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Post-Operative Nausea & Vomiting

I. Scope & Definitions

  • PONV: nausea and/or vomiting within 24–48 h of anesthesia/surgery.

  • Post-op N/V may be benign (PONV, medication-related) or indicate complication (ileus, SBO, anastomotic leak, aspiration, intracranial process).

  • Goals: stabilize → identify driver (PONV vs obstructive/pathological) → treat using class-based antiemetics and prokinetics → prevent recurrence.

II. First-Principles Framework (etiology buckets)

  • CNS/vestibular: anesthetics, opioids, migraine, motion sensitivity.

  • GI motility/obstruction: ileus, SBO, delayed gastric emptying; anastomotic complications if toxic.

  • Chemical/metabolic: opioids, antibiotics, iron, uremia (missed dialysis), DKA, pregnancy.

  • Risk factors for PONV (Apfel): female, non-smoker, prior PONV/motion sickness, post-op opioids (0–4 points ≈ 10/20/40/60% risk).

III. Stepwise Evaluation

Step 1 – Rapid stabilization - Upright position; NPO if active emesis; bedside suction. - O₂ if SpO₂ < 92%; protect airway if aspiration risk. - IV crystalloid; correct electrolytes (targets: K⁺ ≥ 4.0, Mg²⁺ ≥ 2.0).

Step 2 – Focused Hx/Exam - Timing (PACU vs POD 2–3), emesis character (gastric/bilious/feculent), distension/tenderness, last flatus/BM, prior PONV, migraine/vestibular symptoms, opioid dose.

Step 3 – Targeted Workup (as indicated) - Labs: BMP (K/Mg/Ca), glucose; ± lactate if ill; pregnancy test when relevant. - Imaging: upright/supine KUB for ileus/SBO → CT A/P with IV contrast if concerning. - ECG if multiple QT-prolonging meds or baseline risk.

IV. Universal Early Actions

  • NPO, IV fluids, electrolyte repletion to targets.
  • Opioid-sparing analgesia (acetaminophen, regional, NSAIDs if safe).
  • IS and early mobilization when safe; aspiration precautions.

V. Antiemetic & Prokinetic Options (choose by class; avoid duplicating the same class if already used)

5-HT3 antagonist - Ondansetron 4–8 mg IV/PO q8h PRN
Avoid high total IV doses; do not use 32 mg IV single dose. QT caution—correct K/Mg; ECG if high-risk.

D2 antagonists - Prochlorperazine 5–10 mg IV/PO q6h PRN
- Haloperidol 0.5–2 mg IV/IM q6–8h PRN (QT/TdP caution)
- Droperidol 0.625–1.25 mg IV once (boxed warning for QT; use lowest effective dose with ECG and corrected K/Mg)

Antihistamine/anticholinergic - Promethazine 12.5–25 mg PO/IM/IV q6h PRN (sedation, anticholinergic; avoid IV extravasation)
- Scopolamine 1.5 mg TD patch q72h (apply pre- or early post-op in high risk)

Steroid - Dexamethasone 4–8 mg IV (best as prophylaxis at induction; can use if not already given)

NK-1 antagonist - Aprepitant 40 mg PO (often prophylaxis; consider refractory per institutional protocol)

Prokinetic - Metoclopramide 10 mg IV/PO q6h PRN (avoid if mechanical obstruction; EPS/QT caution)
- Erythromycin 250 mg IV/PO q6–8h (short course) for foregut dysmotility (QT/cytochrome interactions; local practice varies)

VI. PONV Prophylaxis (use Apfel risk)

  • 0–1 risk factor: 1 agent (e.g., ondansetron or dexamethasone).
  • 2 risk factors: 2 different classes.
  • 3–4 risk factors: ≥2 classes (often three: dexamethasone + 5-HT3 + scopolamine or droperidol).
  • Rescue rule: if N/V occurs despite prophylaxis, treat with a different class than those already given.

