Page 34 - Physiological based CPAP for preterm infants at birth Tessa Martherus

Chapter 1
CPAP or PPV via facemask when breathing is insufficient in very preterm newborns
PPV is currently initiated at birth when infants are apnoeic or breathe insufficiently (14-16). PPV, however, often fails to support the respiratory need of the infant. In a clinical observational study (5), 36% of all inflations consisted of a tidal volume below 2.5 mL/kg, while healthcare providers aimed to deliver tidal volumes of 4-8 mL/kg. This can be caused by the use of inadequate pressures, incorrect facemask positioning leading to mask leak and by obstruction (Figure 1). Pressing the mask on the face too tight, obstruction of the nose and mouth and overextension or flexion of the neck may obstruct gas flow to the lungs (17, 18).
The physiology of the very preterm newborn also impacts on the success of non-invasive ventilation in the delivery room: closure of the larynx is a contributing factor for PPV failure (19-21). Before birth, the larynx of the fetus is closed to retain lung liquid in the airways to create a positive expanding pressure that stimulates lung growth and development (22-24). After birth, the larynx transitions to create a patent airway for breathing. Phase contrast (PC) X-ray imaging (21) in preterm rabbit pups immediately after birth showed that the larynx is closed if the pup is apnoeic. During a spontaneous breath, the larynx opens, which allows aeration of the lungs, but closes again if the breathing is intermittent. Unlike previously suggested, opening of the larynx throughout the respiratory cycle is closely associated with a stable breathing pattern (21) rather than the degree of lung aeration (25). Establishing a stable breathing pattern by stimulating spontaneous breathing might be the key to accelerate the laryngeal switch from closed fetal to open newborn state. Very preterm infants could benefit from focussing on spontaneous breathing rather than providing PPV against a closed glottis, especially as PPV triggered closure of the larynx again in rabbit pups who already had a stable breathing pattern (21).
PPV can also be injurious to the premature lungs and brains when high tidal volumes are given. As it is hard to estimate the delivered tidal volume during PPV (26), an observational study showed that in 10% of all inflations, tidal volumes were >10 mL/kg despite target values being 4-8 mL/kg (5). While this could be attributed to a high PIP, it has been observed that spontaneous breathing coincided with inflations also contributes to higher delivered tidal volumes (5, 11). Preclinical studies showed that high tidal volumes adversely affect the cardiopulmonary haemodynamics and even can cause lung (27, 28) and brain injury (6, 29). A recent clinical study (30) confirmed the danger of high tidal volumes, as they found more intraventricular haemorrhages in infants receiving tidal volumes >6 mL/kg.
PPV is often ineffective at aerating the lung or can even be injurious. Optimising spontaneous breathing by CPAP might be a better approach. Most very preterm infants breathe at birth, although weakly, and stimulating spontaneous breathing may be the key to accelerate the switch from closed fetal to open newborn larynx state and CPAP might therefore be less obstructive. Also, during CPAP, less mask leak occurs, as most mask leak occurs during
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