Postoperative nausea and vomiting

Introductions

• PONV is a major problem faced in the perioperative setting by anesthesiologists
• It is known to be one of the major factors, along with pain, that prolongs PACU stays, which can be significantly consequential in the ambulatory setting.
  • Each episode of vomiting is thought to prolong the PACU stay by ~ 25 minutes
  • There is also an increase risk of aspiration and airway compromise

Risk Factors

• Patient Related
  • History of PONV or motion sickness
  • Female sex
  • Young age (< 50 years old)
  • Use of volatile anesthetics
  • Use of post-operative opiates
  • Non-smoking status
• Anesthetic Related
  • Use of volatile anesthetics (Sevoflurance, Isoflurane, Desflurane) or N2O
  • Opioid use
  • Etomidate (worse when used w/ opioids)
• Surgery Related
  • Prolonged surgery (therefore, prolonged exposure to anesthetics)
  • Laparoscopic surgery, cholecystectomies, inner/middle ear cases, and gynecological surgery

Apfel Score

• The Apfel score is a points system that is used based on patient risk factors to predict their risk of developing PONV
• 1 point is given for the following risk factors
  • Female Gender
  • Non-Smoker
  • Hx of PONV or Motion Sickness
  • Postoperative Opioids
• Each score is associated with the following risk:
  • 0 = 10%
  • 1 = 20%
  • 2 = 40%
  • 3 = 60%
  • 4 = 80%

Prophylaxis

• Regional nerve blocks can be used to reduce the amount of peri-operative opioids required
• If patient requires general anesthesia, you can substitute volatile anesthetic with a propofol-based TIVA approach
• N2O is a common culprit of PONV, and therefore should be avoided. If it needs to be used, less than 1 hour of exposure is preferred
• Appropriately volume resuscitate the patient to keep them well hydrate
  • Can also be achieved by preoperative administration of carbohydrate drinks
• If the patient has 1-2 risk factors, administer 2 anti-emetic agents
• If the patient has 2+ risk factors, consider administered 3-4 anti-emetic agents

Treatment

• There are many medications that can be used to treat PONV. The main receptors that they work at to prevent/treat nausea and vomiting include: M1 (muscarinic), D2 (Dopamine), H1 (Histamine), 5HT3 (Serotonin), and NK1 (Substance P)
• These receptors are located at the area postrema of the brain

Medication Classes

• 5HT3 Receptor Antagonists
  • Ex (Dose): Ondansetron (4-8 mg IV), Granisetron (0.35-3 mg IV)
  • MoA: Targets the area postrema
  • Side Effects: Headache, lightheadedness, dizziness, constipation, QTc prolongation
• Steroids
  • Ex (Dose): Dexamethasone (4-8 mg IV)
  • MoA: Unclear, believed to inhibit prostaglandins peripherally
  • Side Effects: Insomnia, increased energy, mood changes
  • Be weary of administering in patient's with uncontrolled diabetes or sepsis
• NK1 Receptor Antagonists
  • Ex (Dose): Aprepitant (40 mg PO)
  • MoA: Targets the nucleus tractus solitaries and area postrema
  • Side Effects: Moderate inhibitor of CYP3A4
• Dopamine Antagonists
  • Ex (Dose): Metoclopramide (10 mg), Prochlorperazine (5-10 mg IV)
  • MoA: Targets the area postrema
  • Side Effects: Extrapyramidal effects muscle stiffness, tremors, restlessness (akathisia), or involuntary facial movements (dyskinesia) and dystonia
• Anticholingerics
  • Ex (Dose): Scopolamine (patch administered 2-4 hours pre op), Promethazine (6.25 mg)
  • MoA: Antagonizes muscarinic receptors of the vestibular apparatus and the nucleus of the tractus solitarus
  • Side Effects: Sedation, dry mouth, visual disturbance. Can precipitate acute angle closure glaucoma in susceptible patients
• Phenothiazines
  • Ex (Dose): Promethazine (6.25 mg), Prochlorperazine (5-10 mg)
  • MoA: Antagonize D2-dopamine receptors in the area postrema of the midbrain; also have M1-muscarinic and H1-histamine blocking effects⁵
  • Side Effects: Sedation, extrapyramidal effects, hypotension
• Butyrophenones
  • Ex (Dose): Droperidol (0.625 mg IV), Haloperidol (0.5-2 mg IM/IV)
  • MoA: Antagonize central dopaminergic receptors
  • Side Effects: Sedation, agitation, extrapyramidal effects, hypotension, QT prolongation/Torsades