Page 36 - Physiological based CPAP for preterm infants at birth Tessa Martherus

Chapter 1
Which CPAP strategy?
Although CPAP levels of 5-6 cmH2O are commonly used in the delivery room, CPAP levels and titration strategies vary widely between neonatal centres (13, 14) To date, no clinical trials have been performed assessing different CPAP strategies in very preterm infants at birth. Preclinical studies (Table 1) have provided fundamental evidence comparing the use of different CPAP (31) and positive-end expiratory pressure (PEEP) strategies (32-36) in preterm newborns in the delivery room. During mechanical ventilation (MV), both PEEP and PIP are used to ventilate the infant via an endotracheal tube, whereas PPV is applied non-invasively via facemask or prongs. On CPAP, infants breathe spontaneously on a continuous pressure to prevent the alveoli from collapse. In this review, we distinct PEEP (as part of PPV or MV) and CPAP. The preclinical studies investigated (changing) CPAP and PEEP levels of 0-12 cmH2O, and some studies (31, 32, 34, 36) were performed after the lungs were aerated as part of the ventilation strategy.
Mulrooney et al. (31) compared bubble CPAP in preterm lambs, whereas other studies (32-34, 36) compared various PEEP strategies as part of MV (Table 1). All studies concluded that increasing and/or initiating with higher PEEP levels improved oxygenation and was more effective at supporting the respiratory transition at birth.
A PC X-ray imaging study (35) in premature rabbit pups found that the initial levels of PEEP also influence the distribution of air throughout the lungs, and this effect even remains after pressure levels are adjusted over time. The study highlighted that when initial PEEP levels of 10 cmH2O were used in preterm rabbits during MV, the air distributed uniformly across the lungs. When the PEEP level was reduced, the uniformity of lung aeration deteriorated but could easily be restored by increasing the PEEP pressure. When MV was initiated with 0 or 5 cmH2O PEEP, lungs were not uniformly aerated, and this could not be improved by increasing the PEEP. This finding suggests that uniform lung aeration is best achieved by starting respiratory support with higher PEEP levels.
Pressure levels also affect essential markers of the cardiorespiratory transition at birth to establish an independent circulation: the pulmonary vascular resistance and pulmonary blood flow (PBF). As initial high PEEP levels improve lung aeration, it is likely to promote the increase in PBF. Due to the non-compliant nature of the liquid-filled lung at birth, high PEEP levels will not compress the perialveolar capillaries initially (33, 37). As lung compliance increases as the lung aerates, maintaining high PEEP levels will eventually compress the intra-alveolar capillaries and reduce PBF (32, 34, 36). Other cardiovascular haemodynamic components, that is, ductus arteriosus shunting and heart rate, are affected by the PEEP level and can reduce the PBF. Decreasing the PEEP, however, will not restore PBF to initial values due to volume hysteresis within the lungs (32, 36).
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