Dehydration in children

What is dehydration?

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.

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 may also be either hyponatraemic or hypernatraemic:

• Hyponatraemic (hypotonic) dehydration: sodium (or solute) is lost from the intravascular space proportionally more than water. Subsequent water shifts exaggerate intravascular volume depletion for a given amount of total body water loss.

• Hypernatraemic (hypertonic) dehydration (see also the separate Hypernatraemia article):
  

  • Sodium (or solute) is lost from the intravascular space proportionally less than water.

  • Extravascular water subsequently shifts to the intravascular space, reducing intravascular volume depletion for a given amount of total body water loss.

  • Hypertonicity also occurs in diabetic ketoacidosis. A falsely low sodium concentration may occur due to the high glucose concentration.

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 in children

Gastrointestinal

• Gastroenteritis.

• Gastrointestinal obstruction - eg, pyloric stenosis: often associated with poor intake, vomiting.

• Bowel ischaemia may cause extensive capillary leak and shock.

Oropharyngeal

• Mouth ulcers, stomatitis, pharyngitis, tonsillitis: pain may severely limit oral intake.

Endocrine

• Diabetic ketoacidosis (DKA).

• Diabetes insipidus: excessive output of very dilute urine.

• Thyrotoxicosis: increased insensible losses and diarrhoea.

• Congenital adrenal hyperplasia (CAH): may have associated hypoglycaemia, hypotension, hyperkalaemia, and hyponatraemia.

Others

• Febrile illness: fever causes increased insensible fluid losses.

• Burns: fluid losses may be extreme and require aggressive fluid management.

• Heat stroke.

• Cystic fibrosis: excessive sodium and chloride losses in sweat.

Assessment

Clinical assessment of dehydration can be difficult, especially in young infants, and rarely predicts the exact degree of dehydration. Clinical assessment may be particularly inaccurate when assessing children with moderate dehydration. The history and laboratory tests provide only modest benefit in assessing dehydration.

The most useful individual signs for predicting 5% dehydration in children are an abnormal capillary refill time, abnormal skin turgor and abnormal respiratory pattern.¹

Combining examination signs (eg, using general appearance, eyes, mucous membranes, and tears) provides 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.

Clinical assessment therefore comprises some of the following indicators of dehydration:

• Loss of body weight:
  

  • Mild dehydration: 1-5% weight loss.

  • Mild-to-moderate dehydration: 6-10% loss of body weight.

  • Severe: over 10% loss of body weight.

• Clinical features of mild-to-moderate dehydration; two or more of:
  

  • Restlessness or irritability.

  • Sunken eyes (also ask the parent).

  • Thirsty and drinks eagerly.

• Clinical features of severe dehydration; two 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 two seconds.

    • Severe dehydration: very slow; skin fold visible for longer than two 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.

Red flags²

• Appears to be unwell or deteriorating.

• Altered responsiveness (eg, irritable, lethargic).

• Sunken eyes.

• Tachycardia.

• Tachypnoea.

• Reduced skin turgor.

Shock

The clinical definition of shock used by the World Health Organization (WHO) is the presence of three clinical signs at one time, ie cold extremities with capillary refill time >3 and a weak and fast pulse.³

• Arrange emergency transfer to secondary care:⁴
  

  • Pale or mottled skin.

  • Cold extremities.

  • Decreased level of consciousness.

  • Tachycardia.

  • Tachypnoea.

  • Weak peripheral pulses.

  • Prolonged capillary refill time.

  • Hypotension.

Diagnosing dehydration in children (investigations)

• Urine tests:
  

  • Urinalysis: ketones and glucose in DKA.

  • Urine specific gravity: may be elevated (but diabetes insipidus causes the urine to be dilute).

• Blood tests:
  

  • Serum sodium: hyponatraemia and hypernatraemia require specific management.

  • Potassium may be raised (eg, congenital adrenal hyperplasia, acute kidney injury) 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 DKA.

  • 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.

Management of dehydration in children

See also the separate Gastroenteritis in Children and Hypokalaemia articles.

The treatment of mild-to-moderate dehydration does not require intravenous therapy as long as oral fluids are tolerated. Oral rehydration solutions such as Dioralyte® may be used. Breast milk should be continued if possible.

Oral rehydration solutions with an osmolarity of ≤270 mOsm/L are safe and more effective than rehydration solutions with an osmolarity of ≥310 mOsm/L. Oral rehydration therapy may have a higher risk of paralytic ileus than intravenous fluid.

Intravenous fluid therapy should be used if:

• Shock is suspected or confirmed.

• Red flag symptoms or signs show clinical evidence of deterioration despite oral rehydration therapy.

• The child persistently vomits the oral rehydration solution, given orally or via a nasogastric tube.

Venous access

The preferred sites for venous access in children are, in order of preference: peripheral vein, femoral vein, external jugular vein (do not use if there is airway compromise or a cervical collar applied), venous cut-down (saphenous vein at the ankle).

Intraosseous infusion

• Cannulating the marrow cavity of a long bone in an uninjured extremity is safe, effective, and requires less time than venous cut-down. Intraosseous infusion should be discontinued when suitable peripheral venous access has been established.

• Indications for intraosseous infusion are limited to when venous access is impossible due to circulatory collapse in resuscitation situations or when attempts at the percutaneous peripheral venous route have failed.⁵

• However, further attempts at intravenous access by senior staff or anaesthetists, using a nasogastric tube or persevering with oral rehydration, tend to be normal practice in non-resuscitation situations.

