Page 20 - Physiological based CPAP for preterm infants at birth Tessa Martherus

General introduction
causes tissue damage leading to bronchopulmonary dysplasia and retinopathy of prematurity (68, 69). Recently, Dekker et al. (70) showed that initiating respiratory support with 100% oxygen improves the respiratory effort, oxygenation and reduces the duration of mask ventilation, without increasing exposure to of hyperoxia or the total exposure high inspired oxygen levels, as the inspired oxygen concentration was carefully titrated down, guided by the infant’s oxygenation.
While studies have investigated the benefits of stimulating breathing at birth, very little data is available on the optimal approach for supporting their breathing effort. A recent study in animals (71) found that improving the breathing rate does not directly lead to an enhanced degree of lung aeration, indicating that other factors could be involved, such as the depth of inspiration. As the main factor driving lung aeration is the transpulmonary pressure gradient between the airways and interstitial tissue, increasing the CPAP level could increase the transpulmonary pressure gradient. In the era of stimulating and supporting spontaneous breathing, CPAP may be the key facilitator to improve lung aeration and the use of CPAP at birth needs to be evaluated thoroughly.
CPAP strategy in the delivery room
Currently, 4-8 cmH2O CPAP is widely adopted in the delivery room, but this approach has been extrapolated from strategies used in the intensive care unit. However, scientific evidence to support this pressure range is lacking and the large variability in CPAP protocols used between neonatal centres, highlights this knowledge gap (53, 65, 72). Until recently, only two preclinical studies had investigated the effect of different CPAP levels at birth. In intubated preterm sheep (73), CPAP levels of 8 cmH2O CPAP improved lung gas volumes and oxygenation compared to 5 cmH2O CPAP, yet breathing rates were reduced. Similarly, breathing rates of preterm rabbits declined after increasing non-invasive CPAP above 7 cmH2O (17).
It is also pertinent to note that the available scientific evidence for using specific CPAP levels was extrapolated from animal studies where different positive end-expiratory pressures (PEEP) levels were compared in intubated and mechanically ventilated preterm rabbits (74) and sheep (75-78). While these studies showed that a PEEP level above 8 cmH2O improved lung aeration and newborn oxygenation, it also caused pulmonary overexpansion, reduced pulmonary blood flow and heart rates and increased the risk on pneumothoraxes. However, these animals were anesthetised, intubated and mechanically ventilated, which is a completely different mode of respiratory support than the application of CPAP in spontaneously breathing preterm infant going through transition at birth. Indeed, although the CPAP level and PEEP level may be the same, the CPAP is the highest positive pressure applied to the airways, whereas PEEP is the lowest pressure and the applied pressures cycle considerably above this during iPPV. Even more important, the animals in these experiments
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