Understanding the Transition to Newborn Life

The transition from fetal to newborn life represents one of the greatest physiologic challenges that all humans encounter. During fetal life, the lungs are liquid-filled, and at birth this liquid must be rapidly cleared from the airways to allow the entry of air and the onset of pulmonary gas exchange. Pulmonary blood flow (PBF) must also markedly increase and several specialized vascular shunts must close to separate the pulmonary and systemic circulations. While it is often considered that these events are independent, we now know that they are intimately linked. Lung aeration is the primary trigger that not only facilitates the onset of pulmonary gas exchange but also stimulates an increase in PBF, which in turn initiates the cardiovascular changes. The fact that lung aeration triggers the physiologic transition at birth underpins the well-established tenet of neonatal resuscitation. That is, establishing effective pulmonary ventilation is the key.

Recent radiographic imaging studies have demonstrated that lung aeration can occur very rapidly (in three to five breaths) and mostly occurs during inspiration or during positive-pressure inflations in ventilated neonates ( Fig. 10.1 ). It is thought that hydrostatic pressure gradients generated by inspiration (or positive-pressure inflations) drive liquid from the airways into the surrounding lung tissue. However, as the interstitial tissue compartment of the lung has a fixed volume, the clearance of airway liquid into this compartment during lung aeration increases lung interstitial tissue pressures. Thus immediately following lung aeration, the neonatal lung is essentially edematous, which affects lung tissue mechanics and increases the likelihood of liquid reentering the airways during expiration. Use of positive end-expiratory pressure (PEEP) opposes liquid reentry and ensures that air remains in the distal gas exchange units throughout the respiratory cycle ( Fig. 10.2 ). Thus PEEP not only reduces distal airway collapse at end-expiration, it also reduces airway liquid reentry and by retaining air in the distal airways allows gas exchange to continue throughout the respiratory cycle.

Phase-contrast radiographic images and a plethysmograph recording of a preterm newborn rabbit immediately after birth ventilated from birth in the absence of a positive end-expiratory pressure (PEEP). In the absence of PEEP, preterm rabbits failed to develop a functional residual capacity (FRC), resulting in liquid reentry or airway collapse at end-expiration. Phase-contrast radiographic images (A and B) were recorded at each time point on the plethysmograph trace. Image A was acquired at end inspiration, whereas image B was acquired at FRC.

Phase contrast radiographic images and a plethysmograph recording of a preterm newborn rabbit immediately after birth ventilated from birth with a positive end-expiratory pressure (PEEP) of 5 cm H ₂ O. With this level of PEEP, preterm rabbits gradually develop a significant functional residual capacity (FRC) with most distal airways (not all, see basal lung regions) remaining aerated at FRC. Phase contrast X-ray images (A and B) were recorded at each time point on the plethysmograph trace. Image A was acquired at end inspiration, whereas image B was acquired at FRC.

The entry of air into the lung also triggers the cardiovascular transition at birth. Before birth, the majority of right ventricular output bypasses the lung and flows through the ductus arteriosus into the systemic circulation mainly because pulmonary vascular resistance (PVR) is high. As a result, fetal PBF is low and contributes little to venous return and the supply of preload for the left ventricle. Instead, this mainly comes from umbilical venous return via the ductus venosus and foramen ovale. Thus blood flow through the placenta is not only vital for oxygen and nutrient supply during fetal life, but is also vital for supplying preload for the left ventricle. Clamping the umbilical cord at birth therefore greatly reduces preload for the left ventricle, causing a large reduction in cardiac output. Furthermore, cardiac output remains low until the lungs aerate and PBF increases to restore preload for the left ventricle. Recognition of this shift in dependence from umbilical venous return to pulmonary venous return for sustaining ventricular preload at birth has led to the concept of physiology-based cord clamping. That is, if cord clamping is delayed until after the lungs have aerated and PBF has increased, then PBF can immediately replace umbilical venous return as the major source of ventricular preload as soon as the cord is clamped, with no diminution in supply. This procedure greatly mitigates the large decreases and increases in cardiac output associated with cord clamping followed by ventilation onset. It also greatly reduces the instantaneous increase in arterial blood pressure associated with cord clamping that is caused by the removal of the low-resistance placental vascular bed.

