22.3: Physiological Adaptation and Transition
By the end of this section, you will be able to:
- Describe the newborn’s physiologic adaptation to extrauterine life
- Identify cardiac and respiratory physiologic adaptation changes that occur during the transition to extrauterine life and stabilization
- Compare and contrast neonatal periods of reactivity in the immediate period post birth
For the nurse to understand and recognize abnormal events in the newborn immediate period after birth, they must first understand the normal changes in physiology that occur within the first several hours of life. In those first hours, tremendous respiratory and circulatory adaptations occur to allow the newborn to transition from intrauterine life to extrauterine life. This transition is the most complex physiologic adaptation that occurs in any human body system in their lifetime. The nurse responsible for monitoring the newborn needs to have a solid knowledge base about normal physiologic adaptation and accurate assessment skills to recognize any alteration in normal adaptation.
Fetal Circulation
While the fetus is in utero, the placenta acts as a gas-exchange organ. The fetal lungs are bypassed during development in the womb. Oxygen from the birthing person’s blood crosses the placenta and enters the fetal bloodstream through the umbilical vein. The oxygenated blood in the umbilical vein bypasses hepatic circulation and is delivered to the inferior vena cava (IVC) via the ductus venosus. The ductus venosus is a fetal shunt allowing oxygenated blood in the umbilical vein to bypass the liver. The oxygenated blood is then shunted from the right atrium to the left atrium through a second shunt called the foramen ovale (Elshazzly et al., 2022). From the left atrium, the oxygenated blood then travels to the left ventricle and into coronary arteries and the aorta (Elshazzly et al., 2022). A tiny amount of blood from the right atrium bypasses the foramen ovale and flows through the right atrium to the right ventricle into the pulmonary artery to perfuse the fetal lungs and promote lung development. Most of the blood goes from the pulmonary artery directly to the aorta via a third shunt, the ductus arteriosus. From there, the oxygenated blood is delivered to the fetus’s systemic circulation (Elshazzly et al., 2022). Figure 10.18 summarizes fetal circulation .
Many changes occur at the time of birth. The fetal circulation structures become unnecessary as the birthing person draws closer to the actual birthing event. Two main triggers induce the structural changes: cessation of blood flow within the placenta and initiation of respiration. The structural changes that occur are listed in Table 22.2, and Figure 22.5 compares fetal and neonatal circulation .
| Structure | Structural Change Occurring | Pathophysiology of Change |
|---|---|---|
| Systemic circulation | Lung expansion |
|
| Ductus venosus |
This duct stays open at the time of birth, which allows umbilical vein catheterization, if needed.
Shortly after birth, this duct will begin to narrow and shrink. The duct will close completely during the first week of life in most full-term neonates but will take longer in preterm neonates. |
Once the umbilical cord is cut, the process of duct closing begins. Mechanical pressure and a redistribution of blood in the neonate’s body and changes in the cardiac output occur.
In simpler terms, closure of this duct forces perfusion of the fetal liver. Anatomic closure of this duct occurs within 2 weeks after birth, at which time the structure is known as the ligamentum venosum connected to the round ligaments of the liver. |
| Foramen ovale | Increased pressure in the left atrium attempts to reverse blood flow and closes this shunt, making it a one-way valve. | In utero, pressure is greater in the right atrium, with the foramen ovale open, allowing blood to shunt from the right atrium to the left. Decreased pulmonary vascular resistance and decreased umbilical venous return to the right atrium also cause a decrease in right atrial pressure. Pressure gradients are now reversed, allowing left atrial pressure to be greater than right atrial pressure, causing the foramen ovale to close 1–2 hours after birth. Anatomic closure occurs in about half of all 6-month-olds, while one-quarter of the adult population have a patent foramen ovale (PFO), though they are unaware of it. |
| Ductus arteriosus | Due to increased systemic vascular pressures and increased left atrial pressure, a reversal of blood flow and aorta–to–pulmonary artery (or left-to- right) shunting occurs, closing the shunt. It will functionally close within a few days after birth. |
|
Ductus Venosus
The primary function of the ductus venosus is to direct oxygenated blood from the umbilical vein to the inferior vena cava and eventually to the left heart for circulation. This duct also supplies oxygenated blood to the fetal liver (Pradbit & Forshing, 2022). Fetal hydrops, chromosomal aberration, in utero heart failure, and portal vein absence can be caused by absence or dysfunction of the ductus venosus (Pradbit & Forshing, 2022).
