Paediatric fluid management

Contents

Overview

Fluid management in children is a distinct skill from adult practice. Children have different body composition, haemodynamic parameters, and metabolic rates at different ages. The evidence base for paediatric fluid resuscitation — particularly in sepsis — has been profoundly shaped by the FEAST trial, which demonstrated harm from fluid bolus therapy in a resource-limited setting, challenging assumptions that had been extrapolated from adult practice.

Physiological Differences from Adults

Body composition: Infants have proportionally more total body water (75–80% of body weight in neonates, decreasing to approximately 60% in adults). Extracellular fluid fraction is larger in neonates. This affects the volume of distribution of drugs and the response to fluid loading.

Heart rate as the primary cardiac output determinant: Neonates and infants have limited ability to increase stroke volume — cardiac output is primarily rate-dependent. Tachycardia is an early and important compensatory response to hypovolaemia.

Blood pressure: Normal values are age-dependent and lower than adults. A systolic BP of 70 mmHg is acceptable in a 1-year-old; the lower limit of normal systolic BP is approximately 70 + (2 × age in years) mmHg for children over 1 year.

Oxygen consumption: Higher per kilogram than adults, making children more sensitive to respiratory compromise and anaemia.

Renal reserve: Neonates and infants have immature renal tubular function — limited concentrating ability and increased susceptibility to fluid overload and electrolyte disturbance.

Fluid Resuscitation in Shock

Recognition of Shock

Clinical signs of shock in children:

  • Tachycardia (age-appropriate upper limits: neonate >160, infant >150, child >140, adolescent >120 bpm)
  • Prolonged capillary refill time (>2 seconds centrally)
  • Weak peripheral pulses
  • Cool/mottled peripheries (cold shock) or warm vasodilated peripheries (warm/distributive shock)
  • Altered mental status, irritability, or lethargy
  • Decreased urine output
  • Hypotension is a LATE sign in children — do not wait for it before treating shock

Fluid Resuscitation

APLS/PALS guidelines: 10–20 mL/kg IV or IO boluses of isotonic crystalloid (0.9% sodium chloride or Hartmann's). Reassess after each bolus.

The starting bolus volume of 20 mL/kg over 5–15 minutes was derived from adult practice. After the FEAST trial (see below), current UK APLS guidance uses 10 mL/kg incremental boluses with reassessment, titrated to clinical response, and a maximum of 40–60 mL/kg before considering inotropic support.

Septic shock:

  • Start IV/IO antibiotics within 1 hour of recognition
  • Fluid bolus 10 mL/kg, reassess, repeat as needed
  • If not responding: adrenaline is first-line inotrope for cold shock with poor cardiac output; noradrenaline for warm distributive shock
  • Dopamine is no longer recommended as first-line based on paediatric evidence

Hypovolaemic shock (trauma, DKA, bleeding): Fluid resuscitation targets organ perfusion. In trauma, haemostatic resuscitation principles apply; in DKA, fluid and electrolyte replacement follows specific DKA guidelines (see below).

DKA in children: 10 mL/kg isotonic saline for resuscitation if shocked; then replacement over 48 hours with careful sodium and fluid calculations to minimise risk of cerebral oedema. No fluid boluses beyond resuscitation in DKA unless there is shock.

Maintenance Fluid Calculation

Holliday-Segar Method

The Holliday-Segar formula calculates daily maintenance fluid requirements based on body weight:

  • 0–10 kg: 100 mL/kg/day (4 mL/kg/hour)
  • 10–20 kg: 1000 mL + 50 mL/kg for each kg above 10 kg (add 2 mL/kg/hour for each kg above 10)

  • 20 kg: 1500 mL + 20 mL/kg for each kg above 20 kg (add 1 mL/kg/hour for each kg above 20)

This can be summarised as 4-2-1 rule for hourly rates.

Example: a 25 kg child requires:

  • 4 × 10 = 40 mL/hour for first 10 kg
  • 2 × 10 = 20 mL/hour for next 10 kg
  • 1 × 5 = 5 mL/hour for final 5 kg
  • Total = 65 mL/hour

Adjustment for Clinical Situation

Maintenance rates should be reduced to two-thirds in conditions associated with inappropriate ADH secretion (meningitis, post-operatively, pain, nausea) to reduce the risk of hyponatraemia. The NICE guideline (2015) recommends isotonic fluids for maintenance in hospitalised children.

Fluid Choice

Resuscitation: 0.9% sodium chloride (normal saline) or Hartmann's/Ringer's lactate as isotonic crystalloid. Either is acceptable for bolus resuscitation. Colloids (albumin 4.5%) may be used in specific circumstances but are not superior to crystalloid for resuscitation.

Maintenance: Isotonic fluids (0.9% NaCl or 0.9% NaCl + 5% dextrose). Hypotonic fluids (0.45% NaCl, 0.18% NaCl) should not be used routinely as maintenance in children — NICE guidance removed them following multiple reports of hospital-acquired hyponatraemia and associated deaths. Hypotonic fluids may be used in specific situations (neonates, certain metabolic conditions) under specialist guidance.

Blood products: Haemorrhagic shock requires early blood transfusion. Transfusion threshold in stable critically ill children without active bleeding: Hb <70 g/L (TRIPICU trial: restrictive strategy at Hb <70 g/L was non-inferior to a liberal strategy at Hb <95 g/L).

