IV contrast is the investigation. It confirms the diagnosis, grades severity, identifies an abscess amenable to drainage, and — importantly — reduces subsequent endoscopy.

The decision tree

Hinchey I (pericolic phlegmon or small abscess) → Antibiotics. Drain if the abscess is >3–4 cm.

Hinchey II (pelvic or intra-abdominal abscess) → Radiologically guided percutaneous drainage plus antibiotics. This is the answer, not theatre. Most resolve.

Hinchey III (generalised purulent peritonitis) → Theatre. Hartmann's remains the default in an unstable or contaminated patient. Primary anastomosis with defunctioning loop ileostomy is a reasonable alternative in a stable, fit patient — the LADIES and DIVA data show substantially higher stoma reversal rates. Discuss with your consultant; this is a consultant-level decision.

Laparoscopic lavage for Hinchey III has largely fallen out of favour — SCANDIV, LOLA and DILALA collectively showed higher reintervention rates. Know it exists and know why it isn't standard.

Hinchey IV (faeculent peritonitis) → Theatre. Hartmann's.

When to call the consultant

• Any patient going to theatre — always.
• Hinchey III or IV on CT.
• Failure to improve at 48 hours on treatment.
• Immunosuppressed patient with complicated disease — low threshold, they deteriorate without warning.
• Any consideration of primary anastomosis in the emergency setting.

The traps

The immunosuppressed soft abdomen. A patient on prednisolone with a perforated diverticulum may have a nearly normal examination. Believe the CT, not your hands.

Assuming it's diverticulitis. A first presentation of "diverticulitis" in someone under 50, or with any red flag features, needs a colonoscopy to exclude a perforated colonic cancer — which can look identical on CT.

Interval colonoscopy. No longer routine after uncomplicated diverticulitis. Is indicated after complicated diverticulitis (abscess, perforation), usually at 6–8 weeks, to exclude an underlying malignancy.

Elective resection is not decided by attack count. Not "two attacks and out." Decide on symptoms, complications (stricture, fistula), immunosuppression and patient preference.

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2. BOWEL OBSTRUCTION

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2a. SMALL BOWEL OBSTRUCTION

The call

"Vomiting, distended, not opened bowels, previous laparotomy."

What you need to establish

• Previous abdominal surgery? Adhesions cause 60–70%. No previous surgery changes the whole approach.
• Any hernias? Examine the groins and the umbilicus. Every time. An unexamined femoral hernia is the classic missed cause.
• Complete or partial? Passing flatus suggests partial.
• How long?
• Any features of strangulation?

The question that actually matters: is it strangulating?

Everything else is timing. This is the decision.

Clinical features suggesting strangulation:

• Constant pain rather than colicky
• Localised tenderness or peritonism
• Tachycardia disproportionate to dehydration
• Fever
• Rising lactate on serial gases
• Failure to settle on conservative management

CT features suggesting strangulation or closed loop:

• Closed loop configuration (two adjacent transition points)
• Reduced or absent bowel wall enhancement — the most specific sign
• Mesenteric oedema, engorged vessels, "whirl sign"
• Free fluid between loops
• Bowel wall thickening
• Pneumatosis intestinalis or portal venous gas — very late and very bad

Imaging

CT abdomen-pelvis with IV contrast for essentially all suspected SBO. Plain films are not sufficient — CT identifies the transition point, the cause, and — crucially — signs of ischaemia. Do not accept an AXR as an answer.

The decision tree

Strangulation, closed loop, peritonism, or systemic toxicity → Theatre tonight. Resuscitate en route, do not "trial conservative management."

Virgin abdomen (no previous surgery, no hernia) → Low threshold for surgery. The cause is more likely to be something that needs an operation — malignancy, internal hernia, congenital band, Meckel's, intussusception. Prolonged conservative management here is a common error.

Adhesional, no strangulation features, stable → Conservative trial: NBM, NG tube on free drainage with 4-hourly aspiration, IV fluids, correct electrolytes, catheter, serial examination and serial lactate.

The water-soluble contrast (Gastrografin) challenge — both diagnostic and therapeutic. Give 100 mL via the NG tube, clamp for 2 hours, plain abdominal film at 8–24 hours. Contrast reaching the colon predicts successful non-operative resolution with high accuracy, and the hyperosmolar contrast itself draws fluid into the lumen and often relieves the obstruction. It shortens length of stay and reduces the need for surgery.

Failure to resolve → most units operate at 48–72 hours. Prolonging beyond this increases the risk of ischaemia without increasing the chance of resolution.

