Page 111 - Physiological based CPAP for preterm infants at birth Tessa Martherus

High-CPAP does not impede cardiovascular changes at birth in preterm sheep
secondary to the metabolic acidosis. As lambs were not hypoxic, the metabolic acidosis is unlikely to have resulted from anaerobic glucose metabolism. It could have resulted from activation of the sympathetic nervous system due to birth related stress or to a cold stimulus as the lambs were not sedated. Indeed, while we measured core body temperatures and applied external heat as required, activation of non-shivering thermogenesis may have contributed to maintaining core body temperature. Furthermore, as caffeine is a non-specific phosphodiesterase inhibitor (57, 58), it may have enhanced these cAMP mediated responses. This is consistent with the finding that HCPAP lambs received less caffeine and tended to have higher pH and lower PCO2 levels. While acidosis and high PCO2 levels can adversely affect the cardiovascular system and reduce PBF, we found no evidence for this as all lambs, that completed the 30 min experimental period, achieved high PBFs with significant left-to-right shunting despite many of them had a low pH; the latter is indicative of a low pulmonary vascular resistance.
In summary, high-CPAP levels resulted in PBF levels that were markedly higher than those
seen with low-CPAP levels when applied from birth, and successfully supported preterm
lambs throughout the neonatal transition after birth. We did not find any indication that high-CPAP caused pulmonary overexpansion, compromised the cardiovascular system or increased risk factors for IVH when given directly at birth. However, at 30 min after birth, 4 while increasing CPAP levels reduced the FiO2 requirement, it also caused a small reduction
in PBF. This indicates that the timing after birth, and the type of positive pressure respiratory support applied, determines whether high airway pressures adversely affect the cardiovascular system at birth.
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