Acute abdominal pain — the emergency department approach

Acute abdominal pain is one of the commonest presentations to the emergency department, accounting for up to 10 per cent of the adult attendances, and it spans the entire spectrum from the self-limiting gastroenteritis to the time-critical ruptured aneurysm. The Fellowship candidate's task is not to make a single diagnosis on the first contact but to apply a structured framework that triages the abdomen safely: to separate the surgical abdomen from the medical, the time-critical from the benign, and the patient who goes to the theatre from the patient who goes home. The recurring error is not missing a rare diagnosis — it is anchoring on a common, benign explanation (the gastroenteritis, the gastritis, the constipation) in a patient who harbours a lethal mimic such as the mesenteric ischaemia, the ectopic pregnancy or the ruptured aneurysm.[1][2][3]

When and why to use the framework

The abdominal pain framework exists because the abdomen is diagnostically opaque — the symptoms are non-specific, the examination is confounded by the body habitus and the analgesia, and the differentials span every organ system. The framework forces the candidate to think in axes rather than in a single linear differential. The first decision is the sick versus the not-sick — the airway, the breathing, the circulation and the perfusion are assessed before any history, and the unstable patient is resuscitated while the workup proceeds. The second decision is the surgical versus the medical — the patient who needs the theatre is identified early, because the delay to the surgery is the modifiable mortality in the perforation, the ischaemia and the ruptured aneurysm. The third decision is the disposition — the admission, the observation, the theatre or the safe discharge with the safety-net. The framework prevents the two classic failures: the premature closure on a benign diagnosis, and the open-ended investigation of every abdomen with the indiscriminate CT. [1]

The three clinical axes

The Fellowship candidate dissects every abdominal pain presentation along three axes, and each axis narrows the differential. [1]

The colicky-versus-constant distinction is the single most useful bedside discriminator. The patient who is writhing around the bed, doubling over and unable to find a position of comfort, is obstructing a hollow viscus — the ureteric colic, the biliary colic, the small-bowel obstruction. The patient who is lying dead still, splinting the abdomen, with the knees drawn up, and who winces on every movement or jolt of the ambulance trolley, has the peritoneal irritation or the bowel ischaemia. Confusing the two leads to the missed diagnosis: the mesenteric ischaemia is frequently labelled as the gastroenteritis because the early examination is soft, while the patient with the ureteric colic is over-investigated for the peritonitis that is not there. [1]

The demographic sieve — the age and the sex

The single most powerful diagnostic aid is the patient's demographic, because the incidence of the surgical causes clusters tightly by the age and the sex. The Fellowship candidate builds a different differential for the child, the woman of the reproductive age, and the elderly patient. [1]

The child presents with the appendicitis as the most common surgical emergency (the peak incidence between 10 and 20 years), but the younger child (under 5) is more likely to present atypically and to perforate before the diagnosis. The intussusception peaks between 3 months and 3 years and presents with the intermittent colicky pain, the drawing-up of the legs, the vomiting and the classic redcurrant-jelly stool (a late sign). The woman of the reproductive age carries the ectopic pregnancy, the pelvic inflammatory disease, the ovarian torsion and the ruptured corpus luteum cyst as the leading gynaecological diagnoses — every one of these patients receives a urinary or serum beta-hCG before any imaging, because the ectopic is the leading cause of the first-trimester maternal death. The elderly patient is the high-risk abdomen: the muted pain, the lower fever, the less pronounced leukocytosis, and the dangerous causes — the ruptured AAA, the mesenteric ischaemia, the strangulated hernia, the perforated diverticulum, the biliary sepsis. The threshold for the imaging, the admission and the surgical review is lower in the elderly. [1]

The pain patterns by location

The location of the pain, combined with the migration, the radiation and the character, generates the location-specific shortlist. The Fellowship candidate knows the classic pattern for each abdominal quadrant. [1]

The epigastric pain is the danger zone because it overlaps with the thorax. The myocardial infarction, the aortic dissection and the basal pneumonia all present with the epigastric or the upper-abdominal pain, and the missed cardiac or aortic cause is the high-frequency litigation. An ECG and a bedside ultrasound are part of every epigastric pain workup, particularly in the elderly, the diabetic and the hypertensive patient. The sudden-onset severe epigastric pain that radiates to the back raises the perforated ulcer, the pancreatitis and the aortic dissection together — the erect CXR (the free air), the lipase (the pancreatitis) and the CT angiogram (the dissection) are the discriminating tests. [1]

