Paediatric fluid management

Surgical approach (context-dependent)

• Not a single operation; fluid strategy depends on procedure and expected losses
  • Minor surgery: minimal third-space loss; aim euvolaemia; early oral fluids where appropriate
  • Major abdominal / bowel surgery: significant evaporative + third-space losses; may have NG losses; consider stoma losses post-op
  • ENT/tonsil: risk dehydration pre-op; blood loss can be underestimated; swallowed blood
  • Burns: large capillary leak; formal resuscitation formulae (outside routine perioperative maintenance)
• Typical surgical sources of fluid loss to anticipate
  • Blood loss (suction, swabs, drapes, floor; hidden loss)
  • Evaporative loss from exposed viscera / large wounds
  • Third-space / inflammatory losses (esp. bowel obstruction, peritonitis)
  • Ongoing GI losses: NG aspirate, vomiting, diarrhoea, high-output stoma

Anaesthetic management (perioperative fluid management framework)

• Type of anaesthesia: usually GA; regional/neuraxial adjuncts reduce stress response and opioid requirement but do not replace fluid strategy
• Airway: SGA for short/minor procedures; ETT for major surgery, aspiration risk, laparoscopic, prone, or expected significant fluid shifts/bleeding
• Duration: varies (minutes to many hours); longer cases increase risk of hypothermia, insensible losses, and cumulative iatrogenic fluid
• Pain: procedure-dependent; adequate analgesia reduces catecholamine-driven fluid shifts; consider multimodal + regional where appropriate
• Monitoring: tailor to risk (standard monitoring; consider arterial line for major blood loss/vasoactive support; urine output useful but not sole endpoint)
• Core principles: avoid hypovolaemia and avoid iatrogenic hyponatraemia; use isotonic balanced crystalloids for most perioperative needs

Aims and physiology (why children are different)

• Maintain intravascular volume, organ perfusion, and electrolyte/glucose homeostasis while avoiding fluid overload
• Higher metabolic rate and oxygen consumption; smaller absolute reserves → deterioration can be rapid
• Neonates/infants: higher total body water; higher ECF fraction; immature renal concentrating ability; limited sodium handling; greater insensible losses
• Hyponatraemia risk is increased by non-osmotic ADH secretion (pain, nausea, stress, opioids, hypovolaemia) + hypotonic fluids

Preoperative assessment relevant to fluids

• History: intake, vomiting/diarrhoea, fever, polyuria, weight change, diuretics, endocrine disease (e.g., CAH, diabetes), renal/cardiac disease
• Examination: HR, capillary refill, mental state, mucous membranes, tears, skin turgor, fontanelle (infants), work of breathing, BP (late sign), peripheral temperature
• Investigations (as indicated): U&E, glucose, blood gas/lactate, Hb; consider ketones in prolonged fasting/illness
• Fasting: follow current local/NICE/RCoA guidance; prolonged fasting increases dehydration/ketosis risk—minimise and allow clear fluids up to 1 hour where policy supports

Maintenance fluids (perioperative)

• Traditional Holliday–Segar maintenance (24 h): 100 mL/kg for first 10 kg + 50 mL/kg for next 10 kg + 20 mL/kg for each kg >20 kg
  • Hourly equivalent (4-2-1 rule): 4 mL/kg/h for first 10 kg + 2 mL/kg/h for next 10 kg + 1 mL/kg/h thereafter
• Modern practice: avoid hypotonic maintenance perioperatively; use isotonic balanced crystalloid with added glucose where needed
  • Common approach: balanced isotonic crystalloid (e.g., Plasma-Lyte 148 / Hartmann’s) + 1–2.5% glucose (or separate glucose-containing isotonic solution) depending on age/risk
  • Neonates/young infants: higher risk of hypoglycaemia → ensure glucose provision and monitor blood glucose
• When to reduce maintenance rate: major surgery with significant inflammatory response/ADH, postoperative period, renal/cardiac impairment, risk of SIADH

Choice of fluid (what to use and why)

• Balanced isotonic crystalloids (preferred for most perioperative use): closer to plasma strong ion difference; less hyperchloraemic acidosis than 0.9% saline
• 0.9% saline: useful for hypochloraemic metabolic alkalosis (e.g., pyloric stenosis) and hyponatraemia with hypovolaemia; watch hyperchloraemia and acidosis with large volumes
• Glucose-containing fluids: prevent hypoglycaemia/ketosis (esp. neonates/infants); avoid excessive free water and hyponatraemia by using isotonic base where possible
• Colloids: limited routine role; consider albumin in specific contexts (e.g., hypoalbuminaemia with oedema, liver disease) per local policy; synthetic starches generally avoided
• Blood products: treat haemorrhage with component therapy; avoid dilutional coagulopathy; use local major haemorrhage paediatric guidance

