Surfactant replacement was established decades ago as an efective and safe therapy for RDS. Treatment reduces rates of mortality and pneumothorax and improves survival without BPD (Polin, 2014). It has been used for prophyxis of preterm, at-risk newborns and for rescue of those with established disease. Given together, antenatal corticosteroids and surfactant result in an even greater reduction in the overall death rate. However, randomized trials indicate that in populations with high use of antenatal steroids and routine use of CP P in the delivery room, prophylactant surfactant is no longer beneficial and is associated with more risk of death or BPD (Rojas-Reyes, 2012; Sardesai, 2017). Exploration of diferent, less invasive ways to deliver rescue surfactant to spontaneously breathing preterm neonates is currently underway. Potential routes include surfactant application into the pharynx, surfactant nebulization, or application via laryngeal mask or via a thin catheter placed in the trachea (Kribs, 2016).
The NIH (1994, 2000) has concluded that a single course of antenatal corticosteroid therapy reduces RDS and intraventricular hemorrhage rates in preterm neonates born between 24 and 34 weeks' gestation (p. 640). he American College of Obstetricians and Gynecologists (2016a) considers all women at risk for preterm birth in this gestational-age range to be potential candidates for therapy. It also may be considered for pregnant women starting at 23 weeks' gestation who are at risk of preterm delivery within 7 days. his is discussed further is Chapter 42 (p. 823). More recently, administration of antenatal corticosteroids to women at risk for late-preterm delivery (34 to 36 weeks' gestation) was found to significantly reduce the rate of neonatal respiratory complications (Gyami-Bannerman, 2016).
Amniocentesis to Assess Fetal Lung Maturity
In some instances, when gestational age is uncertain, knowledge of fetal lung maturity may inluence plans for delivery. One example is the woman with a prior classical cesarean delivery in whom repeat operation is planned and gestational age cannot be confirmed. Several tests are used to ensure fetal pulmonary maturity by analysis of amnionic fluid obtained by sonographically guided amniocentesis. At Parkland Hospital, we still find an occasional indication for such testing, however, the American College of Obstetricians and Gynecologists (2017 a, b) counsels against its use in most of these cases. Instead the College recommends late-term delivery at "41 weeks' gestation" using the best clinical estimate of gestational age (Chap. 10, p. 183).
If amniocentesis is elected, luid acquisition is similar to that described for second-trimester amniocentesis (Chap. 14, p. 292). Complications requiring urgent delivery are rare (Zalud, 2008). Following analysis, the probability of RDS developing in a given newborn depends on the test used and fetal gestational age. Importantly, administration of corticosteroids to induce pulmonary maturation has variable efects on some of these tests. Varner and colleagues (2013) have provided a review of testing options.
Of biochemical tests, the labor-intensive lecithin-sphingomyelin (LIS) ratio for many years was the gold-standard test.
2•..J• .-E c.o .-8 8c .0ll,� 2
FIGURE 34-1 Changes in mean concentrations of lecithin and sphingomyelin in amnionic fluid during gestation in normal pregnancy. (Modified with permission from Gluck L, Kulovich MV: