Effects Of High-flow Oxygen Therapy On Local Lung Ventilation, Lung Recruitment And Lung Hyperinflation In High-risk Patients After Extubation

Background:Postextubation high-flow nasal cannula(HFNC)is used as a support therapy in high-risk patients in ICU.This study aimed to determine the effects of HFNC therapy on regional lung ventilation,recruitment,overdistension assessed by electrical impedance tomography(EIT).Methods:Twenty-four patients who received HFNC within 24 h after extubation were prospectively enrolled in this study.EIT was used to monitor regional lung ventilation distributions at baseline(conventional oxygen therapy)and three flow rate levels of HFNC therapy(20,40,and 60 L/min).Change of end-expiratory lung impedance(?EELI),regional recruitment(recruited-pixels)and overdistension(overdistended-pixels)were determined by EIT.EIT images were equally divided into four ventral-to-dorsal horizontal regions of interest(ROIs 1,2,3,and 4).Lung recruitment(pixels)are defined as newly aerated pixels at different flow rates of 20,40,and 60 L/min compared to baseline.Lung overdistension(pixels)are defined as aerated pixels that did not join in tidal ventilation at the same flow rate."Overdistension-by HFNC" due to HFNC is defined as an increase of overdistened-pixels>10 than baseline.Patients were divided into two groups:(1)high potential of recruitment(HPR),recruited-pixels>10 pixels at 60 L/min than baseline,and(2)low potential of recruitment(LPR),recruited-pixels ?10 pixels at 60 L/min than baseline.Results:When the flow rate gradually increased from baseline to 60 L/min,a significant and consistent increasing trend of global ?EELI(%)(p<0.0001),recruited-pixels(p<0.001),and overdistended-pixels(p=0.101)was observed.Moreover,the increase of ?EELI was mainly distributed in ROI2(p=0.001)and ROI3(p<0.0001).The HPR group(13/24 patients)had significantly higher recruited-pixels than the LPR group(11/24 patients)at 20,40,and 60 L/min.There were no significant differences in PaO2/FiO2,?EELI(%),and overdistention pixels between the two groups.The HPR group had 13 patients in which no one had "overdistension-by HFNC",and the LPR group had 11 patients in which 4 patients had "overdistension-by HFNC"(0/13 vs.4/11,P=0.017).Conclusions:There were diverse responses of lung regional ventilation and aeration(recruitment,non-recruitment,and over-distension)to HFNC.However,the effect varied among individuals.Identification of lung recruitment,lung non-recruitment,and overdistension by EIT might be helpful to guide HFNC therapy in post-extubation situations.