gms | German Medical Science

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 20 l/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 25 l/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.