The FEAST Trial

The Fluid Expansion As Supportive Therapy (FEAST) trial (Maitland et al., NEJM 2011) was a landmark randomised controlled trial conducted in sub-Saharan Africa. 3170 children (aged 60 days to 12 years) with febrile illness and impaired perfusion were randomised to albumin bolus (20–40 mL/kg), saline bolus (20–40 mL/kg), or no bolus.

Contrary to expectation, the trial found that fluid bolus therapy significantly increased 48-hour mortality compared with no bolus (10.5% vs 7.3%; RR 1.45). The finding was consistent across the albumin and saline arms.

Proposed mechanisms for harm: impairment of compensatory mechanisms in children with malaria (who have high intracranial pressure and may have impaired myocardial function), hyponatraemia from fluid administration, and increased risk of pulmonary oedema.

The FEAST trial applies to a specific African context with high malaria prevalence, malnutrition, and limited ICU backup. It should not be directly extrapolated to high-income ICU settings. However, it has reshaped paediatric fluid practice globally:

  • Routine 20 mL/kg boluses have been replaced by 10 mL/kg incremental boluses with careful reassessment
  • Fluid should be given to treat documented shock, not prophylactically
  • Ongoing fluid balance should aim for euvolaemia, not positive balance

Ongoing Fluid Management

Fluid overload in critically ill children is associated with worse outcomes — increased ventilator days, AKI, and mortality. A positive fluid balance of greater than 10–20% body weight is independently associated with adverse outcomes in paediatric critical illness.

Principles:

  • Aim for euvolaemia; avoid fluid accumulation
  • Reassess the need for ongoing IV fluids daily
  • Transition to oral or enteral hydration as early as possible
  • Use diuretics (furosemide) to achieve negative balance once the acute resuscitation phase is complete
  • Avoid unnecessary fluid boluses — ensure each bolus has a clear indication and is followed by clinical reassessment

Viva Questions

How does the approach to fluid resuscitation in a child with septic shock differ from an adult?

The principles are similar — restore tissue perfusion by correcting intravascular volume deficit — but there are important differences in execution. Children compensate more effectively than adults through tachycardia; hypotension is a late and pre-terminal sign in paediatric shock, and waiting for it before intervening risks irreversible deterioration. The initial bolus volume in current APLS guidance is 10 mL/kg isotonic crystalloid (rather than the adult 500 mL or 10–20 mL/kg depending on context), given over 5–15 minutes with immediate reassessment. This cautious approach is informed partly by the FEAST trial, which showed harm from larger volume boluses in African children with febrile illness and impaired perfusion. If there is no adequate response to 40–60 mL/kg total fluid and clinical signs of shock persist, inotrope support should be started — adrenaline for cold shock with reduced cardiac output, and noradrenaline for warm distributive shock. Glucose should also be monitored closely in children, as hypoglycaemia can occur rapidly during critical illness.

What is the FEAST trial and how has it changed paediatric fluid practice?

The FEAST trial (Maitland et al., NEJM 2011) randomised over 3000 children in sub-Saharan Africa with febrile illness and impaired perfusion to bolus fluid therapy (albumin or saline at 20–40 mL/kg) versus no bolus. Despite the established dogma that fluid resuscitation saves lives in shock, the trial found a significantly higher 48-hour mortality in the bolus groups (approximately 10.5%) compared with the no-bolus group (7.3%). This was an unexpected finding and caused substantial debate. The clinical context must be considered: the majority of patients had malaria, many were malnourished, and intensive care resources were very limited. Boluses may have caused harm through unmasking raised intracranial pressure in malaria, causing pulmonary oedema in patients with anaemia-induced high-output cardiac states, or inducing hyponatraemia. The trial is not directly applicable to high-income paediatric ICU settings where patients have different diagnoses and intensive monitoring and support are available. Nevertheless, its conclusions have influenced guidelines worldwide: standard bolus volumes have reduced from 20 mL/kg to 10 mL/kg increments with mandatory reassessment after each, and routine bolusing without clinical evidence of shock is no longer recommended.

How do you calculate maintenance fluid requirements for a 22 kg child and what fluid would you use?

Using the Holliday-Segar 4-2-1 rule: 4 mL/kg/hour for the first 10 kg = 40 mL/hour, plus 2 mL/kg/hour for the next 10 kg = 20 mL/hour, plus 1 mL/kg/hour for the remaining 2 kg = 2 mL/hour, giving a total of 62 mL/hour. If calculating the daily total: (10 × 100) + (10 × 50) + (2 × 20) = 1000 + 500 + 40 = 1540 mL/day. The fluid of choice for maintenance in hospitalised children is an isotonic solution — either 0.9% sodium chloride or 0.9% sodium chloride with 5% glucose (if glucose supplementation is also needed), in line with NICE NG29 (2015). Hypotonic fluids such as 0.18% or 0.45% NaCl should not be used routinely, as they cause hospital-acquired hyponatraemia. In certain situations — neonates, known syndrome of inappropriate ADH secretion, post-operative patients — the maintenance rate may need to be reduced to two-thirds of the calculated volume, with the electrolyte composition determined by clinical status and measured electrolytes.