Aeration Strategy at Birth Does Not Impact Carotid Haemodynamics in Preterm Lambs

Abstract

ObjectiveTo examine the effect of three different ventilation strategies at birth on markers of cerebral haemodynamics and oxygenation.DesignAnimal research.SettingAnimal research facility.Subjects124-127 day gestation apnoeic preterm lambs (n=68) born via caesarean section.InterventionsLambs were randomised to either positive pressure ventilation with positive end-expiratory pressure (PEEP) 8 cmH2O (No-RM; n=12), sustained inflation (SI; n=15) or a dynamic PEEP strategy (DynPEEP; n=41) at birth, followed by 90 minutes of standardised ventilation. Prior to birth a carotid artery flow probe was placed, with occlusive cannulation of the contralateral carotid artery. Carotid blood flow, ventilation data, peripheral oxygen saturation (SpO2), heart rate and arterial blood pressure were continuously recorded, with intermittent arterial blood gas analysis at set time points.Main outcome measuresCarotid blood flow, carotid artery oxygen content and carotid oxygen delivery (product of carotid artery blood flow and oxygen content).ResultsOverall carotid blood flow measures were comparable between strategies. The exception being mean carotid blood flow during the first 3 minutes after birth, which was significantly lower for the SI group compared to the No-RM and DynPEEP groups respectively (p<0.0001; repeated-measure mixed effect ANOVA). Carotid arterial oxygen content (p=0.19) and oxygen delivery (p=0.50) were similar between strategies. Maximum PEEP did not alter cerebral haemodynamic measures.ConclusionsThis is the first study to compare cerebral haemodynamics during different PEEP strategies with SI at birth. Although there were some short-term variations, there were no sustained differences.What is already known on this topicFacilitating the respiratory transition at birth for preterm infants is essential for the lungs as well as the brain. Whilst our understanding of the impact of different respiratory strategies on the lungs is well understood, preclinical data involving other organs is sparse. Concerns have been raised that aggressive lung recruitment may impede cerebral haemodynamics in the preterm infant.What this study addsTo our knowledge, this is the first study that assesses the effect of the three different aeration strategies currently being considered in clinical practice; sustained inflation, dynamic and static positive end-expiratory pressure (PEEP), on cerebral haemodynamics. We found that differing ventilation strategies did not alter carotid blood flow, carotid oxygen content or carotid oxygen delivery. Specifically, there was no difference between sustained inflation (to 35 cmH2O) and maximum PEEP levels of 8, 14 and 20 cmll.O applied during the first three minutes after birth.How this study might affect research, practice or policyFollowing preterm birth it is important to consider the effect of ventilation strategies on other organs, especially the brain. This preclinical study provides some reassurance that respiratory strategies designed to focus on lung aeration at birth may not impact cerebral haemodynamics in preterm neonates.