When to call the consultant

• Any strangulation feature — immediately, not after the CT report.
• Virgin abdomen SBO.
• Deciding to operate, or deciding not to at 48 hours.
• Rising lactate in a patient you were managing conservatively.
• Obstruction in a patient with known metastatic malignancy — this may be a palliative decision rather than a surgical one, and needs a senior and often an oncology conversation.

The traps

Not examining the groins. It remains the commonest genuinely avoidable miss in general surgery.

A soft abdomen doesn't exclude ischaemia. Early strangulation can present with pain out of proportion and an unimpressive abdomen.

"Conservative management" without a deadline. Set an explicit review point and an explicit endpoint. Document both.

Treating recurrent adhesional SBO as automatically benign. Each episode still carries a risk of strangulation, and repeated admissions may warrant a discussion about definitive surgery.

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2b. LARGE BOWEL OBSTRUCTION

The call

"Distended, absolute constipation, dilated colon on AXR."

Causes, in order

1. Colorectal malignancy (~60%)
2. Volvulus — sigmoid, then caecal
3. Diverticular stricture
4. Pseudo-obstruction (Ogilvie's)

The urgent anatomical question: is the ileocaecal valve competent?

• Competent valve → closed loop obstruction. The colon cannot decompress backwards into the small bowel. Pressure rises, and by Laplace's law (tension proportional to radius) the caecum — the widest segment — is at greatest risk of perforation.
• Caecal diameter >12 cm on imaging is the classic threshold for imminent perforation risk. Do not sit on this.
• Incompetent valve → small bowel also dilates, decompressing the colon. Less immediately dangerous, but muddies the picture.

Imaging

CT abdomen-pelvis with IV contrast. Identifies the level, the cause, caecal diameter, evidence of perforation or ischaemia, and stages malignancy at the same time.

If pseudo-obstruction is suspected, mechanical obstruction must be excluded first — water-soluble contrast enema or CT.

The decision tree

Perforation, peritonitis, ischaemia, or caecal diameter >12 cm with tenderness → Theatre now.

Sigmoid volvulus (coffee bean sign, stable, no peritonism) → Endoscopic decompression — rigid or flexible sigmoidoscopy with flatus tube left in for 24–48 hours. Success 70–90%. Then plan elective sigmoid colectomy during the same admission — recurrence without surgery is 50–70%. → Peritonism, gangrene or failed decompression → theatre (Hartmann's).

Caecal volvulus → Surgery — right hemicolectomy. It cannot be decompressed endoscopically; the caecum is genuinely twisted on its mesentery.

Malignant left-sided obstruction, stable, curative intent → This is where practice has changed. ESGE updated its position in 2020: self-expanding metal stent as a bridge to surgery is now a valid option to discuss with the patient, as an alternative to emergency resection — not restricted, as it was in 2014, to high-risk patients only. Interval to elective resection approximately 2 weeks. Requires stenting expertise and no evidence of perforation. If stenting isn't available, a decompressing stoma as a bridge is a legitimate alternative. → Emergency resection remains appropriate — Hartmann's, subtotal colectomy, or resection with primary anastomosis depending on site and patient.

Malignant obstruction, palliative → Stenting is the preferred treatment for palliation (strong recommendation, high-quality evidence). Caveat: avoid in patients on or being considered for antiangiogenic therapy such as bevacizumab — perforation risk.

Right-sided malignant obstruction → Usually right hemicolectomy with primary anastomosis. Stenting is a weaker recommendation here but is increasingly used.

Pseudo-obstruction (Ogilvie's) — mechanical obstruction excluded → Correct electrolytes (especially K⁺, Mg²⁺), stop opioids and anticholinergics, mobilise, NG tube. → IV neostigmine 2 mg slowly with continuous cardiac monitoring and atropine available. Response rate 80–90%. Contraindicated in bradycardia, bronchospasm, mechanical obstruction and urinary obstruction. → Failure → colonoscopic decompression. Surgery only for perforation or ischaemia.

When to call the consultant

• Every LBO. This is a consultant-level decision in almost every case.
• Caecal diameter >10–12 cm — before it perforates, not after.
• Any consideration of stenting — needs an MDT-flavoured conversation even out of hours.
• Volvulus that fails endoscopic decompression.

The traps

Calling it pseudo-obstruction without excluding mechanical obstruction. Neostigmine into a genuine mechanical obstruction is dangerous.

