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Nausea: Definition, Pathophysiology, Causes & Management

Definition

Nausea = subjective sensation of urge to vomit; often precedes emesis but can occur alone. Mediated by the vomiting center (medulla) and chemoreceptor trigger zone (CTZ) (area postrema, outside BBB).

Pathophysiology

  • Vestibular: Motion sickness (mismatch visual/vestibular) → histamine (H1), acetylcholine (muscarinic).
  • CTZ (Chemoreceptor Trigger Zone): Blood-borne toxins, drugs (chemo, opioids, digoxin) → dopamine (D2), serotonin (5-HT3), NK1.
  • GI Mucosa: Distension, inflammation, obstruction → vagal afferents → 5-HT3.
  • Higher Cortex: Sight, smell, anxiety, anticipation.

Common Causes

CategoryExamples
GIGastroenteritis, obstruction, pancreatitis, hepatitis, GERD, constipation
DrugsChemo (highly emetogenic: cisplatin), opioids, antibiotics, digoxin, NSAIDs, iron
MetabolicUremia, ketoacidosis, hyperglycemia, thyroid storm, Addisonian crisis
NeurologicMigraine, increased ICP, concussion, vestibular neuritis
PregnancyNVP (nausea/vomiting of pregnancy), hyperemesis gravidarum
PsychogenicAnxiety, eating disorders, conversion

Antiemetic Classes (Receptor Targets)

  • 5-HT3 antagonists (ondansetron) – chemo, post-op, GI.
  • D2 antagonists (metoclopramide, prochlorperazine) – migraine, gastroparesis.
  • NK1 antagonists (aprepitant) – delayed chemo nausea.
  • H1 antagonists (meclizine, dimenhydrinate) – motion sickness.
  • Anticholinergics (scopolamine) – motion sickness.
  • Corticosteroids (dexamethasone) – chemo adjunct, brain edema.
  • Benzodiazepines (lorazepam) – anticipatory nausea.
  • Cannabinoids (dronabinol) – refractory chemo.

Red Flags

Hematemesis, bilious vomiting, severe abdominal pain, signs of dehydration, neurologic deficits, weight loss → urgent evaluation.

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