Acute Abdomen — ED & ICU Approach

📘 1 · Tintinalli's Emergency Medicine, 9th Ed

Find the Surgical Abdomen, Fast

"The evaluation of abdominal pain is one of medicine's great humblers: the physical examination is unreliable, the elderly and immunosuppressed hide catastrophe behind an unimpressive belly, and the most dangerous diagnoses — mesenteric ischaemia, ruptured aneurysm, perforation — are precisely those in which delay is lethal. The emergency question is not 'what is the exact diagnosis?' but 'does this patient need a surgeon and an operating theatre now?'"

Tintinalli's Emergency Medicine, 9th Ed. Acute Abdominal Pain. McGraw-Hill; 2020.

The time-critical surgical/vascular catastrophes

Ruptured abdominal aortic aneurysm — abdominal/back pain + hypotension + pulsatile mass (may mimic renal colic in the elderly)
Mesenteric ischaemia — pain out of proportion to exam, AF/vascular disease, rising lactate
Perforated viscus — sudden severe pain, rigidity, free gas
Bowel obstruction with strangulation — colicky pain, vomiting, distension, no flatus; localised tenderness = strangulation
Ruptured ectopic pregnancy — any woman of childbearing age with pain/shock → β-hCG
Acute pancreatitis, cholangitis, ischaemic/perforated appendicitis/diverticulitis

RUQ

Cholecystitis, cholangitis, hepatitis, biliary colic; also lower-lobe pneumonia

Epigastric

Pancreatitis, perforated ulcer, gastritis; MI/inferior ischaemia

RIF

Appendicitis, ileocaecal/Crohn's, ovarian, ectopic

LIF

Diverticulitis, colitis, ovarian, ectopic

Loin / flank

Renal colic, pyelonephritis — but beware AAA mimicking colic in the elderly

Diffuse / poorly localised

Mesenteric ischaemia, obstruction, peritonitis, DKA, early appendicitis

⚠️ The bellies that lie

The elderly, diabetics, the immunosuppressed, and patients on steroids can have catastrophic intra-abdominal pathology (perforation, ischaemia) with a soft, minimally tender abdomen and near-normal observations — until they collapse. And do not forget the extra-abdominal causes: inferior MI, lower-lobe pneumonia, DKA, and testicular torsion all masquerade as an acute abdomen.

📗 2 · Pathophysiology (Sabiston / Marino)

Why the Acute Abdomen Becomes a Critical-Care Problem

"Peritoneal contamination — by gastrointestinal contents, blood, bile or pus — triggers a systemic inflammatory response that is functionally identical to sepsis from any other source. Fluid sequesters into the gut lumen, the peritoneum and the third space; the patient becomes profoundly hypovolaemic before a drop of blood is lost externally. Definitive treatment is not a drug — it is source control."

Adapted from Sabiston Textbook of Surgery & Marino's The ICU Book, 5th Ed. Intra-abdominal Sepsis.

🔬 How intra-abdominal catastrophe drives shock

InsultPerforation · ischaemia · obstruction · haemorrhage

Peritoneal contamination / bowel-wall injury → local & systemic inflammation

Massive third-space & luminal fluid loss → hypovolaemiatachycardia, oliguria, then hypotension

Bacterial translocation / gut necrosis → sepsis + rising lactatemetabolic acidosis, organ dysfunction

Distributive + hypovolaemic shock, ± abdominal compartment syndrome

CureResuscitation + timely surgical/radiological SOURCE CONTROL

📗 Mesenteric ischaemia — the great missed diagnosis

The hallmark is severe pain out of proportion to a soft, unremarkable abdomen, classically in a patient with atrial fibrillation (embolic), atherosclerosis (thrombotic) or a low-flow state (non-occlusive). A normal early lactate does not exclude it; lactate rises as bowel becomes frankly necrotic — by which point mortality soars. CT angiography and early surgical/vascular involvement are the only way to catch it in time.

📗 Why these patients need aggressive resuscitation

Hypovolaemia is hidden: litres sequester into the gut lumen, oedematous bowel wall and peritoneal cavity — "third spacing" — before any external loss. Tachycardia and oliguria precede hypotension.
Sepsis physiology: vasodilatation, capillary leak and myocardial depression compound the hypovolaemia.
Abdominal compartment syndrome may develop from oedema/fluids — a rising bladder pressure with organ dysfunction that can require decompression.

📋 3 · WSES · Surviving Sepsis 2021

Work-up & the Two Non-negotiables

Bedside & laboratory work-up

Every woman of childbearing age gets a β-hCG. Send FBC, U&E, LFTs, amylase/lipase, glucose, lactate, VBG, coagulation and group-and-save/crossmatch; urinalysis. An ECG for epigastric pain (inferior MI). Serial examination by the same clinician is more informative than any single exam.

