Page 159 - Physiological based CPAP for preterm infants at birth Tessa Martherus

there were also concerns regarding the use of higher pressures. In intubated preterm sheep whose lungs were already aerated, 8 cmH2O CPAP did not cause pneumothoraxes (15), however 8-12 cmH2O PEEP reduced pulmonary blood flow (PBF) and increased the risk of pneumothoraxes (23-26). Clinical studies found no indications of adverse events when 6-15 cmH2O PEEP was implemented in the DR (20-22) and it is possible that 15 cmH2O CPAP does not over-expand the lungs immediately at birth. However, harm may be caused if pressures remain above 8 cmH2O after lung aeration.
In Chapter 2 we report our findings of a retrospective comparison study, in which we evaluated the CPAP strategies of two centers (5-8 cmH2O vs 12-35 cmH2O CPAP). We included 27 pairs of infants, who were born before 28 weeks of gestation and were matched based on birthweight and gestational age. We could not detect the effect of different CPAP levels on oxygen saturation (SpO2), which could be due to the fact that the larynx hampered support from reaching the lungs during apnea. However, the SpO2/FiO2 ratio remained similar between groups when FiO2 was increased in the 5-8 cmH2O but not in the 12-35 cmH2O group, which is likely due to the fact that higher CPAP levels facilitated increased aeration that was needed to attain similar SpO2/FiO2 ratios. We also found that most infants who were supported with 5-8 cmH2O CPAP received iPPV and were then subjected to MAPs of ~15 cmH2O. There were no signs of pulmonary over-expansion and cardiovascular impairment in both groups. Yet, infants in the 12-35 cmH2O CPAP group developed a higher pneumothorax rate later on and while different factors may have contributed to the development of these pneumothoraxes, it could also emphasize the risks of continuing high CPAP levels after lung aeration has been established.
Proposed physiological based CPAP approach
Based on our findings in Chapter 1 and 2, we know that higher pressures are beneficial for promoting lung aeration (15, 17, 18) and that infants commonly receive MAPs of ~15 cmH2O
as a result of iPPV during stabilization. We also know that once lung aeration has been established, continuation of pressures above 8 cmH2O could cause harm (23-26) (Chapter 2). S Taking this in consideration and that 8 cmH2O CPAP is the upper range commonly used in the
NICU, we decided that our PB-CPAP approach should commence with 15 cmH2O and be reduced to 8 cmH2O once the infant is stabilized.
Evaluating physiological based CPAP
In Chapter 3 we examined the potential benefits of PB-CPAP, as we measured the effects of CPAP on lung aeration. Spontaneously breathing preterm rabbits (~26-28 weeks human gestation) received 0, 5, 8, 12, 15 cmH2O of CPAP or variable CPAP of 15 to 5 or 15 to 8 cmH2O (decreasing ~2 cmH2O/min) for up to 10 min after birth. Lung function was measured using phase contrast x-ray imaging. We demonstrated that 15 cmH2O indeed improved lung aeration and reduced the occurrence of apnea when compared to the currently used CPAP
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Summary
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