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Cole The Case of the Premature Infant Case Presentation Rep Wendy was a pregnant 27-year-old. She was estimated to be at 35 weeks pregnancy. Wendy had been having labor pains the last few days, and her cervix was dilating. Her doctor, Dr. Pratt, was concerned, justifiably so. "You may be going into premature labor," she explained to Wendy. "Our main concem is that your baby's lungs are ready to breathe when baby enters the world. We are going to take a sample of amniotic fluid to test the maturity of baby's lungs." Dr. Pratt took a ample of amniotic fluid and sent it to the laboratory for surfactant analysis. The lab sent back the results as "L:S (lecithin:sphingomyelin) ratio 1.5:1." Dr. Pratt came into Wendy's room to talk to her. "Our tests show that baby's lungs are not yet fully mature, but there is a good chance that if you do deliver early we can help your baby with oxygen if need be, and baby should have a good chance." Wendy delivered the next day. The baby had APGAR scores of 5 and 7 at 1 and 5 minutes after delivery. respectively. Because Dr. Pratt was concerned that the baby had respiratory distress syndrome (RDS), she bad a sample of arterial blood analyzed for blood gases. The blood gas results were pH 7.25 (low), P.CO, 52 (elevated), P.0, 78 (decreased), HCO, 14 (decreased). The baby was sent to the neonatal intensive care unit (NICU) for careful treatment of infantile respiratory distress syndrome (IRDS. RDS). The baby was placed in a warm, humidified chamber. Nasal prongs were placed on the baby's nose and CPAP (continuous positive airway pressure) oxygen delivery was administered. Serial blood gas measurements would be followed to ascertain baby's lung maturation, Case Background Respiratory distress syndrome (RDS) is a condition in which the lung alveoli collapse and contain fluid in place of air. It can occur in both infants and adults. Adult respiratory distress syndrome (ARDS) occurs following trauma for reasons not entirely understood. Infantile respiratory distress syndrome (IRDS, RDS, hyaline membrane disease) occurs in premature infants born with immature lungs. Whether ARDS or IRDS, alveoli filled with fluid lead to improper oxygenation of blood. Lung alveoli are composed of several types of cells. Type I alveolar cells are simple squamous epithelium across which gas diffusion occurs, between blood and the air in the alveoli. Lung macrophages also exist in the alveoli to clean up any debris in the alveoli. Type II alveolar cells are hin; they
delivery was administered. Senal blood gas measurements would be followed to ascertain baby's lung maturation. Case Background Respiratory distress syndrome (RDS) is a condition in which the lung alveoli collapse and contain fluid in place of air. It can occur in both infants and adults. Adult respiratory distress syndrome (ARDS) occurs following trauma for reasons not entirely understood. Infantile respiratory distress syndrome (IRDS, RDS, hyaline membrane disease) occurs in premature infants born with immature lungs. Whether ARDS or IRDS, alveoli filled with fluid lead to improper oxygenation of blood. Lung alveoli are composed of several types of cells. Type I alveolar cells are simple squamous epithelium across which gas diffusion occurs, between blood and the air in the alveoli. Lung macrophages also exist in the alveoli to clean up any debris in the alveoli. Type II alveolar cells are somewhat cuboidal, yet thin; they manufacture an important substance that reduces surface tension between the walls of the alveoli, helping to keep alveoli from remaining in a collapsed condition. That substance is surfactant, an acronym for surface acting detergent. Surfactant contains various wetting and emulsifier agents such as lecithin and sphingomyelin. Without adequate surfactant, collapsed alveoli would have great difficulty reopening following expiration. When an alveolus collapses on expiration, water molecules on opposite walls of the alveolus can hydrogen bond to each other (H20: :: H20), making it very difficult for the alveolus to reopen upon inspiration (the same phenomenon occurs when two pieces of plate glass having a film of water between them are held together by hydrogen bonding). Surfactant, coating the walls of the alveoli, greatly decreases hydrogen bonding. Premature infants have lungs in which the type Il cells do not make enough surfactant. In addition, the surfactant produced is not of the proper mixture of molecular substances. With collapsed alveoli, there exists a great deal of negative pressure in the alveoli when the newborn attempts to inspire air. This negative pressure draws fluid from the lung capillaries into the alveoli making them "wet." A biopsy specimen of the wet alveoli shows the walls of the alveoli to resemble ground glass, hence the alternative term for RDS-hyaline (Greek hyalos, glass) membrane disease of the newborn. Mature surfactant (surfactant with maximal function) should have a ratio of lecithin to sphingomyelin of 2:1, more commonly reported as LS 2:1. If the L:S ratio is 1: 1 the fetus will probably not survive outside the womb; the lungs would remain collapsed and gas exchange would be minimal. A LS ratio of 1.5:1 implies that the fetus might survive outside the womb; with proper supportive care. Surfactant from the alveoli will diffuse out to the amniotic fluid that the fetus is immersed in. Because the amniotic fluid freely diffuses into and out of the fetal lungs, a sampling of the amniotic fluid by amniocentesis can be performed if needed to determine the L:S ratio.
needed to determine the L:S ratio. A newborn infant should be checked at 1 and 5 minutes using what is called the APGAR score. APGAR is an acronym standing for appearance, pulse, grimace. activity, and respiration. The scoring is done as follows: If the infant scores low on color and pulse, there is a good chance that the infant may have lung immaturity. The 5 minute APGAR score is more important than the 1 minute score. An infant with RDS and low APGAR scoring is normally placed in a warm, humidified chamber and given oxygen by nasal prong. If the RDS is serious, continuous positive airway pressure (CPAP) can be given. CPAP helps prevent collapse of alveoli. Arterial blood gases (usually obtained from umbilical vessel catheterization) can be followed to ascertain treatment effectiveness. Questions 1. What important molecule does the lung make to prevent collapsed alveoli? What cell makes this molecule? Explain why lung alveoli would remain collapsed without the production of this molecule. 2. What do the following L:S ratios imply: 1:1, 1.5:1, 2:1? Would a premature infant born with any of the listed L:S ratios be likely to survive outside of the womb? Explain each condition. 3. What do the baby's initial blood gas values indicate in terms of lung function? Are oxygen and carbon dioxide being properly exchanged? 4. Name three cell types in a lung alveolus, then state the primary function of each. 5. What is an APGAR score and how does it inform Dr. Pratt about the baby's condition? 6. What happens to the alveoli that cause it to be referred to as hyaline membrane disease?