Page 160 - Physiological based CPAP for preterm infants at birth Tessa Martherus

Summary
levels but that there was no effect on breathing rate. Once lung aeration was established, at least 8 cmH2O CPAP was required to maintain aeration and breathing rate. We also observed that the use of 15 cmH2O did not increase the risk of lung over-expansion, pneumothorax or CPAP belly, which were rare in this study.
In Chapter 4 we investigated the potential adverse effects of PB-CPAP on pulmonary and cerebral blood flow (PBF). We hypothesized that 15 cmH2O may over-expand the lungs, which may reduce physiological increase in PBF caused by lung aeration at birth. Preterm lambs received 5, 15 continuous or 15 to 8 cmH2O CPAP while we measured cardiovascular parameters. In this study, we demonstrated that 15 cmH2O CPAP improved the physiological increase in PBF and heart rate at birth, which reflects improved lung aeration. The increase in PBF, as well as higher arterial pressures and normal jugular venous pressures, indicates that PB-CPAP does not cause pulmonary over-expansion or impede cardiovascular function. Similarly, as cerebral blood flow and jugular venous pressure were not affected, B-CPAP did not increase the risk for intraventricular hemorrhage. Furthermore, 15 cmH2O seemed to positively benefit oxygenation and better support spontaneous breathing as lambs achieved higher SpO2, required lower FiO2, lower apnea incidences, higher breathing rates and lower intubation rates. We found that the decrease of CPAP levels caused an increase in FiO2 requirement, which may indicate that CPAP levels were decreased too soon. There were no indications of increased risk on pneumothoraxes, as these were not found in the lambs receiving 15 cmH2O CPAP during post-mortem examination. Because we observed that 15 cmH2O CPAP was only partially (~75%) transmitted below the trachea and 5-8 cmH2O CPAP was fully transmitted to the lungs, we suggest that the larynx regulates pressure transmission to the lungs and functions as a preventive mechanism to protect the infant from possible harm.
Finally, in Chapter 5 we describe a small randomized controlled trial where we tested the feasibility and effects of PB-CPAP in infants born between 24-30 weeks gestation. Infants were randomized to PB-CPAP or 5-8 cmH2O CPAP for the first 10 min after birth. PB-CPAP involved applying an initial CPAP level of 15 cmH2O, which was decreased stepwise until 8 cmH2O once infants were stabilized (defined as: spontaneous breathing and heart rate ≥100 bpm, SpO2 ≥85% with FiO2 ≤0.4). Planned enrollment was 42 infants, however the study was halted prematurely due to a low inclusion rate and recent changes in the local resuscitation guideline that conflicted with the study protocol. We evaluated the feasibility of our PB-CPAP approach by checking protocol adherence and via post-trial evaluations. We found that there were only few minor protocol deviations, which occurred in both groups. Yet, the PB-CPAP protocol was too complex for caregivers and requires simplification. This was due to the need to make many CPAP changes and evaluations. We measured the effects of PB-CPAP in 28 infants (PB-CPAP n=8, 5-8 cmH2O n=20). We found evidence to indicate that PB-CPAP improves lung aeration, which was reflected by improved heart rate and the course of change in breathing rates and tidal volumes. While improved lung aeration may explain the shortened duration of mask ventilation and faster stabilization of infants supported with PB-CPAP, there were no
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