Global and Regional Ventilation during High Flow Nasal Cannula in Patients with Hypoxia.
Background
High flow nasal cannula (HFNC) is known to increase global ventilation volume in healthy subjects. We sought to investigate the effect of HFNC on global and regional ventilation patterns in patients with hypoxia.


Methods
Patients were randomized to receive one of two oxygen therapies in sequence: nasal cannula (NC) followed by HFNC or HFNC followed by NC. Global and regional ventilation was assessed using electric impedance tomography.


Results
Twenty-four patients participated. Global tidal variation (TV) in the lung was higher during HFNC (NC, 2,241 ± 1,381 arbitrary units (AU); HFNC, 2,543 ± 1,534 AU; P < 0.001). Regional TVs for four iso-gravitational quadrants of the lung were also all higher during HFNC than NC. The coefficient of variation for the four quadrants of the lung was 0.90 ± 0.61 during NC and 0.77 ± 0.48 during HFNC (P = 0.035). Within the four gravitational layers of the lung, regional TVs were higher in the two middle layers during HFNC when compared to NC. Regional TV values in the most ventral and dorsal layers of the lung were not higher during HFNC compared with NC. The coefficient of variation for the four gravitational layers of the lung were 1.00 ± 0.57 during NC and 0.97 ± 0.42 during HFNC (P = 0.574).


Conclusions
In patients with hypoxia, ventilation of iso-gravitational regions of the lung during HFNC was higher and more homogenized compared with NC. However, ventilation of gravitational layers increased only in the middle layers. (Clinical trials registration number: NCT02943863).
['Lee|Dong Hyun|DH|0000-0001-6253-3396', 'Kim|Eun Young|EY|', 'Seo|Ga Jin|GJ|', 'Suh|Hee Jung|HJ|', 'Huh|Jin Won|JW|0000-0002-3449-0461', 'Hong|Sang-Bum|SB|0000-0003-2737-7695', 'Koh|Younsuck|Y|0000-0001-5066-2027', 'Lim|Chae-Man|CM|0000-0001-5400-6588']
electric impedance oxygen inhalation therapy pulmonary ventilation