Ductus Arteriosus
The ductus arteriosus is a shunt that allows the fetal circulation to avoid the lungs by shunting blood from the right ventricle, bypassing pulmonary circulation and entering the descending aorta. Progressive increase in oxygenation (increased partial pressure of oxygen [PO 2 ]) and elimination of prostaglandin as a ductal relaxant cause the functional closure of the ductus arteriosus. At the time of birth, the newborn’s lungs fill with air, causing pulmonary vascular resistance and leading to blood flowing from the right ventricle to the lungs for oxygenation. The shunt then constricts due to increased arterial oxygen tension and the decreased flow-through, causing anatomic closure within 2 to 3 weeks.
Foramen Ovale
The foramen ovale directs intra-arterial blood flow from right to left in the fetal heart, bypassing the fetal lungs from the right atrium directly into the left atrium. The blood travels through the foramen ovale to the left atrium through the mitral valve to the left ventricle and out to the aorta and body. It finally flows to the ascending aorta, entering the systemic circulation.
Neonatal Circulation
Neonatal circulation is the same as adult circulation, once the newborn has completed the transition to extrauterine life . However, some things can go wrong, and the nurse needs to be able to identify those issues through assessment and accurate history taking. Some cardiac defects that a newborn might experience can be congenital (i.e., related to family history), so it is important that the nurse knows to assess for family congenital defects, cardiac issues, or issues during the pregnancy. During the postpartum period, the nurse must monitor the newborn for any signs or symptoms of cardiopulmonary dysfunction, such as apnea, cyanosis, and respiratory distress.
Patent Ductus Arteriosus and Murmur
When the ductus arteriosus of the newborn remains open after birth, it is called a patent ductus arteriosus (PDA) (Figure 22.6). As a result, blood flows from the descending aorta, across the PDA, and into pulmonary circulation, which can cause pulmonary edema (Gillam-Krakauer & Mahajan, 2022). The nurse will hear a murmur upon assessment of a newborn with a PDA, which will sound like a continuous, machine-like rumble below the clavicle, radiating to the back. Clinical manifestations will appear as tachycardia, bounding peripheral pulses, possible increased respiratory distress, and hypoxia, if pulmonary edema is present (Gillam-Krakauer & Mahajan, 2022).
Patent Foramen Ovale and Murmur
The foramen ovale closes completely in only about 75 percent of newborns (Marty et al., 2022). In the other 25 percent, a patent foramen ovale occurs. A patent foramen ovale (PFO) appears as a flap-like opening between the atrial septum secundum and primum at the fossa ovalis (Hampton et al., 2022) (Figure 22.7). Because left atrial pressure in the heart is higher than right atrial pressure, only a minuscule amount of blood may be shunted back to the right atrium, usually without any clinical significance for the newborn. This is generally a benign finding during the newborn period. However, if it persists into adulthood, it can lead to right-to-left shunting of deoxygenated blood and be symptomatic or asymptomatic.
However, the nurse may hear a murmur upon auscultation during a cardiac assessment that sounds like a quiet, muffled extra heart sound at the apex. Neonates have a 75 percent chance that these are transient and not associated with any other anomalies (Children’s Hospital of Philadelphia, 2022). Nonetheless, the nurse will report this finding to the health-care provider on call for the newborn.
Patent Ductus Venosus and Murmur
Failure of the ductus venosus to close leads to a condition called patent ductus venosus, which causes galactosemia , or galactose in the blood. This is an inherited disorder preventing the newborn from breaking down the sugar galactose, causing a buildup to toxic levels in their bloodstream. These newborns must avoid dairy products, breast milk, and most baby formulas. Additional problems from lack of closure of the ductus arteriosus are hypoxia, hepatic dysfunction, and encephalopathy with hyperammonemia , high levels of ammonia in the blood that cause brain damage (Marty et al., 2022).
