Preventing PONV in Outpatients

PONV: Risk Factors & Scores - The Queasy Question

Postoperative Nausea & Vomiting (PONV): Distressing, common in outpatients (~30-50%). Impacts: delayed discharge, dissatisfaction, ↑ costs, unplanned admission.

• Key Risk Factors (Apfel Score):
  • Female gender
  • Non-smoker
  • History of PONV / Motion Sickness
  • Postoperative opioids
  • 📌 Mnemonic: FANS (Female, Anesthesia [opioids], Non-smoker, Sickness Hx)
• Apfel Score & PONV Risk: (Score = sum of positive factors)
  • 0 factors: Low risk (~10%)
  • 1 factor: Low risk (~20%)
  • 2 factors: Moderate risk (~40%)
  • 3 factors: High risk (~60%)
  • 4 factors: High risk (~80%)
• Simplified scores also exist for rapid assessment.

⭐ Apfel score is the most widely validated tool for predicting PONV risk.

PONV: Pharmacological Prophylaxis - Pill Power Plays

Pharmacological prophylaxis is crucial. Key agents include:

• 5-HT3 Antagonists: Ondansetron (4mg IV/PO, pre-op/end). Block 5-HT3 receptors (periphery/CTZ). Broad efficacy.
• NK-1 Antagonists: Aprepitant (40mg PO, 1-3h pre-op). Block Substance P at NK-1 receptors (brainstem). High-risk, long duration.
• Corticosteroids: Dexamethasone (4-8mg IV, post-induction). Anti-inflammatory, prostaglandin inhibition. Reduces pain.
• Dopamine Antagonists: Metoclopramide (10mg IV, end). D2 receptor blockade (CTZ). Prokinetic; less effective alone. (Avoid Droperidol: QTc risk).
• Antihistamines (H1): Dimenhydrinate (25-50mg PO/IV). H1 blockade (vestibular, CTZ). For motion sickness hx; sedation.
• Anticholinergics: Scopolamine patch (1.5mg TD, pre-op). Muscarinic blockade (vestibular). Motion sickness; dry mouth.

📌 Mnemonic (Classes): Serotonin antags, NK-1 antags, Dexamethasone (Corticosteroids), Antihistamines, Anticholinergics, Dopamine antags (S.N.D.A.A.D - 'Send Dad').

⭐ Combining antiemetics from different classes is more effective than single-agent prophylaxis for high-risk patients.

PONV: Non-Pharmacological Methods - Gentle Guards

• Regional Anesthesia: Utilise whenever feasible; significantly ↓ PONV risk compared to general anesthesia.
• Hydration: Ensure adequate intravenous fluid administration perioperatively.
• Anesthetic Choice:
  • Avoid Nitrous Oxide ($N_2O$) if possible.
  • Consider TIVA or minimize volatile anesthetics.
• Acupressure/Acupuncture:
  • Stimulate P6 (Neiguan) point on the wrist.
  • 📌 P6 - 'Pressure 6 stops sick'.
• Supplemental Oxygen: Administer routinely in PACU.

⭐ Acupressure at the P6 (Neiguan) point is a recognized non-pharmacological method for PONV prevention, often comparable to antiemetics for mild to moderate risk_._

PONV: Multimodal & Rescue - Team Tactics Triumph

• Multimodal Prophylaxis: Key for moderate/high PONV risk (≥2 risk factors). Combine ≥2 antiemetics from different classes.
• Risk-Stratified Prophylaxis (Apfel Score):

• Rescue Therapy: If PONV occurs.
  • Use agent from a different class than prophylactic drugs.
  • Options: Ondansetron 4 mg IV, Promethazine 6.25-12.5 mg IV, Dexamethasone 2-4 mg IV (if not used).

⭐ For rescue treatment, an antiemetic from a different pharmacological class than that used for prophylaxis should be administered.

High-Yield Points - ⚡ Biggest Takeaways

• Risk stratification using tools like the Apfel score is paramount.
• A multimodal approach is superior to single-agent therapy for PONV prevention.
• Administer prophylaxis if ≥2 Apfel risk factors are present.
• Key drugs: Ondansetron (5-HT3 antagonist), Dexamethasone; add Aprepitant (NK-1 antagonist) for high risk.
• Prefer regional anesthesia or TIVA (e.g., propofol) over volatile anesthetics.
• Avoid nitrous oxide and minimize postoperative opioids.
• Ensure adequate hydration and analgesia to reduce baseline nausea triggers_._