Sending a decompressed sigmoid volvulus home. They come back, often worse, often out of hours. Plan the resection during the admission.

Forgetting that this is often the presentation of a new cancer. Staging CT chest is part of the workup, and the patient will need an MDT and a conversation.

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3. MESENTERIC ISCHAEMIA

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The call

"Severe abdominal pain, soft abdomen, doesn't look right."

This is the diagnosis most often made too late, and mortality remains 60–80%. Suspicion is the whole game.

The cardinal feature

Pain out of proportion to the clinical findings.

Early on, the visceral peritoneum is ischaemic but the parietal peritoneum is not yet inflamed — so the patient is in severe distress with a soft, unimpressive abdomen. By the time there is peritonism, the bowel is infarcted.

Who to suspect it in

• Atrial fibrillation — embolic, the classic
• Recent MI — mural thrombus
• Known atherosclerosis / peripheral arterial disease — thrombosis on plaque
• Post-prandial pain and weight loss — chronic mesenteric ischaemia now decompensated
• Low cardiac output states, vasopressors, dialysis — non-occlusive (NOMI)
• Hypercoagulable, portal hypertension, recent abdominal surgery, malignancy — mesenteric venous thrombosis

The four types — they matter

Investigations — the two things people get wrong

1. Lactate is not a screening test. It rises late. A normal lactate does not exclude mesenteric ischaemia. By the time lactate is markedly raised, the bowel is usually dead. Use trends, not single values.

2. CT angiography, arterial phase — and no oral contrast. Oral contrast obscures the mesenteric vessels and delays the scan. Ask explicitly for a CT mesenteric angiogram. Say the words "suspected mesenteric ischaemia" to the radiologist — it changes the protocol.

CT findings: arterial filling defect, absent bowel wall enhancement, bowel wall thickening or thinning, mesenteric fat stranding, pneumatosis intestinalis, portal venous gas, free fluid.

The decision tree

Peritonitis or systemic collapse → Laparotomy. Do not delay for angiography in a peritonitic patient.

No peritonitis, CT confirms arterial occlusion → Systemic heparinisation immediately. → Urgent discussion with vascular surgery and interventional radiology. Options: endovascular thrombectomy/thrombolysis/stenting, or open embolectomy or bypass. → Revascularise before resecting where the sequence allows — bowel that looks non-viable can recover once perfused.

Mesenteric venous thrombosis, no peritonism → Anticoagulation is the primary treatment. Many are managed non-operatively.

NOMI → Treat the cause — optimise cardiac output, reduce vasopressors where possible. Intra-arterial vasodilators (papaverine) in some centres.

At laparotomy → Resect frankly necrotic bowel. → If viability is uncertain, resect, staple off, leave in discontinuity, and plan a second-look laparotomy at 24–48 hours. Do not create an anastomosis in questionable bowel. → Extensive infarction in a frail patient may be a decision to close and palliate — a consultant decision, and one that requires an honest conversation with the family.

When to call the consultant

Immediately, on suspicion. Not after the CT. This is the one where you phone early and apologise later if you're wrong. Nobody has ever been criticised for calling too early about possible mesenteric ischaemia.

The traps

Being reassured by a soft abdomen. That is the disease.

Being reassured by a normal lactate. Also the disease.

Waiting for the formal CT report. Look at the images with the radiologist.

Giving oral contrast. Delays the scan and degrades the arterial phase.

Forgetting the AF. An irregular pulse in a patient with severe abdominal pain and a soft abdomen is the exam question and, often enough, the real one.

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4. INCARCERATED AND STRANGULATED HERNIA

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The call

"Painful lump in the groin, vomiting."

The words, used precisely

• Reducible — returns to the abdomen.
• Irreducible (incarcerated) — will not reduce, but the contents are viable and not obstructed.
• Obstructed — the contained bowel is obstructed; the blood supply is intact.
• Strangulated — the blood supply is compromised. Surgical emergency.

What you need to establish

• Tender or not? Tenderness over an irreducible hernia is strangulation until proven otherwise.
• How long? Hours matter.
• Systemic features? Tachycardia, fever, raised lactate, toxicity.
• Skin changes? Erythema, oedema over the hernia are late and ominous.
• Which hernia? — this genuinely changes urgency.

Risk by hernia type

A femoral hernia should be repaired even if asymptomatic, and an irreducible tender femoral hernia goes to theatre.

Should you attempt reduction?

