1. History
- Key HPI questions: Onset and duration of symptoms; volume and frequency of vomiting, diarrhea, or both; last oral intake and estimated fluid intake over the past 24 hours; urine output (frequency, color, last void); presence of fever, blood in stool, or abdominal pain
- Symptom characterization: Thirst, dry mouth, dizziness/lightheadedness, weakness, fatigue, headache, muscle cramps
- Timing/triggers: Acute gastroenteritis, heat exposure, exercise, medication changes (new diuretic, SGLT2 inhibitor), recent travel, sick contacts, dietary changes
- Severity/progression: Ability to tolerate oral fluids, worsening lethargy, syncope or near-syncope, decreased urine output
- Important negatives: Chest pain, dyspnea, hematemesis, melena, focal neurologic deficits, pregnancy status
2. Alarm Features
- Altered mental status (lethargy, confusion, obtundation) — suggests severe dehydration (>10% fluid deficit) or hypovolemic shock [1-2]
- Hemodynamic instability: persistent tachycardia, hypotension, weak/thready pulses
- Prolonged capillary refill >2 seconds [3]
- Sunken eyes, absent tears, very dry mucous membranes (combination increases likelihood of ≥10% dehydration; LR+ 8.4 for ≥7 of 10 Gorelick signs) [3-4]
- Inability to tolerate any oral intake
- Signs of hypovolemic shock: cool/clammy skin, flat neck veins, oliguria/anuria [2]
- In children: sunken fontanelle, skin fold recoil >2 seconds
- In elderly: confusion, extremity weakness, nonfluent speech, furrowed tongue [5]
3. Medications
Contributors to dehydration
- Diuretics (loop, thiazide) — most common medication cause of volume depletion [5]
- SGLT2 inhibitors (empagliflozin, dapagliflozin, canagliflozin) — cause osmotic diuresis and volume depletion (RR 1.14 vs placebo); risk is higher in elderly and when combined with diuretics [6-7]
- ACE inhibitors/ARBs (compounded risk with SGLT2i) [8]
- Laxatives, lithium, amphotericin B
Common treatments
- Ondansetron (oral/IV): Reduces vomiting and facilitates oral rehydration in the ED. Single dose in children reduces IV fluid need (RR 0.46). A 2025 RCT showed multidose post-discharge ondansetron reduced moderate-to-severe gastroenteritis (5.1% vs 12.5%; aOR 0.50) [9-10]
- Loperamide: May be used for watery diarrhea in adults; avoid in bloody/inflammatory diarrhea (risk of toxic megacolon) [11]
- Bismuth subsalicylate: Safe alternative in inflammatory diarrhea [11]
Contraindicated/caution
- Antimotility agents in dysenteric/bloody diarrhea
- Hold SGLT2 inhibitors during acute illness ("sick day rules") [7]
4. Diet
- Acute phase: Low-osmolarity ORS (200–250 mOsm/L) is first-line for mild-moderate dehydration — commercial options include Pedialyte, CeraLyte, Enfalyte [12-13]
- Avoid apple juice, Gatorade, soft drinks, and other high-osmolarity beverages for rehydration [12]
- Refeeding: Resume age-appropriate normal diet as early as tolerated (within 4–6 hours of rehydration); early refeeding shortens illness duration [13-14]
- BRAT diet (bananas, rice, applesauce, toast) is commonly recommended but supporting data are limited [14]
- Breastfed infants should continue nursing throughout illness [12]
- Lactose-containing formula can generally be continued; diluted formula offers no benefit [12]
- Long-term: Adequate daily fluid intake; elderly patients in particular require proactive hydration strategies [2]
5. Review of Systems
- GI: Nausea, vomiting (frequency, bilious?), diarrhea (watery vs bloody), abdominal pain/cramping, anorexia
- Cardiovascular: Palpitations, chest pain, orthostatic dizziness, syncope
- Neurologic: Confusion, headache, weakness, seizures (consider hypernatremia)