Recent imaging studies have demonstrated that at birth, only partial lung aeration is required to stimulate a global increase in PBF and while increased oxygenation enhances this response, it is not oxygen dependent ( Fig. 10.3 ). Although partial aeration has the potential to cause large ventilation-perfusion mismatches in the lung at birth, this response arguably has an overall benefit during transition. As a redistribution of cardiac output and increased blood flow to the brain is critical for protecting the fetal brain from hypoxia, any constraint on cardiac output caused by a lack of venous return at birth is potentially catastrophic. By not limiting the increase in PBF to the degree of lung aeration, venous return and cardiac output will also not be limited by the degree of lung aeration immediately after birth.

Simultaneous phase-contrast and angiographic radiographic image of a near-term rabbit kitten following partial ventilation of the right lung. Aerated lung regions can be seen as “speckle” in the image and are due to refraction at the air/water interface. Although only part of the right lung is aerated, pulmonary blood flow is increased in both lungs equally. MPA, Main pulmonary artery; PA, pulmonary artery; RV, right ventricle.

At birth, lung aeration is important not only for establishing pulmonary gas exchange. It also triggers the increase in PBF required for facilitating pulmonary gas exchange and for replacing left ventricular preload lost following cord clamping, which is required to maintain cardiac output.

Anticipating the Need for Resuscitation

While the majority of newly born infants successfully transition from in utero to ex utero life without any intervention, approximately 4% to 10% of term and late preterm newborns require assistance to establish spontaneous respiratory effort, and a very small number require chest compressions or epinephrine during the transition period. Given the nearly 131 million births per year worldwide, this means that many newborns each year require skilled assistance to support transition immediately after birth. Asphyxiation is the most common reason that newborns fail to transition successfully. Asphyxia is defined as a lack of gas exchange that results in simultaneous hypoxia and carbon dioxide (CO ₂ ) elevation, leading to a mixed metabolic and respiratory acidosis. The asphyxial insult can result from either failure of placental gas exchange before birth or deficient pulmonary gas exchange once the newborn is delivered.

Premature or postterm gestation, fetal hydrops, intrauterine growth restriction, gestational diabetes, multiple gestation, abnormal placentation, maternal illness, and maternal drug abuse are examples of antenatal risk factors that increase the likelihood of impaired gas exchange before delivery and increase the probability that the newborn will require resuscitation after birth. Intrapartum risk factors for impaired gas exchange include abnormal presentation (breech or transverse position), fetal bradycardia, umbilical cord compression or prolapse, placental abruption, intrapartum bleeding, meconium-stained amniotic fluid (MSAF), and chorioamnionitis. Risk factors that could affect gas exchange of the newborn include drug-induced respiratory depression (maternal magnesium exposure, opiates, and prolonged maternal general anesthesia), airway obstruction, prematurity, pneumonia, pneumothorax, and congenital malformations of the brain, airway, abdomen, heart, or lungs.

Although the likelihood of requiring resuscitation is higher in the presence of risk factors, individual risk factors and scoring systems that combine risk factors have limited discriminatory power and identify many births where no interventions are needed. Moreover, some newborns require intervention in the absence of any risk factors. In one large cohort study, approximately 7% of newborns who received positive-pressure ventilation in the delivery room had no identifiable risk factors. Thus for every delivery, the appropriate personnel must be present to immediately assess the newborn and initiate resuscitation.

After evaluating the obstetric history and known risk factors, the necessary neonatal health providers should be assembled. The number and qualifications of providers will vary depending on the specific circumstances. However, at every birth at least one person trained in neonatal resuscitation should be present whose only responsibility is to assess the infant, perform the initial steps of newborn care, and administer positive-pressure ventilation if necessary. A qualified team proficient in all resuscitation skills should be immediately available if resuscitation is required. If risk factors suggest a high likelihood of the need for resuscitation, the team should be present at the time of birth to perform the necessary procedures without delay. Depending on the setting, this team may include providers from a variety of disciplines, such as respiratory therapy, anesthesiology, and emergency medicine.

