FLUID ELECTROLYTE MANAGEMENT OF NEWBORN

FLUID AND ELECTROLYTE MANAGEMENT OF THE NEWBORN
Management goals
FE management is a balancing act between intake and output. Primary goals are to maintain the appropriate ECF volume, ECF and ICF osmolality, and ionic concentrations. Allow the initial loss of ECF over the first week, as reflected by weight loss, while maintaining normal intravascular volume and tonicity, as reflected by heart rate, urine output, and electrolyte and pH values. Subsequently, maintain water and electrolytes while supplying requirements for body growth. Individualize the approach rather than relying on a cookbook formula.

Total fluids required
Total fluid equals maintenance requirements (IWL plus urine plus stool water) plus growth requirements. In the first few days, IWL is the largest component of lost fluids. Later, as the renal solute load increases, the amount of water the kidneys need to excrete this load increases (80-120 cal/kg/d equals 15-20 mOsm/kg/d, which means that 60-80 mL/kg/d is needed to excrete wastes). Stool requirement usually is 5-10 mL/kg/d. As infants add tissue, they also need to add water to maintain normal ECF and ICF volumes. Since weight gain is 70% water, an infant growing 30-40 g/d requires 20-25 mL/kg/d of water.

Factors modifying fluid requirements
As the skin matures postnatally, the IWL decreases. Elevated body and environmental temperatures increase IWL. Radiant warmers increase IWL by 50%, phototherapy increases IWL by 50%, and the use of a plastic heat shield reduces IWL by 10-30%. Environmental humidification decreases IWL from the skin and respiratory mucosa by up to 30%. Skin breakdown and skin defects (eg, omphalocele) increase IWL proportionally to the area affected.

Electrolyte requirements
• For the first 12-24 hours, sodium, potassium, and chloride usually are not required.
• Later in the first week, needs are 1-2 mEq/kg/d for potassium and 2-4 mEq/kg/d for sodium and chloride.
• During the active growth period after the first week, needs for potassium increase to 2-3 mEq/kg/d, and for sodium and chloride to 3-5 mEq/kg/d.
• Some of the smallest preterm infants have sodium requirements as high as 6-8 mEq/kg/d because of the decreased capacity of the kidneys to retain sodium.

Fluids and electrolytes in common neonatal conditions
• Respiratory distress syndrome (RDS): Infants with RDS need appropriate fluid replacement. Administration of excessive fluid can lead to hyponatremia and volume overload, worsening the pulmonary condition and increasing the risk of developing bronchopulmonary dysplasia (BPD). Inadequate fluid administration leads to hypernatremia and dehydration
• Bronchopulmonary dysplasia: As a result of an increased work of breathing, infants with BPD have higher energy requirements. Diuretics often are prescribed in these infants, which can lead to electrolyte disturbances.
• Patent ductus arteriosus (PDA): Avoiding volume overloading is critical in infants with a PDA, since this often significantly worsens their respiratory status. This is especially important when indomethacin is prescribed to treat PDA, since indomethacin can decrease urine output significantly.
• Perinatal asphyxia: Infants who have experienced perinatal asphyxia usual have involvement of multiple organ systems. They are prone to acute tubular necrosis and significant oliguria, and the degree of CNS injury may produce the syndrome of inappropriate secretion of antidiuretic hormone (SIADH). Restricting fluid intake to minimize the risk of volume overload often is necessary.

Common electrolyte problems
• Sodium (Na)
o Hyponatremia is defined as a serum sodium level less than 130 mEq/L. Usually, this is not a cause for concern until the serum sodium has dropped to less than 125 mEq/L. Remember that hyponatremia usually results from excessive free water intake. However, especially in the extremely premature infant or infants with increased sodium losses, inadequate sodium intake can contribute to the development of hyponatremia.
o Hypernatremia is defined as a serum sodium level greater than 150 mEq/L. Usually, this is not a cause for concern until the serum sodium level has risen to greater than 150-155 mEq/L. Hypernatremia typically is seen in the first few days of life in ELBW micropremies and is most often the result of inadequate free water intake to compensate for very high IWLs. Very rarely, hypernatremia is the result of excessive administration of sodium in either the diet or intravenous fluids. The usual causes of excessive administration of sodium are administration of sodium bicarbonate to infants with pulmonary hypertension or metabolic acidosis in an effort to increase pH levels.

