Hygrometric Performances of Different High-Flow Nasal Cannula Devices: Bench Evaluation and Clinical Tolerance

Background: High-flow nasal cannula (HFNC) is increasingly used for the management of respiratory failure. Settings include [Formula: see text], total gas flow, and temperature target. Resulting absolute humidity (AH) at the nasal cannula may affect clinical tolerance, and optimal settings with respect to hygrometry remain poorly documented.

Methods: A bench study was designed to assess AH delivered by 4 HFNC devices (Optiflow, Airvo 2, Precision Flow, and Hydrate) according to flow, ambient temperature, and other available settings. Clinical tolerance of different levels of hygrometry (20, 30, and 40 mg H₂O/L) was evaluated in 15 healthy volunteers.

Results: With [Formula: see text] set at 1.0, normal ambient temperature, and settings made accordingly to the manufacturers' recommendations, mean ± SD AH was 42.2 ± 3.1, 39.5 ± 1.8, 35.7 ± 2.0, and 32.9 ± 2.7 mg H₂O/L for the Airvo 2, Optiflow, Hydrate, and Precision Flow, respectively, (P < .001). AH dropped from -3.5 to -10.7 mg H₂O/L (P <. 001) with high ambient temperature, except for the Precision Flow. Increasing flow did not significantly affect AH except for the Precision Flow (from 36.4 ± 1.6 to 29.8 ± 0.2 mg H₂O/L at 10 and 40 L/min, respectively, [P < .001]). The lowest AH was encountered with the Optiflow set with noninvasive ventilation (NIV) mode, without compensation algorithm, and at high ambient temperature (14.2 ± 1.5 mg H₂O/L). In studied subjects, AH significantly affected breathing comfort, reduced from 7.0 ± 1.0 to 3.0 ± 2.0 at 40 and 20 mg H₂O/L, respectively, (P < .001). Comfort was similar at 30 and 40 mg H₂O/L.

Conclusions: When used according to manufacturer's recommendations and at normal ambient temperature, all the HFNC devices evaluated achieved satisfactory hygrometric output with respect to breathing comfort evaluated in healthy subjects (≥ 30 mg H₂O/L). Substantial differences exist between devices, and optimal knowledge of their working principles is required as inappropriate usage may dramatically alter efficacy and clinical tolerance.