This video from the Khan Academy shows a visual interpretation of the fetal to neonatal transition in circulation , including all the changes that happen during the moments immediately after birth.
Cardiopulmonary Adaptation
Many additional changes occur in the cardiopulmonary system after birth of the newborn. Late in gestation, the newborn completes lung development, fluid secretion in the lungs decreases, and surfactant production increases. In the lungs, surfactant is a phospholipid that lowers alveolar surface tension, prevents alveolar collapse at expiration, and maintains functional residual capacity. Production of catecholamines, causing fetal pulmonary epithelial cells to reabsorb fluid from alveolar spaces, is caused by the onset of labor (Rehman & Bacha, 2022). The first breath of air initiates a sequence of events that helps to expand the lungs, establish lung volume, clear the airways of amniotic fluid, and help the newborn transition from fetal circulation to newborn circulation. The first breath generates a high negative pressure system, filling the alveoli with air and removing any fluid in those spaces. Once the neonatal lungs expand fully with high concentrations of room air, pulmonary vascular resistance falls, which triggers pulmonary vasodilation increasing blood flow to the newly inflated lungs (Rehman & Bacha, 2022).
Approximately 10 percent of neonates do not sustain effective respiratory effort in the immediate transition period. Respiratory distress is a common complication seen in the neonatal period and is a major cause of morbidity and mortality (Reuter et al., 2014). The cause of neonatal respiratory distress varies, but the result is inadequate ventilation and impaired oxygenation, accompanied by retained carbon dioxide and alterations in acid-base balance. Respiratory distress syndrome can be an isolated incident that requires supportive care, or it can be a product of a functional abnormality of the pulmonary system that requires more intensive care. Table 22.3 shows common causes of neonatal respiratory distress, clinical findings, and their causes.
| Diagnosis | Cause | Incidence | Clinical Signs |
|---|---|---|---|
|
Meconium aspiration
syndrome (MAS) |
Aspiration of meconium during vaginal or cesarean birth that interferes with surfactant activity | 2%–10% of term and postterm infants exposed to meconium-stained amniotic fluid; 5%–30% of postterm and term births have meconium-stained amniotic fluid |
|
| Transient tachypnea of the newborn (TTN) | Failure to clear lung fluid by usual mechanism |
0.3%–0.5% of term and late-preterm infants
Onset within the first 24 hours of life |
Self-limiting condition presenting with tachypnea and no other abnormalities, lasting 12–72 hours |
| Respiratory distress syndrome (RDS) | Insufficient surfactant production |
Inversely related to gestational age:
Less than 28 weeks: 60% Older than 34 weeks: 5% |
Tachypnea, grunting, nasal flaring, retracting, hypoxemia, hypercarbia, respiratory acidosis beginning soon after birth |
| Persistent pulmonary hypertension of the newborn (PPHN) | Failure to relax the pulmonary vasculature after breathing oxygen at birth |
1:500–1:5000 live births
Affects term and postterm newborns due to pulmonary and nonpulmonary issues, though many times is idiopathic in nature |
Tachypnea, grunting, nasal flaring, retracting, hypoxemia, hypercarbia, respiratory acidosis; often hypoxic and intractable |
Nurse:
Clare, BSN
Years in practice:
5
Clinical Setting:
OBGYN unit of an academic medical center hospital
Geographic location:
Urban center
I was assigned to be the baby nurse for a scheduled cesarean section of a 35-year-old cisgender woman G1P0 at 36 weeks and zero days’ gestation. She had placenta previa with an active bleed over the prior 48 hours.
Upon arrival in the preoperative area, the fetal heart tones were 130 to 135 bpm, with moderate variability, no accelerations, and no decelerations. The patient, Kelsey, was experiencing no contractions. The clinical team determined that a cesarean section was necessary, and the patient agreed.
I helped my coworker Kaitlyn, a labor and delivery nurse, prepare the patient for the cesarean section by educating the patient and her partner about all the things they might see and hear in the operating room. My coworker placed Kelsey into a hospital gown, started an 18-gauge intravenous line in her right antecubital space, and initiated lactated Ringer’s solution at 125 mL/hour. Kelsey received consultations from the anesthetist and her obstetrical surgeon, and then it was time to deliver the baby.
