Paediatric IV Fluid Therapy
NICE NG29 — IV fluid therapy in children and young people in hospital
Intravenous fluid therapy in children is fundamentally different from adult practice. NICE NG29 (2015) sets out the national framework for safe IV fluid prescribing in children and young people in hospital. Weight-based dosing, isotonic fluid selection, and vigilant electrolyte monitoring are mandatory. Errors in paediatric IV fluid prescribing — particularly the use of hypotonic fluids — have led to preventable deaths from acute hyponatraemia and cerebral oedema. This article covers assessment, fluid resuscitation, maintenance, DKA, neonatal requirements, and escalation. Careful evaluation of every child's clinical state before prescribing is essential.
Why Paediatric IV Fluids Are Different
Children are not small adults. Their physiology, fluid compartments, and responses to illness differ significantly from those of adults. Children compensate well for hypovolaemia — blood pressure may remain normal until 40% of circulating volume is lost. This means hypotension is a late and pre-arrest sign. Early recognition of compensated shock (tachycardia, prolonged capillary refill, reduced peripheral perfusion) is critical. Children have proportionally larger body surface areas and higher metabolic rates, leading to higher insensible losses. Neonates and infants are at particular risk of hypoglycaemia as glycogen stores are limited. Historically, hypotonic maintenance fluids caused numerous preventable paediatric deaths from hospital-acquired hyponatraemia — NICE NG29 mandates isotonic fluids for all paediatric maintenance to eliminate this risk.
Assessment — Dehydration and Shock Recognition
NICE NG29 classifies dehydration as no clinically detectable dehydration (<5% body weight loss), mild to moderate dehydration (5–10%), and severe dehydration (>10%). Clinical signs of mild to moderate dehydration include dry mucous membranes, sunken fontanelle in infants, reduced skin turgor, tachycardia, and reduced urine output. Signs of severe dehydration add markedly sunken eyes, absent tears, cold and mottled skin, significant tachycardia, reduced GCS, and oliguria or anuria. Shock is recognised by tachycardia for age, prolonged capillary refill time greater than 2 seconds, weak peripheral pulses, and altered consciousness — hypotension is a late pre-arrest sign in children and must not be awaited before treatment. Weight-based fluid deficit calculation: percentage dehydration × weight (kg) × 10 = fluid deficit in millilitres. Normal urine output targets are 1–3 mL/kg/hour in infants and 0.5–1 mL/kg/hour in children.
Fluid Resuscitation in Shock
When shock is identified, immediate IV fluid resuscitation is required. NICE NG29 recommends 0.9% sodium chloride (isotonic saline) as the bolus fluid of choice. The initial dose is 10–20 mL/kg IV or intraosseous (IO) over 15 minutes. Reassess after each bolus — look for improvement in heart rate, capillary refill, blood pressure, and level of consciousness. If the child improves, continue monitoring and begin maintenance fluids. If there is no improvement, repeat the bolus. After a cumulative total of 40–60 mL/kg without adequate response, immediate escalation to a senior clinician and PICU review is required. Continued fluid loading beyond this without expert review can be harmful. Cardiogenic shock is a key exception — large fluid boluses may worsen cardiac function and should not be given without senior guidance. Call the paediatric team early and do not delay PICU involvement in any child with refractory shock.
Maintenance Fluids — Holliday-Segar Formula
The Holliday-Segar formula calculates daily maintenance fluid requirements: 100 mL/kg for the first 10 kg, plus 50 mL/kg for the second 10 kg (between 10 and 20 kg), plus 20 mL/kg for every kilogram above 20 kg. For example, a 25 kg child requires 1000 + 500 + 100 = 1600 mL per day. The equivalent hourly rate can be derived using the 4–2–1 rule: 4 mL/kg/hour for the first 10 kg, 2 mL/kg/hour for the next 10 kg, 1 mL/kg/hour for each additional kilogram. NICE NG29 mandates isotonic fluids for all paediatric maintenance — specifically 0.9% NaCl with 5% glucose, with added potassium chloride (20 mmol/500 mL) once urine output is confirmed. Hypotonic fluids (0.18% NaCl with 4% glucose or 0.45% NaCl) must never be used for maintenance in children as they carry a well-documented risk of fatal acute hyponatraemia. Fluid volumes should be reduced to 50–80% of calculated maintenance in children with conditions associated with SIADH or raised intracranial pressure — including meningitis, encephalitis, head injury, post-operative state, and bronchiolitis.
Replacement Fluids — Ongoing Losses
Replacement fluids are prescribed to correct losses beyond normal daily maintenance — for example, from gastroenteritis, surgical drains, or nasogastric aspirate. The cardinal principle is to replace like-for-like: match the replacement fluid to the electrolyte composition of what is being lost. Gastric losses from vomiting or nasogastric aspiration are high in hydrogen ions, chloride, and potassium — replace with 0.9% NaCl and added KCl. Lower GI losses from diarrhoea or ileostomy are high in bicarbonate and potassium — replace with 0.9% NaCl and KCl, and monitor for metabolic acidosis. Surgical drain losses should be replaced with 0.9% NaCl or Hartmann's depending on the source, with electrolytes guided by local protocol. For burns, the paediatric Parkland formula (3 mL/kg/% TBSA burned of Hartmann's over 24 hours — half in first 8 hours from time of burn, half over next 16 hours) provides resuscitation volumes, with maintenance calculated separately. Electrolytes should be monitored every 4–6 hours in high-loss states.
