Influence of Gestational Age on Dead Space and Alveolar Ventilation in Preterm Infants Ventilated with Volume Guarantee

Background: Ventilated preterm infant lungs are vulnerable to overdistension and underinflation. The optimal ventilator-delivered tidal volume (V-T) in these infants is unknown and may depend on the extent of alveolarisation at birth. Objectives: We aimed to calculate respiratory dead space (V-D) from the molar mass (MM) signal of an ultrasonic flowmeter (V-D,(MM)) in very preterm infants on volume-targeted ventilation (V-T target, 4-5 ml/kg) and to study the association between gestational age (GA) and V-D,V- MM-to-V-T ratio (V-D,V- MM/V-T), alveolar tidal volume (V-A) and alveolar minute volume (AMV). Methods: This was a single-centre, prospective, observational, cohort study in a neonatal intensive care unit. Tidal breathing analysis was performed in ventilated very preterm infants (GA range 23-32 weeks) on day 1 of life. Results: Valid measurements were obtained in 43/51 (87%) infants. Tidal breathing variables were analysed using multivariable linear regression. V-D,V- MM/V-T was negatively associated with GA after adjusting for birth weight Z score (p < 0.001, R-2 = 0.26). This association was primarily influenced by the appliance dead space. Despite similar V-T/kg and V-A/kg across all studied infants, respiratory rate and AMV/kg increased with GA. Conclusions: V-D,V- app rather than anatomical V-D is the major factor influencing increased V-D,V- MM/V-T at a younger GA. A volume guarantee setting of 4-5 ml/kg in the Drager Babylog (R) 8000 plus ventilator may be inappropriate as a universal target across the GA range of 23-32 weeks. Differences between measured and set V-T and the dependence of this difference on GA require further investigation. (C) 2014 S. Karger AG, Basel