The right lower quadrant pain is the appendicitis until proven otherwise, but the differential is broad and the lethal mimics — the ectopic, the torsion, the mesenteric ischaemia — must be excluded by the beta-hCG, the ultrasound and the high index of suspicion. The diffuse abdominal pain is the peritonitis or the ischaemia until proven otherwise; the rigid abdomen with the guarding and the rebound is the surgical emergency, and the pain out of proportion to the examination is the mesenteric ischaemia until the CT angiogram proves otherwise. [1]

Surgical versus medical causes by quadrant

The Fellowship candidate maps every quadrant to a paired surgical and a medical shortlist, because the surgical diagnosis drives the theatre, the analgesia, the antibiotics and the disposition, while the medical diagnosis drives the ward pathway. The table below is the exam-exhaustive quadrant map; commit it to memory and rehearse the lethal surgical entry in each cell. [1]

Pain characteristics — the colicky, the constant-progressive, the burning

The character of the pain is the second great discriminator after the location, and it predicts the underlying mechanism — the obstruction, the ischaemia, the inflammation or the ulceration. The Fellowship candidate elicits the character explicitly and never settles for the generic "the pain came on". [1]

The ED approach — the structured ABCDE to the disposition

The Fellowship candidate applies a reproducible sequence to every acute abdomen, so that no high-risk diagnosis is missed under the cognitive load of the busy resuscitation bay. The sequence runs the resuscitation, the focused history and exam, the targeted investigations, and the disposition — in parallel, not in series. [1]

Surgical emergency indicators — the triggers for the theatre

The Fellowship candidate identifies the surgical abdomen by a set of convergent signs, because the delay to the surgery is the modifiable mortality in the perforation, the ischaemia and the ruptured aneurysm. Any ONE of these indicators in the right clinical context escalates the patient to the surgical or the vascular pathway, and the formal imaging does not delay the call. [1]

Differential diagnosis — the broad list distinguished

The acute abdomen has a long differential, and the Fellowship candidate must distinguish the time-critical surgical causes from the medical and the benign. The differentials below are the core list the examiner expects.[2][3]

The medical and the extra-abdominal mimics complete the differential and must not be missed: the myocardial infarction (the epigastric pain in the elderly — the ECG), the diabetic ketoacidosis (the abdominal pain and the vomiting — the glucose and the ketones), the lower-lobe pneumonia (the referred upper-abdominal pain — the chest exam and the X-ray), the gastroenteritis (the vomiting and the diarrhoea preceding the pain), the sickle-cell crisis (the vaso-occlusive pain in the relevant population), the porphyria and the lead poisoning (the rare but the classic abdominal-pain-with-the-normal-examination presentations), the herpes zoster (the dermatomal pain preceding the rash), and the spider-bite envenomation (the redback in the ANZ setting). The testicular torsion presents with the referred lower-abdominal pain — the scrotum is examined in every male with the lower-abdominal pain. [1]

Bedside assessment — the history and the examination

The history uses the SOCRATES structure — the Site, the Onset, the Character, the Radiation, the Associations, the Time course, the Exacerbating and the relieving factors, the Severity. The onset is the high-yield element: the sudden-onset (seconds to minutes) pain raises the ruptured aneurysm, the perforated viscus, the ectopic and the dissection; the rapidly progressive (over hours) pain raises the appendicitis, the pancreatitis, the cholecystitis; the insidious (over days) pain raises the obstruction, the diverticulitis, the malignancy. The associated symptoms — the vomiting (the onset relative to the pain: the pain before the vomiting is the surgical abdomen; the vomiting before the pain is the medical), the fever, the rigors, the jaundice, the change in the bowel habit, the urinary symptoms, the vaginal bleeding — narrow the differential further. The past history — the previous surgery (the adhesions), the gallstones, the AAA, the vascular disease, the atrial fibrillation (the mesenteric ischaemia), the medications (the anticoagulation, the NSAIDs, the steroids) — is sought. [1]

The examination begins with the vital signs and the perfusion (the shock is the surgical emergency), then the inspection (the distension, the scars, the visible peristalsis, the hernial orifices), the auscultation (the tinkling or the absent bowel sounds of the obstruction; the hyperactive of the gastroenteritis), and finally the palpation. The palpation starts in the quadrant furthest from the pain, with the warm hands, and assesses the tenderness, the guarding (the voluntary, the involuntary), the rigidity, the rebound and the organomegaly. The named peritoneal signs (the McBurney point, the Rovsing, the psoas, the obturator, the Murphy) localise the pathology. The rectal and the pelvic examination are performed when indicated — the rectal for the mass, the blood and the prostate, the pelvic for the cervical motion tenderness and the adnexal masses. The scrotum is examined in every male with the lower-abdominal pain (the testicular torsion). The bedside ultrasound (the FAST for the free fluid, the aorta for the AAA, the gallbladder for the stones, the kidneys for the hydronephrosis) is part of the modern abdominal examination. [1]

