Fluids and Electrolytes in the Newborn

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Fluids and Electrolytes in the Newborn

• Vandana Nayal

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Body fluid composition in the fetus and
newborn

• Total Body Water ICF ECF (IntravascularInters
  titial)
• As gestational age increases, TBW and ECF
  decrease while ICF increases
• At birth, TBW 75 of body weight in term
  infants and about 80 in premature infants
• ECF decreases from 70 to 45
• At 32 wks gestation, TBW 83 and ECF 53

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Perinatal changes

• During the first week to 10 days of life,
  reduction in body weight is due to the reduction
  in the ECF
• Term infants- wt loss 5-10 within 3-5 days of
  birth
• LBW infants lose about 10-15 of body weight
  during the first 5 days of life
• Can lead to imbalances in sodium and water
  homeostasis

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Sodium balance in the
newborn

• Renal sodium losses are inversely proportional
  to gestational age
• Term infants have Fractional excretion of sodium
  1 with transient increases on day 2 and 3
• At 28 weeks- Fractional excretion of Sodium 5
  to 6
• Preterm infants lt35wks display negative sodium
  balance and hyponatremia during first 2-3 wks of
  life

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Sodium balance in the
newborn

• Preterm infants may need 4-5mEq/kg of sodium per
  day to offset high renal losses
• Increased urinary sodium losses
• hypoxia
• respiratory distress
• hyperbilirubinemia
• ATN
• polycythemia
• increased fluid and salt intake
• diuretics.

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Sodium balance in the
newborn

• Pharmacologic agents like dopamine, labetalol,
  propranolol, captopril and enalaprilat increase
  urinary sodium losses
• Fetal and postnatal kidneys exhibit diminished
  responsiveness to aldosterone compared to adult
  kidneys

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Water balance in the newborn

• Primarily controlled by ADH which enables water
  to be reabsorbed by the distal nephron collecting
  duct
• Stimulation of ADH occurs when blood volume is
  diminished or when serum osmolality increases
  above 285mOsm/kg
• Intravascular volume has a greater influence on
  ADH secretion than serum osmolality

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Renal concentration and diluting capacity

• Adults can concentrate urine up to 1500mOsm/kg of
  plasma water and dilute as low as 50mOsm/kg of
  plasma water
• Concentrating capacity is 800 mOsm/kg in term
  infants and 600 mOsm/kg in preterm
• Diluting capacity is 50 mOsm/kg in term and 70
  mOsm/kg in preterm
• Newborns have reduction in GFR and decreased
  activity of transporters in the early distal
  tubule

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Fluid requirements in the first
month of life

• Birth weight Water requirements
• D 1-2 D3-7
  D8-30
• lt750 100-200 150-200 120-180
• 750-1000 80-150 100-150 120-180
• 1000-1500 60-100 80-150 120-180
• gt1500 60-80 100-150 120-180

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Factors affecting insensible water losses in the
neonate

• Level of maturity
• Elevated body temperature increases loss by 10
• Radiant warmer - increased by 50 compared to
  thermo-neutral with high humidity
• Phototherapy increases losses by 50
• High ambient or inspired humidity - reduced by
  30
• Double walled isolette or plastic shield reduces
  losses by 10-30

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Electrolyte requirements

• Day 1-2
• Sodium or chloride are not provided in IVF due to
  high content of these electrolytes in body fluids
  (unless serum Na lt135 mEq/l)
• Potassium is not added until urinary flow has
  been established
• Day 3-7
• Na, K, Cl requirements are about 2-3mEq/kg/day
  for term infants and 3-5 mEq/kg per day for
  preterm infants
• After the first week
• 2-3mEq/kg/day of sodium and chloride are needed

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Monitoring fluid and electrolyte
balance

• Body weight
• Fluid intake
• Urine and stool output
• Serum electrolytes
• Urine osmolarity or specific gravity

• Oral mucosal integrity
• Heart rate and blood pressure
• Capillary refill
• Sunken anterior
• fontanelle

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Monitoring fluid and electrolytes

