Effect of high-flow nasal cannula and body position on end-expiratory lung volume: a cohort study using electrical impedance tomography.
BACKGROUND
Electrical impedance tomography measures changes in lung impedance, which are mainly related to changes in lung volume. We used electrical impedance tomography to investigate the effects of high-flow nasal cannula (HFNC) and body position on global and regional end-expiratory lung impedance variation (ΔEELI).


METHODS
Prospective study with 20 healthy adults. Two periods were defined: the first in supine position and the second in prone position. Each period was divided into 3 phases. In the first and the third phases the subjects were breathing ambient air, and in the second HFNC was implemented. Four regions of interest were defined: 2 ventral and 2 dorsal. For each respiratory cycle, global and regional ΔEELI were measured by electrical impedance tomography and were expressed as a function of the tidal variation of the first stable respiratory cycle (units).


RESULTS
HFNC increased global EELI by 1.26 units (95% CI 1.20-1.31, P < .001) in supine position, and by 0.87 units (95% CI 0.82-0.91, P < .001) in prone position. The distribution of ΔEELI was homogeneous in prone position, with no difference between ventral and dorsal lung regions (-0.01 units, 95% CI -0.01 to 0, P = .18), while in supine position a significant difference was found (0.22 units, 95% CI 0.21-0.23, P < .001) with increased EELI in ventral areas.


CONCLUSIONS
HFNC increased global EELI in our population, regardless of body position, suggesting an increase in functional residual capacity. Prone positioning was related to a more homogeneous distribution of ΔEELI, while in supine position ΔEELI was higher in the ventral lung regions.
Critical Care Department, Vall d'Hebron Research Institut, Vall d'Hebron University Hospital, Universitat Autònoma de Barcelona, Barcelona, Spain. jorriera@vhebron.net
Jordi
J
Riera
Purificación
P
Pérez
Jordi
J
Cortés
Oriol
O
Roca
Joan Ramon
JR
Masclans
Jordi
J
Rello
D000328:Adult; D015331:Cohort Studies; D017097:Electric Impedance; D005260:Female; D005652:Functional Residual Capacity / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D063087:Noninvasive Ventilation; D016684:Prone Position / Q000502:physiology*; D012123:Pulmonary Ventilation / Q000502:physiology*; D016683:Supine Position / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology; D014057:Tomography, X-Ray Computed; D055815:Young Adult