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RESPIRATORY DISTRESS SYNDROME

STAGES OF LUNG DEVELOPMENT

 5 Stages of Lung Development  Embryonic  Pseudoglandular  Canalicular  Saccular (Terminal Sac)  Alveolar

RESPIRATORY DISTRESS SYNDROME Statistics

 The more premature, the higher the RDS risk

 Estimated to cause 30% of neonatal deaths

 As many as 70% of all preterm deaths are also attributed to RDS

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RESPIRATORY DISTRESS SYNDROME

 Surfactant Deficiency  Surfactant is composed of:  Phospholipids  Dipalmitoyl phosphatidylcholine (DPPC) (Lecithin)  Peaks at around 35 wks  Phosphatidylglycerol (PG)  Sphingomyelin  Formed at around 18 wks  Stable throughout gestation  Immature surfactant  Neutral lipids (cholesterol)  Surfactant proteins  Produced by Type II pneumocytes

L/S RATIO

SURFACTANT FUNCTION

 Reduces alveolar surface tension  Enhances alveolar expansion  Optimizes compliance  Lessens WOB  Helps to maintain FRC  Allows optimal gas exchange

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SURFACTANT

SURFACTANT INTERUPTION/INHIBITION

 Hypoxia  Hypercapnea  Acidosis  Shock  Pulmonary edema  Smaller of twins  IDM  Underinflation  Overdistention  Mechanical ventilation

WHY DO BELLY FLOPS HURT?

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SURFACE TENSION!!!!

RESPIRATORY DISTRESS SYNDROME Physiology

 Decreased compliance  Increased incidence of atelectasis  Intrapulmonary shunting – V/Q mismatch  Hypoxemia  Hypercarbia  Acidosis

RESPIRATORY DISTRESS SYNDROME Physiology (cont’d)

 Hypoxemia and Acidosis leads to:  Pulmonary vasoconstriction  Increased PVR  Intracardiac shunting (Right to left)  PFO  PDA  Cascade of events intensifying V/Q mismatch

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RESPIRATORY DISTRESS SYNDROME Physiology (cont’d)

 Immaturity of terminal air sacs/vasculature  Chest wall immaturity/non-ossified bone  Poor stability during inspiration  Immaturity of diaphragm and other respiratory muscles  CNS immaturity leading to apnea

RESPIRATORY DISTRESS SYNDROME

 Neonates at greatest risk:  Born before 35 wks (especially 28)  IDM  History of RDS in siblings  Male  C-section without labor  Poor Apgar scores

RESPIRATORY DISTRESS SYNDROME Clinical Symptoms

 Symptoms arise to compensate for increasing atelectasis  Tachypnea  Retractions  Nasal flaring  Grunting  Diminished breath sounds  Inspiratory crackles  Cyanosis  Pallor

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MANAGEMENT

 Goal of treatment:  Maintain alveolar ventilation and support the respiratory system while minimizing damage and minimizing complications.

Easy to envision, difficult to accomplish.

MANAGEMENT (cont’d)

 Prevent pre-term deliveries  Antenatal corticosteroids (betamethasone or dexamethasone)  Thermoregulation  Fluid management  Optimizing nutrition  Early institution of CPAP  Avoidance of mechanical ventilation  Selective surfactant administration

CPAP

 CPAP  Stents airways  Establishes and maintains functional residual capacity (FRC)  Increases pharyngeal cross-sectional area  Improves pulmonary compliance  Decreases airway resistance  Increases tidal volumes  Improves diaphragmatic activity  Prevents further alveolar collapse  Reduces labored breathing

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CPAP (cont’d)

 Promotes surfactant production  Improves oxygenation via enhanced diffusion  Increases V/Q matching  Decreases shunting (intrapulmonary and intracardiac)  Stabilizes the compliant chest wall  Reduces obstructive apnea  May decrease central apnea by promoting a regular breathing pattern

IMPORTANCE OF FUNCTIONAL RESIDUAL CAPACITY (FRC) IN RDS

 Functional residual capacity  Resting volume of the lung at end-expiration  Expiratory reserve volume (ERV) + residual volume (RV)  Approximately 20% of total lung volume  Infants with RDS have an abnormally low FRC  Poor compliance, lung volumes and increased WOB  Severe RDS requires positive end-expiratory pressure to establish FRC  Decreases the risk of developing BPD

FRC

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FRC (cont’d)

MAXIMIZE CPAP SUCCESS

 Give every baby an opportunity to succeed on CPAP  Start CPAP in delivery (T-piece)  Use “liberal” definition of CPAP failure  Deliver an appropriate level of support (5-8 cm H2O)  Routine monitoring of pressures/positioning  Choose appropriate interface and fixation

