Neonatal nasal intermittent positive pressure ventilation efficacy and lung pressure transmission

OBJECTIVE: The objective of this study was to evaluate carbon dioxide (CO2) clearance, delivered pressures and tidal volume (V-T) during neonatal nasal intermittent positive pressure ventilation (NIPPV) with two commonly used interfaces. STUDY DESIGN: A neonatal lung model, with either short binasal prongs (SBP) or a small caliber nasal cannula (RAM) interface, was tested over a range of clinically relevant settings. A fixed amount of CO2 was infused and the fraction remaining in the lung 100 s postinfusion was measured. Pressure transmission to the lung and V-T was measured at the level of the trachea. RESULT: CO2 elimination was directly proportional to the inspiratory pressure during NIPPV. At peak pressures of 22 to 34 cm H2O, CO2 clearance was greater (P<0.001) with SBP as compared with RAM. Relative to the set ventilator parameters, a substantial pressure dampening effect was documented at the lung level, which was significantly lower with RAM when compared with SBP (2.8% (0.2) versus 11.9% (1.5), P<0.0001). CO2 elimination was dependent on VT and effective despite only a small fraction of physiological V-T (maximum delivered V-T%: SBP 15.5 (0.7) versus RAM 6.1 (1.4), P<0.0001). CONCLUSION: NIPPV promotes CO2 elimination even at low transmitted airway pressures, but less effective with RAM as compared with SBP. CO2 elimination despite small V-T suggests that NIPPV may depend on a non-conventional gas-exchange mechanism.