Page 61 - Physiological based CPAP for preterm infants at birth Tessa Martherus

Comparison of two respiratory support strategies for stabilization of very preterm infants at birth
these findings, preclinical studies comparing CPAP (17) or PEEP (13-16, 18) suggested that high-pressure levels improve oxygen saturation and uniformity of lung aeration. Theoretically, high-pressure levels increase the surface area of the alveoli, and thereby the
gas exchange surface area, which increases the efficiency of oxygen exchange, leading to increased oxygen saturations. A reason for achieving similar physiological outcomes, despite
the different airway pressures, could be the closure of the glottis and the inability of the
pressure to be transmitted down into the lower airways. In previous preclinical studies,
animals were intubated and mechanically ventilated, whereas the preterm infants in this
study received non-invasive support. A recent animal study (19) highlighted that closure of
the glottis directly after birth can prevent the transmission of PPV into the lower airways and
whether it is closed or open is closely associated with the breathing pattern. Infants in this
study were initially hypoxic, which likely suppressed breathing activity and caused the glottis 2 to adduct (19). This could impede the delivery of respiratory support and explain the similar physiological outcomes while using different pressure levels.
During phase II, the FiO2 was increased in the low-pressure group, resulting in a significantly higher SpO2 in this group. It is interesting that the SpO2/FiO2 ratio was not statistically different, suggesting that the gas exchange potential was similar between groups. Reasons for different SpO2 but similar SpO2/FiO2 ratios could be that while higher airway pressures increased the surface area for gas exchange, it was insufficient to equal a higher oxygen gradient for O2 diffusion across the alveolocapillary border. Clearly, the high-pressure group could have achieved the same SpO2 levels if more supplemental oxygen was given, but the FiO2 required to achieve the same SpO2 would likely be less in this group.
Short-term clinical outcomes were statistically similar between groups with exception of the intubation rate. Different cut-off values for intubation for e.g., pH and FiO2 potentially contributed to this difference. In the low-pressure group the threshold for intubation was lower and infants were directly intubated when CPAP failed the infant’s respiratory needs, whereas infants of the high-pressure group first received non-invasive bi-level positive airway pressure or high frequency oscillation before being intubated. The occurrence of spontaneous intestinal perforations and pneumothoraxes during admission tended to be higher in the high-pressure group. The difference was not statistically different, most likely due to the limited sample size. It remains unknown to what extent the high-pressure in the delivery room may increase the risks, as infants in the high-pressure group continued to receive higher pressures at the ward. However, preclinical studies in lambs (14, 15) have also recorded a high pneumothorax incidence after using high PEEP pressures in recruited lungs. It has been suggested that neonatal resuscitation should commence with higher pressures to facilitate lung aeration when the lungs are liquid-filled, airway resistance is high and the lungs are less compliant (33). Currently, higher airway pressures are already used in the delivery room for lung aeration when using sustained inflations and PPV; in the low-pressure group 74% of the infants received sustained inflations of 20 and 24 cmH2O and 81% of infants received PPV using inflation pressures of 26 cmH2O for 2:08 of the 7 min. Once lung liquid is replaced by
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