Investigations — the bloods, the urine, the X-ray, the ultrasound, the CT

The investigation strategy runs in parallel with the resuscitation, not after it. The first-line bloods are the full blood count (the leukocytosis, the anaemia), the CRP (the inflammation), the urea and electrolytes (the dehydration, the renal function, the metabolic acidosis of the ischaemia), the liver function tests (the biliary obstruction, the hepatitis), the lipase (over three times the upper limit confirms the pancreatitis), the lactate (the tissue hypoperfusion — the mesenteric ischaemia, the sepsis, the shock; a raised lactate supports but a normal lactate does NOT exclude the mesenteric ischaemia), the venous or the arterial blood gas (the metabolic acidosis), the amylase (less specific than the lipase), and the beta-hCG in every woman of the reproductive age — the ectopic is the non-negotiable exclusion.[2][3][9][10][13]

The urinalysis screens for the haematuria (the ureteric colic, the malignancy), the leucocytes and the nitrites (the urinary tract infection, the pyelonephritis), the ketones (the DKA), and the glucose (the hyperglycaemia). The pregnancy test (the urinary beta-hCG, backed by the serum) is performed on every woman of the reproductive age. [1]

The erect chest X-ray (or the left lateral decubitus film in the patient who cannot stand) detects the free subdiaphragmatic air of the perforated viscus — sensitivity around 70 per cent, and a positive film precludes the need for further imaging before the surgery. The supine abdominal X-ray shows the dilated bowel loops and the step-pattern of the small-bowel obstruction, the coffee-bean sign of the sigmoid volvulus, and occasionally the calcified aneurysm or the radiopaque stones. The plain X-ray has a limited role in the modern era but remains the cheap, accessible, first-line screen in the obstruction and the perforation. [1]

The ultrasound is the first-line imaging in the child, the young woman and the pregnant patient — it avoids the ionising radiation and it evaluates the gallbladder (the stones, the wall thickening, the sonographic Murphy), the gynaecological organs (the ectopic, the torsion), the kidneys (the hydronephrosis) and the appendix. The bedside ultrasound by the emergency physician evaluates the aorta (the AAA), the free fluid (the FAST) and the gallbladder at the bedside. The CT of the abdomen and the pelvis with the intravenous contrast is the first-line investigation in the adult male, the elderly, and the atypical or the undifferentiated abdomen — it has the highest diagnostic accuracy, the sensitivity and the specificity over 90 per cent for most surgical causes, and it is the test of choice for the mesenteric ischaemia (the CT angiogram), the diverticulitis, the complicated appendicitis, the bowel obstruction and the intra-abdominal abscess. The imaging is matched to the patient — the ultrasound first in the young and the pregnant, the CT first in the older and the atypical — to balance the diagnostic yield against the radiation and the contrast risk.[1][2]

Immediate management and resuscitation — the drug doses

The management follows the ABCDE and the treat-the-cause, with the resuscitation running in parallel with the workup. The unstable patient — the hypotension, the tachycardia, the altered mental state, the metabolic acidosis — is resuscitated first and investigated second. The fluid resuscitation with the balanced crystalloid (the Hartmann or the normal saline) 500 mL intravenous bolus, repeated to the endpoint of the perfusion (the mean arterial pressure over 65, the urine output over 0.5 mL/kg/h, the normal mentation), is the first intervention. The analgesia is given early and adequately — the morphine 5 mg intravenously (titrated, every 5 to 10 minutes, to the pain relief) is the standard opioid; the modern evidence confirms the analgesia does not mask the abdominal signs or delay the diagnosis, and the systematic-review data support the early opioid in the abdominal pain of the child and the adult alike.[14] The withholding of the analgesia for the examination is the outdated and the harmful practice. The antiemetic — the ondansetron 4 mg intravenously — is given for the nausea and the vomiting, and it complements the analgesia. The broad-spectrum antibiotics — the ceftriaxone 2 g intravenously plus the metronidazole 500 mg intravenously — are started for the suspected sepsis, the perforation, the cholangitis, the complicated diverticulitis and the appendicitis, after the cultures (the blood, the urine) are taken.[2][3][7]

