Physiologic variability during transition to extrauterine life.

The first 24 hours of life can be the most precarious in a person's lifespan. Physical changes occur so quickly during the transformation from fetus to neonate that any deviations from the expected need to be identified and acted on immediately to assist the baby toward successful adaptation to extrauterine life. Newborns respond to physiologic stress by becoming less responsive, often giving few cues that a problem is arising. Transition and physiologic stability have traditionally been measured in the time domain. However, heart beat or respiratory rate per minute are gross measures that do not reliably alert the health care provider to subtle signs of stress. Physiologic variability is mainly due to the interaction of the sympathetic and parasympathetic nervous systems. Patterns in the variability may be used as indexing variables for the assessment of neurophysiologic status. Linear and non-linear analysis of the variability promises to provide a sensitive, noninvasive measure for the identification of neurophysiologic stress that can better inform the health care provider of the fetal and neonatal response to stress.