Fluid Management in Transient Tachypnea of the Newborn

1. Project Abstract Transient tachypnea of the newborn (TTN) is a self-limited respiratory distress syndrome of term and late pre-term neonates.1 Respiratory distress attributed to TTN requires management of otherwise healthy infants in an intensive care setting, thus increasing cost, and often length, of hospitalization as well as decreasing opportunity for parent-child bonding in the first days of life. Although hundreds of thousands of children are treated for TTN every year (over 250 in the Mount Sinai NICU in 2005 alone), little data underlie standard of care medical management. We are conducting a prospective study of neonates diagnosed with TTN to determine if changes in fluid management affects course of disease.
2. Specific Aims To determine whether fluid restriction in the first 72 hours of life speeds resolution of respiratory distress in neonates diagnosed with TTN.
3. Concise statement of Significance/Background Transient tachypnea of the newborn (TTN) is a self-limited respiratory distress syndrome of term and late pre-term neonates.1 Newborns with TTN develop clinical signs of respiratory distress within the first hours after birth, in the absence of other pathology such as surfactant deficiency, infection, meconium aspiration, or anatomic cardiac or pulmonary anomaly. Signs of TTN include tachypnea (respiratory rate consistently > 60), subcostal, intercostals, and suprasternal retractions, nasal flaring, grunting, and hypoxia correctable with low FiO2 supplemental oxygen (< 0.40) via conventional nasal cannula or continuous positive airway pressure (CPAP). The condition usually resolves with supportive care within 72 hours without significant long-term adverse sequelae. Transient tachypnea of the newborn is associated with transient pulmonary edema diagnosed by typical chest x-ray findings. The traditional explanation for postnatal pulmonary edema is poor clearance of fluid from the fetal lungs in the perinatal period. Retained fluid leads to bronchioalveolar collapse with variable areas of hyperinflation and air trapping in the neonatal lung. The newborn compensates for this ventilation/perfusion mismatch with tachypnea and increased work of breathing, but often cannot completely compensate, becoming hypoxic through the period of fluid reabsorption. This pathophysiologic argument has been supported by the findings that brief or absent labor and short or absent time in the birth canal have been associated with TTN.2, 3 It has long been hypothesized that mechanical forces of labor and delivery work to "squeeze" edema away from air-exchange surfaces of the lung into the lymphatics. More recently, studies have demonstrated that immaturity of sodium ion channel transporters in the lung epithelium may play a more significant role in the failure of pulmonary fluid reabsorption than mechanical forces.4, 5 Data from animal models show that absent labor, such as found in scheduled Cesarean sections, may lead to delivery before the normal hormonally-mediated upregulation or activation of these sodium transporters occurs and thus may explain the increased likelihood of developing TTN seen in this patient cohort. Conditions that increase central venous pressure or decrease thoracic duct clearance have also been associated with TTN.6 Additionally, maternal diagnosis of asthma7 or gestational diabetes8 and male gender of the newborn9 have been associated with TTN, although the mechanism of these associations is incompletely understood. Although TTN is an exceedingly common cause of newborn morbidity, it is relatively understudied. Due to the low mortality of TTN there has been little interest in investigating either the range of pathologies underlying the clinical presentation of TTN or the evidence base behind the standard of care treatments of TTN. The high incidence of TTN and the significant increase in hospital care acuity and length of stay to otherwise healthy infants diagnosed with TTN, however, indicates a need for study.10 As the rate of Cesarean section and late pre-term delivery,11 as well as maternal morbidities such as asthma12 and gestational diabetes,13 rise it is particularly important to minimize the morbidity and cost of TTN. A better understanding of the pathogenesis of TTN and a thorough evaluation of current treatment strategies and their relationship to timely patient discharge is sorely needed.
4. Concise statement of Preliminary Data (if available) No evidence base underlies current fluid management of neonates with TTN. Data exists demonstrating the inefficacy of loop diuretics as treatment for pulmonary fluid overload in newborns with TTN,14 but no systematic evaluation of intravenous fluid management exists. Exclusively breastfed babies typically have minimal fluid intake during the first four days of life as lactogenesis II (initial postpartum milk production) proceeds. Enteral intake by term infants begins at less than 100mL in the first day (equivalent to 40mL/kg for a 2.5kg neonate; this represents a term newborn at the 5th percentile or a 34 week gestational age newborn at the 70th percentile for weight) and increase gradually until milk production reaches sustenance levels, usually around the fourth day of life.15 Regardless of gestational age, all neonates lose water weight during the first week of life during physiologic diuresis of extracellular fluid accumulated throughout gestation.16 Current management of both preterm and term neonates includes an effort to facilitate this physiologic diuresis by gradually increasing amounts of IV fluids until maintenance levels are reached between the third and fifth day of life. 17, 18
5. Research Design and Methods In this study, we will conduct a prospective study of 68 neonates born between 34 and 42 weeks gestation diagnosed with TTN and managed in the Mount Sinai Neonatal Intensive Care Unit (NICU). The study period will include the first three days (72 hours) of life. On admission to the NICU, parents will be consented for their child's inclusion in the study. If consent is given, the child will be randomized to "standard fluids" or "physiologic fluids" groups. "Standard fluids" refer to current standard clinical practice of IV fluid administration, not based on experimental evidence. "Physiologic fluids" refers to IV fluid amounts more similar to fluid volumes typically ingested during initiation of breastfeeding. Term infants assigned to the "standard fluids" group will be started on 60 mL/kg/day of glucose-containing intravenous fluids as is standard practice. Term infants assigned to the "physiologic fluids" group will be started on 40 mL/kg/day glucose-containing intravenous fluids. Late preterm infants (gestational age between 34 and 37 weeks) assigned to the "standard fluids" group will be started on 80 mL/kg/day of glucose-containing intravenous fluids as is standard practice. Late preterm infants (gestational age between 34 and 37 weeks) assigned to the "physiologic fluids" group will be started on 60 mL/kg/day glucose-containing intravenous fluids. For all groups, intravenous fluid rate will be increased by 20 mL/kg/day daily, as is current standard practice. Consistent with current standard management for newborns with respiratory distress, no infant will be allowed to take oral nutrition until respiratory distress abates. Newborns will be carefully monitored, and infants in the "physiologic fluid" group will be removed from the study and total daily fluids will be increased if they show signs of dehydration. Primary outcomes will be duration of respiratory distress, defined as respiratory rate consistently greater than 50 breaths/minute and oxygen saturation on room air consistently less than 95%. Secondary outcomes will be length of time to first oral feed and time to discharge from the intensive care unit.

This research poses a minor increase over minimal risk for subjects enrolled in the intervention group. The anticipated risks include mild dehydration and/or hypoglycemia of neonates in the "physiologic fluid" intervention group. This risk is minor as all newborns in the NICU have urine output recorded every three hours, point-of-care glucose monitoring on admission and at least once every twelve hours thereafter, and serum electrolytes checked between 12 and 24 hours of life. If neonatal dehydration is noted as defined by urine output < 2mL/kg/hour over a twelve hour period, serum sodium < 130 mEq/L or > 150 mEq/L, weight loss of more than 10% of birth weight, or blood glucose by point-of-care testing of < 40 mg/dL, the child will be removed from the study and appropriate fluid resuscitation will be initiated. These guidelines for removal from the study are the same as or more conservative than criteria used for rehydration in clinical care, so long-term adverse sequelae of this level of brief mild dehydration or hypoglycemia are not expected.