How should I evaluate and manage a patient presenting with acute abdominal pain in the emergency department?

Evaluation and Management of Acute Abdominal Pain in the Emergency Department

Begin with immediate assessment of hemodynamic stability and mechanism of injury, as this fundamentally determines your diagnostic pathway—unstable patients require bedside FAST ultrasound and potential immediate surgery, while stable patients proceed to CT imaging with specific clinical decision rules to avoid unnecessary radiation. 1, 2

Initial Assessment: The ABCDE Approach

Start with rapid evaluation of Airway, Breathing, Circulation, Disability, and Exposure to identify immediately life-threatening conditions. 3 Focus specifically on:

• Vital signs: Systolic blood pressure <90 mm Hg defines hemodynamic instability requiring immediate intervention 1
• Pain characteristics: Pain out of proportion to physical exam findings is the hallmark of acute mesenteric ischemia—this demands immediate imaging as mortality increases with every hour of delay 2
• Peritoneal signs: Abdominal rigidity indicates perforated viscus requiring immediate surgical evaluation 2

Critical pitfall: Physical examination alone is unreliable—19% of patients with intra-abdominal injuries have no abdominal tenderness, and altered mental status or distracting injuries further compromise exam accuracy. 1

Hemodynamically Unstable Patients (SBP <90 mm Hg)

For unstable patients, bedside FAST ultrasound should be your initial diagnostic modality performed within 5 minutes of arrival. 1

FAST Ultrasound Protocol

• Perform at bedside during concurrent resuscitation efforts 1
• Evaluate four views: perihepatic, perisplenic, pelvic, and pericardial spaces 4
• Positive FAST with instability = immediate laparotomy 1, 4
• Sensitivity 83-88% for intra-abdominal injury, specificity approaching 100% 1

Important limitation: A negative FAST does NOT exclude significant injury—sensitivity is only 79% in hypotensive patients with negative predictive value of 93%. 4 FAST effectively detects free fluid from liver and spleen injuries (sensitivity 96-100%) but routinely misses pancreatic and bowel injuries. 5

Management Algorithm for Unstable Patients

1. Positive FAST + instability: Proceed directly to operating room 1, 4
2. Negative FAST + persistent instability: Consider diagnostic peritoneal lavage (DPL) or proceed to surgery based on clinical suspicion 1
3. Transient response to resuscitation: May proceed to CT if patient stabilizes, but maintain low threshold for surgery 6

Critical pearl: Even "hemodynamically stable" patients with peritonitis may have significant ongoing hemorrhage—25% develop intraoperative hypotension and 39% require blood transfusion. Peritonitis should trigger emergent operation regardless of vital signs. 6

Hemodynamically Stable Patients

CT abdomen/pelvis with IV contrast is the gold standard imaging modality with 97% sensitivity and 95% specificity for injuries requiring intervention. 5, 2

Clinical Decision Rules to Avoid Unnecessary CT

Patients at LOW risk for significant injury (who may NOT need immediate CT) must meet ALL of the following criteria:

• Normal vital signs (not just transiently normal) 1
• No abdominal tenderness or peritoneal signs 1
• No distracting injuries 1
• Normal mental status 1
• No significant mechanism of injury 1

If any of these criteria are NOT met, proceed with CT imaging. 1

CT Imaging Specifications

• IV contrast is mandatory—provides 97% sensitivity for intra-abdominal injuries 5
• Oral contrast is NOT routinely needed and delays imaging without improving diagnostic performance for acute trauma 1
• CT is superior to FAST for detecting solid organ injuries, retroperitoneal injuries, and pancreatic trauma 1, 5

Specific High-Risk Scenarios

Suspected Mesenteric Ischemia

• Elderly patients with cardiovascular disease, atrial fibrillation, or recent MI 2
• Pain out of proportion to exam findings 2
• Early labs: leukocytosis, lactic acidosis, elevated amylase, occult blood in stool 2
• Requires immediate CT angiography—mortality increases hourly with delayed treatment 2

Suspected Pancreatic Injury

• FAST has poor sensitivity (68-91%) and routinely misses pancreatic injuries 5
• CT with IV contrast is essential (sensitivity 97%, specificity 95%) 5
• Time-dependent findings: Serial amylase/lipase measurements starting 3-6 hours post-injury are crucial 5
• Elevated or rising enzymes mandate CT even if initial imaging negative 5
• Consider repeat CT at 12-24 hours if high clinical suspicion despite negative initial scan 5

Special Populations

Elderly patients: Laboratory values may be normal despite serious infection; imaging is critical even with nonspecific findings. 2

Neutropenic patients: Typical signs of abdominal sepsis may be masked, leading to delayed diagnosis and high mortality. 2

Women of reproductive age: Obtain beta-hCG before any imaging to exclude ectopic pregnancy. 2

Common Diagnoses by Frequency

Approximately one-third of ED presentations with acute abdominal pain have: 2

• Appendicitis (33%)
• No diagnosis established (33%)
• Other documented pathology (33%): acute cholecystitis (9-11%), small bowel obstruction (4-5%), acute pancreatitis, renal colic, perforated peptic ulcer, diverticulitis

Left-sided abdominal pain: Diverticulitis is the most common cause in adults and may present with free fluid on imaging. 4

Disposition Decisions

Stable patients with negative CT: Safe for discharge with appropriate precautions and follow-up instructions. 1

Patients with free fluid identified on imaging:

• Trauma context: Stable patients undergo CT for definitive evaluation 4
• Non-trauma context: Low threshold for surgical exploration if peritoneal signs present; stable patients with identified pathology may undergo medical management with possible interventional drainage 4