- Renal/GU: Urine output, color, dysuria
- Endocrine: Polyuria/polydipsia (new-onset diabetes, DKA, diabetes insipidus)
- Skin: Turgor, rash (viral exanthem), burns
6. Collateral History and Family History
- Caregiver report of oral intake, wet diapers (pediatrics), behavioral changes
- Sick contacts, daycare/institutional exposure, recent travel
- Access to fluids (elderly, disabled, or cognitively impaired patients are at particular risk) [5]
- Family history of diabetes insipidus, adrenal insufficiency, or renal tubular disorders
- Social context: living alone (elderly), food insecurity, substance use
7. Risk Factors
- Age extremes: Infants/young children (higher surface-area-to-volume ratio, dependence on caregivers) and elderly (blunted thirst, polypharmacy, comorbidities) [2][5]
- Elderly-specific: Female sex, age >85, >4 chronic conditions, >4 medications, bed-bound status [5]
- Acute gastroenteritis (most common cause)
- Heat exposure, strenuous exercise
- Chronic kidney disease, heart failure, diabetes mellitus
- Medications: diuretics, SGLT2 inhibitors [6]
- Burns, fever, polyuria (DKA, diabetes insipidus)
- Cognitive impairment, dysphagia, restricted fluid access
8. Differential Diagnosis
- Hypovolemic shock (hemorrhagic, distributive) — must distinguish from pure dehydration; volume depletion causes prominent circulatory instability and requires NS rapidly, whereas pure dehydration (intracellular water loss) may lack circulatory instability and is corrected with hypotonic fluids [5]
- Diabetic ketoacidosis — polyuria, Kussmaul breathing, ketonemia
- Adrenal crisis — hypotension, hyperkalemia, hyponatremia
- Diabetes insipidus — massive polyuria, dilute urine, hypernatremia
- Sepsis — fever, tachycardia, hypotension with infectious source
- Third-spacing (pancreatitis, bowel obstruction, peritonitis)
- Thyrotoxicosis — tachycardia, weight loss, diarrhea
- Hypercalcemia — polyuria, confusion, constipation
9. Past Medical History
- Prior episodes of dehydration or hospitalization for gastroenteritis
- Chronic kidney disease (impaired concentrating ability)
- Heart failure (baseline diuretic use, fluid restriction)
- Diabetes mellitus (DKA risk, SGLT2i use)
- Inflammatory bowel disease, short bowel syndrome
- Eating disorders, chronic vomiting
- Prior bariatric surgery
- Adrenal insufficiency
10. Physical Exam
Vital signs
- Tachycardia (often the earliest sign), hypotension, orthostatic changes (drop in SBP ≥20 mmHg or rise in HR ≥20 bpm on standing)
- Fever (may worsen insensible losses)
Focused exam
- General appearance: Ill-appearing, lethargic, or irritable (children) [3]
- Mucous membranes: Dry vs moist — moist membranes argue against significant hypovolemia (most helpful negative finding) [5]
- Eyes: Sunken appearance; absence of tears in children [4]
- Skin: Turgor (test over abdomen in children, sternum/forearm in adults; poor turgor is less reliable in elderly) [5]
- Capillary refill: >2 seconds suggests ≥5% dehydration [3]
- Tongue: Dry, furrowed tongue correlates with dehydration in elderly [5]
- Fontanelle: Sunken in infants
- Cardiovascular: Weak/thready pulses, flat neck veins
Clinical pearl: The best 4-sign simplified assessment in children is: capillary refill >2 sec, absent tears, dry mucous membranes, and ill general appearance — presence of ≥2 of these 4 signs yields LR+ 6.1 for ≥5% dehydration [3-4]
11. Lab Studies
- BMP/CMP: Sodium (hypernatremia = hallmark of water-loss dehydration), potassium, chloride, bicarbonate, BUN, creatinine, glucose [5]
- Elevated BUN:Cr ratio (>20:1) suggests prerenal azotemia/volume depletion
- BUN >45 mg/dL is very specific for ≥5% dehydration in children [4]