The surgical referral is made early and explicitly — the emergency physician does not wait for the morning or the formal imaging in the patient with the peritonitis, the obstruction with the strangulation, the ruptured aneurysm or the perforation. The referral states the working diagnosis, the vitals, the resuscitation given, the relevant findings and the imaging — the structured ISBAR handover. The disposition follows the working diagnosis: the theatre for the surgical emergency, the ward or the HDU for the severe medical abdomen (the pancreatitis, the cholangitis), the ED observation unit for the undifferentiated but the stable abdomen, and the discharge with the safety-net for the clearly benign diagnosis (the gastroenteritis, the resolved biliary colic) with the explicit return precautions. [1]

Escalation triggers

The escalation triggers identify the patient who cannot wait. The haemodynamic instability (the systolic BP under 90, the tachycardia over 120, the altered mentation) in the abdominal pain is the surgical or the vascular emergency until proven otherwise — the bedside ultrasound (the aorta, the FAST), the simultaneous resuscitation and the immediate surgical and the vascular call. The peritonitis (the rigid abdomen, the guarding, the rebound) is the surgical emergency. The sepsis (the fever or the hypothermia, the raised lactate, the organ dysfunction) receives the broad-spectrum antibiotics within the hour and the source control. The abnormal lactate (over 2 mmol/L) with the severe pain, particularly in the AF or the vascular patient, escalates to the CT angiogram for the mesenteric ischaemia. The positive beta-hCG with the abdominal pain escalates to the transvaginal ultrasound for the ectopic. The beta-hCG with the haemodynamic instability is the ruptured ectopic until proven otherwise — the simultaneous resuscitation, the group-and-save and the gynaecology call, without the delay for the CT. [1]

Special populations

The elderly patient is the high-risk abdomen — the atypical presentation (the mild pain, the absent fever, the minimal tenderness), the dangerous causes (the AAA, the mesenteric ischaemia, the perforation, the biliary sepsis, the SBO), the comorbidities, and the high mortality. The threshold for the CT, the admission and the surgical review is lower; the conservative "gastroenteritis" label in the elderly is the classic missed-diagnosis error. The pregnant patient has the physiological changes (the gravid uterus displacing the appendix upwards and to the right in the third trimester, the mild leukocytosis and the nausea that are normal in the pregnancy) and the imaging constraints — the ultrasound first, the MRI second, the CT only if life-saving. The immunocompromised patient (the steroids, the chemotherapy, the transplant, the neutropenia) presents with the muted signs and the opportunistic pathology — the neutropenic enterocolitis (the typhlitis), the CMV colitis, the atypical infections. The child is approached with the paediatric dosing, the ultrasound-first imaging, and the awareness that the appendicitis is the most common surgical emergency and the intussusception is the classic under-3 diagnosis. The anticoagulated patient with the abdominal pain has the intra-abdominal bleeding (the retroperitoneal, the intramural haematoma) until proven otherwise — the CT and the coagulation reversal are considered. [1]

Common errors and pitfalls

The recurring errors are: the premature closure on the benign diagnosis (the gastroenteritis, the gastritis, the constipation) in the patient with the lethal mimic; the failure to take the beta-hCG in the woman of the reproductive age (the missed ectopic); the failure to examine the scrotum in the male with the lower-abdominal pain (the missed testicular torsion); the failure to perform the ECG in the elderly patient with the epigastric pain (the missed MI); the failure to check the lipase (the missed pancreatitis) and the lactate (the missed mesenteric ischaemia); the delay to the CT in the unstable patient with the suspected ruptured AAA (the bedside ultrasound and the surgical call precede the CT); the withholding of the analgesia for the examination (the outdated and the harmful practice); the over-reliance on a single investigation (the normal WCC and CRP in the early appendicitis; the soft abdomen in the early mesenteric ischaemia); and the anchoring on the common diagnosis in the elderly (the caecal carcinoma, the ischaemic bowel, the sigmoid volvulus). The recurring trap is the patient with the "soft abdomen" and the severe pain — the mesenteric ischaemia, the early appendicitis, the ureteric colic and the diabetic ketoacidosis all present with the disproportionate pain and the soft abdomen, and the discharge of these patients is the high-risk decision. [1]

