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