Reasonable to attempt gentle taxis if: short duration, no tenderness, no systemic upset, no skin changes, and the patient is comfortable — ideally with analgesia and in Trendelenburg.

Do NOT attempt reduction if: tender, long duration, systemic features, skin discolouration, or any suspicion of strangulation.

The reason is reduction en masse — the hernia sac and its strangulated contents are pushed back into the abdomen as a unit. The lump disappears, everyone relaxes, and the bowel inside continues to necrose unobserved. If a hernia reduces and the patient does not improve — or deteriorates — assume reduction en masse and treat as an emergency.

If it does reduce successfully: admit and observe. Do not discharge. Arrange repair — ideally on that admission or urgently thereafter.

Imaging

Often unnecessary — this is a clinical diagnosis and imaging delays theatre.

CT is useful when: the diagnosis is unclear, obstruction with no obvious external hernia (think obturator, internal, or Spigelian), a large or complex incisional hernia where planning matters, or the patient is obese and examination is limited.

Do not delay theatre for a CT in an obviously strangulated hernia.

The decision tree

Strangulated — tender, irreducible, systemically unwell → Theatre now. Resuscitate en route.

Obstructed hernia → Theatre, usually the same day.

Irreducible, non-tender, no obstruction → Admit, analgesia, attempt gentle reduction. If it reduces, repair on this admission or urgently. If not, semi-urgent repair.

Reducible, asymptomatic → Elective pathway. Femoral hernias should still be listed promptly.

In theatre — the things to have thought about first

• Approach: groin incision for most emergency groin hernias. A low approach for femoral hernia gives limited access to bowel — if you suspect resection is needed, consider a high (McEvedy) approach or be prepared to convert or add a laparotomy.
• Do not let the bowel slip back before you have inspected it. If it retracts, you must look — laparoscopy or laparotomy.
• Assessing viability: colour, sheen, peristalsis, mesenteric pulsation, bleeding from cut edges. Warm packs and a few minutes of observation. When in doubt, resect.
• Mesh in a contaminated field: if there is frank contamination or bowel resection with spillage, avoid permanent synthetic mesh — use a suture repair, or a biological or biosynthetic mesh. In clean cases with viable bowel, mesh is appropriate.
• Consent must include bowel resection and stoma — even if you think it's unlikely. This is the single most common consent omission in emergency hernia surgery, and it is not a conversation you want to have retrospectively.

When to call the consultant

• Any suspected strangulation — before theatre.
• Any likelihood of bowel resection.
• Femoral hernia requiring resection — the approach decision matters.
• Suspected reduction en masse.
• Complex or recurrent incisional hernia in the emergency setting.

The traps

Missing the femoral hernia. Below and lateral to the pubic tubercle; inguinal is above and medial. In an obese patient it can be genuinely difficult — if there's obstruction and no obvious cause, image.

Reduction en masse. Covered above, and it is the single most dangerous outcome of enthusiastic taxis.

The obturator hernia. Elderly, thin, female, bowel obstruction, no lump. If you don't think of it, the CT report will tell you — but only if someone ordered the CT.

Richter's hernia. Only part of the bowel circumference is trapped. There is no obstruction — the patient passes flatus and stool — but that segment strangulates and perforates. Most common in femoral hernias. A non-obstructed but tender irreducible hernia is not reassuring.

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QUICK REFERENCE — Theatre Tonight?

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CALLING THE CONSULTANT

Returning after time out, this is often the hardest part — not the medicine, but the calibration of when to phone.

Call, without hesitation, for:

• Anyone going to theatre
• Anyone you are considering not taking to theatre who might need it
• Any deterioration you can't explain
• Any decision that might reasonably be palliative rather than surgical
• Suspected mesenteric ischaemia
• Anything where you find yourself hoping the patient will look better in an hour

Structure the call: SBAR, then say what you think and what you want. "I think this is a strangulated femoral hernia, I've booked theatre and consented for possible bowel resection, I'd like you to come in." That is a good call. "I've got a patient in A&E with a groin lump…" is a worse one.

Nobody has ever been criticised for calling too early. People are criticised for calling late. If you are new back and uncertain where the line is, err towards phoning — and say explicitly that you're recently back and recalibrating. Consultants respond well to that; they respond much less well to being surprised at 6am.

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Reflects NICE NG147, ESGE 2020 (colonic stenting), ACPGBI and AUGIS positions current at August 2026. Guidelines are revised periodically and local pathways vary — always verify against current guidance and trust protocol. Educational resource; not a substitute for senior clinical advice or clinical judgement.