PassFinals
General Surgery

The Acute Abdomen

The acute abdomen is a high-risk presentation rather than a diagnosis: assess physiology, pregnancy and surgical red flags in parallel with analgesia, targeted tests and imaging, then obtain early senior review and source control when needed.

In a nutshell

The acute abdomen is triaged by physiology, peritonism, bleeding, obstruction, ischaemia and pregnancy risk before the final diagnosis is known. Relieve symptoms, resuscitate, investigate in parallel, involve senior surgery early and obtain source control without unsafe delay.

Classic presentation

A patient with sudden or worsening abdominal pain whose immediate risk is determined by shock, peritonism, pain out of proportion, obstruction, bleeding, pregnancy possibility or high-risk comorbidity rather than by pain location alone.

Key points

  • The acute abdomen is a presentation, not a diagnosis: decide how unwell the patient is and whether a time-critical intervention is possible.
  • Give analgesia and antiemetics while assessing; symptom relief does not replace serial examination and physiological reassessment.
  • Peritonism, shock, pain out of proportion, rising lactate or deterioration despite treatment require early senior surgical or relevant specialist review.
  • Screen deliberately for pregnancy, DKA, ACS, urinary disease and respiratory mimics.
  • For suspected intra-abdominal sepsis, use NEWS2 and the current NICE NG253 risk-based antibiotic and fluid pathway.
  • Use targeted ultrasound or CT; emergency contrast CT should not be delayed solely for renal function, metformin, age or pre-hydration when life or limb may be at risk.
  • A positive pregnancy test with pain or tenderness requires urgent early-pregnancy or gynaecology assessment.
  • A negative scan does not override persistent symptoms, peritonism or worsening physiology.

First-line investigation

ABCDE and NEWS2 with bedside glucose/ketones, urinalysis, pregnancy testing when relevant and targeted bloods, followed by ultrasound or CT chosen by the working differential.

Management

Stabilise and recognise the dangerous presentation

  • Use ABCDE, monitoring, IV access, analgesia, antiemetics and appropriate fluid or blood support; repeat observations and examination after each intervention.1,2
  • Treat shock, generalised peritonism, severe sepsis, pain out of proportion, uncontrolled bleeding or deterioration as reasons for immediate senior surgical or relevant specialist involvement.1,2,3

Screen mimics and high-risk groups

  • Check glucose/ketones, urinalysis and pregnancy status when relevant; obtain ECG or cardiopulmonary assessment when the presentation could be ACS or respiratory disease.1,4
  • Prioritise older or frail adults, people with cognitive or learning disability and immunocompromised patients because serious intra-abdominal disease may have limited peritonism.1

Investigate in parallel and treat sepsis

  • Send targeted bloods including lactate and amylase/lipase when indicated, and select ultrasound or CT for the clinical question; use low-dose non-contrast CT within 24 hours for suspected adult renal colic, with ultrasound in pregnancy.1,5
  • For suspected intra-abdominal sepsis, apply NEWS2 and NICE NG253; high-risk adults need broad-spectrum IV antibiotics within 1 hour and an IV crystalloid bolus without delay unless contraindicated.2,1

Obtain senior assessment and source control

  • Do not delay surgical referral for CT reporting when perforation, ischaemia, obstruction, infection, haemorrhage or another emergency-laparotomy indication is suspected.1,3
  • If emergency contrast CT is needed for a life- or limb-threatening question, do not delay it solely for renal-function results, metformin, age or pre-hydration; act on the balance of diagnostic delay versus contrast risk.6,1
  • Generalised peritonitis, perforation, infarction, strangulation, rupture or uncontrolled haemorrhage require urgent operative or procedural source-control decisions with anaesthetic and critical-care support.1,2

Reassess and make disposition safe

  • A stable non-peritonitic patient may follow a disease-specific conservative, radiological, endoscopic or planned-operative pathway, but the working diagnosis, uncertainty, reassessment interval and escalation triggers must be explicit.1,5
  • Before discharge or transfer, document repeat observations and examination, symptom control, oral intake, results, follow-up and return precautions for worsening pain, collapse, bleeding, obstruction, urinary retention, breathing symptoms or pregnancy-related pain or bleeding.7,1,4

Exam traps

  • Do not wait for CT before resuscitating or calling surgeons in an unstable, peritonitic or deteriorating patient.
  • Pain out of proportion to a soft abdomen is an early mesenteric-ischaemia warning; peritonism can be late.
  • A normal early lactate, white cell count or haemoglobin does not exclude serious intra-abdominal disease.
  • Do not use plain abdominal radiographs as a universal first test or use a negative erect chest film to exclude perforation.
  • A pregnancy test is part of acute abdominal-pain assessment in anyone who could be pregnant, even without classic risk factors.
  • Emergency contrast CT may proceed without waiting for renal-function results or pre-hydration when delay risks life or limb.
  • Analgesia is appropriate and should not be withheld while waiting for diagnostic certainty.

Illustrations

Abdominal pain by region: causes to considerNine-region map of the abdomen with common and important causes of pain in each region. Location guides the differential but is not diagnostic because pain may be referred or migrate.PassFinals · original
Erect chest X-ray showing free airErect chest radiograph demonstrating free sub-diaphragmatic gas indicating a possible perforated viscus; a negative film does not exclude perforation.ClinicalCases.com, Wikimedia Commons · CC-BY-SA-2.5

Key sources

  1. RCEM, Advisory Statement regarding adults presenting to the Emergency Department who may require an emergency laparotomyUpdated 1 Oct 2024
  2. NICE NG253, Suspected sepsis in people aged 16 or over: recognition, assessment and early managementUpdated 5 Dec 2025
  3. National Emergency Laparotomy Audit, Tenth Patient ReportUpdated 1 Oct 2025
  4. NICE NG126, Ectopic pregnancy and miscarriage: diagnosis and initial managementUpdated 17 Jun 2026
  5. NICE NG118, Renal and ureteric stones: assessment and managementUpdated 1 May 2026
  6. Joint Advisory Statement between the Royal College of Radiologists and RCEM on emergency CT and intravenous iodinated contrastUpdated 31 May 2023
  7. NHS, stomach acheUpdated 26 May 2023

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.