How should I assess and manage a patient presenting with vomiting?

Assessment and Management of Vomiting

Initial Assessment and Risk Stratification

Begin by determining whether vomiting is acute (≤7 days) or chronic (≥4 weeks), as this fundamentally changes your diagnostic and therapeutic approach. 1, 2

Critical Red Flag Signs Requiring Immediate Evaluation

• Bilious or bloody vomiting 3, 4
• Altered mental status or toxic/septic appearance 4
• Severe dehydration with shock 3
• Bent-over posture suggesting acute abdomen 4
• Inconsolable crying or excessive irritability in children 4

Essential Initial Laboratory Testing

Obtain complete blood count, serum electrolytes (particularly potassium and magnesium), glucose, liver function tests, lipase, and urinalysis to exclude metabolic causes and assess dehydration severity. 3

• Consider hypercalcemia, hypothyroidism, and Addison's disease testing if clinically indicated 3
• Urine drug screen is warranted, particularly for cannabis use in younger adults, as Cannabis Hyperemesis Syndrome is increasingly common 3
• Monitor for hypokalemia, hypochloremia, and metabolic alkalosis in prolonged vomiting 3

Acute Vomiting (≤7 Days)

Most Common Causes

• Gastroenteritis or viral syndromes 1, 5
• Foodborne illness 1
• Medication adverse effects 1, 5
• Early pregnancy 1
• Acute migraine 1

Immediate Management Priorities

Oral rehydration solution (ORS) is first-line therapy for mild to moderate dehydration in all age groups, even when vomiting is present. 3

• Reduced-osmolarity ORS dosing for rehydration:

  • Infants/children: 50-100 mL/kg over 3-4 hours 3
  • Adolescents/adults (≥30 kg): 2-4 L over 3-4 hours 3

• Isotonic IV crystalloids (lactated Ringer's or normal saline) are reserved for:

  • Severe dehydration (≥10% fluid deficit) 3
  • Shock or altered mental status 3
  • Failure of oral rehydration 3
  • Ileus 3

• Initial IV bolus: 20 mL/kg repeated until pulse, perfusion, and mental status normalize 3

Antiemetic Therapy for Acute Vomiting

Ondansetron is the preferred first-line antiemetic for acute vomiting when oral intake is compromised. 4

• Dosing:

  • Adults: 8-16 mg IV/PO 3
  • Children ≥4 years: 0.2 mg/kg oral (max 4 mg) or 0.15 mg/kg IV (max 4 mg) 4

• Important caveat: Ondansetron may increase stool volume/diarrhea in gastroenteritis 3

• Monitor for QT prolongation, especially with other QT-prolonging agents 3, 6

Chronic Vomiting (≥4 Weeks)

Diagnostic Evaluation

Perform one-time esophagogastroduodenoscopy (EGD) or upper GI imaging to exclude obstructive lesions, but avoid repeated endoscopy unless new symptoms develop. 3

Special Consideration: Cyclic Vomiting Syndrome

CVS should be suspected in any adult with episodic bouts of repetitive vomiting separated by symptom-free intervals. 7

• Prevalence is approximately 2% in US adults, more common in women 7

• Key diagnostic features:

  • Stereotypic pattern with prodromal symptoms (65% of patients) 7
  • Prodromal phase lasting median 1 hour before vomiting onset 7
  • Associated constitutional symptoms: fatigue, mental fog, anxiety, diaphoresis, abdominal pain 7
  • Episodes often occur in early morning hours 7

• Cannabis Hyperemesis Syndrome must be excluded through detailed cannabis use history 3

• Definitive CHS diagnosis requires 6 months cannabis cessation or 3 typical cycle lengths without vomiting 3

Stepwise Pharmacologic Management for Chronic Vomiting

Initiate dopamine receptor antagonists as first-line therapy, titrated to maximum benefit and tolerance. 3

First-Line Options:

• Metoclopramide 10 mg IV/PO every 6 hours (particularly effective for gastric stasis) 3
• Prochlorperazine 3
• Haloperidol 1 mg IV/PO every 4 hours as needed 3

Monitor for extrapyramidal symptoms, particularly in young males, and treat with diphenhydramine 50 mg IV if they develop. 3

Second-Line Therapy (if symptoms persist after 4 weeks):

Add 5-HT3 antagonist (ondansetron 8-16 mg) combined with dexamethasone 10-20 mg IV, as this combination is superior to either agent alone. 3

• This represents category 1 evidence in guideline recommendations 3
• Acts on different receptors than dopamine antagonists, providing complementary coverage 3

Refractory Cases:

Administer antiemetics on a scheduled basis rather than PRN, as prevention is far easier than treating established vomiting. 3

• Use agents from different drug classes simultaneously rather than sequential monotherapy 3
• Consider alternating routes (IV, rectal, sublingual) if oral route not feasible 3
• Dronabinol 2.5-7.5 mg PO every 4 hours as needed is FDA-approved for refractory nausea unresponsive to conventional antiemetics 3

Adjunctive Therapies

• Add proton pump inhibitor or H2 blocker if dyspepsia is present, as patients may confuse heartburn with nausea 3
• Thiamin supplementation to prevent Wernicke's encephalopathy in persistent vomiting 3
• Ensure adequate fluid intake of at least 1.5 L/day with small, frequent meals 3

Cancer-Related Vomiting

Chemotherapy-Induced Nausea and Vomiting

For highly emetogenic chemotherapy, use three-drug prophylaxis: 5-HT3 antagonist + dexamethasone + NK-1 receptor antagonist. 7

• Dexamethasone should be administered once daily for every day of moderately or highly emetogenic chemotherapy, and for 2-3 days after for delayed emesis 7
• 5-HT3 antagonist should be given each day before first dose of chemotherapy 7
• Approximately 25-32% of patients still experience delayed emesis even with optimal two-drug regimen 7

Radiation-Induced Vomiting

Patients undergoing upper abdominal radiation should receive oral ondansetron or granisetron, with or without oral dexamethasone. 7

Anticipatory Nausea and Vomiting

The most effective treatment is prevention using optimal antiemetic therapy during every cycle. 7

• Behavioral therapy, hypnosis, and guided imagery may be helpful 7
• Alprazolam 0.25-0.5 mg PO three times daily starting night before treatment can be combined with antiemetics 7

Malignant Bowel Obstruction

Patients with symptomatic malignant bowel obstruction should be offered at least one of the following: surgery, stenting, decompression percutaneous gastrostomy tube, nasogastric tube, or octreotide. 7

• Emergency surgical intervention is appropriate in patients with reversible cause, good performance status, and lack of complicating factors 7
• Stenting successful in 97% of patients with symptom resolution in 89% 7

Critical Pitfalls to Avoid

Never use antiemetics in suspected mechanical bowel obstruction, as this can mask progressive ileus and gastric distension. 3, 6

Do not stigmatize patients with cannabis use—offer abortive and prophylactic therapy even with ongoing use, as treatments can still be effective. 3

Avoid repeated endoscopy or imaging unless new symptoms develop. 3

Antimotility agents (loperamide) must not be used in children under 18 years with acute diarrhea or in any patient with inflammatory diarrhea or fever. 3

High-sugar fluids (fruit juices, sports drinks, soft drinks) should be avoided for rehydration in gastroenteritis. 3