Fluid prescribing for neonates
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Brief information about neonatal fluid prescribing
Physiology at birth
A newborn baby has an expanded extracellular fluid (ECF) compartment, with premature babies having ECF of 85% of body weight and term babies 75% (compared to adults with approx 60%). A physiological diuresis (driven largely by ANP) causes the ECF compartment to contract during the first few days after birth, resulting in a negative sodium/water balance during this time. Fluids should be restricted during this period, and too liberal fluid regimes have been shown to cause increased incidence of patent ductus arteriosus, necrotising enterocolitis, and worse overall mortality in premature infants.
Normal fluid regime in term uncomplicated babies:
- Day 1: 60 ml/kg/day
- Day 2: 90 ml/kg/day
- Day 3: 120 ml/kg/day
- Day 4: consider increasing to 150 ml/kg/day, and sometimes eventually up to 180 ml/kg/day in a premature infant with high evaporative losses
- Prematurity - premature babies can have increased fluid requirements, as they can have high insensible loses as a result of their thin, immature skin which can allow significant evaporative (and heat) losses. Humidication in an incubator is therefore very important to minimise this.
- Hypoxic ischaemic injury - babies can need fluid restriction as a result of acute renal impairment or raised ADH levels. Can become hypocalcaemic early.
- Hypernatraemia/hyponatraemia - plasma sodium should be monitored at least daily, and up to 2-3 times daily in extremely preterm babies. Good guide to hydration status, where hypernatraemia (>145 mmol/L) = dehydration and hyponatraemia (< 135 mmol/L) = water excess.
- Urine output - should be monitored carefully, aiming fr > 1 ml/kg/hr.
Electrolyte requirements (mmol/kg/day)
|< 30 weeks||4 - 8||2 - 4||1.5|
|30-36 weeks||4||2||0.5 - 1.5|
|Term||2 - 3||2||0.5|