Paediatric Diabetic Ketoacidosis (DKA)
Paediatric DKA management differs crucially from adult DKA. The most important principle from the BSPED 2020 guidelines and NICE NG18 is that IV fluid boluses must NOT be given in paediatric DKA unless the child is in haemodynamic shock. Over-rapid fluid administration is the primary risk factor for cerebral oedema — the leading cause of death in paediatric DKA. If the child is shocked, give 10 mL/kg 0.9% NaCl bolus, reassess, and repeat once if required (maximum 20 mL/kg total) before calling PICU. For non-shocked DKA, calculate total fluid requirements by adding the calculated fluid deficit (based on percentage dehydration × weight × 10) to 48-hour maintenance (Holliday-Segar × 2). Subtract any boluses already given. Replace this total over 48 hours — not 24 — to minimise cerebral oedema risk. Fluid of choice is 0.9% NaCl with KCl added once serum K+ is below 5.5 mmol/L and urine output is confirmed. Switch to 0.9% NaCl with 5% glucose when blood glucose falls below 14 mmol/L. Insulin is started as a fixed-rate infusion at 0.05–0.1 units/kg/hour — not before at least one hour of IV fluids, and not if K+ is below 3.5 mmol/L. Cerebral oedema is heralded by headache, deteriorating GCS, bradycardia, rising BP, and abnormal posturing — treat immediately with 2.5–5 mL/kg of 3% hypertonic saline IV over 10–15 minutes, restrict fluids, and call PICU. This article has been prepared following careful evaluation of NICE NG29, BSPED Paediatric DKA Guidelines 2020, and NICE NG18.
Neonates — Specific Fluid Requirements
Neonates require a highly individualised approach to IV fluid therapy. Term neonates begin at 60 mL/kg/day on Day 1, increasing to 90 mL/kg/day on Day 2, 120 mL/kg/day on Day 3, and 150 mL/kg/day by Day 4 onwards. Preterm neonates have greater insensible losses from immature skin but are also at higher risk of fluid overload causing patent ductus arteriosus, intraventricular haemorrhage, and bronchopulmonary dysplasia — increases should be more cautious. The standard maintenance fluid for neonates is 10% glucose to provide adequate glucose substrate and prevent hypoglycaemia. Sodium is added from Day 2–3 once urine output is established (typically 0.45% NaCl in 10% glucose, but exact composition per local neonatal unit protocol). Potassium is not added until urine output is confirmed. Target blood glucose in neonates is 2.5–7 mmol/L. Glucose infusion rates of 4–8 mg/kg/minute are appropriate for term neonates; preterm neonates may require up to 10–12 mg/kg/minute. Electrolytes should be checked every 12–24 hours in the first week of life. Hypoglycaemia (blood glucose <2.0 mmol/L with symptoms) requires immediate 2 mL/kg 10% glucose IV bolus followed by continuous 10% glucose infusion.
Electrolyte Monitoring — Frequency and Thresholds
NICE NG29 requires U&E to be checked within one hour of starting IV fluids in children, repeated at 4–8 hours, and then at a minimum of 12-hourly in all children receiving IV fluids. Increase to 4-hourly monitoring in DKA, shock, neurological conditions, sodium abnormalities under active correction, neonates, and suspected SIADH. For sodium: hyponatraemia below 128 mmol/L or hypernatraemia above 155 mmol/L require immediate senior review. Acute symptomatic hyponatraemia (seizures, reduced GCS) requires 2 mL/kg 3% NaCl IV over 10–15 minutes. Correction must not exceed 10–12 mmol/L per 24 hours to avoid osmotic demyelination. For potassium: hypokalaemia below 3.0 mmol/L requires active replacement (maximum 0.2 mmol/kg/hour via peripheral line). Hyperkalaemia above 6.0 mmol/L in children beyond the neonatal period (>28 days) requires senior review and treatment; above 6.5 mmol/L with ECG changes is an emergency. Blood glucose should be monitored 4-hourly in all children on IV fluids, hourly in DKA, and 30-minutely during neonatal hypoglycaemia treatment. Urea and creatinine should be checked at least daily, with urgent review if creatinine is rising or urine output is falling.
Patient and Carer Advice
Parents and carers play a vital role in monitoring their child during IV fluid therapy. Explain clearly why the drip is being used and reassure them it is a temporary measure. Teach parents to report immediately: no wet nappy for more than 6 hours in infants, the child becoming less responsive or drowsy, worsening vomiting preventing all oral intake, or any rapid clinical change. In DKA, explain that rehydration is deliberately slow over 48 hours to protect the brain — this is intentional and evidence-based. Reassure parents that IV fluids will be stepped down as soon as their child can drink adequately. For infants, encourage continued breastfeeding alongside IV fluids wherever possible. For children with diabetes, ensure parents receive BSPED sick-day rules before discharge — including when to check ketones, when to attend emergency services, and how to prevent future DKA episodes.