• During the first few days of life
• Urine output should be about 1-3ml/kg/hour
• SG of urine 1.008-1.012
• Wt loss of 5-8 in term and 15 in VLBW infants
• Monitor serum electrolytes at 8-24 hour intervals
• After the first week
• weight gain of 20-30gm/day
• Monitor electrolytes at intervals based on use of
  TPN

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Hyponatremia

• Serum sodium lt 130mmol/L
• Early onset in the first week is due to excess
  free water or increased vasopressin release
• perinatal asphyxia, respiratory distress,
  bilateral pneumothoraces, IVH
• Increased free water or suboptimal sodium in
  formula or IV fluids

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Congenital Adrenal Hyperplasia

• Cause
• Most common form of CAH is complete absence of 21
  hydroxylase activity
• Severe renal sodium wasting due to deficient
  aldosterone production and inhibition of sodium
  absorption in the distal nephron
• Symptoms
• Ambiguous genitalia, hyponatremia, hyperkalemia,
  and metabolic acidosis

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Congenital Adrenal Hyperplasia

• Treatment
• Normal saline or 3 saline used to correct the
  sodium to at least 125mEq/L, glucoseinsulin, and
  NaHCO3
• Glucocorticoid and sodium replacement

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Hyponatremia in late newborn

• Caused by negative sodium balance
• Excess renal losses, SIADH, renal failure, edema
• Low sodium intake, diuretics, mineralocorticoid
  deficiency (hypoNa, hyperK, metabolic acidosis,
  shock)
• Treat with water restriction and repletion of
  deficit

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Treatment of Hyponatremia

• Fluid restriction which results in a slow return
  to normal levels
• Urgent correction necessary if serum sodium is lt
  120 mEq/L b/c obtundation or seizure activity may
  develop
• Hypertonic saline 3, 6ml/kg infused over 1 hour
  (increases Na by 5 mEq/L)
• Administer to increase Na to 120-125mEq/L and
  eliminate seizures

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Correction of hyponatremia

• Based on sodium deficit X volume of distribution
  of sodium
• mEq Na needed (Goal Na-Serum Na) X TBW (60) X
  body weight in kg
• Prevents rapid correction (no more than 0.5
  mEq/L/h)
• mEq Na (140-serum Na) X 0.6 X body weight

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Hypernatremia

• Serum sodium gt 150mEq/L
• Most often in ELBW infants
• High rates of insensible water losses and reduced
  ECF volume
• Treat by reducing sodium administration and
  increasing free water
• Rapid correction of more than 0.5mEq/L/h should
  be avoided
• causes cerebral edema, seizures, and death

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Hypokalemia

• Serum Potassium lt 3mEq/L
• Causes
• Diuretic use, renal tubular defects, NG tube
  drainage, or ileostomy
• Can lead to weakness, paralysis, ileus,
  conduction defects (ST depression, low voltage T
  waves, U waves)
• Treat by increasing the intake by 1-2 mEq/kg
• If severe, 0.5-1mEq/kg is infused IV over 1 hour
  with EKG monitoring

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Hyperkalemia

• Serum potassium gt 6mEq/L
• Causes
• renal failure, CAH, IVH, cephalohematoma,
  hemolysis, excess administration
• EKG- Peaked T waves, flat P waves, increased PR
  interval, widening of QRS
• Bradycardia, SVT, VT may occur

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Treatment of Hyperkalemia

• D/C K in IVF
• Reverse the effect of hyperkalemia on the cell
  membranes
• infuse 10 Calcium gluconate (100mg/kg/dose)
• Promote movement of K from the ECF into the cells
• NaHCO3 1-2 mEq/kg IV over 5-10 min
• Insulin-0.05 units/kg with 2ml/kg/hr of D10
• Furosemide 1mg/kg/dose if there is adequate renal
  function to increase renal excretion
• Peritoneal dialysis in case of oliguria/anuria

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Fluid and electrolyte therapy in common conditions

• Perinatal asphyxia resulting in ATN
• Fluid restriction urine outputinsensible
  losses, no potassium
• Anuric term infant 30ml/kg/day
• Anuric preterm 80ml/kg/day
• If the cause of the anuria is unclear give
  10ml/kg of crystalloid or colloid