Before the delivery, all members of the team should assemble to complete a briefing similar to the “time out” performed before any medical procedure. During this briefing, the team identifies a team leader, reviews the pregnancy history and risk factors, discusses the anticipated clinical scenario, delegates roles and responsibilities, considers contingency plans, and prepares the necessary supplies and equipment.

Preparation

Prior to delivery, all resuscitation supplies and equipment should be identified and checked for working order using a standardized checklist. Standardized checklists help to ensure adequate preparation by improving communication and rapidly identifying missing equipment. The environmental temperature of the delivery room should be maintained at least 23°C (74°F) and free from drafts to help prevent hypothermia. Warm blankets and a radiant warmer should be prepared. Depending on the circumstances, additional equipment and supplies including hats, thermal mattresses, and polyethylene plastic bags or wraps should be available. A functioning positive-pressure ventilation (PPV) device (such as a self-inflating bag, a flow-inflating bag, or a T -piece device) and an appropriate sized face mask, manometer, and the capability to deliver blended oxygen are the most important equipment needed for newborn resuscitation. Suction devices (bulb syringe as well as wall suction and suction catheters), a functioning laryngoscope with appropriate sized blade and endotracheal tube, and a CO ₂ detector for confirmation of correct tube placement should be ready for immediate use. Laryngeal masks are alternative airway devices that may provide a lifesaving airway when both face mask ventilation and endotracheal intubation are unsuccessful and should be readily available. Pulse oximetry to measure oxygen saturation and an electronic cardiac (electrocardiograph [ECG]) monitor to accurately measure the newborn’s heart rate if resuscitation is required should be immediately accessible. In certain high-risk circumstances, an umbilical venous line should be prepared and epinephrine drawn into a labeled syringe for rapid use.

Initial Assessment

Immediately after birth, a rapid initial assessment is performed to determine if the newborn is vigorous and can remain with the mother to complete transition or should be moved to a radiant warmer for the initial steps of newborn care. This assessment can be performed during the interval between birth and umbilical cord clamping. Within 10 to 30 seconds of birth, approximately 85% of term newborns are vigorous with good muscle tone and strong respiratory effort, and an additional 10% becoming vigorous as they are dried and stimulated. The healthy, term newborn’s heart rate rapidly rises and remains above 100 beats/min within the first 2 minutes (median 123 beats/min at 1.5 minutes). Clinical judgment of the newborn’s color is notoriously difficult and is not an accurate predictor of the newborn’s arterial oxygenation. When measured by preductal pulse oximetry, the healthy newborn’s oxygen saturation increases gradually from a median of near 60% at 1 minute of life to around 90% by 10 minutes of life.

Vigorous term newborns with good tone and adequate respiratory effort should remain with their mother after birth to receive routine newborn care. The infant may be placed on the mother’s chest or abdomen and covered with a warm, dry blanket. Warmth is maintained by drying the newborn’s skin and maintaining direct skin-to-skin contact with the mother. Secretions may be gently wiped from the face, mouth, and nose with a soft cloth or towel. Clearing secretions from the mouth and nose with a suction device should be reserved for those infants who have respiratory depression or cannot clear secretions on their own. If the infant is crying vigorously, there is no need for routine oral suction. Additional steps of routine newborn care include drying, gentle stimulation, and continued observation during the transition period.

Initial Steps for Nonvigorous and Preterm Newborns

Infants who are not vigorous after birth and those who are born preterm should be taken to a radiant warmer for assessment, the initial steps of newborn care, and possible resuscitative interventions ( Fig. 10.4 ). In some settings, this may performed on a specially designed resuscitation trolley placed immediately adjacent to the mother, allowing the steps to be performed without dividing the umbilical cord.

Neonatal resuscitation algorithm. CPAP, Continuous positive airway pressure; ECG, electrocardiograph; ETT, endotracheal tube; HR, heart rate; IV, intravenous; O ₂ , oxygen; PPV, positive-pressure ventilation; Sp o ₂ , oxygen saturation measured by pulse oximetry; UVC, umbilical venous catheter.

