Page 141 - Physiological based CPAP for preterm infants at birth Tessa Martherus

Physiological based CPAP
Physiological based (PB)-CPAP considers the physiological changes that are required to transition from fetus to a newborn (Figure 1). In utero, the future airways are filled with lung liquid. Immediately at birth, the role of CPAP is to increase the pressure gradient generated by inspiration and assist the movement of lung liquid across the distal airway wall into the interstitial tissue. This process occurs across the distal airsacs and so requires the distal movement through the airways. As a result, initially the resistance in the airways is high due to the high viscosity of liquid (compared with air) and to its movement across the airway epithelium (11-13). As such a high pressure gradient is needed to overcome the high airway resistance (17, 18). Once the lungs become aerated and liquid accumulates in the interstitial tissue, the role of CPAP converts to maintaining lung aeration. During this phase of the transition, airway resistance is considerably lower (~100 fold), but lung recoil increases due to the formation of surface tension and interstitial tissue pressure are increased which promote alveolar collapse and liquid re-entry at end-expiration (11-13, 17-22). At this time, continuation of high CPAP levels risk over-expanding the lungs and lower levels are sufficient to fulfil the role in maintaining aeration. If the CPAP decrease is guided by real time parameters, PB-CPAP can be individualized and CPAP levels suit the different phases of the transition.
The aim of this thesis was to investigate the effect of PB-CPAP in preterm infants at birth. We hypothesized that an initial higher CPAP would improve lung aeration and that adverse effects would be avoided by decreasing CPAP after establishing lung aeration, as these lower levels are sufficient to maintain lung aeration. We investigated the effect of PB-CPAP on lung aeration, oxygenation, breathing effort and potential adverse effects in experimental setting using preterm animal models and tested the feasibility and effect of PB-CPAP in clinical setting.
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