How to manage vomiting in an adult patient with a complex medical history and risk of dehydration?

Management of Vomiting in Adults with Complex Medical History and Dehydration Risk

Prioritize immediate assessment of dehydration severity and initiate oral rehydration solution (ORS) for mild-to-moderate cases or intravenous isotonic fluids for severe dehydration, while addressing the underlying cause and maintaining nutrition throughout treatment. 1, 2

Initial Assessment of Dehydration Severity

Rapidly categorize dehydration through physical examination:

• Mild dehydration (3-5% fluid deficit): Increased thirst, slightly dry mucous membranes 1, 2
• Moderate dehydration (6-9% fluid deficit): Loss of skin turgor, dry mucous membranes 1, 2
• Severe dehydration (≥10% fluid deficit): Severe lethargy or altered consciousness, prolonged skin tenting, hypovolemic shock 3, 1

For older adults specifically, assess for at least four of these seven signs to identify moderate-to-severe volume depletion: confusion, non-fluent speech, extremity weakness, dry mucous membranes, dry tongue, furrowed tongue, sunken eyes 3

Immediate Rehydration Protocol

For Mild-to-Moderate Dehydration

Administer reduced osmolarity ORS as first-line therapy:

• Mild dehydration: 50 mL/kg over 2-4 hours 1, 2
• Moderate dehydration: 100 mL/kg over 2-4 hours 1, 2
• After each vomiting episode: Adults should consume as much ORS as desired 3, 1

If oral intake is not tolerated due to persistent vomiting, use nasogastric tube administration at 15 mL/kg/hour 1, 2

For Severe Dehydration

Severe dehydration constitutes a medical emergency requiring immediate action:

• Administer isotonic intravenous fluids (lactated Ringer's or normal saline) in 20 mL/kg boluses immediately 1, 2
• Continue IV rehydration until pulse, perfusion, and mental status normalize 3, 1
• Once stabilized, transition remaining fluid deficit replacement to ORS 1, 2

For elderly patients, initiate 0.45% or 0.9% normal saline at 4-14 mL/kg/hour with careful monitoring for fluid overload 4

Antiemetic Therapy

Antiemetic agents should only be considered after adequate hydration is achieved, not as a substitute for fluid therapy:

• Ondansetron (serotonin 5-HT3 receptor antagonist) can facilitate tolerance of oral rehydration in adults with significant vomiting 3
• Ondansetron dosing: 4 mg intravenous over 2-5 minutes or 0.15 mg/kg (maximum 4 mg) 5, 6
• Critical caveat: Ondansetron may increase stool volume/diarrhea as a side effect 3
• Avoid antimotility drugs (loperamide) in suspected inflammatory diarrhea, fever, or bloody stools due to risk of toxic megacolon 3

Ongoing Management and Monitoring

After initial rehydration:

• Provide maintenance fluids and replace ongoing losses with ORS until vomiting resolves 1, 2
• Reassess hydration status after 3-4 hours and adjust treatment accordingly 1, 4
• Resume age-appropriate diet immediately after rehydration—do not "rest the bowel" through fasting, as this delays recovery 1, 2

Critical Pitfalls to Avoid

• Never delay treatment for severe dehydration—it is a medical emergency requiring immediate IV access 1, 2
• Do not use popular beverages (apple juice, Gatorade, commercial soft drinks) for rehydration—they lack appropriate electrolyte composition and high osmolality can worsen dehydration 1, 2
• Do not withhold food—early refeeding decreases intestinal permeability, reduces illness duration, and improves nutritional outcomes 3
• Do not give antiemetics before adequate hydration—they are ancillary treatment only, not a substitute for fluid therapy 3

Special Considerations for Complex Medical History

Post-Bariatric Surgery Patients

• Refractory vomiting despite nutritional compliance may indicate surgical complications (band slippage, stricture, obstruction, reflux, ulcers) 3
• When vomiting persists >2-3 weeks, administer thiamin supplementation to prevent Wernicke's encephalopathy 3
• Maintain prolonged adequate hydration—one-third of post-bariatric emergency visits within 3 months are dehydration-related 3

Patients with Persistent Vomiting

• Test and treat for potassium deficiency before emergent general anesthesia, especially if paralysis is planned 3
• Screen regularly for thiamine deficiency, particularly with severe food intolerance 3
• Evaluate for magnesium and calcium deficiency in patients on proton pump inhibitors with severe food intolerance 3
• Address psychological factors (depression, anxiety) which are often neglected but significantly impact outcomes 3

Infectious Diarrhea Context

• Antibiotics are contraindicated for routine uncomplicated watery diarrhea 4
• Specific antimicrobial indications only include cholera, Shigella dysentery, amoebic dysentery, and acute giardiasis 4