ABSTRACT
The neonate, infant, child, and adolescent differ significantly from each other and from the adult. The most distinctive and rapidly changing physiologic characteristics occur during the neonatal period. This is due to the newborn infant’s adaptation from complete placental support to the extrauterine environment, differences in the physiologic maturity of individual neonates, the small size of these patients, and the demands of growth and development. Recent advances in neonatal care have resulted in the survival of increasing numbers of extremely low birth-weight (LBW) infants. Extreme prematurity magnifies the already dynamic and relatively fragile physiology of the newborn period, predisposing these tiny infants to physiologic derangements in temperature regulation, fluid and electrolyte homeostasis, glucose metabolism, hematologic regulation, and immune function. In addition, physiologic and anatomic organ system immaturity makes the preterm neonate vulnerable to specific problems such as intraventricular hemorrhage, hyaline membrane disease, and hyperbilirubinemia. From a surgical standpoint, these dynamic and fragile physiologic parameters are often the primary components that dictate the preoperative and postoperative management of the neonatal surgical patient. This chapter focuses on the physiology of the neonate undergoing surgery, highlighting the practical considerations of preoperative and postoperative management.
