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.


OBJECTIVE
We aimed to calculate respiratory dead space (VD) 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 (VA) 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, R(2) = 0.26). This association was primarily influenced by the appliance dead space. Despite similar VT/kg and VA/kg across all studied infants, respiratory rate and AMV/kg increased with GA.


CONCLUSIONS
VD,app rather than anatomical VD 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.
Department of Neonatology, University Children's Hospital Basel (UKBB), Basel, Switzerland.
Roland P
RP
Neumann
Jane J
JJ
Pillow
Cindy
C
Thamrin
Alexander N
AN
Larcombe
Graham L
GL
Hall
Sven M
SM
Schulzke
D001315:Australia; D015331:Cohort Studies; D005260:Female; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D007234:Infant, Premature; D019102:Infant, Very Low Birth Weight; D008297:Male; D011446:Prospective Studies; D012121:Respiration, Artificial / Q000009:adverse effects / Q000379:methods; D012126:Respiratory Dead Space; D012212:Rheology / Q000379:methods; D013990:Tidal Volume; D055397:Ventilator-Induced Lung Injury / Q000503:physiopathology / Q000517:prevention & control*