Saidala 24: Dehydration

Introduction

Dehydration is a condition resulting from a deficit of body water relative to physiological needs. It may be due to reduced intake, increased losses, or abnormal fluid distribution.

It is a global health issue, especially in low-resource settings, where diarrhoeal diseases remain a leading cause of childhood mortality. In hospitals, dehydration is a frequent complication of acute illness, surgery, and medication.

Physiology of Body Water Balance

Total body water: ~60% of adult body weight (higher in infants, lower in elderly/obese).
Daily intake: ~2–2.5 L (fluids, food, metabolic water).
Daily losses: ~2–2.5 L (urine, sweat, feces, respiration).
Regulation: Kidneys (ADH, aldosterone), thirst mechanism, GI tract.

Types of Dehydration

Isotonic (most common): Equal loss of water and sodium → normal serum sodium.
- Seen in diarrhoea, vomiting, bleeding.
Hypertonic (water loss > sodium loss): Increased serum sodium (>145 mmol/L).
- Seen in fever, heat stroke, inadequate water intake, diabetes insipidus.
Hypotonic (sodium loss > water loss): Reduced serum sodium (<135 mmol/L).
- Seen in diuretic use, adrenal insufficiency.

Causes of Dehydration

1. Increased Fluid Loss

Gastrointestinal: Diarrhoea, vomiting, NG suction, fistula.
Renal: Diuretics (furosemide, hydrochlorothiazide), diabetes mellitus (osmotic diuresis), diabetes insipidus.
Skin: Excess sweating (fever, heat stroke), burns.
Hemorrhage: Acute blood loss.

2. Inadequate Intake

Poor oral intake (elderly, infants, disabled).
Neurological disorders (stroke, dementia).
Anorexia, nausea.
Restricted access (neglect, wilderness).

3. Redistribution/Third Spacing

Sepsis, pancreatitis, peritonitis.
Major trauma, burns, postoperative states.

Risk Groups

Infants and young children.
Elderly (impaired thirst, renal function, polypharmacy).
Patients with chronic illness (renal failure, diabetes).
Athletes in hot climates.

Clinical Features

Mild Dehydration (~3–5% body weight loss)

Thirst, dry mouth.
Decreased urine output.
Fatigue, headache.

Moderate Dehydration (~6–10%)

Sunken eyes, poor skin turgor.
Tachycardia, postural hypotension.
Dry mucous membranes.
Oliguria (urine output <0.5 mL/kg/h).

Severe Dehydration (>10–15%)

Hypotension, weak/absent pulse.
Altered mental status, confusion, coma.
Cold extremities, capillary refill >3 sec.
Shock, organ failure.

Diagnostic Approach

1. Clinical Assessment

History of fluid loss, intake, comorbidities.
Signs: vitals, skin turgor, mucous membranes, urine output, mental status.

2. Laboratory Tests

Serum electrolytes: Sodium, potassium, chloride.
Renal function: Urea, creatinine (prerenal azotemia).
Glucose: DKA, hyperglycemia.
Urine osmolality and specific gravity.
Blood gases: Metabolic acidosis in severe diarrhoea/shock.

3. Special Considerations

Infants: sunken fontanelle, irritability.
Elderly: may present with confusion, delirium rather than thirst.

Management and Treatment

Principle: Replace fluid and electrolytes + treat underlying cause.

A. Oral Rehydration (Mild to Moderate)

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 clean water.
Administration: 50–100 mL/kg over 4 hours, then maintenance.
Homemade ORS (if commercial unavailable): 6 teaspoons sugar + ½ teaspoon salt in 1 liter clean water.

B. Intravenous Rehydration (Moderate to Severe)

1. Crystalloids (preferred)

Normal saline (0.9% NaCl).
Ringer’s lactate.
Adults: Initial bolus 1–2 L IV rapidly (in shock).
Children: 20 mL/kg IV bolus over 20 min; repeat as needed.

2. Electrolyte Correction

Hypokalemia: Potassium chloride 20–40 mEq IV per liter, cautiously.
Hyponatremia: Correct slowly; avoid >8–10 mmol/L per 24 h.
Hypernatremia: Correct slowly with hypotonic fluids (5% dextrose).

3. Colloids

Rarely indicated, crystalloids preferred.

C. Pharmacological Adjuncts

Antiemetics (for vomiting):
- Ondansetron: 4–8 mg orally/IV every 8 h.
- Metoclopramide: 10 mg orally/IV every 6–8 h.
Antidiarrhoeals:
- Loperamide: 2–4 mg orally after first loose stool, then 2 mg after each episode (max 16 mg/day).
- Avoid in children <12 years or bloody diarrhoea.
Antibiotics (if infective diarrhoea with systemic features):
- Ciprofloxacin 500 mg orally twice daily for 3 days.
- Azithromycin 500 mg orally once daily for 3 days (traveler’s diarrhoea, resistant regions).
- Metronidazole 500 mg orally three times daily for 7–10 days (Giardia, Entamoeba).
Antipyretics:
- Paracetamol 500–1000 mg orally every 6–8 h for fever.

D. Underlying Cause Management

Stop offending medications (diuretics, laxatives).
Control diabetes (DKA → insulin + fluids).
Treat infections (antibiotics as above).
Manage heat stroke (cooling + IV fluids).

Complications

Hypovolemic shock.
Acute kidney injury.
Electrolyte imbalances (hypo/hypernatremia, hypokalemia).
Seizures (from electrolyte disturbances).
Death (especially in children/elderly if untreated).

Prognosis

Mild dehydration: Excellent, resolves with oral rehydration.
Moderate to severe: Good prognosis if treated early.
Delayed recognition: High risk of complications, mortality in frail populations.

Prevention

Adequate daily fluid intake (~2 L adults, adjusted for activity/climate).
Early ORS use in diarrhoeal illness.
Hygiene and sanitation to prevent infectious diarrhoea.
Monitoring hydration in elderly, infants, postoperative patients.
Educate athletes/workers in hot climates about hydration strategies.

Patient and Family Education

Recognize early signs: thirst, dry mouth, reduced urine.
Encourage small frequent sips of ORS during diarrhoea.
Avoid self-medicating with strong antidiarrhoeals without medical advice.
When to seek urgent care: persistent vomiting, blood in stool, inability to drink, confusion, reduced urine, lethargy.

Saidala 24

الصفحات

Saturday, August 23, 2025

Dehydration