Flashcards in Neonatal Fluid and Electrolytes Deck (127)
What is the most abundant component of the human body?
How is water distributed in the body?
into two compartments: intracellular and extracellular fluid
What is extracellular water composed of?
interstitial and intravascular spaces; total amount of water outside the cell
what is intracellular water?
total amount of water inside the cell
What is the main solute of the ECW?
plasma proteins; affects the colloid osmotic pressure
How is total body water affected by GA?
total body water decreases over age; over the first trimester, it composes about 90% of total body wt; at 32 wks, 80% of total body wt; by term GA about 78% and by 1 yr of age, it is about 65%: the ratio of ICW:ECW ∆ as well, with ECW gradually decreasing
What determines osmolality?
determined by the total # of solute particles in a solution
What is the net result of the fact that cell membranes are completely permeable to H2O, but not to solutes?
H2O will shift from one compartment to another until the osmolality on both sides as the membrane is equal
What is the major determinant of osmolality?
serum Na concentration
What is the formula to predict the serum osmolality?
2(plasma Na) + BUN/ 2.8 + Glucose/ 18
Why do newborns normally lose 5-15% of their birthweight?
- at birth, their is an acute increase in the ECW as H20 and lytes shift from the IC space to the EC space
- this puts infants in a state of excess ECF
- this excess ECW is then lost through diuresis as the expanded ECF compartment ctx
- (can also be r/t circulating levels of hormones)
What is the expected degree of weight loss in a newborn?
What is the state of fetal nephrons before 34 weeks GA?
functional but immature
What happens to a FT baby's renal fx after delivery compared with a PT baby?
improves more than PT; term and preterm can dilute their urine
- reabsorption of Na, HCO3 and glucose is limited in the newborn
What is characteristic of a PT baby's renal fx?
- can dilute urine, (but are slower at it); when faced with a rapid fluid load they will have a delayed response resulting in fluid retention
- difficulty concentrating their urine
What is the effect of antenatal steroids on the renal system?
- a/w decreased insensible H2O losses
- less frequent incidence of hypernatremia
- earlier diuresis
What is ADH?
hormone released by the posterior pituitary in reponse to a variety of stimuli.
- ADH influences water balance by stimulating the kidneys to CONSERVE water
- in the absence of ADH, the distal tubules remain impermeable to water (restricting reabsorption) and fluid is released as urine
Why can't newborns efficiently concentrate their urine?
decreased responsiveness to ADH
What factors stimulate ADH release?
What is the normal range of UOP in the neonate?
1-4mL/Kg/h; highest rate occurs during the physiologic reduction of ECF
What are insensible water losses?
defined as the non-measureable losses that occur through the skin and respiratory system; influenced by numerous factors
What is tranepidermal water loss?
occurs as body water diffuses through the immature epidermis and is lost to the atmosphere
What influences transepidermal water loss?
- increases with decreasing GA
- a major source of insensible H2O loss in the VLBW
- highest on dol 1 and decreases on subsequent days as barrier fx improves
- closely r/t relative ambient humidity
What skin features predisposed the PT infant to evaporative heat loss?
- poor keratinization
- high H2O content
- low subQ fat
- large surface area
- high degree of skin vascularity
What is the result of failure to account for TWL?
inaccurate calculation/ estimates of TF needs with resultant fluid and electrolyte imbalances
When does skin barrier fx improve?
improvement slows with decreasing GA, may take several weeks to allow for full development of the strateum corneum; skin maturation isn't influenced by antenatal steroids or by gender
what are other sources of fluid loss in the neonate?
gastric drainage, enterostomies, surgical wounds, and pleural fluid drainage
What is the estimated amt of fluid loss d/t respiratory?
roughly 0-10 mL/kg/d- r/t temp and humidity of inspired gases and to minute ventilation
What is the estimated amt of fluid loss d/t feces?
est to be 5mL/kg/d in the first wk of life, then increase to 10mL/kg/d