Deficit and replacement (perioperative practical approach)

• Estimate deficit from fasting/dehydration and replace cautiously; avoid automatic large 'fasting deficit' replacement in well children having short cases
• If clinically dehydrated: resuscitate first (bolus), then re-assess; do not rely on maintenance calculations
• Bolus for hypovolaemia/shock: 10–20 mL/kg isotonic crystalloid, reassess; repeat as needed; escalate early if ongoing losses/bleeding
  • Reassessment endpoints: HR trend, capillary refill, pulse volume, BP, mental state, lactate/base deficit, urine output, response durability
• Ongoing surgical losses: replace with isotonic balanced crystalloid; consider colloid/blood depending on nature and magnitude of loss
• Third-space/evaporative losses: greatest in major open abdominal surgery; use warmed fluids and active warming

Blood loss: estimation, allowable blood loss, and transfusion triggers

• Estimated blood volume (EBV): preterm ~90–100 mL/kg; term neonate ~80–90 mL/kg; infant ~75–80 mL/kg; child ~70–75 mL/kg; adolescent ~65–70 mL/kg
• Allowable blood loss (ABL) concept: ABL = EBV × (Hbi − Hbf) / Hbi (use Hb or Hct consistently)
  • Choose target Hb (Hbf) based on physiology and context (cyanotic CHD, sepsis, major surgery, ongoing bleeding)
• Transfusion: individualise; consider transfusion with significant acute blood loss, haemodynamic instability, or Hb below acceptable threshold for context
• PRBC dose: typically 10–15 mL/kg raises Hb by ~20–30 g/L (rule-of-thumb; depends on product and baseline)
• Massive haemorrhage: early balanced component therapy; monitor coagulation (lab/TEG/ROTEM), calcium, temperature, acid-base; give tranexamic acid per protocol

Urine output and endpoints

• Target urine output: commonly ≥1 mL/kg/h in infants/children (lower may be acceptable intra-op depending on context); interpret with haemodynamics and trend
• Avoid chasing urine output with fluid in isolation; consider anaesthetic depth, ADH, surgical stress, hypotension, obstruction, renal disease
• Use multimodal assessment: HR/BP, cap refill, lactate/base deficit, temperature, Hb, acid-base, surgical field, and (where used) dynamic indices/echo

Glucose management

• At-risk groups for hypoglycaemia: neonates, ex-preterm, low birth weight, sepsis, endocrine/metabolic disease, prolonged fasting, TPN-dependent
• Monitor perioperative blood glucose in at-risk children and during long cases; treat hypoglycaemia promptly per local protocol
• Avoid hyperglycaemia (osmotic diuresis, infection risk); adjust glucose infusion rather than giving large boluses unless symptomatic/severe

Electrolytes and acid–base (high-yield)

• Hyponatraemia: often iatrogenic (hypotonic fluids + ADH); symptoms include headache, vomiting, confusion, seizures; treat as emergency if symptomatic
• Hyperchloraemic metabolic acidosis: large volumes of 0.9% saline; consider switching to balanced crystalloid
• Hypocalcaemia: citrate toxicity during large transfusion; worsened by alkalosis and hypothermia; monitor ionised Ca and replace as needed
• Potassium: avoid K-containing fluids in renal failure or severe tissue injury; do not add K until urine output established in neonates/infants unless specialist indication

Special situations commonly examined

• Pyloric stenosis: hypochloraemic, hypokalaemic metabolic alkalosis + dehydration; resuscitate with 0.9% saline; correct chloride and volume before anaesthesia; add K once urine output confirmed
• Diabetic ketoacidosis (DKA): not routine theatre fluid management; follow paediatric DKA protocol (careful isotonic fluids, insulin, electrolyte monitoring, cerebral oedema risk)
• Sepsis: early bolus resuscitation with reassessment; consider vasoactive support early; avoid fluid overload; monitor lactate and perfusion
• Neonates: higher insensible losses and glucose needs; careful sodium/water balance; meticulous monitoring and warmed humidified gases/fluids
• Renal/cardiac disease: lower thresholds for overload; consider invasive monitoring/echo; adjust maintenance and bolus strategy

Postoperative fluid strategy

• Aim early enteral/oral fluids when safe; reduce IV fluids accordingly to avoid overload
• Continue isotonic fluids if IV required; monitor Na, glucose, and fluid balance in at-risk children
• High-output stoma/NG losses: replace mL-for-mL with appropriate electrolyte solution guided by measured losses and labs