FLUID ELECTROLYTE PRINCIPLES OF THE NEWBORN

FLUID AND ELECTROLYTE PRINCIPLES OF THE NEWBORN
The principles of fluid and electrolyte balancing include the following points:
• Total body water (TBW) equals intracellular fluid (ICF) plus extracellular fluid (ECF).

• ECF equals ICF (plasma and lymph in the vessels) plus interstitial fluid (between cells).

• Characteristics of fluid changes
o Neonates are born with an excess of TBW, primarily ECF, which needs to be removed.
o Adult bodies are 60% water (20% ECF, 40% ICF).
o Term neonate bodies are 75% water (40% ECF, 35% ICF), and term neonates usually lose 5-10% of their weight in the first week.
o Preterm neonates have more water (at 23 weeks' gestation, 90% water composed of 60% ECF and 30% ICF), and they may lose 5-15% of their weight in the first week.

• Characteristics of insensible water loss
o Insensible water loss (IWL) is water loss that is not readily measured, and IWL is water lost via evaporation through the skin (two thirds) or respiratory tract (one third).
o IWL depends on gestational age; the earlier the gestational age of the preterm infant, the greater the IWL.
o The magnitude of IWL also depends on the postnatal age. Since skin thickens with age, the IWL decreases as neonates age.
o All other measurable sources of fluid and electrolyte losses need to be considered as well. Sources include stool (eg, diarrhea and ostomy), nasogastric (NG) or orogastric (OG) drainage, and cerebrospinal fluid (CSF), including ventricular drainage.

• Renal function changes: Neonates have a decreased capacity to concentrate or dilute urine in response to changes in intravascular fluid status, and they are at risk for dehydration or fluid overload. The normal maturation of renal function that occurs with increasing gestational and postnatal age also plays a role in determining fluid requirements.