Neonatal Physiology

The neonate has many unique physiologic characteristics that set it apart from older children and adults. Many of these differences arise from the requirements for fetal growth and development and the abrupt transition from fetal to extrauterine life. All organ systems are impacted, with critical implications for medical management. Understanding the unique features of the neonate is essential for the safe anesthetic care of these patients. This chapter reviews fetal development of the different organ systems, along with their function during the neonatal period. Placental physiology as it pertains to anesthetic management will be reviewed. Special attention will be paid to transitional cardiac and respiratory physiology as well as neonatal respiratory mechanics. Renal acid–base maintenance, fluid and electrolyte management, hematologic and neurologic systems will be discussed. Emphasis is on the term neonate, although preterm neonatal physiology is also briefly reviewed. Common neonatal disease states are also covered. The goal is for the anesthesia practitioner to gain a greater understanding of the unique aspects of the neonate so that they may better care for this vulnerable subset of patients. This review contains 8 figures, 13 tables, and 52 references. Key Words: apnea of prematurity, chronic lung disease, infant lung mechanics, intraventricular hemorrhage, neonate, patent ductus arteriosus, patent foramen ovale, persistent fetal circulation, transitional circulation, retinopathy of prematurity