Assessing Dehydration in Children

Dehydration is a condition that can occur with excess loss of water and other body fluids. Dehydration results from decreased intake, increased output (renal, gastrointestinal or insensible losses), a shift of fluid (e.g. ascites, effusions), or capillary leak of fluid (e.g. burns and sepsis). Children are particularly susceptible to dehydration with acute gastroenteritis or other illnesses that cause vomiting, diarrhoea and fever.

The decrease in total body water causes a reduction in intracellular and extracellular fluid but the clinical manifestations of dehydration are most closely related to intravascular volume depletion. Dehydration is most often isonatraemic (with a normal serum sodium concentration) but in up to 20% of cases there is either hyponatraemic or hypernatraemic dehydration:¹

• Hyponatraemic (hypotonic) dehydration: intravascular water shifts to the extravascular space, exaggerating intravascular volume depletion for a given amount of total body water loss.
• Hypernatraemic (hypertonic) dehydration: extravascular water shifts to the intravascular space, reducing intravascular volume depletion for a given amount of total body water loss.

If dehydration and the cause of dehydration are not adequately corrected, complications such as lethargy, weakness, electrolyte and acid-base disturbances, and ultimately hypovolaemic shock resulting in end organ failure and death may occur.

Considerable care is required in the assessment and management of dehydration in children because under estimation of dehydration may lead to inadequate management and therefore complications, while over estimation of fluid deficit can result in inappropriate rehydration therapy. It is therefore essential to make an accurate assessment of the degree of dehydration in children in order to make appropriate treatment decisions.

• Gastroenteritis
• Mouth ulcers, stomatitis, pharyngitis, tonsillitis: pain may severely limit oral intake
• Diabetic ketoacidosis
• Febrile illness: fever causes increased insensible fluid losses
• Burns: fluid losses may be extreme and require aggressive fluid management
• Congenital adrenal hyperplasia: may have associated hypoglycaemia, hypotension, hyperkalaemia, and hyponatraemia
• Gastrointestinal obstruction, e.g. pyloric stenosis: often associated with poor intake, vomiting
• Bowel ischaemia may cause extensive capillary leak and shock
• Heat stroke
• Cystic fibrosis: excessive sodium and chloride losses in sweat
• Diabetes insipidus: excessive output of very dilute urine
• Thyrotoxicosis: increased insensible losses and diarrhoea

• Clinical assessment of dehydration can be difficult, especially in young infants, and rarely predicts the exact degree of dehydration accurately.
• The most useful individual signs for predicting 5% dehydration in children are an abnormal capillary refill time, abnormal skin turgor and abnormal respiratory pattern.²
• Combinations of examination signs provide a much better method than any individual signs in assessing the degree of dehydration.³
• Of the clinical indicators used, the pinch test (skin turgor) has been shown to be the most reliable in several studies but is still not a reliable test when used without other clinical indicators.⁴
• One proposed assessment scale using general appearance, eyes, mucous membranes, and tears, has been shown to be effective in assessing dehydration in children.⁵
• The assessment of dehydration in diabetic ketoacidosis is particularly difficult in view of extra- and intravascular dehydration, metabolic acidosis affecting the clinical signs of dehydration, and the overall catabolic state of the patient.⁶
• The history and laboratory tests provide only modest benefit in assessing dehydration.
• Clinical assessment therefore comprises of some of the following indicators of dehydration:⁷
  • Loss of body weight:
    • Normal: no loss of body weight
    • Mild dehydration: 5-6% loss of body weight
    • Moderate: 7-10%
    • Severe: over 10%
  • Clinical features of mild to moderate dehydration; 2 or more of:
    • Restlessness or irritability
    • Sunken eyes (also ask parent)
    • Thirsty and drinks eagerly
  • Clinical features of severe dehydration; 2 or more of:
    • Abnormally sleepy or lethargic
    • Sunken eyes
    • Drinking poorly or not at all
  • Pinch test (skin turgor):
    • Skin turgor is assessed by pinching the skin of the abdomen or thigh longitudinally between the thumb and the bent forefinger.
    • The sign is unreliable in obese or severely malnourished children.
      • Normal: skin fold retracts immediately
      • Mild or moderate dehydration: slow; skin fold visible for less than 2 seconds
      • Severe dehydration: very slow; skin fold visible for longer than 2 seconds
  • Other features of dehydration include dry mucous membranes, reduced tears and decreased urine output
  • Additional signs of severe dehydration include circulatory collapse (e.g. weak rapid pulse, cool or blue extremities, hypotension), rapid breathing, sunken anterior fontanelle

• Urinalysis: ketones and glucose in diabetic ketoacidosis
• Urine specific gravity: may be elevated (but diabetes insipidus causes the urine to be dilute)
• Serum sodium: hyponatraemia and hypernatraemia require specific management
• Potassium may be raised (e.g. congenital adrenal hyperplasia, renal failure) or low (e.g. pyloric stenosis, alkalosis)
• Bicarbonate: causes of reduced bicarbonate include diabetic ketoacidosis and diarrhoea.
• Chloride: may be low in pyloric stenosis
• Blood glucose: may be low as a result of poor intake or grossly elevated in diabetic ketoacidosis
• Blood urea and creatinine: raised in renal impairment
• ECG: monitor for cardiac arrhythmias caused by electrolyte disturbance
• Electrolyte analysis of any fluid that is lost, e.g. urine, stool, gastric fluid

See Managing Dehydration in Children - Paediatric Fluid Regimes.