The management of infants with respiratory distress is a basic function of neonatal intensive care. Skillful use of the ever-increasing range of mechanical devices and pharmacologic agents in the treatment of respiratory disease depends on a sound knowledge of respiratory physiology and pathology. Optimal treatment continues to be difficult to define and considerable variability exists in assessing the risk–benefit ratio of various management strategies. This section provides an overview of current techniques used for neonatal respiratory support.
Assessing and monitoring respiratory status
Physical examination. The presence of following signs may be useful in recognizing respiratory distress. The absence of signs may be secondary to neurologic depression rather than absence of pulmonary disease.
Nasal flaring. One of the earliest signs of respiratory distress, nasal flaring may be present in intubated, ventilated patients as well.
Grunting. Commonly seen early in respiratory distress syndrome (RDS) and transient tachypnea, grunting is a physiologic response to end-expiratory alveolar collapse. Grunting helps maintain functional residual capacity (FRC) and therefore oxygenation.
Retractions. Intercostal, subcostal, and sternal retractions are present in conditions of decreased lung compliance or increased airway resistance and may persist during mechanical ventilation if support is inadequate.
Tachypnea. A respiratory rate >60/min implies the inability to generate an adequate tidal volume and may persist during mechanical ventilation.
Cyanosis. Central cyanosis indicates hypoxemia. Cyanosis is difficult to appreciate in the presence of anemia. Acrocyanosis is common shortly after birth and is not a reflection of hypoxemia.
Abnormal breath sounds. Inspiratory stridor, expiratory wheezing, and rales should be appreciable. Unfortunately, unilateral pneumothorax may escape detection on auscultation.
Blood gases. Management of ventilation, oxygenation, and changes of acid-base status is most accurately determined by arterial blood gas studies.
Arterial blood gas studies are the most standardized and accepted measure of respiratory status, especially for the oxygenation of low birthweight infants. They are considered invasive monitoring and require arterial puncture or an indwelling arterial line. Access is now considered routine by the umbilical artery or peripherally in the radial or posterior tibial artery.
Normal arterial blood gas values may not be the same as target values for particular patients, nor acceptable values. Table 7–1 lists examples of normal values for infants.
Calculated arterial blood gas indexes for determining progression of respiratory distress are as follows:
Alveolar-to-arterial oxygen gradient (AaDo2) of >600 mm Hg for successive blood gases over 6 h is associated with high mortality in most infants if treatment and ventilation do not become effective. The formula for AaDo2 is
where Pb = barometric pressure (760 mm Hg at sea level), 47 = water vapor pressure, PaCO2 is assumed to be equal to alveolar PCO2, and R = respiratory quotient (usually assumed to be 1 in neonates).
Arterial-to-alveolar oxygen ratio (a/A ratio) is also an index for effective respiration. The a/A ratio is the most often used index for evaluation of response to surfactant therapy and is used as an indicator for inhaled nitric ...
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