USMLE Prep - Medical Reference Library

Postoperative Nausea and Vomiting - Risk Score and Multimodal Prophylaxis

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

Synopsis:

Estimate risk using simple scores and give multimodal prophylaxis with agents from different classes; use rescue from a different class if vomiting occurs.

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 Postoperative Nausea Vomiting Prophylaxis Risk Score, 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., Common Antiemetic Classes) 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

Common Antiemetic Classes

ClassExample
5 HT3 antagonistOndansetron
CorticosteroidDexamethasone
Dopamine antagonistDroperidol or metoclopramide

Pharmacology

MedicationMechanismOnsetRole in TherapyLimitations
Lidocaine (local)Na⁺ channel blockadeMinutesLocal anesthesia for biopsy/FNALAST (rare)
Epinephrine (with local)α-agonist vasoconstrictionMinutes↓ bleeding, prolong anesthesiaTissue ischemia (avoid end-arterial sites)
Prophylactic antibiotics (not routine)N/AN/AUse only for specific high-risk fields per protocol

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

Document baseline risk factors such as female sex, non smoking, prior PONV, and postoperative opioid use.


References

  1. ASA and Society for Ambulatory Anesthesia PONV guidance — Link
  2. APSF PONV prevention and treatment resources — Link