Approach to the Patient with Vomiting: A Clinical Lecture
Initial Assessment: The ABCs and Red Flags
Your first priority is to identify life-threatening causes immediately—bilious vomiting is a surgical emergency until proven otherwise, and altered mental status, severe dehydration, or hemodynamic instability require urgent intervention. 1, 2
Critical Red Flag Signs to Assess Immediately:
- Bilious or bloody vomiting (suggests obstruction, malrotation with volvulus, or upper GI bleeding) 2, 3
- Altered sensorium or papilledema (intracranial pathology, metabolic encephalopathy) 2, 3, 4
- Severe dehydration (sunken eyes, delayed capillary refill >3 seconds, tachycardia, hypotension) 1, 2, 3
- Toxic/septic appearance (suggests meningitis, sepsis, metabolic crisis) 3, 4
- Bent-over posture (peritonitis, appendicitis) 3
MCQ #1 (Difficult Level)
A 6-month-old infant presents with bilious vomiting for 6 hours. Vital signs are stable. What is your MOST appropriate next step?
A) Start ondansetron and observe
B) Order urgent fluoroscopy upper GI series
C) Obtain basic metabolic panel first
D) Trial oral rehydration solution
Answer: B - Bilious vomiting requires urgent fluoroscopy upper GI series to rule out malrotation with volvulus, a surgical emergency. 2 Delaying imaging for antiemetics or labs can lead to bowel necrosis.
Categorizing Vomiting: Acute vs. Chronic
Acute Vomiting (≤7 days):
The most common causes are gastroenteritis, viral syndromes, foodborne illness, medication adverse effects, and early pregnancy. 5, 6
Key historical features to elicit:
- Timing relative to meals (immediate = esophageal/gastric outlet; delayed 1-4 hours = gastroparesis; unrelated = systemic cause) 2, 5
- Associated symptoms (diarrhea suggests gastroenteritis; headache suggests migraine; vertigo suggests vestibular disorder) 5, 6
- Medication/substance use (opioids, chemotherapy, antibiotics, NSAIDs, cannabis >4x/week) 2, 5
- Pregnancy status (always check in reproductive-age females) 5, 6
Chronic Vomiting (≥4 weeks):
Consider gastroparesis, cyclic vomiting syndrome (CVS), cannabinoid hyperemesis syndrome, psychiatric disorders, and occult malignancy. 2, 5
CVS diagnostic criteria (must meet all): 2
- Stereotypical episodes of acute-onset vomiting lasting <7 days
- ≥3 discrete episodes per year
- Episodes separated by ≥1 week of baseline health
MCQ #2 (Difficult Level)
A 28-year-old presents with recurrent episodes of severe vomiting lasting 2-3 days, occurring every 2-3 months for the past year. Between episodes, she feels completely normal. She uses cannabis 5 times weekly. What distinguishes cannabinoid hyperemesis from cyclic vomiting syndrome?
A) Presence of nausea between episodes
B) Cannabis use >4 times weekly for >1 year
C) Response to hot showers
D) Both B and C
Answer: D - Cannabis use >4 times weekly for >1 year suggests cannabinoid hyperemesis rather than CVS. 2 Additionally, compulsive hot bathing is pathognomonic for cannabinoid hyperemesis (not mentioned in provided evidence but clinically relevant).
Diagnostic Workup: Targeted, Not Routine
The diverse nature of vomiting causes makes a "routine" laboratory screen impossible—your history and physical examination must guide investigation. 3
When to Order Labs:
Obtain basic labs (CMP, LFTs, TSH, pregnancy test, urinalysis) in any patient with: 2, 3
- Moderate-severe dehydration
- Red flag signs
- Chronic vomiting without clear etiology
- Suspected metabolic/endocrine disorder
When to Image:
- Bilious vomiting → Urgent fluoroscopy upper GI series 2
- Suspected obstruction → Abdominal X-ray (upright and supine) 3, 4
- Altered mental status → Head CT 6
- Chronic symptoms with alarm features → Upper endoscopy 6
- Suspected gastroparesis → Gastric emptying scintigraphy 2, 6
MCQ #3 (Difficult Level)
A 45-year-old with diabetes presents with chronic nausea and vomiting, worse after meals. Upper endoscopy is normal. What is the most appropriate next diagnostic test?
A) Abdominal CT with contrast
B) Gastric emptying scintigraphy
C) Small bowel follow-through
D) Repeat endoscopy with biopsies
Answer: B - When gastroparesis is suspected (diabetes, postprandial symptoms, normal endoscopy), gastric emptying scintigraphy is the diagnostic test of choice. 2, 6
Pharmacologic Management: Receptor-Targeted Approach
Ondansetron (5-HT3 antagonist) is the preferred initial agent for acute vomiting, with sublingual formulation potentially improving absorption in actively vomiting patients. 1, 3
First-Line Antiemetic Dosing:
Second-Line Options (if ondansetron fails or contraindicated): 1
- Promethazine: 12.5-25 mg IV/IM/rectal
- Prochlorperazine: 10 mg IV/IM or 25 mg rectal suppository
- Metoclopramide: 10 mg IV/IM (caution: extrapyramidal side effects, avoid in obstruction)
Refractory Vomiting Combination Therapy: 1
- Lorazepam 0.5-1 mg IV + Haloperidol 0.5-2 mg IV
- Critical caveat: Monitor QT interval with haloperidol
MCQ #4 (Difficult Level)
A patient with chemotherapy-induced vomiting fails ondansetron. You add haloperidol. What monitoring is essential?
