To test the oxygen concentrations delivered by some of the available oxygen therapy systems in normal subjects.
Two different groups of ten healthy volunteers participated in two parts of this study. Nasal cannula (NC) O2 delivery was tested in the first group Simple masks (SM) and non-rebreathing (NRB) masks were tested in the second group. Each subject had a # 8 French nasal catheter inserted through a nare with the tip positioned immediately behind the uvula. The nasal catheter’s proximal end was connected to a syringe stopcock “T” piece system with the oxygen analyzer in line. Oxygen was administrated via the high flow NC (model ref 1600, Salter Labs, Alvin, Ca) at flows 6-15 L/min. For the SM (Hudson RCI, Temecula, Ca), oxygen was administer at 6-12 L/m, and for the NRB mask (Hudson RCI, Temecula, Ca), the flow was 6-15 L/min. At each different oxygen flow the subject breathed normally for five minutes. Using the oxygen sampling system, three gas samples (60 mL each) were withdrawn from the pharynx during inspiration and directed to the oxygen analyzer. The average FiO2 delivered was recorded for each one of the oxygen flows administered with the different systems.
Table 1 shows the means ± SD for each device. Figure 1 shows the comparison between the different devices.
The HFNC was able to provide higher mean FiO2 than the SM at flows of 6-10 L/min; at 12 L/min the delivered FiO2 was equal. HFNC compared to NRB mask delivered equal mean FiO2 at flows 8-15 L/min, and was superior at 6 L/min. Both masks will deliver less variable FiO2 than HFNC.
If needed, HFNC can deliver similar FiO2 than NRB mask. Medical personnel should be aware of the high FiO2 variability this system may deliver.When switching from HFNC to SM, a higher O2 flow should be selected to achieve similar delivered FiO2. The simple rule for estimating delivered FiO2 with different oxygen systems is not accurate.
Table 1O2 flow (L/min)Nasal cannula FiO2 % (mean ± SD)Range FiO2 %Simple Mask FiO2 % (mean ± SD)Range FiO2 %Non-rebreather FiO2 % (mean ± SD)Range FiO2 %Predicted FiO2 %654 ± 1335-8943 ± 2.638-4745 ± 2.940-4945858 ± 1433-8741 ±2.637-4757 ± 4.651-65531066 ± 1340-8857 ± 352-6368 ± 2.364-71611269± 1337-9369 ± 3.364-7468 ± 2.764-73691575 ± 1339-98Not tested74 ± 2.468-7777
Juan Garcia, None.