Evidence and regional guidelines

The contemporary framework for the acute abdominal pain in the emergency department is built on the structured history and the examination, the targeted imaging, and the parallel resuscitation. The Laméris BMJ study (2009) established the diagnostic-accuracy hierarchy of the imaging strategies — the ultrasound first in the young and the pregnant, the CT first in the older and the atypical, with the MRI as the problem-solving modality in the pregnancy — and it underpins the modern imaging pathway.[1] The Cartwright American Family Physician reviews (2008, 2015) are the canonical primary-care and the emergency-department references for the evaluation and the imaging of the acute abdominal pain, and they emphasise the location-specific differential, the demographic sieve, and the role of the targeted CT.[2][3] The regional practice: the early analgesia is universal; the ultrasound-first in the child, the young woman and the pregnant patient is the ANZ and the UK standard; the CT-first in the adult male, the elderly and the atypical is the modern standard; and the surgical and the vascular referral thresholds are governed by the local protocols. The disease-specific guidelines refine the management further. The Tokyo Guidelines 2018 (the Yokoe diagnostic criteria and the severity grading, the Gomi antimicrobial recommendations, the Miura initial-management flowchart) standardise the diagnosis, the severity stratification and the antimicrobial therapy of the acute cholecystitis and the cholangitis, and they direct the timing of the early biliary drainage (the ERCP within 24 to 48 hours for the severe cholangitis).[6][7][8] The World Society of Emergency Surgery 2022 mesenteric ischaemia guidelines (Bala, Catena) emphasise the high clinical suspicion, the CT angiography as the diagnostic standard, the normal-lactate-does-not-exclude caveat, and the time-critical surgical or the endovascular revascularisation.[9][10] The ACOG Practice Bulletin on the tubal ectopic pregnancy (2018) codifies the transvaginal-ultrasound-and-beta-hCG diagnostic paradigm and the methotrexate-versus-surgery management thresholds.[13] The Alvarado score (1986) remains the most widely taught bedside stratification of the appendicitis, and the Snyder AFP review (2018) updates the efficient modern diagnosis and the management.[4][5] The Golledge European Heart Journal review (2023) summarises the contemporary pathogenesis, the screening and the management of the AAA.[12] The Rodrigues neutropenic-enterocolitis review (2017) describes the typhlitis of the immunocompromised.[11]

Exam pearls

• The three axes: the surgical versus the medical, the upper versus the lower, the colicky versus the constant.
• The demographic sieve: the child (the appendicitis, the intussusception), the woman of the reproductive age (the ectopic, the PID, the torsion), the elderly (the AAA, the mesenteric ischaemia, the SBO, the perforation, the biliary).
• The beta-hCG in every woman of the reproductive age — non-negotiable; the ectopic is the lethal mimic.
• The epigastric pain gets the ECG — the MI is the high-frequency missed diagnosis in the elderly.
• The pain out of proportion to the examination is the mesenteric ischaemia — the lactate and the CT angiogram.
• The rigid, board-like abdomen is the perforation — the erect CXR for the free air, the resuscitation, the urgent surgery.
• The analgesia is given BEFORE the surgical review — the morphine 5 mg IV does not mask the signs or the diagnosis.
• The ultrasound first in the child, the young woman and the pregnant; the CT first in the adult male, the elderly and the atypical.
• Examine the scrotum in every male with the lower-abdominal pain — the testicular torsion.
• The onset is the highest-yield history element: the sudden (seconds) pain is the AAA, the perforation, the ectopic, the dissection; the progressive (hours) is the appendicitis, the pancreatitis, the cholecystitis; the insidious (days) is the obstruction, the diverticulitis.
• The pain-vomiting sequence: the PAIN before the vomiting is the surgical abdomen; the vomiting before the pain is the medical (the gastroenteritis, the gastritis).
• The colicky pain (the patient writhing) is the obstructed hollow viscus; the constant pain (the patient still) is the peritonitis or the ischaemia — the bedside behaviour is the discriminator.
• The burning epigastric pain: the duodenal ulcer is RELIEVED by food and the gastric ulcer is WORSENED by food — the nocturnal waking is the duodenal ulcer.
• The Alvarado score (the MANTRELS) stratifies the appendicitis; the score over 7 is the probable appendicitis — but the negative score does NOT exclude it.
• The Charcot triad (the RUQ pain, the fever, the jaundice) is the cholangitis; the Reynolds pentad adds the shock and the confusion — the severe cholangitis gets the ERCP within 24 to 48 hours.
• The lipase over three times the upper limit confirms the pancreatitis; the amylase is less specific and may be raised in the mesenteric ischaemia (a red herring).
• The elderly abdomen is the high-risk abdomen — the muted signs, the dangerous causes (the AAA always), and the lower threshold for the CT and the surgical review; the "gastroenteritis" label is the classic error.
• The immunocompromised or the neutropenic patient with the RIF pain has the neutropenic enterocolitis (the typhlitis) — the CT, the broad-spectrum antibiotics and the G-CSF. [1]

Red flags