At the end of pregnancy, the fetus must take the journey of childbirth to leave the reproductive mother. Upon its entry to the air-breathing world, the newborn must begin to adjust to life outside the uterus. This is true for all viviparous animals; this article discusses humans as the most-researched example.
The outside environment is a drastic change for the neonate; therefore, the neonate must be assessed frequently and thoroughly. The Apgar scale is an assessment performed immediately following birth. It consists of assessing heart rate, respiratory effort, muscle tone, reflex irritability, and overall skin color. Apgar scoring is performed one minute and five minutes after birth. Scoring ranges from 0 to 10, with 0 indicating severe neonatal distress and 10 indicating a smooth transition to extrauterine life.
Newborns transitioning into extrauterine life will undergo periods of reactivity. These periods are divided into three stages. The first stage occurs in the first 30 minutes of life; during this stage, the infant is alert and responsive with heart rate peaking at 160–180 beats per minute and then stabilizes to a baseline rate of 100–120 beats per minute. Crackles upon auscultation and irregular respirations are a normal finding. In the second stage, there is a decrease in responsiveness and motor activity, often manifesting as sleep. This period can last from 1–2 hours. The third stage marks the second period of reactivity. This period can occur anywhere from 2 to 8 hours after birth and lasts from 10 minutes to several hours. Tachycardia and tachypnea may be present during brief periods. Passing of meconium also occurs. The left atrium now has higher pressure than the right atrium, causing the foramen ovale to close. Within the first 10 minutes of birth, blood begins to flow left-to-right through the ductus arteriosus. This causes a significant increase in the output of the left ventricle and an increase in stroke volume. Subsequently, calcium channel activity increases and potassium channel decreases, furthering ductal constriction. Functional closure of the ductus arteriosus occurs within the first 24 hours, with permanent closure following within 4 weeks. Lastly, cardiac output increases to nearly double what it was in utero.
All of these cardiovascular system changes result in the adaptation from fetal circulation patterns to an adult circulation pattern. During this transition, some types of congenital heart disease that were not symptomatic in utero during fetal circulation will present with cyanosis or respiratory signs.
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Manifestations
When the newborn cries, there is a reversal of blood flow through the foramen ovale, which causes the newborn to appear mildly cyanotic in the first few days of life.
The heart rate of the newborn should be between 110 and 160 beats per minute, and it is common for the heart rate to be irregular in the first few hours following birth. The heart sounds will have a variation in pitch, duration, and intensity than that of an adult. Blood pressure readings should range from 60 to 80 mm Hg systolic and 40–50 mm Hg diastolic. Mean arterial pressure should be the same as the weeks of gestation at birth. Within the first hour after birth, there may be a drop of up to 15 mm Hg in the systolic blood pressure.
Assessments/interventions
Assessment and monitoring of vital signs and skin color are important in detecting cardiovascular issues in the infant.
The apical pulse rate should be auscultated for one full minute when the newborn is calm or sleeping. Any irregular heart rate after the first few hours of life that is not related to crying or another outside factor should be monitored and evaluated.