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Fluids and Electrolytes in the Newborn

Fluids and Electrolytes in the Newborn. Vandana Nayal. Body fluid composition in the fetus and newborn. Total Body Water = ICF + ECF (Intravascular+Interstitial) As gestational age increases, TBW and ECF decrease while ICF increases

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Fluids and Electrolytes in the Newborn

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  1. Fluids and Electrolytes in the Newborn Vandana Nayal

  2. Body fluid composition in the fetus and newborn • Total Body Water = ICF + ECF (Intravascular+Interstitial) • 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%

  3. 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

  4. 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 <35wks display negative sodium balance and hyponatremia during first 2-3 wks of life

  5. 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.

  6. 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

  7. 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

  8. 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

  9. Fluid requirements in the first month of life Birth weight Water requirements D 1-2 D3-7 D8-30 <750 100-200 150-200 120-180 750-1000 80-150 100-150 120-180 1000-1500 60-100 80-150 120-180 >1500 60-80 100-150 120-180

  10. 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%

  11. 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 <135 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

  12. 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 Monitoring fluid and electrolyte balance

  13. 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

  14. Hyponatremia • Serum sodium < 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

  15. 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

  16. Congenital Adrenal Hyperplasia • Treatment • Normal saline or 3% saline used to correct the sodium to at least 125mEq/L, glucose+insulin, and NaHCO3 • Glucocorticoid and sodium replacement

  17. 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

  18. Treatment of Hyponatremia • Fluid restriction which results in a slow return to normal levels • Urgent correction necessary if serum sodium is < 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

  19. 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

  20. Hypernatremia • Serum sodium > 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

  21. Hypokalemia • Serum Potassium < 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

  22. Hyperkalemia • Serum potassium > 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

  23. 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

  24. Fluid and electrolyte therapy in common conditions • Perinatal asphyxia resulting in ATN • Fluid restriction = urine output+insensible 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

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