Effect of high flow nasal oxygen on inspiratory effort of patients with acute hypoxic respiratory failure and do not intubate order.

Background- High flow nasal oxygen (HFNO) is recommended as a first line respiratory support during acute hypoxic respiratory failure (AHRF) and represents a proportionate treatment option for patients with do not intubate (DNI) orders. The aim of the study is to assess the effect of HFNO on inspiratory effort as assessed by esophageal manometry in a population of DNI patients suffering from AHRF. Methods- Patients with AHRF and DNI orders admitted to Respiratory intermediate Care Unit between January 1st, 2018 and May 31st, 2023 to receive HFNO and subjected to esophageal manometry were enrolled. Esophageal pressure swing (ΔPes), clinical variables before and after 2 hours of HFNO and clinical outcome (including HFNO failure) were collected and compared as appropriate. The change in physiological and clinical parameters according to the intensity of baseline breathing effort was assessed and the correlation between baseline ΔPes values and the relative change in breathing effort and clinical variables after 2 hours of HFNO was explored. Results- Eighty-two consecutive patients were enrolled according to sample size calculation. Two hours after HFNO start, patients presented significant improvement in ΔPes (12 vs 16 cmH2O, p<0.0001), respiratory rate (RR) (22 VS 28 bpm, p<0.0001), PaO2/FiO2 (133 VS 126 mmHg, p<0.0001), Heart rate, Acidosis, Consciousness, Oxygenation and respiratory rate (HACOR) score, (4 VS 6, p<0.0001), Respiratory rate Oxygenation (ROX) index (8.5 VS 6.1, p<0.0001) and BORG (1 VS 4, p<000.1). Patients with baseline ΔPes below 20 cmH2O where those who improved all the explored variables, while patients with baseline ΔPes above 30 cmH2O did not report significant changes in physiological or clinical features. A significant correlation was found between baseline ΔPes values and after 2 hours of HFNO (R2= 0.9, p<0.0001). ΔPes change 2 hours after HFNO significantly correlated with change in BORG (p<0.0001), ROX index (p<0.0001), HACOR score (p<0.001) and RR (p<0.001). Conclusions- In DNI patients with AHRF, HFNO was effective in reducing breathing effort and improving respiratory and clinical variables only for those patients with not excessive inspiratory effort.