Treatment of hypoxemia requires knowledge of normal values. In term infants, the arterial Pao2 level is 55 to 60 mm Hg at 30 minutes of life, 75 mm Hg at 4 hours, and 90 mm Hg at 24 hours. Preterm infants have lower values. Paco2 levels should be 35 to 40 mm Hg, and the pH should be 7.35 to 7.40. It is imperative that arterial blood gas analysis be performed in all infants with significant respiratory distress, whether or not cyanosis is perceived. Cyanosis becomes evident when there is 5 g of unsaturated hemoglobin; anemia may interfere with the perception of cyanosis. Jaundice also may interfere with the appearance of cyanosis. Capillary blood gas determinations are useful in determining blood pH and the Paco2 level but may result in falsely low blood Pao2 readings. Serial blood gas levels may be monitored by an indwelling arterial catheter placed in a peripheral artery or through the umbilical artery. Another method for monitoring blood gas levels is to combine capillary blood gas techniques with noninvasive methods used
Primary pulmonary hypertension of the neonate* Meconium aspiration pneumonia* Polycythemia Amniotic fluid aspiration
Bacterial sepsis (GBS)* Transient tachypnea* Spontaneous pneumothorax Congenital anomalies (e.g., congenital lobar emphysema, cystic adenomatoid malformation, diaphragmatic hernia) Congenital heart disease Pulmonary hypoplasia Viral infection (e.g., herpes simplex, CMV) Inborn metabolic errors
CMV, Cytomegalovirus; GBS, group B streptococcus. *Common.
Chest radiograph To determine reticular granular pattern of RDS; to determine presence of pneumothorax, cardiomegaly, life-threatening congenital anomalies
Arterial blood gas To determine severity of respiratory compromise, hypoxemia, and hypercapnia and type of acidosis; severity determines treatment strategy
Complete blood count Hemoglobin/hematocrit to determine anemia and polycythemia; white blood cell count to determine neutropenia/ sepsis; platelet count and smear to determine DIC
Blood glucose To determine presence of hypoglycemia, which may produce or occur simultaneously with respiratory distress; to determine stress hyperglycemia
Echocardiogram, ECG In the presence of a murmur, cardiomegaly, or refractory hypoxia; to determine structural heart disease or PPHN
DIC, Disseminated intravascular coagulation; ECG, electrocardiogram; PPHN, primary pulmonary hypertension of the newborn; RDS, respiratory distress syndrome.
to monitor oxygen (pulse oximetry or transcutaneous oxygen diffusion).