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Dehydration

Specialties > Child health

Background knowledge 🧠

Definition

  • Dehydration refers to a deficit of total body water with or without a sodium deficit.
  • It occurs when fluid loss exceeds fluid intake, leading to a negative fluid balance.
  • Classified based on severity: mild (3-5% body weight loss), moderate (6-9%), severe (10% or more).

Epidemiology

  • Common across all age groups but more severe in infants, elderly, and those with chronic illnesses.
  • Particularly prevalent in the hospital setting, especially in patients who are acutely unwell.
  • Higher incidence in warmer climates and during heatwaves.
  • Significant cause of morbidity and mortality in developing countries, especially in children.

Aetiology and Pathophysiology

  • Causes include inadequate fluid intake, excessive fluid loss (e.g., vomiting, diarrhoea, sweating), or a combination.
  • Pathophysiology involves loss of water from the extracellular space, leading to intracellular dehydration.
  • Compensatory mechanisms include thirst, release of antidiuretic hormone (ADH), and renal conservation of water.
  • Severe dehydration can result in hypovolaemic shock.

Types

  • Isotonic dehydration: equal loss of water and sodium; most common form.
  • Hypertonic dehydration: more water is lost than sodium, leading to hypernatraemia.
  • Hypotonic dehydration: more sodium is lost than water, leading to hyponatraemia.
  • Severity can be gauged by clinical assessment and laboratory tests.

Clinical Features 🌡️

Symptoms

  • Thirst and dry mouth.
  • Fatigue and weakness.
  • Dizziness or light-headedness, particularly on standing (orthostatic hypotension).
  • Reduced urine output (oliguria) and concentrated urine.
  • In severe cases, confusion or loss of consciousness.

Signs

  • Tachycardia and hypotension.
  • Sunken eyes and dry mucous membranes.
  • Reduced skin turgor.
  • Capillary refill time prolonged (more than 2 seconds).
  • In infants: sunken fontanelle, absence of tears when crying.
  • Severe dehydration: altered mental state, cool extremities, cyanosis.

Investigations 🧪

Tests

  • Urea and electrolytes (U&Es): elevated urea, creatinine, and sodium levels may indicate dehydration.
  • Serum osmolality: increased in hypertonic dehydration.
  • Full blood count (FBC): haemoconcentration may be present.
  • Urine specific gravity: elevated in dehydration.
  • ABG/VBG: may show metabolic acidosis.

Management 🥼

Management

  • Initial focus on fluid resuscitation: oral rehydration salts (ORS) for mild-moderate cases, IV fluids for severe cases.
  • Choice of fluid: isotonic solutions (e.g., 0.9% sodium chloride or Hartmann’s) are preferred.
  • Monitor vital signs, urine output, and electrolytes closely during rehydration.
  • Address underlying cause (e.g., treat diarrhoea, vomiting, or fever).
  • Consider antiemetics if vomiting is a prominent feature.
  • Avoid rapid overcorrection of sodium levels, particularly in chronic cases.

Complications

  • Hypovolaemic shock: life-threatening complication of severe dehydration.
  • Acute kidney injury (AKI) due to reduced renal perfusion.
  • Electrolyte imbalances: hypernatraemia, hyperkalaemia or hypokalaemia.
  • Seizures: especially in hypernatraemia or in children.
  • Long-term cognitive impairment in severe cases.
  • Potentially fatal in extremes of age without timely treatment.

Prognosis

  • Good with prompt recognition and treatment.
  • Delayed treatment may lead to complications and increased mortality, especially in vulnerable populations.
  • Prognosis depends on underlying cause and speed of intervention.
  • Chronic or recurrent dehydration may have longer-term health impacts.

Key Points

  • Early recognition and management are crucial to prevent complications.
  • Consider dehydration in any patient with reduced intake or excessive loss of fluids.
  • Close monitoring of fluid balance, electrolytes, and renal function is essential during treatment.
  • Tailor rehydration strategy to the severity and type of dehydration.

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Child health