Reprinted with permission. From Circulation 132:S543-S560, 2015. ©2015 American Heart Association, Inc.

Effective Ventilation: The Key!

Any newborn who does not establish spontaneous respiratory effort after the initial steps or who remains bradycardic (heart rate <100 beats/min) should be given PPV. Effective ventilation of the lungs is the single most important action to stabilize a newborn infant who is compromised following delivery. The goal is to provide aeration and ventilation that supports gas exchange without causing lung injury. PPV can be administered with a self-inflating bag, flow-inflating bag, T -piece resuscitator, or a neonatal ventilator. Each device has advantages and disadvantages and the choice of device may be made based on cost; availability of compressed gas; the desire to deliver sustained inflation, PEEP, and continuous positive airway pressure (CPAP); or personal preference. Self-inflating bags are always ready for immediate use and reexpand without a compressed gas source. Although inadvertent high peak pressures have been demonstrated with self-inflating bags when operators use only a pop-off safety valve, if providers use an appropriately designed manometer they can accurately achieve the targeted peak inspiratory pressure. Self-inflating bags are not routinely used to administer free-flow oxygen or continuous positive airway pressure (CPAP). Even when outfitted with a positive end-expiratory pressure (PEEP) valve, traditional self-inflating bags do not reliably deliver PEEP through the face mask. A novel PEEP valve designed to work with a self-inflating bag in resource-limited settings without an external gas source may be effective. The flow-inflating bag requires more time and practice to set up and a compressed gas source. Because the bag does inflate without a tight seal, large mask leaks are easy to identify. PEEP and CPAP can be generated by balancing the gas flow into the bag and the amount of gas leaking out of a control valve; however, this adjustment requires experience. T -piece resuscitators more accurately and consistently deliver set inspiratory pressures and PEEP than the other devices, but they require a compressed gas source and changing the inflation pressures during resuscitation is more difficult. Among infants born at 26 weeks’ gestation or later requiring resuscitation, Szyld et al. found no difference between the T -piece resuscitator and self-inflating bag in achieving a heart rate of 100 beats/min or higher within 2 minutes; however, the T -piece decreased the maximum applied inspiratory pressure and the need for intubation. Among extremely low-birth-weight infants, Dawson et al. found the self-inflating bag to be as effective as the T -piece resuscitator in achieving goal oxygen saturation values by 5 minutes of life. If either a T -piece device or a flow-inflating bag is used, there must be a backup self-inflating bag in case compressed gas is lost. Whichever PPV device is chosen, the most important thing is to become proficient using and troubleshooting the selected device.

Ventilation can be provided via an appropriately sized face mask, endotracheal tube, or laryngeal mask. To achieve effective ventilation via face mask, the provider must first open the airway by placing the infant in the “sniffing” position. To achieve a good seal, the mask should rest on the chin and snugly cover the mouth and nose, but not the eyes to avoid trauma and a vagal response. Lack of appropriate airway positioning and inadequate seal are the most frequent causes of ineffective ventilation. A delivery room study of mask ventilation of premature infants documented that up to 25% of breaths had evidence of airway obstruction and 75% had mask leak. Even experienced providers have difficulty identifying obstruction, leak, changes in compliance, and the tidal volume of their manual ventilations. Simple disposable CO ₂ detectors or continuous capnography may help confirm airway patency and effective lung aeration during bag-mask ventilation. More sophisticated respiratory function monitors might also be helpful in detection of airway obstruction, mask leak, and delivered tidal volume. Because providers have difficulty sensing changes in compliance, if the compliance suddenly improves, they may inadvertently deliver excessive tidal volumes that could lead to lung injury. When tidal volume is displayed, operator performance is markedly improved. The currently available manual ventilation devices do not measure tidal volume; however, incorporating a respiratory function monitor to measure and display this information during manual ventilation may be useful.

Ventilation rates of 40 to 60 breaths/min are recommended. Faster rates should be avoided to allow adequate exhalation time and to prevent stacked breaths, which could increase the risk of pneumothorax. Counting the ventilation rhythm out loud or using a metronome for pacing may be helpful.