In the operating room, the decision was made that there should be two nurses responsible for the neonate because of the preterm gestational age of the baby. In addition, the main nurse called the neonatal intensive care unit to notify them that there was a preterm delivery happening in labor and delivery just in case they were needed. Furthermore, because the presence of placenta previa increases the risk of postpartum hemorrhage, I called my charge nurse and asked her to come to the cesarean section with a postpartum hemorrhage kit. I also asked the blood bank for two units of packed red blood cells in Kelsey’s correct blood type to be placed on hold for her following the provider’s orders.
Once the surgery was underway, I monitored the fetal heart tones, watching for any signs of distress, and prepared the radiant warmer for the arrival of the baby. I made sure to have all the equipment that I would need, including the following: suction connected to the wall; oxygen with bag-valve mask and neonatal-size mask; nasal bulb; warm blankets; laryngoscope and ET tubes appropriate for a 35-week fetus; pulse oximetry ; temperature sensor ; hat; and diaper.
The baby arrived, was given to me, and placed under the radiant warmer. The neonate was very small, had very poor tone, was pale and cyanotic, gasping for breaths, had shallow breathing, but responded to stimulation and had a heartbeat of 140. I immediately started stimulating and drying the baby off while my coworker auscultated for breath sounds and placed a pulse oximeter on the neonate’s foot. After getting a pulse ox reading of 40 percent, my coworker rolled a baby blanket into a log and placed it under the neonate’s neck to point the chin of the neonate toward the ceiling. This allowed the infant’s jaw and airway to fall open, which facilitated more efficient breathing. The airway was assessed and cleared using a bulb syringe . At that point, Apgar scores for the neonate were 7. Blow-by oxygen was provided, and I continued stimulating and drying the baby. The baby continued to gasp for breaths, was still pale, and had poor tone; the heart rate was 145, and the newborn responded to stimulation. At 5 minutes, the Apgar scoring total was still 7, and I called the NICU for additional assistance. The baby was placed in an incubator and taken to the NICU for help with transition. The neonate’s distress was likely due to early gestational age and being small. The infant is 5 pounds, 3 ounces and named Genevieve.
Hematologic Adaptation
The hematologic adaptations of the newborn happen because of the dramatic changes in circulation and oxygenation that occur after placental detachment. Mean hemoglobin levels in cord blood are 15 g/dL (Eslami et al., 2012), and hemoglobin and hematocrit levels in the newborn will continue to rise in the first several hours post birth. Higher than normal hemoglobin and hematocrit levels will usually self-correct by day 3 to 5. This is when the movement of plasma from intravascular to extravascular spaces is completed (Eslami et al., 2012).
Oxygen Saturation Levels in the Newborn
Blood oxygen in the immediate newborn is significantly lower than in a newborn that is 24 hours old (Lara-Canton, et al., 2022). Partial pressures of the oxygen gradient between maternal, placental, and fetal blood are thought to be the driving force that regulates fetal oxygen supply. In the uterus, the fetus grew in a relatively low oxygen environment due to fetal hemoglobin’s high affinity for oxygen (Lara-Canton, et al., 2022) and due to the mixing nature of the fetal circulatory system. Delayed cord clamping has been associated with improved fetal-to-neonatal transition and increased newborn oxygen saturation levels by 85 percent to 90 percent (Lara-Canton, et al., 2022). Delayed cord clamping at birth can also lead to fewer episodes of tachycardia in the immediate transition period for the newborn. As seen in Table 22.4, in the period immediately following birth, oxygen saturation rates of 60 percent to 65 percent are expected in the newborn, rising to 85 percent to 90 percent at 10 minutes post birth, according to the American Academy of Pediatrics (AAP) , American Heart Association (AHA) , and the Guidelines for Neonatal Resuscitation (NRP) (Hammer, 2021).
| Time after Birth | Oxygen Saturation Level |
|---|---|
| 1 min | 60%–65% |
| 2 min | 65%–70% |
| 3 min | 70%–75% |
| 4 min | 75%–80% |
| 5 min | 80%–85% |
| 10 min | 85%–95% |
American Academy of Pediatrics, American Heart Association and Guidelines for Neonatal Resuscitation (NRP) all agree that the guidelines for saturation of peripheral oxygen (SpO 2 ) should be used to determine the need for initiating supplemental oxygen or increasing/decreasing its concentration (Hammer, 2021).
