Introduction: Different study results in hypercapnic respiratory failure leads to inconclusive implications regarding the use of NHF in this patient group. Flow rate influences directly the elimination of CO2 in the blood. Therefor insufficient flow rates influence study results, especially in case of hypercapnia.
Methods: First, we measured the effective flow rate with a preset flow rate of 20l/min of two turbine-driven NHF devices with a flowmeter. In the second part we measured the elimination of CO2 in a physiological lung model. CO2 was inserted through a catheter in the distal airways. The concentration of CO2 (ppm) was measured in the distal trachea via a catheter. The sheep lung was ventilated with different respiratory rates (15-30 l/min) and tidal volumes (300,700 ml). After achieve a steady state (CO2) NHF with a flow of 25l/min was administered.
Results: In our comparison of the effective flow rate of two devices regarding the CO2 removal in a ventilated sheep lung we found significant differences. The difference between the devices was stronger in higher tidal volume.
Discussion: Our data suggests that there may be a clinical important difference in turbine driven NHF devices. These could explain different study results especially regarding decarboxylation.