Objective Upper airway distention during mask ventilation could reduce gas volumes entering the lung compared with ventilation via an endotracheal tube. Therefore, respiratory tract volumes were measured in lambs and tidal volumes were compared in preterm infants before and after intubation. Design: In seven preterm lambs, volumes of the airways (oropharynx, trachea, lungs) were assessed. In 10 preterm infants, delta pressures, tidal volumes and leak were measured during ventilation 2 min before (mask ventilation) and 2 min after intubation (endotracheal ventilation). Inflations coinciding with breaths were excluded.

Outcome measures Amount of upper airway distention in lambs and differences in inspiratory and expiratory tidal volume before and after intubation.

Results In lambs, the combined trachea and oropharynx contributed to 14 (12–21) % (median (IQR), whereas the oropharynx contributed to 9 (7–10) % of the total tidal volume measured at the mouth. In preterm infants, inspiratory (11.1 (7.9–22.6) mL/kg vs 5.8 (3.9–9.6) mL/kg (p=0.01)) and expiratory (8.3 (6.8–15.4) mL/kg vs 4.9 (3.9–9.6) mL/kg (p=0.02)) tidal volumes were significantly larger during mask ventilation compared with endotracheal ventilation. Leak was 18.7 (3.3–28.7) % before versus 0 (0–2.3) % after intubation (p<0.0001). Delta pressure was 23.7 (20.8–25.6) cm H₂O before versus 24.8 (20.8–26.0) cm H₂O after intubation (p>0.05). During mask ventilation, expiratory tidal volume increased from 10.0 (5.4–15.6) mL/kg to 11.3 (7.6–17.0) mL/kg (p=0.01), but remained unchanged during endotracheal ventilation.

Conclusions During neonatal mask ventilation, distention of the upper respiratory tract contributes to the tidal volumes measured and should be taken into account when targeting tidal volumes during mask ventilation.