Page 132 - Physiological based CPAP for preterm infants at birth Tessa Martherus
P. 132

Chapter 5
for using the escape strategy was good breathing effort, however we now know that this is not reflective of lung aeration (30) and infants with good breathing efforts may still benefit from PB-CPAP. Second, the number of predefined evaluation moments could be reduced by leaving the decision to adjust CPAP levels to the discretion of the caregiver. Third, a consistent CPAP level could be used until the infant stabilizes and interfaces are switched and/or the infant is transferred to the NICU. This would be the most pragmatic option and is already common practice in some centers. While details of how PB-CPAP can be used may differ between centres depending on how it best fits into the overall DR care, early involvement of the medical team and scenario trainings may increase the usability of PB-CPAP.
We hypothesized that PB-CPAP would improve lung aeration and subsequently improve physiological parameters but found no effects on SpO2 or FiO2. Recent rabbit studies have demonstrated that the increase in lung aeration and oxygenation are not necessarily co-dependent (25, 30), yet they are likely to be additive and at least some lung aeration is essential. Aeration must positively affect SpO2 but the relative contribution of aeration versus the gradient for oxygen diffusion is complex and influenced by other factors such as pulmonary blood flow and cardiac output. The difference in gestational age and the high FiO2 levels in both groups could have diminished the effects of PB-CPAP compared to lower CPAP levels on SpO2 and FiO2. Also, given that power requirements with respect to sample size could not be met, it is not possible to draw negative conclusions from our study. In preterm sheep, 8 and 15 cmH2O CPAP improved oxygenation and lowered FiO2 requirements as compared to 5 cmH2O CPAP (26, 31). This study found no effect on the initial and overall FiO2 requirement, yet the course of change in FiO2 levels suggests that PB-CPAP potentially facilitates an earlier decrease in FiO2 requirement.
PB-CPAP led to a larger increase in heart rate, which may reflect a better lung aeration. When infants are born and aerate their lungs, this stimulates a very large increase in pulmonary blood flow. Recent evidence suggests that as lung liquid moves into the interstitial tissue it triggers J-receptors located in the alveolar wall (15, 23). Stimulation of these receptors is thought to initiate a vagal reflex facilitating global pulmonary vasodilation and a subsequent increase in pulmonary blood flow and heart rate (32, 33). The outcomes of this study resemble preclinical studies demonstrating that 15 cmH2O CPAP improves lung aeration (25), PBF and heart rate (26) compared to the currently used CPAP levels. Improved lung aeration would explain why infants required a shortened duration of mask ventilation and were stabilized three minutes earlier in the PB-CPAP group.
Two infants restarted breathing during iPPV but stopped when CPAP was increased to 15 cmH2O. We speculate that these infants had already established lung aeration and apnea had been caused by a Hering-Breuer reflex or trigeminal reflex (34). Similar findings have been described in preterm rabbits that had established lung aeration, but became apneic as CPAP was suddenly increased from below to above 7 cmH2O (4). While this is speculative, some infants may establish aeration during iPPV (25) and future studies have to investigate if
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