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 ( VT ) 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 (VD,MM ) in very preterm infants on volume-targeted ventilation (VT target, 4-5 ml/kg) and to study the association between gestational age (GA) and VD,MM -to- VT ratio (VD,MM /VT ), 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. VD,MM / VT was negatively associated with GA after adjusting for birth weight Z score (p <0.001, R2 = 0.26). This association was primarily influenced by the appliance dead space. Despite similar VT /kg and V A /kg across all studied infants, respiratory rate and AMV/kg increased with GA.

 Conclusions: V D,app rather than anatomical V D is the major factor influencing increased VD,MM / VT at a younger GA. A volume guarantee setting of 4-5 ml/kg in the Dräger Babylog ® 8000 plus ventilator may be inappropriate as a universal target across the GA range of 23-32 weeks. Differences between measured and set VT and the dependence of this difference on GA require further investigation.© 2014 S. Karger AG, Basel.