Page 37 - Physiological based CPAP for preterm infants at birth Tessa Martherus

Increasing to higher pressure levels after lung aeration also affect the breathing rate. Crawshaw et al. (21) showed that increasing CPAP levels after lung aeration decreases the breathing rate in very premature rabbit pups. In pups who already established a stable breathing pattern, the respiratory rate was reduced as CPAP levels were increased above 7 cmH2O.
High PEEP levels could also overexpand the lungs. However, it is unknown at what level overexpansion occurs. Probyn et al. (33) reported optimal lung compliance at 8 cmH2O and
Crossley et al. (34) found no difference comparing different PEEP levels. Both studies started 1 their intervention after the lungs were aerated (Table 1). As they observed pneumothoraxes
when ventilating premature lambs with 12 cmH2O PEEP, it could be too high to use in human
infants once the lungs are aerated.
While these studies highlight the fundamental physiology underpinning the newborn transition, the results cannot directly be translated into the clinical setting where we aim to support spontaneous breathing by CPAP and PPV via prongs or facemask. During the experiments, animals were sedated and intubated to provide PEEP as part of MV. During intubation, the larynx is bypassed resulting in less leak and obstruction. In addition, most studies were performed after the lungs were aerated and therefore have not characterised the effect of CPAP during the respiratory transition. The animal experiments are, however, a unique opportunity to investigate the underlying physiology and factors that cannot be measured in humans. The experiments provide a basis for further (pre)clinical trials investigating different CPAP levels. We expect that high CPAP levels improve (the uniformity of) lung aeration, oxygenation and subsequent PBF. Maintaining high CPAP levels after lung aeration can reduce the PBF and respiratory rate and can increase the risk of overexpansion and pneumothoraxes in preterm sheep. Very preterm infants therefore might benefit initial higher PEEP levels that are titrated after lung aeration
Supporting breathing of preterm infants at birth
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