1. Fluid & Electrolytes in the Neonate
Nancy Roberto, CNP
Children’s Hospital Medical Center
7/02

2. Importance of F&E Balance
Shown to play a role in the development of morbitities in ELBW infants:
IVH
NEC
PDA
BPD

3. Fluid Balance
A function of the distribution of water in the body, water intake and water losses
Fluid distribution in the body changes with increasing gestation
Water losses change with GA, with differences in renal function & insensible water loss between term & preterm infants

4. Total Body Water (TBW) 75% of body weight at birth (> in preterms)
TBW divided into intracellular fluid (ICF) & extracellular fluid (ECF)
ECF includes vascular volume and interstitial volume (3rd space)

5. TBW in Neonates
TBW & ECF decreases as GA increases, while ICF increases
During the 1st week of life all infants experience a reduction in body weight
LBW infants during the 1st 5 days of life lose 10-15% of ECF with concurrent diuretics phase resulting in negative fluid & sodium balance
High fluid intake in LBW infants may be associated with PDA & NEC

6. Role of Antidiuretic Hormone (ADH)
Water balance is primarily controlled by ADH which enables water to be absorbed in the distal nephron collecting duct
ADH secretion is regulated by hypothalamic osmoreceptors that monitor serum osmolality and baroreceptors of the carotid sinus & left atrium that monitor intravascular blood volume
Stimulation of ADH secretion occurs when serum osmolality increases > 285 mOsm/kg or when effective blood volume is diminished

7. Renal Function
Maximum renal concentration & dilution require structural maturity, well-developed tubular transport mechanisms & an intact hypothalamic-renal vasopressin axis
Term and preterm infants have low GFRs (lower in preterm) secondary to low renal blood flow
Newborn kidney ability to concentrate urine is 1/2 that of adult kidney
Creatinine levels in 1st 24 hours of life reflect maternal creatinine
ELBW infants <1000 gms or GA <28 weeks will need to have electrolytes checked at 12 hrs of life, more mature infants at 24 hrs of life

8. Insensible Water Loss (IWL)
Evaporation of water through the skin & mucous membranes
In newborns IWL is 1/3 respiratory, 2/3 skin
Maturity is most important variable
Preterm infants have higher IWL due to:
immature epithelial layer
larger surface area-body weight ratio
greater skin vascularity

9. Environmental Factors Affecting IWL
Increase IWL
Environmental temperature > neutral thermal zone
Severe prematurity
Open radiant warmer bed
Phototherapy
Hyperthermia
Tachypnea
Skin breakdown
Congenital defects
Decrease IWL
Incubator humidification
Incubator plastic head shield or double walled isolette
Plastic blanket/mattress under radiant warmer
Tracheal intubation with humidification

10. Concept of “Third-Spacing”
Accumulation of fluid and electrolytes in static body compartments (interstitial tissue/fluid spaces)
Occurs in conditions such as sepsis, hydrops fetalis, hypoalbuminemia, intra-abdominal infections & following abdominal or cardiac surgery
Goal is to replenish extracellular fluid compartments with colloid and crytalloid

11. Calculation of F&E Requirements
Based on maintenance needs, deficits and ongoing losses (urine, GI tract)
Sodium, potassium and chloride requirements vary depending on infant’s condition and age
Important to consider growth (TF needs increases as weight increases)

12. F&E Therapy: Guidelines
Preterm infants require more fluid and are less tolerant of glucose during the first weeks of life
Prior to initiation of K+ supplementation, need adequate renal function (UOP 1-2cc/kg/hr)
TPN and or enteral feedings should be initiated as soon as the infants condition allows to give additional vitamins, trace elements, and basic protein, fat & carbohydrate

13. F&E Therapy: Term infants
Day 1: D10W at cc/kg/day (GIR of 6-7 mg/kg/min)
Day 2-7: D10W at cc/kg/day (advance cc/kg/day with 10-15% advance in GIR)
Na+ requirements= 2-4 meq/kg/day
K+ requirements= 1-2 meq/kg/day

14. F&E Therapy: Preterm infants Day 1-3
D5W for BW gms-begin fluid at cc/kg/day, BW <800 gms give cc/kg/day
Advance GIR 0.5-1cc/kg/day as tolerates (occasionally need insulin to treat hyperglycemia)
Na+ requirements low (usually 1meq/kg/day)
K+ requirements 1-3 meq/kg/day
Ca+ best supplemented by use of early TPN

15. F&E Therapy: Preterm Infants Day 3-7
After the transitional phase of volume contraction, the preterm enters a maintenance phase & fluids can be decreased as the skin matures
Fluid & electrolyte needs begins to resemble that of term infant other than an increased need for Na+ supplementation due to limited renal conservation and incorporation of Na+ into bone during rapid growth

16. Clinical Conditions Resulting in Ongoing Fluid Losses
Diarrhea
Dehydration
Chest tube drainage
Surgical wound drainage
Excessive urinary losses from osmotic diuresis
Accurate measurement of the volume & composition of the abnormal losses will guide replacement therapy (fluid & electrolyte)

17. Monitoring of F&E Balance
Clinical Assessment
Heart rate
Blood pressure
Skin turgor
Capillary refill
Oral mucosa integrity
Fullness of the anterior fontanelle
Body weight
Fluid intake
Urine & stool output
Serum electrolytes
Urine osmolarity or specific gravity
Blood gases for metabolic acidosis
Hematocrit

18. Monitoring during the 1st week of life
Urine output should be 1-3cc/kg/hr
Urine specific gravity
Weight loss 5%-15%
Weight gain after the first week of life should be grams/day

