Neonatology is defined as a subspecialty of pediatrics that comprises the care of a newborn infant child especially the ill and premature. Specifically, a newborn is a child under 28 days of age.
Population of Newborn Infants in the United States
There are around 4 million births each year in the United States. Of these, around 10 % (or 400,000) require some kind of intervention at the moment of birth. Of this 10 %, 10 % (or 1 % of the total population) require resuscitation at birth. As such, it is imperative for medical students to be comfortable with all manner of newborn interventions, not limited to resuscitation.
Risk Factors for Needing Resuscitation at Birth
There are a number of risk factors you should be aware of that increase the probability of an infant needing resuscitation at birth. These are divided below into pregnancy and labor risk factors. Women with a high-risk pregnancy will be flagged prior to labor, but women whose pregnancy becomes complicated during labor need a watchful eye to identify if the birth is high-risk for the child needing resuscitation.
Pregnancy risk factors:
- Multiple gestations (e.g. twins, triplets)
- Maternal infection (blood should be collected from the mother, serial blood tests may be required to monitor progression)
- Magnesium for preterm labor (premature newborns are likely to develop “floppy baby syndrome” and many need resuscitation)
- Maternal substance abuse (should be flagged in pre-labor questioning) or use of depressive anesthetics and analgesics such as opioids
Labor-associated risk factors:
Breech presentation: This is generally described as a fetal presentation in which the buttocks or feet lie closest to the cervix. The standard and most common birthing position is described as cephalic and occurs when the child is born head first. A breech presentation has an increased risk of complications (e.g. fetal hypoxia) and, as such, is a risk factor for infant resuscitation.
- Failure to progress: This is generally described as labor that has continued for more than 20 hours with little dilation (or dilation between 1-2 cm per hour). Many of these women will never reach full dilation and an emergency C-section is required. However, if a vaginal delivery is achieved, the newborn is at a significantly increased chance of being in distress and requiring resuscitation.
- Nuchal cord: occurs when the umbilical cord becomes wrapped around the newborn’s neck. This is reasonably common and most will spontaneously resolve before the delivery. However, this can have significant mortality and morbidity and is a significant risk factor for infant resuscitation upon birth.
Meconium-stained liquor or stained amniotic fluid: meconium is the infant’s first stool. It is often described as “green and tenacious”. Amniotic fluid that is stained with meconium indicates that an infant has passed meconium while in the womb and is typically in distress; as such, the probability they will require resuscitation upon birth is significantly increased. In a healthy neonate, meconium is passed after labor.
- Chorioamnionitis: This is an inflammation of the fetal membranes (the amnion and chorion), which can be due to an infection. The infection is usually bacterial in nature. In women with a prolonged labor, the risk to the fetus increases significantly and is one reason prolonged labor is not advised.
- Placental abruption/previa: placenta previa is an abnormal location of the implantation site of the placenta, in which it is inserted lower down in the uterus; possibly partially or fully covering the cervix. In some cases of placenta previa, a vaginal delivery is, in fact, possible but the risk of newborn resuscitation is increased. In many, an emergency C-section may have to be performed. Rupture of the placenta denies the infant the only source of nourishment and, thus, the newborn is likely to be in distress.
Development of the chambers of the heart during pregnancy
Embryology is a crucial part of the clinical practice of neonatology and needs to be refreshed.
The septation of the chambers of the heart proceeds as follows. To begin with, the septum primum grows upwards toward the endocardial cushions which narrow the previously formed foramen primum, then the second foramen (foramen secundum) forms in the septum primum. The septum secundum develops. Whilst this occurs, there is a right-to-left shunt which is maintained by the foramen secundum. The septum secundum grows to cover most of the foramen secundum; the hole left behind is the foramen ovale. When it does not close after birth, this is known as a patent foramen ovale.
It is also important to remember that the septum secundum and septum primum eventually fuse with each other making the atrial septum. As evidenced below, the foramen ovale will close after birth because of the pressure in the left atrium (which stops the right-to-left shunting).
The ventricles form in a far simpler series of events. Firstly, the muscular ventricular septum forms. The opening of this is called the interventricular foramen. The aorticopulmonary septum then fuses (via rotation) with the ventricular septum; this closes the interventricular foramen. A ventricular septal defect can form. This usually arises from the membranous septum. Again, these defects are important to remember and a solid understanding of embryology will leave you in good stead to understand congenital defects and their relevant symptomatology often seen in neonates.
In the fetus, blood from the right ventricle mainly flows through the ductus arteriosus, bypassing the lungs. This is because the lungs are full of fluid and the fetus does not receive oxygenated blood via gas exchange. Blood in the inferior vena cava mainly passes through the foramen ovale. Blood from the superior vena cava mainly flows into the right ventricle. The deoxygenated blood is not disposed of in the lungs but, in fact, crosses the placenta via the umbilical arteries. The mother will eliminate the deoxygenated blood through her systemic circulation and provide the fetus with oxygenated blood through the umbilical vessels.
Physiology of Birth
The first breath of the infant causes a rapid expansion of the lungs. This hugely decreases the resistance in the pulmonary vasculature. Via active transport, fluid is rapidly pulled out of the airspace through osmosis and into the interstitium. Oxygen causes a rapid dilatation of the pulmonary arteries which, in turn, decreases the pulmonary vascular resistance.
At this point, the sympathetic nervous system increases systemic vascular resistance. The differences in vascular resistance result in the transformation from fetal to adult circulation with the patent ductus arteriosus and patent foramen ovale closing definitively over the first 1 – 2 days. After its close, the foramen ovale is referred to as the fossa ovalis. The ductus arteriosus will then close due to an increase in oxygen. There is also a decrease in the concentration of prostaglandins due to placental abruption. The prostaglandins PGE1 and PGE2 kept this ductus arteriosus open during pregnancy and their decreasing concentration results in the closure of this foramen.
Make sure you have obtained information about the prenatal history and delivery history. This includes a full history of the mother’s past medical history (e.g. previous cerebrovascular events) and social history (e.g. intravenous drug use, HIV-status). The room should be set accordingly. There should be a warmer on standby, clean and dry cloth for drying, suction, airway equipment, etc. The physician should also know the gestational age and estimated weight in advance.
The first 60 seconds
Once the child is born, ask yourself three critical questions:
- Is the infant full term?
- Does the infant have a good tone?
- Is the infant breathing or crying?