Effect of interface dead space on the time taken to achieve changes in set FiO during T-piece ventilation: is face mask the optimal interface for neonatal stabilisation?

Background: T-piece is recommended for respiratory support during neonatal stabilisation. Bench studies have shown a delay >30 s in achieving changes in fraction of inspired oxygen (FiO) at the airway when using the T-piece. Using a face mask adds dead space (DS) to the patient airway. We hypothesised that adding face mask to T-piece systems adversely affects the time required for a change in FiO to reach the patient.

Methods: Neopuff (Fisher and Paykel, Auckland, New Zealand) and rPAP (Inspiration Healthcare, Croydon, UK) were used to ventilate a test lung. DS equivalent to neonatal face masks was added between the T-piece and test lung. Additionally, rPAP was tested with nasal prongs. Time course for change in FiO to be achieved at the airway was measured for increase (0.3-0.6) and decrease (1.0-0.5) in FiO. Primary outcome was time to reach FiO+/-0.05 of the set target. One-way analysis of variance was used to compare mean time to reach the primary outcome between different DS volumes.

Results: In all experiments, the mean time to reach the primary outcome was significantly shorter for rPAP with prongs compared with Neopuff and rPAP with face mask DS (p<0.001). The largest observed difference occurred when testing a decrease in FiO with 10 mL tidal volume (TV) without leakage (18.3 s for rPAP with prongs vs 153.4 s for Neopuff with face mask DS). The shortest observed time was 13.3 s when increasing FiO with 10 mL TV with prongs with leakage and the longest time was 172.7 s when decreasing FiO with 4 mL TV and added face mask DS without leak.

Conclusion: There was a delay in achieving changes in oxygen delivery at the airway during simulated ventilation attributable to the mask volume. This delay was greatly reduced when using nasal prongs as an interface. This should be examined in clinical trials.