EVALUATION OF THE NEWBORNS BLOOD-GAS STATUS

Blood gas measurements and complementary, noninvasive monitoring techn iques provide the clinician with information essential to patient asse ssment, therapeutic decision making, and prognostication. Blood gas me asurements are as important for ill newborns as for other critically i ll patients, but rapidly changing physiology, difficult access to arte rial and mixed venous sampling sites, and small blood volumes present unique challenges. This paper discusses considerations for interpretat ion of blood gases in the newborn period. Blood gas measurements and n oninvasive estimations provide important information about oxygenation . The general goals of oxygen therapy in the neonate are to maintain a dequate arterial PaO2 and SaO2 and to minimize cardiac work and the wo rk of breathing. Pulse oximetry and transcutaneous oxygen monitoring a re extraordinarily useful techniques of estimating and noninvasively m onitoring the neonate's oxygenation, but each method has limitations. Arterial blood gas determinations of pCO(2) provide the most accurate determinations of the adequacy of alveolar ventilation, but capillary, transcutaneous, and end-tidal techniques are also useful. An approach to and examples of acid-base disorders are presented. Three hemoglobi n variants relevant to the newborn are considered: fetal hemoglobin, c arboxyhemoglobin, and methemoglobin. Blood gases obtained in the immed iate perinatal period can help assess perinatal asphyxia, but particul ar attention must be paid to the sampling site, the time of life, and the possible and proven diagnoses.