Instrumental dead space: A glass ceiling for extremely low birth weight preterm infants? A dead space washout bench...

When ventilating extremely low birth weight infants, clinicians face the problem of instrumental dead space, which is often larger than tidal volume. Hence, aggressive ventilation is necessary to achieve CO₂ removal. Continuous tracheal gas insufflation can wash out CO₂ from dead space and might also have an impact on O₂ and water vapor transport. The objective of this bench study is to test the impact of instrumental dead space on the transport of CO₂ , O₂ , and water vapor and the ability of continuous tracheal gas insufflation to remedy this problem during small tidal volume ventilation.

A test-lung located in an incubator at 37°C was ventilated with pressure levels needed to reach different tidal volumes from 1.5 to 5 mL. End-tidal CO₂ at the test-lung exit, O₂ concentration, and relative humidity in the test-lung were measured for each tidal volume with and without a 0.2 L/min continuous tracheal gas insufflation flow.

CO₂ clearance was improved by continuous tracheal gas insufflation allowing a 28%-44% of tidal volume reduction. With continuous tracheal gas insufflation, time to reach desired O₂ concentration was reduced from 20% to 80% and relative humidity was restored. These results are inversely related to tidal volume and are particularly critical below 3 mL.

For the smallest tidal volumes, reduction of instrumental dead space seems mandatory for CO₂ , O₂ , and water vapor transfer. Continuous tracheal gas insufflation improved CO₂ clearance, time to reach desired O₂ concentration and humidification of airways and, thus, may be an option to protect lung development.