The effects of asymmetrical versus symmetrical high-flow nasal cannula on respiratory muscle activity in acute hypoxaemic respiratory failure and chronic obstructive pulmonary disease: A randomised crossover study

Background High-flow nasal cannula (HFNC) is standard therapy for acute hypoxaemic respiratory failure and is increasingly used in hypercapnic COPD. Comparative data between the asymmetrical and conventional HFNC interfaces regarding respiratory muscle work of breathing is limited. This study aimed to compare the effects of both HFNC interfaces on diaphragm and parasternal intercostal thickening fraction (TFdi and TFpi), and other physiological variables.Methods This randomised crossover study enrolled two cohorts: 20 subjects with acute hypoxaemic respiratory failure and 18 subjects with COPD exacerbation. At baseline, subjects received low-flow oxygen cannula for 15 min then underwent randomised 15 min-sequences of asymmetrical and symmetrical HFNC at flow rates of 40 and 60 L/min, with 5-min washouts. Primary outcome was change in TFdi. Secondary outcomes were TFpi, power of breathing (TFdi × respiratory rate), and other physiological variables.Results TFdi, TFpi, power of breathing, and PtcCO2 were significantly lower than baseline with both HFNC interfaces at 40 and 60 L/min in both groups (p < 0.05). In acute hypoxaemic respiratory failure, compared to symmetrical HFNC, asymmetrical HFNC was associated with greater reduction in respiratory rate (p < 0.001) and power of breathing (p < 0.001) at both flow rates. In COPD exacerbation, compared to symmetrical HFNC, asymmetrical HFNC reduced respiratory rate at both flow rates (p < 0.001).Conclusions Both HFNC interfaces reduced respiratory muscle workload compared to baseline in both cohorts. In acute hypoxaemic respiratory failure, asymmetrical HFNC reduced respiratory rate and power of breathing more than symmetrical HFNC. In COPD exacerbation, the asymmetrical HFNC lowered respiratory rate more than the symmetrical HFNC.Clinical Trial Registration This study was registered with ClinicalTrial.gov (registration number: NCT06204276) before enrolment and approved by the Siriraj Institutional Review Board (certificate of approval – Si873/2023).