The optimal inflation pressure, inflation time, and target volume required to establish an effective functional residual capacity (FRC) have not been determined but likely vary among infants. Inflation pressures should be monitored and every ventilation device should include a manometer. Guidelines suggest initial peak pressures in the range of 20 to 30 cm H ₂ O, but the pressure required to aerate the liquid filled lungs of an apneic infant may be as high as 30 to 40 cm H ₂ O. Infants without respiratory effort may require higher pressures initially, but pressures should be reduced as the lungs aerate and become more compliant. The goal is to provide the minimum inflating pressure necessary to quickly achieve and maintain a heart rate greater than 100 beats/min. The actual delivered volume varies widely depending on the newborn’s spontaneous effort, lung compliance, glottic closure, face mask leak, and airway obstruction. In animal models, prolonged initial sustained inflations of 10 to 20 seconds have been shown to achieve functional residual capacity faster and to improve lung function without adverse circulatory effects. However, randomized trials enrolling preterm newborns (25–32 weeks’ gestation) with sustained inflations (20–25 cm H ₂ O for 10–15 seconds) compared with either CPAP or conventional ventilation have not shown a consistent benefit with regard to mortality or significant morbidities.

The majority of newborns who require resuscitation improve promptly with assisted ventilation alone. The best sign that the lungs are being effectively aerated and ventilated is a rapid rise in heart rate, followed by improvement in oxygen saturation and the infant’s tone. If monitored, expired CO ₂ levels higher than 10 mm Hg, indicating lung aeration, may be detected before the heart rate increases. If the heart rate has not increased within 15 seconds of initiating PPV, the most likely reason is that the lungs are not being adequately ventilated because of an airway obstruction or large mask leak. The provider should attempt to improve the efficacy of ventilation by using the series of steps described in the MRSOPA mnemonic:

• •
  

  M ask—ensure a good seal.

  
  
• •
  

  R eposition—ensure the head and neck are in the sniffing position.

  
  
• •
  

  S uction—clear the airway of any obstructing secretions.

  
  
• •
  

  O pen the mouth—and reapply mask.

  
  
• •
  

  P ressure—gradually increase the pressure until you see chest movement.

  
  
• •
  

  A irway alternative—consider using an endotracheal tube or laryngeal mask airway.

If the heart rate remains less than 60 beats/min despite face mask ventilation that achieves chest movement, or if chest movement cannot be achieved with the basic corrective steps, insertion of an alternative airway (endotracheal tube or laryngeal mask) is strongly recommended. In the unusual case when the infant does not improve with ventilation through an appropriately placed alternative airway and the heart rate remains lower than 60 beats/min, chest compressions are indicated.

Continuous Positive Airway Pressure

If an infant is breathing spontaneously but has labored breathing or persistently low oxygen saturation, CPAP may help establish and maintain an FRC. For premature infants, applying CPAP shortly after birth with subsequent selective surfactant administration has been recommended as an alternative to routine intubation with prophylactic surfactant administration. Pooled analysis of four randomized controlled trials in preterm infants born at less than 32 weeks’ gestation showed a significant benefit for the combined outcome of death or bronchopulmonary dysplasia for infants treated with nasal CPAP (risk difference –0.04, 95% confidence interval –0.08 to –0.00). In one study that used CPAP levels of 8 cm H ₂ O in the delivery room, an increased risk of pneumothorax was observed, but this higher risk was not seen in the other studies that used lower CPAP levels. For term infants there is no evidence to support or refute the use of CPAP in the delivery room, but it is frequently used in the situation of respiratory distress. Although CPAP may help establish and maintain an FRC, thus improving respiratory distress, it should not be used in place of PPV when the infant is apneic or bradycardic.

Alternative Airways: Endotracheal Tube or Laryngeal Mask Airway

Insertion of an alternative airway may be performed at various points during resuscitation and for several different indications. Examples include prolonged or ineffective face mask ventilation, heart rate remaining below 100 beats/min after 30 seconds of otherwise effective ventilation, or the need for chest compressions are needed. An endotracheal tube should be inserted promptly if the infant has a congenital diaphragmatic hernia.

