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WHO Collaborative Centre for WHO Collaborative Centre for Training and Research in Newborn CareTraining and Research in Newborn Care
Ashok DeorariAshok Deorari MD, FNNF,FAMSMD, FNNF,FAMS
Department of Pediatrics All India Institute of Medical Sciences
Science & Physiology Science & Physiology behind C P A Pbehind C P A P
DefinitionDefinition
Maintenance of an increased (positive) Maintenance of an increased (positive) trans-pulmonary pressure during the trans-pulmonary pressure during the
inspiratory & inspiratory & expiratoryexpiratory phase of phase of respiration, with the patient breathing respiration, with the patient breathing
spontaneously.spontaneously.
Physiology of CPAPPhysiology of CPAPPulmonaryPulmonary
Increases FRCIncreases FRC
Decreases V/Q mismatch Decreases V/Q mismatch
Splints upper airway – Splints upper airway – airway resistance airway resistance Tidal volumeTidal volume
Work of breathingWork of breathing
Conserves surfactantConserves surfactant
lung compliancelung compliance
Effect of Ventilator on Preterm Lamb Lung
No ventilation
24 h ventilation
Limitations of premature lung 1.Underdeveloped architect to hold the lung open
2.Thicker and few septa so less SA for gas exchange
Pinkerton KE, et al J Appl Physiol, 1994
nCPAPnCPAPC VC V
Preterm Lambs at 72 HoursPreterm Lambs at 72 Hours- Distal Airspace Wall Thickness -Distal Airspace Wall Thickness -
Ventilator induced lung Ventilator induced lung injuryinjury
•Biotrauma with tubeBiotrauma with tube•Atelectotrauma Atelectotrauma
Ventilator induced lung Ventilator induced lung injuryinjury
•Barotrauma Barotrauma •VolutraumaVolutrauma
CPAP magicCPAP magic
• Opens the lung at FRCOpens the lung at FRC
• Keeps it open by minimal Keeps it open by minimal constant pressure –constant pressure –least least baro baro and volutraumaand volutrauma
• No ET tubes- No ET tubes- nono biotraumabiotrauma
•Pulmonary arterial pressure are Pulmonary arterial pressure are least with improved blood flow, least with improved blood flow, hence less V/Q mismatch hence less V/Q mismatch
PVR Increases at Lung PVR Increases at Lung Volumes Below and Above Volumes Below and Above
FRCFRC
PVR
Lung Volume
r = 3 T = 6P = (2 x 6) / 3P = 4
Law of LaPlace : P = 2T/rP : pressure T : surface tension r : radius
Larger alveolus
r = 1.5T = 3
P = (2 x 3) / 1.5P = 4
Smaller alveolus
r = 1T = 3
P = (2 x 3) / 1P = 6
CPAP
Law of LaPlace : P = 2T/r P : pressure T : surface tension r : radius
Surface tensionImagine a human chain !!
CPAP Surfactant
What did we learn ?1. CPAP causes less lung injury 2. Give adequate CPAP to open lung at
FRC 3. Surfactant and CPAP have additive
effect 4. Maximum dividends if -Good delivery room care ; ANS for preterm labor
-Acceptance by TEAM
The Best Ventilator… Least The Best Ventilator… Least damagedamage