Page 145 - Physiological based CPAP for preterm infants at birth Tessa Martherus

also could indicate that while initial high CPAP does not over-expand the lungs, reducing CPAP levels following lung aeration may reduce the risk of adverse effects such as pneumothoraxes. It is important to note, while there is much concern centred around the application of high airway pressures at birth, most infants in the 5-8 cmH2O CPAP cohort received iPPV and as such, were subjected to MAPs of ~15 cmH2O across the 10 min resuscitation period
The findings in Chapter 1 and 2 implied that 6-20 cmH2O CPAP/PEEP may have beneficial effects on lung aeration at birth, but previous studies have shown that continuation of PEEP levels above 8 cmH2O after lung aeration may cause harm. Taking into account that infants already are subject to a MAP of ~15 mH2O during iPPV in the DR and that 8 cmH2O is the upper range of the CPAP levels used on the NICU, we decided to use an initial 15 cmH2O for our PB-CPAP approach, that is then gradually reduced to 8 cmH2O once lung aeration has been established and the infant has been stabilized.
Effects of physiological based CPAP
We investigated the effects of PB-CPAP in experimental setting using preterm animals models in Chapter 3 and 4. We investigated the effect CPAP levels on aeration and breathing rate in preterm animals receiving 0, 5, 8, 12, 15 continuous, 15 to 5 or 15 8 cmH2O CPAP at birth. In Chapter 3 we focussed on the ability of PB-CPAP to promote lung aeration in preterm rabbits, whereas in Chapter 4 we focussed on the potential adverse effects of PB-CPAP on PBF in preterm sheep. In Chapter 5 we reported the introduction PB-CPAP in the DR and tested the feasibility and effect of PB-CPAP in preterm infants. In this small randomized clinical trial, infants were randomized to receive either CPAP of 5-8 cmH2O or PB-CPAP starting with 15 cmH2O that was reduced to 8 cmH2O.
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General discussion
Lung aeration
GD
The use of phase contrast x-ray imaging allowed us to directly visualise and measure lung aeration, specifically functional residual capacity (FRC), in preterm rabbits (Chapter 3). We demonstrated that (initial) 15 cmH2O CPAP facilitates higher FRCs compared to the currently used CPAP levels and that rabbits supported with 15 cmH2O more often reached physiological FRCs (≥15 mL/kg). After lung aeration was established, at least 8 cmH2O CPAP was required to maintain lung aeration.
In Chapter 4 and 5, we demonstrated that PB-CPAP, which commenced with 15 cmH2O CPAP, accelerates and/or elevates the physiological increase in heart rate and PBF. While lung aeration was not measured, the elevated physiological increase in PBF and heart rate likely reflected a higher degree of lung aeration than those supported with the currently used CPAP levels of 5-8 cmH2O. When infants are born, lung aeration is known to trigger a large increase in PBF. Recent studies suggest that the movement of lung liquid into the interstitial tissue, triggers the J-receptors located in the alveolar wall (12, 21). The stimulation of these receptors
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