Background and Aims During ventilation, size and length of endotracheal tube affects the dead space (DS) and resistance which is considered important for preterm infants. We aimed to investigate impact of the tube type, length, connector and size on DS and resistance when all variables are controlled on a manikin.

Methods We ventilated a newborn manikin with Draeger Babylog 8000 using regular and surfactant tubes, regular and closed system aspiration connectors. Pressures, inspiratory time and flow were kept constant. Measurements were made at full length of the tubes and after shortening (11 and 13 cm for 2.5–3.0 and 3.5–4.0 mm tubes respectively) when tidal volume (TV) and resistance displayed on the ventilator were recorded. Differences in TV represented differences in DS.

Results With the use of closed system aspiration connector resistance was elevated by 12 % in all tubes and DS of all tubes except 3.0 mm tube were increased by 10 %. Shortening the tube reduced DS by 1–10 % in all sizes except 2.5 mm tube. Resistance was higher in long tubes by 4–27 % however this was less than expected. Resistance of 2.5 and 3.5 mm regular tubes were 2–48 % higher and 3.0 mm tube was 1–17.6 % lower than surfactant tubes. Resistance was higher in smaller tubes but the magnitude of difference was not as big as the theoretical assumption about the impact of radius to the 4^th power.

Conclusion Many variables impact DS and airway resistance during ventilation some of which maybe important for preterm newborn.