A) Blood glucose
B) QT interval on ECG
C) Serum magnesium
D) Liver enzymes
Answer: B - Haloperidol can prolong QT interval, requiring ECG monitoring when used for refractory vomiting. 1 This is especially important in combination with other QT-prolonging agents.
Fluid and Electrolyte Management
For mild dehydration with oral tolerance, use oral rehydration with small, frequent sips of electrolyte-rich fluids (sports drinks); for moderate-severe dehydration or inability to tolerate oral intake, initiate IV therapy with balanced crystalloids. 1
IV Fluid Protocol: 1
- Initial bolus: 500-1000 mL normal saline or lactated Ringer's
- Maintenance rate: Based on ongoing losses and hydration status
- Add dextrose if prolonged fasting or concern for hypoglycemia
Use balanced crystalloid solutions (lactated Ringer's) to avoid hyperchloremic acidosis. 1
Special Populations and Syndromes
Cyclic Vomiting Syndrome Management:
Abortive therapy (during prodromal phase): 2
- Sumatriptan 20 mg intranasal + Ondansetron 8 mg sublingual + Benzodiazepine
- IV dextrose-containing fluids are essential
- Quiet, dark environment to optimize response
Prophylactic therapy: 2
- Amitriptyline 25 mg at bedtime, titrated to 75-150 mg nightly to reduce episode frequency
Common pitfall: Missing the prodromal window dramatically reduces abortive therapy effectiveness. 2 Patients must be educated to recognize early symptoms (nausea, pallor, abdominal discomfort) and treat immediately.
MCQ #5 (Difficult Level)
A patient with known CVS presents during the emetic phase (already vomiting for 4 hours). What is the MOST appropriate management?
A) Sumatriptan + ondansetron + lorazepam
B) IV dextrose + promethazine for sedation
C) Oral amitriptyline prophylaxis
D) Observation only
Answer: B - Once in the emetic phase (not prodromal), abortive therapy with sumatriptan is less effective. 2 Focus shifts to sedation (promethazine or lorazepam), IV dextrose-containing fluids, and supportive care in a quiet environment. 1, 2
Chemotherapy-Induced Nausea and Vomiting:
For high emetic risk chemotherapy, use triple therapy BEFORE chemotherapy: 7
- 5-HT3 antagonist (palonosetron 0.25 mg IV preferred)
- Dexamethasone 12 mg PO/IV day 1, then 8 mg daily days 2-4
- Neurokinin-1 antagonist (aprepitant 125 mg PO day 1, then 80 mg days 2-3)
Prevention is the goal—prophylaxis is superior to rescue therapy. 7 Approximately 70-80% of cancer patients on chemotherapy experience nausea/vomiting without prophylaxis, but optimal antiemetic therapy reduces this to ~25% even with highly emetogenic agents. 7
MCQ #6 (Difficult Level)
Which antiemetic combination reduces chemotherapy-induced vomiting from nearly 100% to approximately 25% with cisplatin?
A) Ondansetron alone
B) Ondansetron + dexamethasone
C) Ondansetron + dexamethasone + aprepitant
D) Metoclopramide + promethazine
Answer: C - Triple therapy with 5-HT3 antagonist + corticosteroid + NK-1 antagonist provides optimal protection against highly emetogenic chemotherapy. 7 This targets multiple neuroreceptor pathways synergistically.
Critical Pitfalls to Avoid
Never give prophylactic antiemetics in radiation exposure cases—vomiting onset helps determine radiation dose and guides treatment. 1
Do not use abdominal thrusts (Heimlich maneuver) for drowning victims with vomiting—this is unnecessary and potentially dangerous. 7 Only suction is appropriate for airway clearance.
Do not overlook psychiatric comorbidities (anxiety, depression) in CVS—these worsen episode frequency and require concurrent management. 2
Do not ignore retching and nausea as equally disabling symptoms—treat these as aggressively as vomiting itself. 2
Do not delay surgical consultation for bilious vomiting—imaging and surgical evaluation must occur urgently, not after "stabilization." 2, 3
Take-Home Messages
🔑 Bilious vomiting = surgical emergency until proven otherwise—obtain urgent fluoroscopy upper GI series. 2
🔑 Ondansetron is first-line for acute vomiting; combination therapy (benzodiazepine + haloperidol with QT monitoring) for refractory cases. 1
🔑 CVS requires recognition of the prodromal phase for effective abortive therapy (sumatriptan + ondansetron + benzodiazepine); once in emetic phase, shift to sedation and IV dextrose. 1, 2
🔑 Prevention trumps rescue in chemotherapy-induced vomiting—use triple therapy (5-HT3 + steroid + NK-1 antagonist) BEFORE high-risk chemotherapy. 7
🔑 Cannabis use >4 times weekly for >1 year suggests cannabinoid hyperemesis, not CVS—cessation is curative. 2
🔑 Use balanced crystalloids (lactated Ringer's) for IV rehydration to avoid hyperchloremic acidosis. 1