The Vitamin K Injection
Neonates do not have enough vitamin K stored in their bodies at birth because very little of it passes from the birthing person through the placenta. Therefore, newborns need a supplement to increase clotting factors and to prevent hemorrhagic disasters and vitamin K deficiency bleeding. The American Academy of Pediatrics recommends that all newborns receive a one-time intramuscular shot of vitamin K within 6 hours after birth. Neonates who do not receive the vitamin K injection are at 81 times greater risk of developing vitamin K deficiency bleeding than neonates who receive this intramuscular injection, compared to 1/100,000 when vitamin K is given at birth (Hand & Noble, 2022)
Generic Name: phytonadine, phytomenadione
Trade Name: Mephyton
Class/Action: vitamin, fat soluble
-
Route/Dosage:
oral, subcutaneous (SubQ; administer undiluted), intramuscular (IM; 1 mg/0.5 mL), intravenous (IV; 1 mg/minute)
- Oral: May be administered with or without food in older children and adults. Parenteral formula may also be used for small oral doses or situations in which tablets cannot be swallowed.
- Parenteral: Limit IV administration to situations where an alternative route of administration is not feasible and the benefit of therapy outweighs the risk of hypersensitivity reactions. Allergic reactions have occurred with IM and SubQ injections.
- High Alert/Black Box Warning:
- Indications: Prophylaxis and treatment of vitamin K deficiency bleeding (formerly known as hemorrhagic disease of the newborn (injection only).
- Mechanism of Action: Promotes liver synthesis of clotting factors (II, VII, IX, X): however, the exact mechanism of this stimulation is unknown. Menadiol is a water-soluble form of vitamin K; phytonadione has a more rapid and prolonged effect than menadione; menadiol sodium diphosphonate (K4) is half as potent as menadione (K3).
- Contraindications: Hypersensitivity to phytonadione or any component of the formula.
-
Adverse Reactions/Side Effects:
Table 22.5 lists adverse drug reactions derived from product labeling unless otherwise specified.
Category Adverse Reaction Cardiovascular Chest pain, flushing, hypotension, tachycardia, weak pulse Central nervous system Dizziness Dermatologic Diaphoresis, eczematous rash, erythema, erythematous rash, pruritic plaques of the skin, urticaria Gastrointestinal Dysgeusia Hepatic Hyperbilirubinemia Hypersensitivity Anaphylactic reaction (anaphylaxis) Local Injection site reaction (pain, swelling, tenderness) Respiratory Cyanosis, dyspnea Miscellaneous Lesion (scleroderma-like)
- Nursing Implications: Witness parental consent. Review patient education with the family. Administer the IM injection in the middle vastus lateralis muscle. Document in the patient’s chart.
- Parent/Family Education: The nurse will provide education to the parents before providing intramuscular injection to neonate. It is mandatory that while providing this information to the parents the nurse provide a written information statement to them so that they can follow along and make an informed decision.
Newborn Coagulation
Platelet values in a neonate are comparable to those of an adult patient; however, the neonate is at risk for complications with platelet function. If the neonate was born to a birthing person who experienced severe hypertension or HELLP syndrome (hemolysis, elevated liver enzymes, and low platelet count), or a birthing person with idiopathic isoimmune thrombocytopenia, the newborn is at increased risk for a platelet dysfunction called transient neonatal thrombocytopenia , or thrombocytopenia (decreased platelets) that develops in neonates. (See Chapter 19 Complications of Labor and Birth for a discussion of HELLP syndrome in depth.) The absence of vitamin K in the newborn gut causes a quick decrease in coagulation factors II, VII, IX, and X after birth. Vitamin K levels do slowly increase but do not reach adult levels for several weeks, which is one reason a vitamin K injection in the immediate period after birth is recommended. The American Academy of Pediatrics recommends that all newborns receive a one-time intramuscular injection of vitamin K within 6 hours after birth. The intramuscular administration of vitamin K (Aquamephyton) effectively prevents vitamin K deficiency disease of the newborn, as well as excessive bleeding after circumcision for the newborn males who have this procedure. (Hand & Noble, 2022).