- Serum bicarbonate ≤16 mmol/L predicts hospital admission and correlates with dehydration severity [15]
- Serum/plasma osmolality: Gold standard for water-loss dehydration; 295–300 mOsm/kg = impending; >300 mOsm/kg = current dehydration [2][16-17]
- Urinalysis: Specific gravity (>1.020 suggests concentration), urine osmolality
- Lactate: If concern for shock or tissue hypoperfusion
- CBC: Hemoconcentration (elevated hematocrit)
- Venous blood gas: Assess for metabolic acidosis (base deficit)
Labs are not routinely needed in mild dehydration but should be obtained in moderate-severe cases, extremes of age, or when the etiology is unclear. [18]
12. Imaging
- Not routinely indicated for straightforward dehydration
- Abdominal imaging (X-ray, CT): If concern for bowel obstruction, intussusception (pediatric), or surgical abdomen
- Point-of-care ultrasound (POCUS): IVC collapsibility index can help assess volume status — IVC collapse >50% with respiration suggests hypovolemia
- Chest X-ray: If concern for pneumonia as a cause of insensible losses or if fluid overload from resuscitation is suspected
13. Special Tests
Dehydration scoring systems
- Clinical Dehydration Scale (CDS): Validated in children; scores 0 (no dehydration), 1–4 (some, 3–6% deficit), 5–8 (moderate-severe, >6% deficit) [1]
- Gorelick 10-point scale: ≥3 signs = sensitivity 87%, specificity 82% for ≥5% dehydration [3]
- WHO dehydration scale: No dehydration / some / severe [1]
Point-of-care tests
- Bedside glucose (rule out DKA, hypoglycemia)
- Urine ketones (starvation ketosis, DKA)
- Point-of-care lactate
Orthostatic vital signs: Useful in adults; a postural pulse increase of ≥30 bpm has the highest sensitivity for hypovolemia [5]
14. ECG
ECG is indicated when there is concern for significant electrolyte derangement or hemodynamic compromise.
Hypokalemia (from vomiting, diarrhea, diuretics)
- ST-segment depression, T-wave flattening, prominent U waves, QTc prolongation [19-20]
- Risk of PVCs, VT, torsades de pointes, VF — especially in patients with underlying heart disease [19]
Hyperkalemia (from AKI/renal failure in severe dehydration):
Hyponatremia (severe)
Hypocalcemia/hypomagnesemia
The following figure illustrates the characteristic ECG morphologies seen with electrolyte abnormalities commonly encountered in dehydration:
15. Assessment
Severity stratification (based on estimated fluid deficit): [1]
- Mild: <5% body weight loss — thirsty, slightly dry mucous membranes, normal hemodynamics
- Moderate: 5–10% — tachycardia, decreased skin turgor, sunken eyes, reduced urine output, irritability
- Severe: >10% — lethargy/obtundation, hemodynamic instability, absent tears, very prolonged capillary refill, shock
Atypical presentations
- Elderly patients may present with confusion, falls, or weakness without classic signs; clinical signs are subtle and unreliable outside extremes [16]
- Hypernatremic dehydration in children may mask clinical signs of dehydration [12]
- Neonates may present with poor feeding and weight loss
Complications: Acute kidney injury, seizures (hypo/hypernatremia), cerebral venous thrombosis, rhabdomyolysis, cardiac arrhythmias
16. Treatment Plan
Mild-moderate dehydration
- ORS is first-line for all ages [12]
- Children: 50–100 mL/kg over 3–4 hours
- Adults/adolescents (≥30 kg): 2–4 L ORS
- Ondansetron if vomiting limits oral intake: reduces IV fluid need by ~50% in children; multidose post-discharge ondansetron reduces moderate-severe gastroenteritis (aOR 0.50) [9-10]
- Nasogastric ORS if unable to tolerate oral intake but mental status is normal [12]