• The preferred site for intraosseous cannulation is the proximal tibia, below the level of the tibial tuberosity. If the tibia is fractured, the needle may be inserted into the distal femur. Intraosseous cannulation should not be performed distal to a fracture site.

• Possible complications include cellulitis, osteomyelitis, compartment syndrome and iatrogenic fracture.

Fluid replacement⁶

• Treat suspected or confirmed shock with a rapid intravenous infusion of 20 ml/kg of 0.9% sodium chloride solution as a bolus given over 15-30 minutes to bring the patient out of shock as quickly as possible.³ Colloids may be preferred if the blood pressure has to be restored urgently, ie in patients with a pulse pressure <10 mm Hg.

• If a child remains shocked after the first rapid intravenous infusion:
  

  • Immediately give another rapid intravenous infusion of 20 ml/kg of 0.9% sodium chloride solution and consider possible causes of shock other than dehydration.

• Consider consulting a paediatric intensive care specialist if a child remains shocked after the second rapid intravenous infusion.

• When symptoms and/or signs of shock resolve after rapid intravenous infusions, start rehydration with intravenous fluid therapy.

• Consider reducing IV fluid earlier if oral fluid intake and urine output improve. The total duration of IV fluid therapy should not exceed 48 hours.³

Calculating replacement

Children with only one or two signs of impaired circulation - either cold extremities or capillary refill time >3 seconds or a weak and fast pulse - but who do not have the full clinical features of shock, ie all three signs present together, should not receive rapid infusions of fluids but should still receive maintenance fluids appropriate for their age and weight.

• The required fluid replacement is the sum total of deficit, ongoing losses and maintenance requirement:
  

  • Correction of deficit: deficit in ml = wt (kg) x % dehydrated x 10 (ideally the pre-dehydration weight should be used). Therefore, a 14 kg child who is 5% dehydrated has a deficit of 14 x 5 x 10 = 700 ml.

  • Ongoing losses: calculated from fluid from nasogastric tubes, drains, urine; also need to consider additional fluid loss in certain situations - eg, pyrexia, tachypnoea.

  • Maintenance requirements:
    

    • 100 ml/kg for the first 10 kg.

    • 50 ml/kg for the next 10 kg.

    • 20 ml/kg for any weight after 20 kg.

Monitoring

• The frequency of monitoring will depend on the degree of dehydration and well-being of the child.

• Monitoring includes general well-being, fontanelle tension, pulse rate and volume, capillary refill, blood pressure, urine output, ECG monitoring, and blood renal function, electrolytes and packed cell volume.

• A return towards haemodynamic normality is indicated by:
  

  • Slowing of the heart rate (to the normal range for the child's age).

  • Improved conscious state and awareness.

  • Return of peripheral pulses, return of normal skin colour and increased warmth of extremities.

  • Increased systolic blood pressure (approximately 90 mm Hg plus twice the age in years), increased pulse pressure (above 20 mm Hg).

  • Urinary output: a urinary catheter should be inserted to measure urinary output accurately. Normal urine output is age-dependent:
    

    • Newborn and infant up to 1 year: normal is 2 ml/kg/hour.

    • Toddler: 1.5 ml/kg/hour.

    • Older child: 1 ml/kg/hour during adolescence.

    • Adult: 0.5 ml/kg/hour.

Isotonic and hypotonic dehydration

• If intravenous fluid therapy is required for rehydration (and the child is not hypernatraemic at presentation):
  

  • Use an isotonic solution such as 0.9% sodium chloride, or 0.9% sodium chloride with 5% glucose, for fluid deficit replacement and maintenance.

  • For those who required initial rapid intravenous fluid boluses for suspected or confirmed shock, add 100 ml/kg for fluid deficit replacement to maintenance fluid requirements, and monitor the clinical response.

  • For those who were not shocked at presentation, add 50 ml/kg for fluid deficit replacement to maintenance fluid requirements, and monitor the clinical response.

  • Measure plasma sodium, potassium, urea, creatinine and glucose at the outset, monitor regularly, and alter the fluid composition or rate of administration if necessary.

  • Consider providing intravenous potassium supplementation once the plasma potassium level is known.

Hypertonic dehydration (hypernatraemia)

• If intravenous fluid therapy is required in a child presenting with hypernatraemic dehydration:
  

  • Obtain urgent expert advice on fluid management.

  • Use an isotonic solution such as 0.9% sodium chloride, or 0.9% sodium chloride with 5% glucose, for fluid deficit replacement and maintenance.

  • Replace the fluid deficit slowly - typically over 48 hours.

  • Monitor the plasma sodium frequently, aiming to reduce it at a rate of less than 0.5 mmol/L per hour.

  • Attempt early and gradual introduction of oral rehydration therapy during intravenous fluid therapy.

  • If tolerated, stop intravenous fluids and complete rehydration with oral rehydration therapy.

Fluid management following dehydration

• Encourage breastfeeding and other milk feeds.

• Encourage fluid intake.

• In children at increased risk of dehydration recurring, consider giving 5 ml/kg of oral rehydration solution after each large watery stool. These include:
  

  • Children younger than 1 year, particularly those younger than 6 months.

  • Infants who were of low birth weight.

  • Children who have passed more than five diarrhoeal stools in the previous 24 hours.

  • Children who have vomited more than twice in the previous 24 hours.

• Restart oral rehydration therapy if dehydration recurs after rehydration.