Page 147 - Physiological based CPAP for preterm infants at birth Tessa Martherus

us to confirm or refute this in our clinical trial (Chapter 5). Larger clinical trials are needed to determine the effect of PB-CPAP on apnea in preterm infants.
While breathing effort was also evaluated by minute volume and breathing rate, the true effect is hard to determine as these are the results of a complex integration of several competing factors. In the rabbit study (Chapter 3), breathing rate was higher when kittens were supported with CPAP compared to no CPAP but there seemed to be little difference in breathing rate between CPAP levels. Kittens were able to maintain breathing rates when CPAP was gradually reduced to 8 cmH2O but not when CPAP was lowered to 5 cmH2O. In preterm lambs (Chapter 4), breathing rates were higher in those supported with 15 cmH2O CPAP as compared to 5 cmH2O and when CPAP levels were gradually reduced to 8 cmH2O lambs were still able to maintain their breathing rate. In a previous study, lambs achieved similar breathing rates when supported by invasive CPAP in the first hours after birth (24).
In preterm infants (Chapter 5), PB-CPAP and CPAP levels of 5-8 cmH2O resulted in statistically similar breathing rates and tidal volumes, however infants supported with PB-CPAP achieved a breathing rate that was ~10 breaths/min higher and tidal volumes seemed to stabilize sooner and at lower volumes. As previous preterm rabbit studies (12, 25) have demonstrated that with each breath tidal volumes decrease while lung aeration increases, we speculate that the time course of changes in breathing rate and tidal volumes may indicate that infants in the PB-CPAP group were breathing more effectively and aeration was established sooner. Increased breathing rates could also result in a Heads paradoxical reflex (47, 48). Lung inflation would then stimulate irritant receptors that provoke the respiratory centre to enhance breathing, which is a common phenomenon in preterm infants who start to breathe during sustained inflations (46, 49-51). However, as tactile stimulation can stimulate breathing (8) this could have led to bias between groups which minimized differences. Tactile stimulation was not standardized and difference in the frequency and method of tactile stimulation in the animal and human infant studies could have occurred, which could explain why CPAP had an effect on breathing rates in preterm infants and sheep but not in preterm rabbits. The CPAP levels may affect breathing effort but there are other factors which can have a larger impact.
Potential adverse effects of physiological based CPAP
Using higher CPAP levels could potentially over-expand the lungs and thereby negatively affect the cardiovascular system. We assessed this in preterm rabbits using PCXI (Chapter 3), where we did not find a difference in the occurrence of bulging (visual over-expansion of the non-dependent lung in between the ribs and pneumothoraxes did not occur.
In preterm sheep (Chapter 4), we assumed that lung over-expansion would adversely affect the cardiovascular system, which would be reflected by lower heart rates and pulmonary blood flow (40). Instead, lambs supported with 15 cmH2O CPAP showed an higher PBF, heart rate and blood pressure when compared to 5 cmH2O, while cerebral blood flow and jugular
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General discussion
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