• Potassium (K)
o Remember that most of the potassium in the body is contained in the intracellular compartment; therefore, serum potassium levels often do not indicate total-body potassium stores accurately.
o Serum potassium levels also depend on blood pH levels, since pH affects the distribution of potassium between ICF and ECF compartments. A handy rule is that each 0.1 unit of pH change results in a 0.3-0.6 mEq/L change in the serum potassium level. The potassium level rises with acidosis, while it drops with alkalosis.
o Hypokalemia is defined as a serum potassium level less than 3.5 mEq/L. Unless the patient is receiving digoxin therapy, hypokalemia is rarely cause for concern until the serum potassium level is less than 3.0 mEq/L. Hypokalemia often results from chronic diuretic use and unreplaced electrolyte loss from NG drainage. ECG manifestations of hypokalemia include a flattened T wave, prolongation of the QT interval, or the appearance of U waves. Severe hypokalemia can produce cardiac arrhythmias, ileus, and lethargy. When significant, this condition is treated by slowly replacing potassium either intravenously or orally.
o Hyperkalemia is defined as a serum potassium level greater than 6 mEq/L, measured in a nonhemolyzed specimen. Hyperkalemia is of far more concern than hypokalemia, especially when serum potassium levels exceed 6.5 mEq/L or if ECG changes have developed. ECG manifestations of hyperkalemia are a progression from peaked T waves, as the earliest sign, to a widened QRS configuration, bradycardia, tachycardia, supraventricular tachycardia (SVT), ventricular tachycardia, and ventricular fibrillation. Causes of hyperkalemia include potassium release from damaged cells following intraventricular hemorrhage (IVH), trauma, and intravenous hemolysis. In addition, severe acidosis and decreased urinary potassium excretion contribute to elevations in serum potassium. Finally, hyperkalemia may be one of the earliest manifestations of congenital adrenal hyperplasia.
o Management of significant hyperkalemia may include the following:
�� All administration of potassium is discontinued.
�� Calcium gluconate 100-200 mg/kg (1-2 mL/kg of 10% solution) is administered as a slow IV infusion over 5-10 minutes.
�� Alkalinization is performed, either with hyperventilation or sodium bicarbonate 1-2 mEq/kg IV.
�� Insulin is administered to assist in driving potassium into the ICF compartment. Insulin must be administered with glucose as a combined infusion to avoid producing hypoglycemia.
�� Medications are administered to enhance potassium excretion, including furosemide 1 mg/kg IV or sodium polystyrene sulfonate (Kayexalate) 1 g/kg PR (do not use sorbitol-containing products and do not administer orally). Several hours must pass before any effect is observed with either of these medications.
�� Dialysis or exchange transfusion may be used to assist in more rapidly removing potassium from the body.

• Calcium (Ca)
o Total serum calcium levels in term infants decline from values of 10-11 mg/dL at birth to 7.5-8.5 mg/dL over the first 2-3 days of life. Approximately 50% of the total calcium is in the ionized form and is the only biologically available form of calcium. Ionized calcium values, rather than total values, correlate better with calcium functions, such as cardiac contractility. Therefore, many centers currently rely exclusively on measurements of ionized calcium.
o Calcium concentrations can be reported either in milligrams per deciliter (mg/dL) or in millimolar units (mmol/L). Conversion between the two methods is accomplished easily by dividing by 4 (eg, 4 mg/dL of ionized calcium equals 1 mmol/L)
o Hypercalcemia is rarely observed in neonates and is defined as a total serum calcium concentration higher than 11 mg/dL or an ionized calcium concentration higher than 5 mg/dL (1.25 mmol/L).
o Hypocalcemia occurs more commonly and is defined as a total serum calcium concentration less than 7 mg/dL or an ionized calcium concentration less than 4 mg/dL (1 mmol/L).
o Early-onset hypocalcemia may occur within the first 3 days in premature infants born to mothers with poorly controlled diabetes or in infants who experienced perinatal asphyxia. If the infant is asymptomatic and has a total serum calcium level higher than 6.5 mg/dL or an ionized calcium level higher than 0.8-0.9 mmol/L, close observation alone is appropriate. Calcium supplementation should be provided if the total serum calcium level is less than 6.5 mg/dL or if the ionized level is less than 0.8-0.9 mmol/L.
o Late-onset hypocalcemia develops after the first week of life and usually is associated with conditions with high serum phosphate levels, including hypoparathyroidism, maternal anticonvulsant use, and vitamin D deficiency. Vitamin D deficiency usually resolves with reduction of the renal phosphate load or vitamin D supplementation.

Common fluid problems
Oliguria is defined as a urine output less than 1 mL/kg/h. Oliguria can be caused by a variety of conditions that can be classified as prerenal, renal, or postrenal problems. Urine output often is less than 1 mL/kg/h during the first 12-18 hours after birth. Most healthy term babies urinate within the first 12 hours; however, a small number of healthy infants may not urinate until 24-36 hours after birth. Persistent oliguria beyond 36 hours should be evaluated in an otherwise healthy infant.