Page 18 - Physiological based CPAP for preterm infants at birth Tessa Martherus

General introduction
The obstacles for a preterm baby to breathe at birth
While most term infants have no difficulties in dealing with the large and abrupt physiological changes that are required to transition to newborn life, preterm infants can experience much difficulty in transitioning into the newborn state. Preterm infants have lungs that are structurally and functionally immature, they lack the essential components for a smooth transition to newborn life, when pulmonary gas exchange is critical. At 24 weeks gestation, lung development is at the saccular stage, which means that the surface area for gas exchange has not increased as the terminal sacs have not undergo septation to form alveoli and the capillaries have not proliferated to form a narrow air/blood gas barrier. Also, the alveolar epithelium and the surfactant system are still immature when infants are born preterm, before alveolar epithelial cells have had an opportunity to trans-differentiate into type-II cells. Therefore, the alveoli are prone to collapse due to high surface tension, which further reduces the surface area for gas exchange (32-35). In addition, preterm infants have very little epithelial sodium channels and the channels that are present are less functional, meaning preterm infants cannot fully benefit from lung-liquid clearance via this mechanism before birth (13, 36, 37). Also, preterm infants have very compliant chest walls, which makes it more difficult to overcome the lung recoil impeding the increase in gas volume (15, 38, 39). Thus, when infants are born preterm, their lack of fully developed alveoli, surfactant and epithelial sodium channels, as well as the high compliance of the chest wall, make it harder for them to clear lung liquid, prevent alveolar collapse and breathe efficiently after birth.
Respiratory support after preterm birth
Until almost a decade ago, most very preterm infants were electively intubated and mechanically ventilated at birth because they were considered to be incapable of sustaining their respiratory needs. However, when studies (40, 41) showed that mechanical ventilation can be injurious and that non-invasive respiratory support lowers the risk of death or oxygen requirement at 28 days, the focus of respiratory support at birth shifted towards non-invasive application of ventilation. This is most commonly in the form of continuous positive airway pressure (CPAP), to support spontaneous breathing, or intermittent positive pressure ventilation (iPPV) with a positive end-expiratory pressure, to provide artificial ventilation of the lung (5). Both modes, commonly use a face mask to apply this respiratory support.
Although the majority of preterm infants breathe at birth, the respiratory effort is often insufficient (42, 43) or breathing is often missed by the caregiver (44) and so iPPV is deemed necessary. Observational clinical studies (45-47) have shown that the iPPV provided is often inefficient or can be injurious to the preterm infant’s lungs and brain. This can occur when high peak pressures are administered, or infants breathe spontaneously during a positive pressure inflation, creating high tidal volumes (48-50). IPPV can be inefficient due to mask leak or airway obstruction, which can occur due to incorrect positioning or applying to much pressure to the mask. In addition, if the infant is apneic or does not have a stable breathing
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