The Newborn Lung

Neonatology Questions and Controversies

Eduardo MD Bancalari

• Éditeur: Elsevier
• Année: 2018
• ISBN:
  9780323568753
• Édition: 3
• Sujet: Medicine
• Sous-sujet: Perinatology & Neonatology

Dr. Richard Polin's Neonatology Questions and Controversies series highlights the most challenging aspects of neonatal care, offering trustworthy guidance on up-to-date diagnostic and treatment options in the field. In each volume, renowned experts address the clinical problems of greatest concern to today's practitioners, helping you handle difficult practice issues and provide optimal, evidence-based care to every patient.

• Stay fully up to date in this fast-changing field with The Newborn Lung, 3rd Edition.
• The most current clinical information throughout, including key management strategies that may reduce some of the chronic sequelae of neonatal respiratory failure.
• New content on the role of microbiome in lung injury and lung development.
• Current coverage of non-invasive respiratory support, perinatal events and their influence on lung development and injury, cell-based lung therapy, automation of respiratory support, and oxygenation targeting in preterm infants.
• Consistent chapter organization to help you find information quickly and easily.
• The most authoritative advice available from world-class neonatologists who share their knowledge of new trends and developments in neonatal care.

Purchase each volume individually, or get the entire 7-volume set! Gastroenterology and Nutrition Hematology, Immunology and Genetics Hemodynamics and Cardiology Infectious Disease and Pharmacology New Volume! Nephrology and Fluid/Electrolyte Physiology Neurology The Newborn Lung

Section B

Management of Respiratory Problems

Outline

Chapter 10. Respiratory and Cardiovascular Support in the Delivery Room

Chapter 11. Noninvasive Ventilation of Preterm Infants: An Alternative to Mechanical Ventilation

Chapter 12. Newer Strategies for Surfactant Delivery

Chapter 13. Respiratory Control and Apnea in Premature Infants

Chapter 14. Oxygenation Instability in the Premature Infant

Chapter 15. Optimal Oxygenation in Extremely Preterm Infants

Chapter 16. Patient-Ventilator Interaction

Chapter 17. Pulmonary-Cardiovascular Interaction

Chapter 18. Ventilator Strategies to Reduce Lung Injury and Duration of Mechanical Ventilation

Chapter 19. Automation of Respiratory Support

Chapter 20. Prenatal and Postnatal Steroids and Pulmonary Outcomes

Chapter 21. Cell-Based Therapy for Neonatal Lung Diseases

Chapter 22. A Physiology-Based Approach to the Respiratory Care of Children With Severe Bronchopulmonary Dysplasia

Chapter 10

Respiratory and Cardiovascular Support in the Delivery Room

Gary M. Weiner, Stuart B. Hooper, Peter G. Davis, and Myra H. Wyckoff

Abstract

Aeration of the lungs following delivery is the key to successful transition to newborn life. Clearance of lung fluid enables the onset of gas exchange and initiates the cardiovascular changes, leading to an increase in pulmonary blood flow and maintenance of systemic cardiac output. Most infants make the transition without interventions but up to 10% require some assistance. In some cases, the need for resuscitation may be anticipated, but others with no risk factors require help. Hence, trained personnel must be available at every delivery to assess the newborn and initiate resuscitation when necessary. Nonvigorous and preterm newborns should be taken to a radiant warmer for assessment. Care should be taken to maintain the infant’s temperature in the normal range. Effective ventilation is the single most important action to stabilize a compromised newborn infant. This may be achieved with a number of devices. Whichever is chosen, it is important that the user is proficient at using and troubleshooting that device. The best indicator of effective ventilation is a rapid rise in heart rate. Airway obstruction and mask leak are the most common causes of ineffective ventilation. Current guidelines recommend starting resuscitation with air for term and near-term infants and 30% oxygen for preterm infants. Pulse oximetry may be used to titrate oxygen therapy to achieve oxygen saturation levels similar to those seen in healthy term newborns. Cardiac compressions are recommended for infants with heart rates persistently lower than 60 beats/min. Compressions should be centered over the lower third of the sternum and delivered to a depth of one-third the anteroposterior diameter of the chest. A compression-to-ventilation ratio of 3:1 is currently recommended. Medications may be required in the setting of very severe asphyxia. Epinephrine is useful for asystole or agonal bradycardia because it improves diastolic blood pressure and hence coronary perfusion.

Keywords

airway management; hypothermia; oxygen therapy; pulse oximetry; resuscitation; ventilation

1. • Following delivery, the processes of lung aeration and increases in pulmonary blood flow are closely linked.
2. • Establishing effective ventilation is the key to successful resuscitation.
3. • Although risk factors indicating likelihood of requiring resuscitation are identified, appropriately trained personnel should be present at all deliveries.
4. • Maintaining normal temperature reduces the risk of adverse outcomes.
5. • Routine tracheal suction for nonvigorous newborns with meconium stained amniotic fluid is no longer recommended.
6. • Air should be used for resuscitation of term and late preterm infants, and oxygen supplementation should be guided by pulse oximetry.
7. • The two-thumb technique should be used to deliver cardiac compressions.

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.¹ Pulmonary blood flow (PBF) must also markedly increase and several specialized vascular shunts must close to separate the pulmonary and systemic circulations.² While it is often considered that these events are independent, we now know that they are intimately linked.³ 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.³ 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).^4,5 It is thought that hydrostatic pressure gradients generated by inspiration (or positive-pressure inflations) drive liquid from the airways into the surrounding lung tissue.^4,5 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.⁶ 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).⁷ 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.⁷

Fig. 10.1 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.

Fig. 10.2 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 H₂O. 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. ...