Imaging — choose by the question

Contrast CT abdomen/pelvis is the workhorse for the undifferentiated or high-risk acute abdomen (perforation, ischaemia, obstruction, collections) — and CT angiography if mesenteric ischaemia or AAA is suspected.
Ultrasound / POCUS first for suspected biliary disease, in pregnancy, in the unstable patient (free fluid/AAA at the bedside), and in gynaecological presentations.
Erect CXR can show free air but a normal film does not exclude perforation. Do not delay the theatre for imaging in a peritonitic, unstable patient.

Resuscitate & treat sepsis Surviving Sepsis 2021

Restore perfusion with balanced crystalloid, obtain cultures, and give broad-spectrum antibiotics early for suspected intra-abdominal sepsis (cover Gram-negatives and anaerobes — e.g. piperacillin-tazobactam, or a carbapenem in severe/resistant cases). Analgesia — opioids do not mask peritonism enough to harm and should not be withheld. Nasogastric decompression and urinary catheter as indicated.

Source control — the definitive treatment WSES · SSC 2021

Antibiotics buy time; they do not cure a perforation, an abscess or dead bowel. Achieve source control as early as feasible (SSC: ideally within 6–12 h) — surgery (repair/resection/washout), percutaneous drainage of a collection, or endoscopic/interventional measures. In the unstable patient, damage-control surgery (control contamination, leave definitive reconstruction for later) is preferred over a prolonged first operation.

🇮🇳 Indian Context

Common and characteristic causes to keep in mind: perforated peptic ulcer (still frequent), enteric (typhoid) ileal perforation, abdominal (ileocaecal) tuberculosis presenting with obstruction/perforation, amoebic liver abscess, obstructed hernias, and hollow-viscus injury in trauma. In the febrile acute abdomen, remember enteric fever, complicated malaria and dengue as medical mimics.

Late presentation is common — patients often arrive septic and volume-depleted. Prioritise rapid resuscitation, early antibiotics, and prompt referral for source control, recognising that CT and interventional radiology may be less immediately available.

💊 4 · Drug Doses

Drug Reference — Acute Abdomen / Intra-abdominal Sepsis

Drug / Measure	Indication	Dose	Notes
Balanced crystalloid	Resuscitation (third-space loss/sepsis)	Titrated boluses to perfusion targets	Reassess frequently; avoid both under- and over-resuscitation
Piperacillin-tazobactam	Community intra-abdominal sepsis	4.5 g IV every 6–8 h (renal-adjusted)	Covers Gram-negatives + anaerobes; give early
Meropenem	Severe / healthcare-associated / resistant	1 g IV every 8 h (renal-adjusted)	Reserve for severe sepsis or MDR risk
Metronidazole	Anaerobic cover (with a cephalosporin)	500 mg IV every 8 h	Add to ceftriaxone where piptaz/carbapenem not used
Morphine / fentanyl	Analgesia	Titrated IV	Do not withhold — does not dangerously mask peritonism
Ondansetron	Nausea / vomiting	4–8 mg IV	With NG decompression in obstruction
Noradrenaline	Septic shock after fluids	Titrate to MAP ≥65	Do not delay source control while chasing MAP
Tranexamic acid	Haemorrhagic cause (e.g. ruptured AAA, trauma)	1 g IV	Adjunct; definitive control is surgical/endovascular

🗺 5 · Clinical Flowchart

Acute Abdomen Pathway

Resuscitate & screen for the crashing abdomen

A–B–C, IV access, fluids; if shocked + pulsatile mass/known AAA → immediate vascular/theatre
β-hCG in every woman of childbearing age; bedside glucose; lactate; ECG for epigastric pain

Is this a surgical abdomen now?

Peritonism/rigidity, free air, pain out of proportion, strangulated obstruction → call the surgeon
Unstable + peritonitic → theatre without waiting for CT

Targeted work-up

Bloods (FBC, U&E, LFTs, lipase, lactate, coag, G&S), urinalysis
Imaging by question: CT (± CTA) for undifferentiated/ischaemia/AAA; US/POCUS for biliary, pregnancy, unstable, gynae

Treat sepsis + achieve source control

Early broad-spectrum antibiotics, cultures, analgesia (don't withhold opioids), NG/catheter as needed
Source control early (ideally 6–12 h): surgery, percutaneous drainage, or interventional/endoscopic — damage-control if unstable

Ongoing critical care

Organ support; monitor for abdominal compartment syndrome (bladder pressure)
Serial re-examination; re-image/relook if not improving; de-escalate antibiotics on cultures

⚠️ 6 · Common Mistakes

Common Mistakes in the Acute Abdomen

❌ Mistake 1 — Being reassured by a soft belly in a high-risk patient

The elderly, diabetic and immunosuppressed can perforate or infarct bowel with an unimpressive abdomen. Weight the risk factors, lactate and trajectory, not just the palpation findings.