Newborn Transitional Period
The neonate shows a very predictable pattern of behavior during the first several hours after birth. Based on these periods of reactivity, the nurse plans activities with the birthing person and the neonate to maximize the attachment between them. The three periods of reactivity the neonate will experience are the first period of reactivity, the period of decreased responsiveness, and the second period of reactivity (Hernandez & Thilo, 2005).
First Period of Reactivity
The first period of reactivity begins with birth and lasts around 30 minutes. In this period, the nurse can expect to see alertness, activity, and responsiveness to interaction from the neonate to the birthing person, their partner, nurses, clinicians, and anyone else who interacts with them (Hernandez & Thilo, 2005). This is an optimal time for the nurse to teach the birthing person about breast-feeding. The neonate is often rooting for food, very interested in their environment, and open to attempting the first latch session during this time. (Hernandez & Thilo, 2005). When this period is over, the neonate will fall into a deep sleep.
The Period of Decreased Responsiveness
In the period of decreased responsiveness , the neonate will be in a deep sleep or have marked decrease in activity for 30 minutes to 2 hours. Their muscle tone will return to normal; they will have fast, shallow respirations (60 breaths per minute) with no dyspnea occurring. The nurse will note that the color of the neonate is pink with excellent perfusion and capillary refill of less than 3 seconds. During assessment, the nurse will note a heart rate between 100 and 120 beats per minute, and the neonate will be less responsive to external stimuli (Hernandez & Thilo, 2005). Additionally, the nurse may assess spontaneous jerks and twitches or an occasional Moro reflex; however, the neonate will return to rest very quickly (Hernandez & Thilo, 2005).
The Second Period of Reactivity
The third and final stage of newborn transition is called the second period of reactivity . This is when the nurse will note the return of responsiveness from the neonate, lasting from 2 to 8 hours. The neonate will experience periods of tachycardia and abrupt changes in tone, color, and bowel sounds. The neonate can experience an excess of oral mucus, sometimes appearing as vomiting, gagging, and choking on amniotic fluid left over from birth. This is an expected finding, and the nurse will reassure the parents and educate them that this may occur for the next 7 days as the newborn clears their airways. Upon assessment during this time, the nurse will note that the neonate often has passed their first meconium stool. During this final stage of reactivity, the nurse will also notice that the neonate demonstrates increased hunger cues, making this an excellent time for another breast-feeding session. During increased alert periods, parent-infant bonding can be established.
Abnormal Transition
Neonatal assessment findings indicating abnormal transition include the following:
- Persistent tachycardia, longer than the first hour of life; fixed bradycardia
- Diffuse and persistent rales upon auscultation, retractions, grunting, nasal flaring lasting longer than the first hour of life
- Persistent cyanosis and pulse oximetry less than 90 percent on room air and requirements for supplemental oxygen after the first hour of life
- Episodes of prolonged apnea (longer than 20 seconds) and bradycardia (less than 80 beats/min)
- Marked pallor
- Temperature instability persistently after 2 to 3 hours of life lower than 36.5º C (97.7º F)
- Poor capillary refill (greater than 3 seconds)
- Unusual neurologic behavior (lethargy, hypotonia, excessive tremors, jitteriness, inconsolable crying, poor feeding)
- Excessive oral secretions (choking, excessive drooling, cyanosis with coughing) (Fraser, 2002)
When the nurse identifies a neonate who is experiencing abnormal transition, they must support the newborn in whatever area the newborn is having difficulty moving through. Suctioning for an open airway, maintaining a stable neutral temperature, or encouraging skin-to-skin would all be independent nursing interventions, while persistent desaturations and marked pallor may require a specialist and further diagnostic evaluation. The nurse needs to know when the newborn requires interventions beyond independent nursing interventions.