- Replace ongoing losses: 60–120 mL ORS per diarrheal stool (<10 kg); 120–240 mL (>10 kg) [12]
Severe dehydration
- IV isotonic crystalloid (NS or LR): 20 mL/kg boluses until pulse, perfusion, and mental status normalize [12]
- Continue IV rehydration until patient can tolerate oral fluids, then transition to ORS [12]
- Monitor and correct electrolytes; administer dextrose as needed
- For hypernatremia: correct slowly (≤10–12 mEq/L per 24 hours) to avoid cerebral edema
Adjunctive
- Antipyretics for fever (reduces insensible losses)
- Loperamide for adults with watery, non-bloody diarrhea [11]
- Zinc supplementation in children in resource-limited settings
17. Disposition
Admission criteria
- Severe dehydration or hypovolemic shock
- Failure of oral/NG rehydration (persistent vomiting despite ondansetron)
- Significant electrolyte abnormalities (severe hypo/hypernatremia, hypokalemia)
- Altered mental status
- Bicarbonate ≤16 mmol/L, physician-estimated dehydration >5%, or need for ≥1 IV bolus (all independently predict admission) [15]
- Inability to maintain adequate oral intake (infants, elderly, comorbid patients)
- Concern for surgical pathology
Discharge criteria
- Tolerating oral fluids without vomiting
- Adequate urine output
- Stable vital signs, normal mental status
- Reliable caregiver and follow-up plan
Observation indications
- Moderate dehydration responding to ED rehydration but requiring extended monitoring
- Borderline oral tolerance
Specialist consultation triggers
- Surgical abdomen, intussusception
- Endocrine emergency (DKA, adrenal crisis, diabetes insipidus)
- Refractory electrolyte abnormalities (nephrology)
A secondary analysis of two RCTs demonstrated that clinical dehydration severity is the strongest predictor of hospitalization, and ED ondansetron administration was associated with approximately half the odds of hospitalization (aOR ~0.50): [24]
18. Follow Up / Return Precautions
Follow-up timing
- Mild: PCP follow-up within 2–3 days if symptoms persist
- Moderate (discharged after ED rehydration): 24–48 hour recheck, especially in infants and elderly
- Severe (post-hospitalization): within 1 week with labs
Return precautions — instruct patients/caregivers to return immediately for:
- Inability to keep down any fluids for >8 hours (adults) or >4–6 hours (children)
- No urine output for >8–12 hours
- Bloody stools or bilious vomiting
- Lethargy, confusion, or unresponsiveness
- High fever unresponsive to antipyretics
- Sunken eyes, no tears, or very dry mouth in children
Patient counseling
- Frequent small sips of ORS are better tolerated than large volumes
- Avoid sugary drinks, juices, and sodas for rehydration [12]
- Expected recovery: most viral gastroenteritis resolves in 1–3 days; diarrhea may persist up to 7 days
- Hand hygiene to prevent household transmission
References
1. Balanced Crystalloid Solutions Versus 0.9% Saline for Treating Acute Diarrhoea and Severe Dehydration in Children. — Florez ID, Sierra J, Pérez-Gaxiola G. The Cochrane Database of Systematic Reviews. 2023.
2. Clinical Symptoms, Signs and Tests for Identification of Impending and Current Water-Loss Dehydration in Older People. — Hooper L, Abdelhamid A, Attreed NJ, et al. The Cochrane Database of Systematic Reviews. 2015.
3. Validity and Reliability of Clinical Signs in the Diagnosis of Dehydration in Children. — Gorelick MH, Shaw KN, Murphy KO. Pediatrics. 1997.
4. Is This Child Dehydrated?. — Steiner MJ, DeWalt DA, Byerley JS. The Journal of the American Medical Association. 2004.
5. Is This Patient Hypovolemic?. — McGee S, Abernethy WB, Simel DL. The Journal of the American Medical Association. 1999.