The equipment for endotracheal intubation should be readily available wherever infants may be born. The correct laryngoscope blade and tube size are based on the infant’s estimated weight and/or gestational age ( Table 10.1 ). An intubating stylet that stiffens the tube may be used with caution to ensure that the tip does not protrude beyond the end of the tube; however, one randomized trial showed that use of a stylet did not significantly improve the intubation success rate of pediatric trainees. Once the procedure is completed, the placement of the tube within the trachea must be verified and the use of a CO ₂ detector is recommended. Use of a flow sensor that displays gas flow in and out of the tube may be a faster and more accurate method to confirm tube placement than a CO ₂ detector. Clinical indicators of tracheal placement include a rapid increase in heart rate, observing chest rise with PPV, auscultating air entry in both axillae, and observing condensation inside the tube during expiration; however, these signs can be misleading. Incomplete intubation attempts should be interrupted and bag mask ventilation resumed if the heart rate starts to fall or remains unstable. Limiting intubation attempts to a duration of seconds has been suggested as a reasonable goal.

Initially, the endotracheal tube should be advanced so the printed vocal cord guide (black line on the distal end of the tube) is level with the vocal cords. At this depth, the tube is expected to be above the carina; however, the marker position varies by manufacturer and should only be used as an initial guide during the insertion procedure. Previous recommendations suggested estimating the insertion depth (tip-to-lip) by adding 6 cm to the infant’s weight in kilograms. In preterm infants, this method may overestimate the insertion depth and place the tube in the infant’s right mainstem bronchus, especially in extremely low-birth-weight infants. More accurate methods for estimating the insertion depth have been validated in term and preterm newborns. One method uses the infant’s estimated weight or gestational age to predict the insertion depth (see Table 10.1 ). Another method estimates the insertion depth by measuring the distance (in centimeters) between the newborn’s nasal septum and ear tragus (the nasal-tragus length). The tube is inserted to the nasal-tragus length distance + 1 cm with the appropriate centimeter mark secured at the infant’s upper lip. Radiographic confirmation of proper tube placement should be obtained as soon as feasible. The goal is to place the tip of the tube in the mid-trachea, above the carina, with the tip aligned between the first and second thoracic vertebrae when assessed by chest radiography.

Intubation is not an easy skill to acquire and requires extensive training to become proficient. Changes in practice have led to fewer infants being intubated in the delivery room and trainees having fewer opportunities to acquire this skill. As a result, resident physicians take longer to complete the procedure, require multiple attempts, are successful in less than half of attempts, and repeated attempts are associated with adverse events. When an alternative airway is needed, insertion of a laryngeal mask may be more successful. Laryngeal mask airways are effective for ventilating newborns who are 34 weeks or more estimated gestational age and weigh more than 2000 g at birth and may be effective for smaller and less mature newborns (≥29 weeks, ≥1000 g). Studies in adult models and patients suggest that placement of a laryngeal mask may be an easier task to learn than endotracheal intubation. In addition, laryngeal masks have been used to administer surfactant and, when compared with standard endotracheal tube administration, decreased the proportion of newborns who ultimately required mechanical ventilation. This technique requires further evaluation before it is widely applied. Insertion of a laryngeal mask should be considered during resuscitation if face mask ventilation is unsuccessful and intubation is either unsuccessful or not feasible, but the technique has not been evaluated for use during chest compressions or for administration of tracheal epinephrine.

Oxygenation

Use of 100% oxygen was routine for newborn resuscitation until recent changes in resuscitation guidelines. Oxygen tension values of the fetus are low compared with those achieved after transition. Pulse oximetry studies of healthy term infants who require no resuscitation at birth demonstrate that preductal oxygen saturation starts at around 60% and takes 5 to 10 minutes to reach 90%. The ideal oxygen saturation range at each minute of life has not been defined, but a reasonable goal is to target a preductal oxygen saturation within the interquartile range for healthy term infants ( Table 10.2 ). Clearly, medical providers should not expect infants to be instantaneously pink at birth and should break the old habit of routinely exposing infants to oxygen at birth. In fact, clinical judgment of color is poor and thus it is recommended that oxygen use be guided by pulse oximetry rather than clinical judgment alone.

Table 10.2

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