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Chapter 39. Neonatal Respiratory Distress Syndrome and Sudden Infant Death Syndrome

Amniotic fluid from a 30-weeks' gestation fetus shows a lecithin/sphingomyelin ratio of 1.5 and is negative for phosphatidylglycerol. The attending obstetrician had planned to give betamethasone to the mother, but the baby delivers before the drug could be administered. The newborn infant is placed on mechanical ventilation with FIO2 = 1.00 and an AP chest x-ray is ordered. Ten minutes later, arterial blood gases show pHa = 7.26, PaCO2 = 58 mm Hg, PaO2 = 65 mm Hg, HCO3 = 25 mM. Which of the following statements about this patient is most accurate?

a. The low PaO2 despite breathing 100% O2 suggests the infant is anemic.

b. The infant has primary metabolic alkalosis with compensatory respiratory acidosis.

c. Placing the endotracheal tube will decrease this infant's V̇D (L/min).

d. The PPEAK needed to achieve a specific VT will likely decrease after surfactant is administered.

e. Additional doses of surfactant are required for several weeks.

The most correct answer is d.

The PPEAK required to sustain any given VT will decline when surfactant dosing has been successful, due to the rapid reduction in alveolar surface tension; additional doses beyond the first or second day are usually unnecessary (answer e). Although CaO2 declines in anemia, PaO2 usually does not (answer a, Chap. 3). The infant has primarily respiratory acidosis (answer b) likely due to diffusion block, and adding only an endotracheal tube will increase VD rather than decrease it (answer c).

A 5-month-old infant is found dead one early morning in his crib. Physical exam is unremarkable except for the presence of petechial patches, and a diagnosis of SIDS is made. The pathologist speculates that this death could have been the result of a 'fetal inhibitory reflex'. Which of the following statements supports such a conclusion?

a. The diving response utilizes brain receptors shown to induce SIDS.

b. The diving response inhibits the chemoreceptive drive for respiration.

c. The laryngeal chemoreceptor reflex (LCR) stimulates inspiration in neonates.

d. Redistribution of blood flow during a diving response causes brain hypoxia.

e. Inhibitory reflexes cause tachycardia and systemic hypertension, inducing petechia.

The most correct answer is b.

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