What's the next step for a patient with nighttime vomiting and normal abdominal ultrasound results?

Next Steps for Nighttime Vomiting with Normal Abdominal Ultrasound

Obtain targeted laboratory studies immediately, including complete blood count, comprehensive metabolic panel (with electrolytes, BUN, creatinine, glucose), liver function tests, lipase, and urinalysis to exclude metabolic causes and assess for dehydration. 1, 2

Essential Laboratory Workup

• Draw serum electrolytes (Na, K), BUN, creatinine, and glucose before initiating any therapy, as prolonged vomiting causes hypokalemia, hypochloremia, and metabolic alkalosis that require correction 1, 3
• Check thyroid function tests and morning cortisol to exclude hypothyroidism and Addison's disease, which can present with vomiting as the primary symptom 1, 2
• Obtain urine drug screen to assess for cannabis use, as Cannabis Hyperemesis Syndrome (CHS) is increasingly common and presents with nighttime/early morning vomiting 1, 2
• Test for hypercalcemia if clinically indicated, as this is a reversible metabolic cause of persistent vomiting 1

Consider Specific Diagnoses

Cannabis Hyperemesis Syndrome

• Heavy cannabis use history is critical in younger patients, and CHS should be suspected if use preceded symptom onset 1
• Definitive diagnosis requires 6 months of cannabis cessation or at least 3 typical cycle lengths without vomiting 1

Cyclic Vomiting Syndrome

• Screen for typical comorbidities including migraine headaches, anxiety, depression, autonomic dysfunction, and sleep disorders if vomiting occurs in stereotypical episodes separated by symptom-free intervals 2
• Prophylactic therapy with amitriptyline 25 mg at bedtime is indicated if episodes occur ≥4 times per year, each lasting >2 days, or requiring ED visits 2

Imaging Beyond Ultrasound

• Perform one-time esophagogastroduodenoscopy (EGD) or upper GI imaging to exclude obstructive lesions, but avoid repeated endoscopy unless new symptoms develop 1
• The normal abdominal ultrasound effectively excludes biliary pathology, liver/kidney abscesses, and most structural abdominal causes 2

Empiric Pharmacologic Management

First-Line Therapy

• Initiate metoclopramide 10 mg three times daily before meals as the preferred dopamine receptor antagonist, titrated to maximum benefit and tolerance 1, 2
• Alternative dopamine antagonists include prochlorperazine or haloperidol if metoclopramide is not tolerated 1
• Monitor for extrapyramidal symptoms, particularly in young males, and treat with diphenhydramine 50 mg IV if they develop 1

Second-Line Therapy

• Add ondansetron 8 mg orally 2-3 times daily if symptoms persist after 4 weeks of dopamine antagonist therapy 1, 2
• Monitor for QTc prolongation when using ondansetron, especially in combination with other QT-prolonging agents 1

Supportive Care

• Ensure adequate fluid intake of at least 1.5 L/day with small, frequent meals 1
• Provide thiamin supplementation to prevent Wernicke's encephalopathy in patients with persistent vomiting 1
• Correct electrolyte abnormalities, particularly hypokalemia and hypomagnesemia, which can perpetuate symptoms 2, 3

Critical Pitfalls to Avoid

• Never use antiemetics if mechanical bowel obstruction is suspected until surgical evaluation is complete, as this can mask progressive ileus 1, 2
• Do not stigmatize patients with cannabis use—offer abortive and prophylactic therapy even with ongoing use, as treatments can still be effective 1
• Avoid repeated endoscopy or imaging unless new symptoms develop 1
• Administer antiemetics on a scheduled basis rather than PRN, as prevention is far easier than treating established vomiting 1