19. Hyponatremia Serum sodium <130 mmol/L
May result from the continued secretion of ADH in the presence of serum hypo-osmolality or when effective blood volume is diminished
May also result from a decreased GFR or an increase in proximal fluid reabsorption, which diminish delivery of fluid to the distal nephron diluting segments
Defects in sodium chloride transport in the cortical and medullary ascending limb of the loop of Henle, which are water-impermeable regions, also limit the diluting capacity of the nephron

20. Early-onset Hyponatremia
Usually reflects free water excess owing to either increased maternal free water intake or perinatal nonosmotic release of vasopressin (Syndrome of inappropriate ADH)
May also occur from excess free water intake or suboptimal sodium intake in formula or IV fluids
Increased vasopressin release (SIADH) may be seen in conditions such as perinatal asphyxia, respiratory distress, bilateral pneumothoraces, and IVH
Results in decreased UOP & hyponatremia treated with fluid restriction of cc/kg/day

21. Late-onset Hyponatremia
Commonly due to negative sodium balance
May occur from either inadequate sodium intake or excessive renal losses due to a high fractional excretion of sodium, particularly in preterm infants <28 weeks gestation
Uncommonly, free water retention from excessive ADH release, renal failure or edemetous disorders may be seen. Water restriction is necessary in treating hyponatremia when these conditions are present

22. Hypernatremia Defined as a serum sodium >150 mmol/L
Results from disturbances in the ability to maximally concentrate the urine
May arise from low levels of circulating ADH (central diabetes insipidous) or impaired renal response to ADH (nephrogenic diabetes insipidous)

23. Hypernatremia Early Onset
Excess sodium intake following resuscitation with sodium bicarbonate
High IWL in LBW infants
Late Onset
Excess sodium supplementation
Inadequate free water intake

24. Diabetes Insipidous (DI)
Results in hypernatremia in the newborn
Infant presents with polyuria, polydipsia, chronic dehydration, irritability, poor feeding and growth restriction
Nephrogenic DI: inability of the kidney to concentrate urine in response to ADH. May present in the first week of life. Treated with low sodium formula and diuretics to reduce extracellular sodium.
Central DI: may be due to midline CNS malformations, anoxic encephalopathy, cerebral edema or trauma. ADH levels are insufficient for promoting appropriate amounts of water absorption in the distal nephron. Treated with intranasal DDAVP.

25. Hyperkalemia Monitor for hyperkalemia (>7 mEq/L)
Monitor for cardiac arrhythmias (peaked T waves, abnormal QRS, PVCs, tachyarrythmias, wide QRS, prolonged PR interval, wide flat P waves, VT, VF, or cardiac arrest
Treatment is calcium chloride or calcium gluconate (stabilize cardiac membrane), combination of insulin & glucose infusion (drive K+ into the cell), kayexalate (exchanges sodium for potassium in the intestine to remove K+ slowly), & sodium bicarbonate in the presence of metabolic acidosis

26. F&E Therapy in Common Neonatal Conditions
Perinatal Asphyxia/Renal Failure
Symptomatic PDA
Chronic Lung Disease
NEC/Short Bowel Syndrome
IVH/Hydrocephalus

27. Perinatal Asphyxia/Renal Failure
Usually secondary to hypoxia or shock
Renal parenchymal injury from asphyxia frequently results in acute tubular necrosis (ATN), commonly accompanied by oliguria or anuria
In acute renal failure fluid restriction to amounts equal to UOP & IWL is critical to avoid volume excess
IWL in term infant is approximately 30 cc/kg/day, in preterm as much as 80 cc/kg/day
Fluids restriction is needed (usually 50-60cc/kg/day)

28. Perinatal Asphyxia/Renal Failure
Urine volumes may require replacement in high output renal failure
10 cc fluid bolus can be given if the cause of the oliguria or anuria are unclear
Potassium should not be given during the oliguric or anuric phase
K+ supplementation should be avoided

29. Symptomatic PDA
PDA with L-R shunt and pulmonary edema is a common cause of morbidity in preterm infants
Fluid overload during this period is associated with an increased incidence of symptomatic PDA (associated with lack of isotonic contraction in this group of infants)
Monitor to ensure that physiologic isotonic body fluid contraction does occur (diuretic phase)

30. Chronic Lung Disease/BPD
Infants with BPD present complex challenges
Higher basal metabolic rate requires increased caloric density and/or volume increase to meet high caloric demands
Goal is optimal fluid & nutrition w/o fluid overload and worsening pulmonary disease
Diuretic therapy is common treatment for BPD and significantly affect F&E balance, can lead to hypokalemic metabolic alkalosis, enhanced urinary excretion of calcium (leading to osteopenia of prematuriy, nephrocalcinosis, urolithiasis)

31. NEC/Short Bowel Syndrome
Infants who have had NEC, particularly those with short bowel syndrome present a challenge due to frequent increased stool losses and malabsorption
Infants with ileostomies, jejunostomies and occasionally colostomies will require sodium and occasionally bicarbonate replacements
Excessive stool losses will require replacement volume
Elemental formulas tolerated by these infants contain less calcium, phosphorus and protein than preterm formulas

32. IVH/Hydrocephalus
Infants with hydrocephalus who require frequent tapping and removal of CFS will require additional sodium supplements
Preterm infants with severe IVH may develop hyponatremia secondary to SIADH

33. References
Fanaroff, A. A., & Martin, R. J. (2002). Neonatal-Perinatal Medicine: Diseases of the fetus and infant (7th ed.). St. Louis: Mosby
Gomella, T. L., Cunningham, M. D., Eyal, F. G., & Zenk, K. E. (1999). Neonatology: Management, procedures, on-call problems, diseases, drugs (4th ed.). Stamford: Appleton & Lange