MAXIMIZE CPAP SUCCESS (cont’d)

 Chinstraps and pacifiers  Avoiding gastric distention  Maximizing positioning  Nipple feeding  Skin-to-skin  Weaning properly (according to guidelines)  Identifying and managing weaning failure

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MAXIMIZE CPAP SUCCESS (cont’d)

 Duration of CPAP (3 clinical considerations)  When does the infant meet “weaning” criteria?  Deciding which is the preferred method to cease CPAP  Toleration of “weaning”  Worsening apnea  Increased FiO2 to maintain sats  Increase WOB  Return to previous CPAP level if not tolerated

MAXIMIZE CPAP SUCCESS (cont’d)

 Implications for Clinical Practice  Columbia approach towards weaning  The more premature the infant at birth, the later the typical PMA at successful CPAP discontinuation  Premature infants vs more mature infants at the same PMA  There may be a trade-off between CPAP support and O2

MECHANICAL VENTILATION

 Prolonged ventilation is a leading factor for development of BPD and poor neurodevelopmental outcomes

 Lung injury is minimized by non-invasive ventilation

 Mechanical ventilation is a last resort

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MECHANICAL VENTILATION (cont’d)

 Effects of mechanical ventilation  Volutrauma  Barotrauma  Atelectotrauma  Rheotrauma  Biotrauma  Increased MAP needed to expand collapsed alveoli  Cytokine release - inflammation  Alveolar endothelial lining damage  Leakage of proteins – hyaline membrane formation

MECHANICAL VENTILATION (cont’d)

 “New approaches” to invasive ventilation have not panned out

 High frequency DOES NOT reduce BPD incidence in the smallest patients

SELECTIVE SURFACTANT ADMINISTRATION

 In the 1990s, CPAP as an initial modality went out of favor  ET intubation and surfactant was believed superior  Improved survival  Decreased air leaks  There were problems:  None of the trials had a control group randomized to CPAP  The widely-accepted intubate and surf didn’t lead to a decrease in BPD

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SELECTIVE SURFACTANT ADMINISTRATION (cont’d)

 Jump to 2008  5 large RCTs examined:  Meta-analysis of those trials have recently been published  Compared early CPAP use with routine intubation and surfactant administration  Infants <30 wks gestation at birth  2 trials:  infants randomized to either CPAP or surfactant  Remaining 3 trials:  Infant’s assessed at birth before randomization

SELECTIVE SURFACTANT ADMINISTRATION (cont’d)

 Results of those analysis:  Initial CPAP decreased the incidence of BPD or death

 Furthermore:  The authors concluded that one additional infant could survive to 36 wks without BPD for every 25 babies treated with NCPAP in DR.

SELECTIVE SURFACTANT ADMINISTRATION (cont’d)

 Cochrane review:  Intubation and prophylactic surfactant administration was associated with a higher BPD and death than infants on CPAP as an initial therapy with selective surfactant delivery

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References

1. Clyde J. Wright, MD; Richard A. Polin, MD; Haresh Kirpalani, BM, MSc. “Continuous Positive Airway Pressure to Prevent Neonatal Lung Injury: How Did We Get here, and How Do We Improve?”. The Journal of Pediatrics. 2016. 2. Nicolas Bamat; Erik A. Jensen, Haresh Kirpalani. “Duration of Continuous Positive Airway Pressure in Premature Infants”. Seminars in Fetal and Neonatal Medicine. 2016: vol 21(189-195). 3. Rakesh Sahni; Maria Schiaratura; Richard A. Polin. “Strategies for the Prevention of Continuous Positive Airway Pressure Failure”. Seminars in Fetal and neonatal medicine. 2016: vol. 21(196-203). 4. Rubarth, Lori, PhD, NNP-BC; Quinn, Jenny, MSN, NNP-BC, MHA. “Respiratory Development and Respiratory Distress Syndrome”. Neonatal Network. July/August 2015: vol . 34, no. 4. 5. Samir Gupta; Steven M. Donn. “Continuous Positive Airway Pressure: Physiology and Comparison of Devices”. Seminars in Fetal and Neonatal Medicine. 2016: vol. 21(204-211).

References (cont’d)

6. Walsh, Brian K. Perinatal and Pediatric Respiratory Care (pg. 248). St. Louis, Missouri: Saunders, 2010. 7. Whitaker, Kent. Comprehensive Perinatal and Pediatric Respiratory Care (pg. 203). Stamford, Connecticut: Cengage Learning, 2015.

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