WHO Collaborative Centre for Training and Research in Newborn Care Science & Physiology behind C P A P Ashok DeorariMD, FNNF,FAMS Department of Pediatrics All India Institute of Medical Sciences
Definition Maintenance of an increased (positive) trans-pulmonary pressure during the inspiratory & expiratory phase of respiration, with the patient breathing spontaneously.
Physiology of CPAP Pulmonary Increases FRC Decreases V/Q mismatch Splints upper airway – airway resistance Tidal volume Work of breathing Conserves surfactant lung 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
Preterm Lambs at 72 Hours • Distal Airspace Wall Thickness - nCPAP C V
Ventilator induced lung injury Biotrauma with tube Atelectotrauma
Ventilator induced lung injury Barotrauma Volutrauma
CPAP magic Opens the lung at FRC Keeps it open by minimal constant pressure –least baro and volutrauma No ET tubes- nobiotrauma Pulmonary arterial pressure are least with improved blood flow, hence less V/Q mismatch
PVR Increases at Lung Volumes Below and Above FRC PVR Lung Volume
Law of LaPlace : P = 2T/r P : pressure T : surface tension r : radius r = 3 T = 6 P = (2 x 6) / 3 P = 4
Law of LaPlace : P = 2T/r P : pressure T : surface tension r : radius CPAP Smaller alveolus r = 1 T = 3 P = (2 x 3) / 1 P = 6 Larger alveolus r = 1.5 T = 3 P = (2 x 3) / 1.5 P = 4
Surfactant CPAP Surface tension Imagine a human chain !!
What did we learn ? CPAP causes less lung injury Give adequate CPAP to open lung at FRC Surfactant and CPAP have additive effect Maximum dividends if -Good delivery room care ; ANS for preterm labor -Acceptance by TEAM