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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 (eg ascites, effusions), or capillary leak of fluid (eg burns and sepsis).
Children are particularly susceptible to dehydration with acute gastroenteritis or other illnesses that cause vomiting, diarrhoea and fever. Considerable care is required in the assessment and management of dehydration in children, because underestimation of dehydration may lead to inadequate management and therefore complications, while overestimation 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.
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:
- 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.
Causes of dehydration
- Mouth ulcers, stomatitis, pharyngitis, tonsillitis: pain may severely limit oral intake.
- Diabetic ketoacidosis (DKA).
- 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, eg 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.
- Combinations of examination signs provide a much better method than any individual signs in assessing the degree of dehydration.
- 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.
- One proposed assessment scale using general appearance, eyes, mucous membranes, and tears, has been shown to be effective in assessing dehydration in children.
- The assessment of dehydration in diabetic ketoacidosis (DKA) is particularly difficult in view of extravascular and intravascular dehydration, metabolic acidosis affecting the clinical signs of dehydration, and the overall catabolic state of the patient. The majority of patients with DKA have moderate (4% to 8%) dehydration, but clinical assessment overestimates the percent dehydration in two thirds of patients.
- The history and laboratory tests provide only modest benefit in assessing dehydration.
- Clinical assessment therefore comprises some of the following indicators of dehydration:
- Loss of body weight:
- Normal: no loss of body weight.
- Mild dehydration: 5-6% loss of body weight.
- Moderate: 7-10% loss of body weight.
- Severe: over 10% loss of body weight.
- Clinical features of mild-to-moderate dehydration; 2 or more of:
- Restlessness or irritability.
- Sunken eyes (also ask the 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 (eg weak rapid pulse, cool or blue extremities, hypotension), rapid breathing, sunken anterior fontanelle.
- Loss of body weight:
- Urinalysis: ketones and glucose in diabetic ketoacidosis (DKA).
- 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 (eg congenital adrenal hyperplasia, renal failure) or low (eg pyloric stenosis, alkalosis).
- Bicarbonate: causes of reduced bicarbonate include DKA 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, eg urine, stool, gastric fluid.
See separate article Dehydration in Children.
Further reading & references
- Huang LH; Dehydration, eMedicine, Nov 2009
- Steiner MJ, DeWalt DA, Byerley JS; Is this child dehydrated? JAMA. 2004 Jun 9;291(22):2746-54.
- Gorelick MH, Shaw KN, Murphy KO; Validity and reliability of clinical signs in the diagnosis of dehydration in children. Pediatrics. 1997 May;99(5):E6.
- Otieno H, Were E, Ahmed I, et al; Are bedside features of shock reproducible between different observers? Arch Dis Child. 2004 Oct;89(10):977-9.
- Friedman JN, Goldman RD, Srivastava R, et al; Development of a clinical dehydration scale for use in children between 1 and 36 months of age. J Pediatr. 2004 Aug;145(2):201-7.
- Goldman RD, Friedman JN, Parkin PC; Validation of the clinical dehydration scale for children with acute Pediatrics. 2008 Sep;122(3):545-9.
- Koves IH, Neutze J, Donath S, et al; The accuracy of clinical assessment of dehydration during diabetic ketoacidosis in childhood. Diabetes Care. 2004 Oct;27(10):2485-7.
- Fagan MJ, Avner J, Khine H; Initial fluid resuscitation for patients with diabetic ketoacidosis: how dry are Clin Pediatr (Phila). 2008 Nov;47(9):851-5. Epub 2008 Jul 14.
- Elliott EJ, Dalby-Payne JR; 2. Acute infectious diarrhoea and dehydration in children. Med J Aust. 2004 Nov 15;181(10):565-70.
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Dr Colin Tidy
Dr Hayley Willacy