USMLE Prep - Medical Reference Library

Small Bowel Obstruction — Initial ED Management

System: General Surgery • Reviewed: Aug 31, 2025 • Step 1Step 2Step 3

Synopsis:

Colicky abdominal pain with vomiting and distension; diagnose with CT when appropriate; treat with fluids, nasogastric decompression for severe vomiting, and early surgical consultation.

Key Points

  • Stabilize ABCs; begin targeted evaluation without delaying life-saving therapy.
  • Use system-specific risk tools to guide testing and disposition.
  • Order high-yield tests first; escalate imaging when indicated.
  • Start evidence-based initial therapy and reassess frequently.

Algorithm

  1. Primary survey and vitals; IV access and monitors.
  2. Focused history/physical; identify red flags and likely etiologies.
  3. Order system-appropriate labs and imaging (see Investigations).
  4. Initiate guideline-based empiric therapy (see Pharmacology).
  5. Reassess response; arrange consultation and definitive management.

Clinical Synopsis & Reasoning

For Small Bowel Obstruction Initial Ed, frame the differential by acuity and pathophysiology, then align diagnostics to the leading hypotheses. Prioritize stabilization while obtaining high‑yield studies such as CBC (Baseline hematology), BMP (Electrolytes/renal). Incorporate bedside imaging and targeted labs to define severity and identify complications; synthesize results with clinical trajectory to refine the working diagnosis and disposition needs.


Treatment Strategy & Disposition

Initiate disease‑directed therapy alongside supportive care, titrating to objective response. Pharmacologic options commonly include Analgesia/Antipyretics. Use validated frameworks (e.g., Red Flags for Ischemia) to guide escalation and site of care. Address precipitating factors, de‑escalate empiric therapies with data, and arrange follow‑up for monitoring and risk‑factor modification; admit patients with instability, high risk of deterioration, or needs for close monitoring.


Epidemiology / Risk Factors

  • Risk factors vary by condition and patient profile

Investigations

TestRole / RationaleTypical FindingsNotes
CBCBaseline hematologyAbnormal counts
BMPElectrolytes/renalDerangements

Red Flags for Ischemia

FindingConcern
Peritonitis or focal tendernessStrangulation
Fever or rising lactateIschemia
Free air or closed loop on CTPerforation risk

Pharmacology

MedicationMechanismOnsetRole in TherapyLimitations
Isotonic fluidsVolume expansionHoursCorrect dehydrationFluid overload; ED use; pregnancy/lactation considerations
Ondansetron5-HT3 antagonismMinutesAntiemesisQT prolongation; ED use; pregnancy/lactation considerations
Piperacillin-tazobactam (if peritonitis/strangulation)Broad antibioticHoursSuspected ischemia/perforationAKI; ED use; pregnancy/lactation considerations

Prognosis / Complications

  • Prognosis depends on severity, comorbidities, and timeliness of care

Patient Education / Counseling

  • Explain red flags and when to seek emergent care.
  • Reinforce medication adherence and follow-up plan.

Notes

Avoid opioids that worsen ileus when possible; use multimodal analgesia. Consider water soluble contrast challenge in selected patients.


References

  1. WSES Bowel Obstruction Guidelines — Link
  2. ACS Acute Care Surgery References — Link