Effect of additional dead space using end-tidal CO₂ measurement on ventilating preterm infants: An experimental study

BACKGROUND: Dead space is the part of the airway where no gas exchange takes place. Any increase in dead space volume has a proportional effect on the required tidal volume and thus on the risk of ventilation-induced lung injury. Inserts that increase dead space are therefore not used in small preterm infants. This includes end-tidal CO2 measurement.OBJECTIVE: The aim of this study was to investigate the effect of the end-tidal CO2 measurement adapter on ventilation.METHODS: In an experimental setup, an end-tidal CO2 measurement adapter, three different pneumotachographs (PNT-A, PNT-B, PNT-Neo), and a closed suction adapter were combined in varying set-ups. The time required for CO2 elimination by a CO 2-flooded preterm infant test lung was measured.RESULTS: PNT-A prolonged CO2 elimination time by 0.9 s (+3.3%), Neo-PNT by 3.2 s (+11.6%) and PNT-B by 9.0 s (+32.7%). The end-tidal CO2 measurement adapter prolonged the elimination time by an additional second without the pneumotachograph (+3.6%) and in combination with PNT-A (+3.1%) and PNT-Neo (+3.1%). In conjunction with PNT-B, the end-tidal CO2 measurement adapter reduced the elimination time by 0.3 seconds (1%). The use of a closed suction adaptor increased the CO2 elimination time by a further second with PNT-Neo (+3.1%) and by an additional two seconds with no flow sensor (+6.9%), with PNT-A (+6.4%) and with PNT-B (+5.5%).CONCLUSION: The flow sensor had the greatest influence on ventilatory effort, while end-tidal CO2 measurement had only a moderate effect. The increased ventilatory effort levied by the CO2 measurement was dependent on the flow sensor selected. The use of closed suctioning more negatively impacted ventilatory effort than did end-tidal CO2 measurement.