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 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%

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

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

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.

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

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

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

Fluid requirements in the first month of life Birth weight Water requirements D 1-2 D3-7 D8-30 < >

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%

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

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

Monitoring fluid and electrolytes During the first few days of life Urine output should be about 1-3ml/kg/hour SG of urine 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

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

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

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

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

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 mEq/L and eliminate seizures

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

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

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

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

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

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