Managing Dehydration in Children - Paediatric Fluid Regimes

The treatment of mild dehydration does not usually require intravenous therapy as long as oral fluids are tolerated. Oral rehydration solutions such as Dioralyte® or Rehydrat® may then be used. Breast milk should be continued if possible. The signs of 5% and 10% dehydration are listed in the separate article on Childhood Diarrhoea. Isotonic and hypotonic dehydration are by far the commonest patterns of dehydration.

The preferred sites for venous access in children are in order of preference:

• Percutaneous into peripheral vein
• Percutaneous into femoral vein
• Percutaneous into external jugular vein (do not use if airway compromise or cervical collar applied).
• Venous cut-down: saphenous vein at the ankle.
• Intraosseous

Intraosseous infusion

• Cannulating the marrow cavity of a long bone in an uninjured extremity is safe,¹ 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 has failed. However further attempts at intravenous access attempts 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.

• When shock is suspected, a fluid bolus of 20 ml/kg of crystalloid solution is required. A child's blood volume is approximately 80 ml/kg.
• Failure to improve haemodynamic abnormalities following the first bolus of fluid requires a second, and perhaps a third 20 ml/kg bolus of crystalloid fluid.
• When starting the third bolus of crystalloid fluid or if the child's condition deteriorates, 10 ml/kg of type-specific or O-negative warmed packed red blood cells may be required. Most children will not require blood.

• 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 14kg child who is 5% dehydrated has a deficit of 14 x 5 x 10 = 700ml.
  • Ongoing losses: calculated from fluid from nasogastric tubes, drains, urine; also need to consider additional fluid loss in certain situations, e.g. 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.

• The frequency of monitoring will depend on the degree of dehydration and wellbeing of the child.
• Monitoring includes general wellbeing, 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
  • Increased warmth of extremities
  • Increased systolic blood pressure (approximately 90 mmHg plus twice the age in years)
  • Increased pulse pressure (above 20 mmHg)
  • Urinary output: a urinary catheter should be inserted to accurately measure urinary output. 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: 1ml/kg/hour during adolescence.
    • Adult: 0.5 ml/kg/hour.

• Fluids lower in sodium content (half-strength physiological saline) are usually used for infants and isotonic saline for older children. Very young infants may need the lower sodium fluids with higher glucose content. Energy is provided as 5% dextrose, e.g. as half-strength physiological saline in 5% dextrose solution.
• Isotonic dehydration can be corrected quite rapidly with a glucose/NSaline fluid using 4hrs of rapid rehydration at 10ml/kg/hr.
• Severe dehydration may require urgent partial correction and the infusion should be started at a relatively fast rate for several hours and progress reviewed on the clinical and biochemical findings.
• Very young infants may initially require a slower infusion rate and more concentrated solutions (e.g. isotonic saline) in order to correct sodium depletion.
• Potassium:
  • Replacement should be based on regular serum potassium levels and ECG monitoring.
  • Potassium chloride is usually added to provide in the region of 3.0 mmol of potassium/kg/day.
  • Emergency management is indicated when hypokalaemia is associated with cardiac arrhythmias, but this is rare.
  • Rate of intravenous correction should not exceed 0.2 to 0.5 meq/kg/hour.
  • Deficits can be calculated from the formula: Potassium deficit (meq/L) = Body weight x (Expected serum K - observed serum K) x 0.32.
  • Intravenous potassium in concentrations of 40mmol per litre or greater should be administered through a central line. Lower concentrations may be given peripherally.
• Continued small amounts of oral fluids to moisten the buccal mucosa should be continued and gradually increased to replace the intravenous fluids.
• Management must also address the cause of the dehydration.

• Hypertonic dehydration is much less clinically obvious than hypotonic or isotonic dehydration and is now uncommon.
• The condition usually affects infants aged less than 1 year and the serum sodium is often greater than 150 mmol/l.
• Infantile gastroenteritis may predispose to the development of hypertonic dehydration, but the risk is increased by the use of over-concentrated artificial feeds.²
• Hypertonicity also occurs in diabetic ketoacidosis³ and a falsely low sodium concentration may occur due to the high glucose concentration.
• Approximately one-third of cases develop convulsions, often in response to sudden alterations of sodium concentration caused by treatment.
• Hypertonic dehydration also predisposes to renal vein thrombosis.
• Because of the risk of cerebral oedema, hypernatraemia (and hyponatraemia) should be corrected relatively slowly.
• A solution of half-normal or normal saline is used with added 2.5-5% dextrose. The rate is adjusted so that an average decline of sodium concentration is 0.5-1mmol/hr.
• The rate of infusion is usually 100-150 ml/kg body weight/day, provided that abnormal losses have stopped and renal function is adequate. The water deficit should be restored slowly over a period of 3-5 days.
• Most cases of acidosis will be vastly improved by initial rehydration but sodium bicarbonate may be required if acidosis is severe.
• Peritoneal dialysis may be required if the child is grossly uraemic, hypernatraemic and hyperosmolar.
• Despite effective therapy, mortality and residual brain damage may occur in up to 8% of patients affected.