❌ Mistake 2 — Missing mesenteric ischaemia

Pain out of proportion to exam, especially with AF or vascular disease, is mesenteric ischaemia until excluded. A normal early lactate does not rule it out — image with CTA and involve surgery early.

❌ Mistake 3 — Mistaking a ruptured AAA for renal colic

An older patient with "first-ever renal colic" and hypotension may have a leaking aneurysm. Examine for a pulsatile mass and use bedside ultrasound before anchoring on colic.

❌ Mistake 4 — Forgetting the pregnancy test

Ruptured ectopic pregnancy is a classic lethal miss. Every woman of childbearing age with abdominal pain or shock needs a β-hCG, early.

❌ Mistake 5 — Withholding analgesia "to preserve the exam"

The old dogma is wrong: adequate opioid analgesia does not mask peritonism enough to cause harm and improves the reliability of examination. Treat the pain.

❌ Mistake 6 — Antibiotics without source control

Antibiotics do not cure a perforation, dead bowel or an undrained abscess. Delayed source control is a leading driver of mortality in intra-abdominal sepsis — escalate for early definitive intervention.

❌ Mistake 7 — Delaying theatre for a scan in the unstable, peritonitic patient

A rigid, shocked abdomen needs a surgeon, not a queue for CT. Imaging should not delay life-saving laparotomy in the clearly surgical, unstable patient.

🎓 7 · Exam Pearls — DrNB / MEM / EDIC

Exam Pearls

Q: What is the classic presentation of mesenteric ischaemia?
Pain out of proportion to a soft, unremarkable abdomen, often with AF (embolic) or vascular disease; lactate rises late once bowel necroses. Diagnose with CT angiography and act early.

Q: What are the two non-negotiable treatments in intra-abdominal sepsis?
Early resuscitation + broad-spectrum antibiotics, and timely source control (surgery/drainage) — ideally within 6–12 hours.

Q: Which single test must every woman of childbearing age get?
A β-hCG — to catch ruptured ectopic pregnancy.

Q: Should opioids be withheld to protect the abdominal exam?
No. Adequate analgesia does not dangerously mask peritonism and improves examination — an outdated dogma to abandon.

Q: How do you choose CT vs ultrasound?
CT (± CTA) for the undifferentiated/high-risk abdomen, ischaemia and AAA; ultrasound/POCUS for biliary disease, pregnancy, the unstable patient (FAST/AAA) and gynaecological presentations.

Q: What extra-abdominal conditions mimic an acute abdomen?
Inferior MI, lower-lobe pneumonia, DKA, and testicular torsion — always check an ECG for epigastric pain and glucose for the unwell.

Q: What is damage-control surgery?
An abbreviated first operation to control contamination/haemorrhage in the physiologically unstable patient, deferring definitive reconstruction until after resuscitation in ICU.

Q: Name characteristic Indian causes of the acute abdomen.
Perforated peptic ulcer, enteric (typhoid) ileal perforation, abdominal (ileocaecal) TB, amoebic liver abscess, and obstructed hernias.

📚 8 · References

References

Tintinalli JE, et al. Tintinalli's Emergency Medicine, 9th Edition. Acute Abdominal Pain. McGraw-Hill; 2020.
Walls RM, et al. Rosen's Emergency Medicine, 10th Edition. Abdominal Pain. Elsevier; 2023.
Evans L, Rhodes A, Alhazzani W, et al. (Surviving Sepsis Campaign). International Guidelines for Management of Sepsis and Septic Shock 2021. Crit Care Med. 2021;49:e1063–e1143.
Sartelli M, Coccolini F, Kluger Y, et al. (WSES). WSES guidelines for the management of intra-abdominal infections. World J Emerg Surg. (current edition).
Townsend CM, Beauchamp RD, Evers BM, Mattox KL. Sabiston Textbook of Surgery, 21st Edition. The Acute Abdomen. Elsevier; 2022.
Bala M, Kashuk J, Moore EE, et al. (WSES). Acute mesenteric ischemia: guidelines of the World Society of Emergency Surgery. World J Emerg Surg. 2017;12:38.
Marino PL. Marino's The ICU Book, 5th Edition. Abdominal Sepsis. Philadelphia, PA: Wolters Kluwer; 2025.