VII. Rescue Ladder (when symptoms occur or persist)

  1. If no prophylaxis was given:

  2. Start one agent (e.g., ondansetron 4 mg IV). Reassess in 30–60 min.

  3. If persistent symptoms:

  4. Add a second agent from a different class (e.g., promethazine 12.5–25 mg IV or prochlorperazine 5–10 mg IV).

  5. If still symptomatic:

  6. Add a third class (e.g., dexamethasone 4–8 mg IV if not yet given, or droperidol 0.625–1.25 mg IV with ECG and corrected K/Mg).

  7. If impaired motility suspected and no mechanical obstruction:

  8. Add metoclopramide 10 mg IV q6h (prokinetic), continue electrolyte optimization, minimize opioids.

  9. Refractory/high-risk:

  10. Consider NK-1 antagonist (aprepitant 40 mg PO) per formulary; review for drug interactions.

  11. At any step, if red flags appear (see Section X):

  12. Escalate evaluation for ileus/SBO/leak and proceed to decompression pathway.

VIII. Ileus / SBO Decompression Pathway

  • Ileus likely (distension, minimal pain, no flatus/BM): NPO, IV fluids, correct K/Mg, minimize opioids, chew gum, early ambulation, metoclopramide if no contraindication.

  • High-grade obstruction or persistent large-volume emesis: NG tube to low continuous suction, resuscitate, possible CT A/P with IV contrast,

IX. Special Situations

  • Missed dialysis / uremia: antiemetics are symptomatic only—nephrology for urgent dialysis.
  • Pregnancy possible: test prior to certain meds; tailor regimen.
  • Migraine phenotype: add migraine therapy (e.g., triptan/NSAID) when safe.
  • QT safety: avoid stacking QT-prolonging agents; correct K/Mg before droperidol/haloperidol/high-dose 5-HT3; obtain ECG in at-risk patients.

X. Red Flags — Call Senior / Escalate Early

  • Bilious or feculent emesis; severe distension; peritonitis; fever/tachycardia.
  • No flatus/BM with worsening distension/pain (ileus/SBO).
  • Hematemesis; aspiration; SpO₂ < 92% despite O₂.
  • Refractory N/V despite ≥2 different antiemetic classes.
  • Severe electrolyte derangements, AKI, or dehydration not improving.

XI. Quick Reference — Antiemetic/Prokinetic Doses

Class Medication Typical Dose & Route Key Safety Notes
5-HT3 Ondansetron 4–8 mg IV/PO q8h PRN Do not use 32 mg IV; QT caution; correct K/Mg
D2 Prochlorperazine 5–10 mg IV/PO q6h PRN EPS/sedation; QT caution
D2 Haloperidol 0.5–2 mg IV/IM q6–8h PRN QT/TdP risk; ECG if high-risk
D2 Droperidol 0.625–1.25 mg IV once Boxed QT warning; ECG + electrolyte correction
H1/ACh Promethazine 12.5–25 mg PO/IM/IV q6h PRN Sedation/anticholinergic; IV tissue injury risk
ACh Scopolamine patch 1.5 mg TD q72h Avoid narrow-angle glaucoma; delirium risk
Steroid Dexamethasone 4–8 mg IV Best prophylaxis at induction; hyperglycemia
NK-1 Aprepitant 40 mg PO CYP interactions; formulary-dependent
Benzamide Metoclopramide 10 mg IV/PO q6h PRN Avoid if obstruction; EPS/QT caution
Macrolide Erythromycin 250 mg IV/PO q6–8h (short course) QT/cytochrome interactions

XII. Intern Pearls

  • Treat airway/oxygenation and dehydration/electrolytes first.
  • Use risk-based prophylaxis and rescue from a different class.
  • Pair N/V + distension + no flatus with imaging and early NG rather than stacking antiemetics.
  • Minimize opioids; mobilize early.

XIII. References

  1. Gan TJ, et al. Fourth Consensus Guidelines for the Management of PONV (2020). Anesth Analg. 2020;131:411–448.
  2. Apfel CC, et al. A simplified risk score for predicting PONV. Anesthesiology. 1999;91:693–700.
  3. FDA Drug Safety Communications: Ondansetron – removal of 32 mg IV dose; QT/TdP risk.
  4. Droperidol safety and QT guidance — contemporary reviews and labeling.