6. Clinical Adverse Events Associated With Sodium-Glucose Cotransporter 2 Inhibitors: A Meta-Analysis Involving 10 Randomized Clinical Trials and 71 553 Individuals. — Lin DS, Lee JK, Chen WJ. The Journal of Clinical Endocrinology and Metabolism. 2021.
7. 13. Older Adults: Standards of Care in Diabetes-2026. — American Diabetes Association Professional Practice Committee for Diabetes*. Diabetes Care. 2026.
8. Management of Hyperglycemia in Type 2 Diabetes, 2018. A Consensus Report by the American Diabetes Association (ADA) and the European Association for the Study of Diabetes (EASD). — Davies MJ, D'Alessio DA, Fradkin J, et al. Diabetes Care. 2018.
9. Oral Ondansetron for Gastroenteritis in a Pediatric Emergency Department. — Freedman SB, Adler M, Seshadri R, Powell EC. The New England Journal of Medicine. 2006.
10. Multidose Ondansetron after Emergency Visits in Children with Gastroenteritis. — Freedman SB, Williamson-Urquhart S, Plint AC, et al. The New England Journal of Medicine. 2025.
11. Acute Diarrhea in Adults. — Meisenheimer ES, Epstein C, Thiel D. American Family Physician. 2022.
12. 2017 Infectious Diseases Society of America Clinical Practice Guidelines for the Diagnosis and Management of Infectious Diarrhea. — Shane AL, Mody RK, Crump JA, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2017.
13. Viral Gastroenteritis. — Flynn TG, Olortegui MP, Kosek MN. Lancet. 2024.
14. Acute Infectious Diarrhea. — Thielman NM, Guerrant RL. The New England Journal of Medicine. 2004.
15. Predictors of Hospital Admissions and Return Visits in Children With Suspected Dehydration Presenting to the Emergency Department. — Sawaya RD, Abdul-Nabi SS, Kebbi OE, et al. The Journal of Emergency Medicine. 2025.
16. A Multidisciplinary Consensus on Dehydration: Definitions, Diagnostic Methods and Clinical Implications. — Lacey J, Corbett J, Forni L, et al. Annals of Medicine. 2019.
17. Biological Variation and Diagnostic Accuracy of Dehydration Assessment Markers. — Cheuvront SN, Ely BR, Kenefick RW, Sawka MN. The American Journal of Clinical Nutrition. 2010.
18. The Management of Children With Gastroenteritis and Dehydration in the Emergency Department. — Colletti JE, Brown KM, Sharieff GQ, Barata IA, Ishimine P. The Journal of Emergency Medicine. 2010.
19. Update to Practice Standards for Electrocardiographic Monitoring in Hospital Settings: A Scientific Statement From the American Heart Association. — Sandau KE, Funk M, Auerbach A, et al. Circulation. 2017.
20. Potassium Disorders: Hypokalemia and Hyperkalemia. — Kim MJ, Valerio C, Knobloch GK. American Family Physician. 2023.
21. Brugada-Like Electrocardiography Pattern Induced by Severe Hyponatraemia. — Tamene A, Sattiraju S, Wang K, Benditt DG. Europace : European Pacing, Arrhythmias, and Cardiac Electrophysiology : Journal of the Working Groups on Cardiac Pacing, Arrhythmias, and Cardiac Cellular Electrophysiology of the European Society of Cardiology. 2010.
22. Electrocardiographic Manifestations: Electrolyte Abnormalities. — Diercks DB, Shumaik GM, Harrigan RA, Brady WJ, Chan TC. The Journal of Emergency Medicine. 2004.
23. Electrocardiography. — Elias Hanna Practical Cardiovascular Medicine 2e. 2022.
24. Variables Associated With Intravenous Rehydration and Hospitalization in Children With Acute Gastroenteritis: A Secondary Analysis of 2 Randomized Clinical Trials. — Poonai N, Powell EC, Schnadower D, et al. JAMA Network Open. 2021.