What laboratory tests and treatments are recommended for a patient presenting with vomiting?

Laboratory Tests and Treatments for Patients Presenting with Vomiting

For patients presenting with vomiting, a basic workup should include complete blood count, serum electrolytes and glucose, liver function testing, lipase, and urinalysis, followed by appropriate antiemetic therapy based on severity and suspected etiology. 1

Initial Laboratory Evaluation

• Complete blood count (CBC) to assess for infection, inflammation, or blood loss 1
• Serum electrolytes and glucose to evaluate for metabolic derangements and dehydration 1
• Liver function tests to rule out hepatic causes 1, 2
• Serum lipase to assess for pancreatitis 1
• Urinalysis to evaluate hydration status and rule out urinary causes 1

Additional Diagnostic Tests Based on Clinical Presentation

• One-time esophagogastroduodenoscopy or upper gastrointestinal imaging to exclude obstructive lesions in cases of persistent vomiting 1
• Abdominal CT scan for suspected bowel obstruction or perforation (higher sensitivity than ultrasound or X-ray) 1
• Water-soluble contrast enema for suspected large bowel obstruction (96% sensitivity, 98% specificity) 1
• ECG baseline in patients receiving certain antiemetics (ondansetron) due to risk of QTc prolongation 1
• Consider brain imaging and neurological referral for patients with localizing neurologic symptoms 1

Special Considerations for Specific Presentations

• For prolonged vomiting: Assess for thiamine deficiency and consider thiamine supplementation (200-300 mg daily) 1
• For suspected cyclic vomiting syndrome (CVS): Consider cannabis use patterns (prolonged use >1 year may indicate cannabinoid hyperemesis syndrome) 1
• For vomiting with abdominal pain: Consider workup for Addison's disease, hypothyroidism, and hepatic porphyria 1
• For vomiting in post-surgical patients: Assess for postoperative complications and consider prophylactic antiemetics 1

Treatment Approach

First-Line Antiemetics

• Ondansetron (5-HT3 receptor antagonist): 8 mg sublingual/oral every 4-6 hours during episode 1, 3

  • Baseline ECG advised due to risk of QTc prolongation 1
  • Particularly effective for chemotherapy-induced nausea and vomiting 3

• Promethazine (dopamine receptor antagonist with antihistaminergic effects): 12.5-25 mg oral/rectal every 4-6 hours 1

  • Caution with peripheral IV administration due to risk of tissue injury 1
  • Side effects include CNS depression and anticholinergic effects 1

• Prochlorperazine (dopamine receptor antagonist): 5-10 mg every 6-8 hours or 25 mg suppository every 12 hours 1

  • Caution in patients with history of leukopenia, dementia, glaucoma, or seizure disorders 1

Adjunctive Medications

• Sedatives for severe episodes:

  • Alprazolam: 0.5-2 mg every 4-6 hours 1
  • Diphenhydramine: 12.5-25 mg every 4-6 hours 1
  • Lorazepam: Useful for anxiety-related nausea 1

• For severe, refractory cases:

  • Haloperidol or droperidol have shown efficacy in treatment-resistant nausea and vomiting 1
  • Dexamethasone can be considered for chemotherapy-induced nausea 1

Supportive Care

• Intravenous crystalloids for dehydration and electrolyte replacement 1
• Nasogastric suction for gastric decompression in cases of bowel obstruction or severe vomiting 1
• Monitor urine output to assess hydration status 1

Treatment Algorithm Based on Suspected Etiology

1. Acute gastroenteritis/food poisoning:

   • Fluid replacement and antiemetics (ondansetron preferred) 1, 4

2. Medication-induced vomiting:

   • Consider medication adjustment or rotation 1
   • Symptomatic treatment with antiemetics 1

3. Cyclic vomiting syndrome:

   • Combination therapy with sumatriptan and antiemetics 1
   • Consider sedation with benzodiazepines 1

4. Bowel obstruction:

   • Nasogastric decompression, IV fluids, and surgical consultation 1

5. Chemotherapy-induced nausea and vomiting:

   • Prophylactic antiemetics based on emetogenic potential of chemotherapy 1, 3
   • 5-HT3 antagonists (ondansetron) plus dexamethasone for moderate to highly emetogenic regimens 1

Common Pitfalls and Caveats

• Avoid repeated esophagogastroduodenoscopy or upper GI imaging studies in patients with known cyclic vomiting syndrome 1
• Gastric emptying scans should not be ordered routinely for vomiting, especially during an acute episode or in patients using cannabis or opiates 1
• Patients using cannabis are often stigmatized, but should still be offered appropriate antiemetic therapy regardless of ongoing use 1
• In patients with prolonged vomiting, thiamine supplementation should be initiated promptly to prevent Wernicke's encephalopathy 1
• Metoclopramide should be used cautiously in pediatric patients due to variable pharmacokinetics and limited efficacy data 5