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Saturday, August 16, 2025

Dehydration


Introduction

Dehydration is a clinical condition resulting from an excessive loss of body water relative to intake, often accompanied by disturbances in electrolytes such as sodium and potassium. It occurs when fluid losses (from sweating, vomiting, diarrhea, fever, polyuria, or hemorrhage) exceed fluid intake.

Dehydration ranges from mild (minor thirst, slight fatigue) to severe (shock, organ failure, death). It is a frequent cause of hospital admissions, particularly in the elderly, children, and patients with chronic illnesses.

Epidemiology

  • Common in all age groups but particularly severe in children under 5 years (often due to diarrhea) and elderly adults (due to impaired thirst and comorbidities).

  • In low-resource countries, dehydration is a leading cause of mortality from diarrheal illnesses.

  • Hospital admissions for dehydration are common in patients with gastroenteritis, uncontrolled diabetes, sepsis, and heat-related illness.

Classification

Dehydration is classified based on serum sodium and volume status:

  1. Isotonic dehydration – Loss of water and sodium in equal proportions (most common, e.g., diarrhea, vomiting).

  2. Hypertonic dehydration – Greater water loss than sodium (e.g., fever, excessive sweating, diabetes insipidus, osmotic diuresis).

  3. Hypotonic dehydration – Greater sodium loss than water (e.g., diuretic overuse, adrenal insufficiency).

Causes

1. Gastrointestinal Losses

  • Acute diarrhea (infectious gastroenteritis, cholera).

  • Vomiting.

  • Excessive fistula or stoma output.

2. Renal Losses

  • Osmotic diuresis (uncontrolled diabetes mellitus).

  • Diuretic medications (e.g., furosemide, hydrochlorothiazide).

  • Diabetes insipidus.

  • Adrenal insufficiency.

3. Skin and Respiratory Losses

  • Sweating (fever, heat exposure, strenuous exercise).

  • Burns.

  • Tachypnea.

4. Inadequate Intake

  • Poor oral intake due to illness, disability, or neglect.

  • Elderly or infants unable to access fluids.

Pathophysiology

  • Water loss leads to reduced plasma volume, causing decreased venous return, stroke volume, and cardiac output.

  • Compensatory mechanisms: tachycardia, vasoconstriction, activation of renin–angiotensin–aldosterone system (RAAS), and antidiuretic hormone (ADH) release.

  • Severe dehydration results in hypovolemic shock, impaired tissue perfusion, and organ dysfunction.

  • Electrolyte imbalances (hyponatremia, hypernatremia, hypokalemia) contribute to neurological and cardiac complications.

Clinical Features

Mild Dehydration (fluid loss <5% body weight)

  • Thirst.

  • Dry mouth, lips.

  • Slight fatigue, headache.

  • Decreased urine output, darker urine.

Moderate Dehydration (5–10% body weight)

  • Dry mucous membranes.

  • Sunken eyes.

  • Tachycardia.

  • Orthostatic hypotension.

  • Poor skin turgor.

  • Reduced urine output.

Severe Dehydration (>10% body weight)

  • Hypotension, weak pulse.

  • Cold extremities, cyanosis.

  • Altered mental status (confusion, lethargy, coma).

  • Oliguria/anuria.

  • Shock (life-threatening).

Complications

  • Electrolyte disturbances (hyponatremia, hypernatremia, hypokalemia).

  • Acute kidney injury.

  • Hypovolemic shock.

  • Multi-organ failure.

  • Death if untreated.

Diagnosis

1. Clinical Assessment

  • History: fluid intake, recent illness (vomiting, diarrhea), diuretic use, environmental exposure.

  • Examination: vital signs (tachycardia, hypotension), dry mucous membranes, reduced skin turgor, altered consciousness.

2. Laboratory Investigations

  • Serum electrolytes: sodium, potassium, chloride.

  • Blood urea nitrogen (BUN) and creatinine: elevated in hypovolemia.

  • Urinalysis: concentrated urine, low urine sodium.

  • Arterial blood gases: metabolic acidosis in severe dehydration (e.g., diarrhea).

Management

The cornerstone of treatment is rehydration therapy, either oral or intravenous, depending on severity.

1. Mild to Moderate Dehydration

  • Oral Rehydration Therapy (ORT) is preferred.

  • WHO Oral Rehydration Solution (ORS):

    • Sodium chloride 2.6 g

    • Potassium chloride 1.5 g

    • Trisodium citrate 2.9 g (or sodium bicarbonate 2.5 g)

    • Glucose 13.5 g

    • Dissolved in 1 liter of clean water.

Administration:

  • Adults: 2–3 liters per day depending on losses.

  • Children: 75 mL/kg over 4 hours (WHO guidelines).

Commercial ORS sachets are widely available. Homemade ORS: 6 teaspoons sugar + ½ teaspoon salt in 1 liter clean water.

2. Severe Dehydration

Requires intravenous (IV) fluid therapy.

a) Isotonic dehydration (most common)

  • 0.9% Normal Saline or Ringer’s lactate.

  • Adults: 1–2 liters IV bolus over 30–60 minutes, then reassess.

  • Further fluids guided by blood pressure, urine output, and labs.

b) Hypernatremic dehydration

  • Correct slowly to avoid cerebral edema.

  • Use 0.45% sodium chloride (half-normal saline) or carefully titrated ORS.

c) Hyponatremic dehydration

  • Cautious sodium replacement.

  • Symptomatic severe hyponatremia: 3% hypertonic saline, 100 mL IV bolus over 10 minutes, repeat up to 3 times.

3. Adjunctive Measures

  • Treat underlying cause (e.g., antibiotics for infection, insulin for hyperglycemia, antidiarrheals when appropriate).

  • Antiemetics for persistent vomiting:

    • Ondansetron 4–8 mg orally/IV every 8 hours as needed.

  • Antibiotics (if dehydration due to bacterial gastroenteritis, e.g., cholera):

    • Doxycycline 300 mg single dose (adults).

    • Alternatives: azithromycin 1 g single dose, ciprofloxacin 500 mg twice daily for 3 days.

4. Pain and Fever Management (if associated)

  • Paracetamol (acetaminophen): 500–1000 mg orally every 6 hours (max 4 g/day).

  • Avoid NSAIDs if renal impairment is present.

Prevention

  • Adequate daily fluid intake (2–3 liters/day for adults, adjusted for activity and climate).

  • Oral rehydration during diarrheal illnesses.

  • Avoid excessive alcohol, caffeine, and diuretics without medical need.

  • Early treatment of diarrhea and vomiting.

  • Extra precautions during hot weather or exercise.

Prognosis

  • With prompt rehydration, prognosis is excellent.

  • Mortality is high in untreated severe dehydration, especially in children and elderly.

  • Long-term complications are rare if fluid and electrolyte balance is restored quickly.

Future Directions

  • Improved access to ready-to-use oral rehydration solutions in low-resource settings.

  • Development of point-of-care dehydration assessment tools (wearables, biomarkers).

  • Enhanced public health interventions for diarrheal disease prevention (vaccines, sanitation).

  • Personalized fluid therapy using bedside electrolyte monitoring and AI-driven IV fluid adjustment.




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