Bedside diaphragmatic ultrasound as a predictor of high-flow nasal cannula outcome in patients with type II respiratory failure

Heated and humidified high-flow nasal cannula (HFNC) oxygen therapy is well recognized in the management of hypoxemic respiratory failure; however, its role in acute hypercapnic respiratory failure remains less well defined and requires further investigation. It is important to detect more predictive factors for HFNC failure to guide early escalation of care. The evaluation of diaphragmatic dysfunction with the ultrasound (US) may provide an important first step. This study aimed to evaluate the value of bedside diaphragmatic ultrasound in predicting the outcome of HFNC in type II respiratory failure. We conducted a prospective study including 25 patients with type II respiratory failure who were admitted to the respiratory ICU at Cairo University and treated with HFNC between June and November 2022. They were divided into two groups according to HFNC outcome: the HFNC success group (11 patients) and the HFNC failure group (14 patients). Diaphragmatic ultrasound was performed in both groups prior to HFNC initiation to assess diaphragm excursion and thickening fraction. In the HFNC success group, follow-up diaphragmatic ultrasound was performed after liberation from HFNC. Results In the HFNC success group, the mean initial excursion was 1.70 ± 0.64 cm and the mean initial thickening fraction was 52.15 ± 22.20%, while in the HFNC failure group, the mean initial excursion was 1.83 ± 0.56 cm and the mean initial thickening fraction was 38.43 ± 16.13%. No statistically significant difference was found between the two groups. All patients with interstitial lung disease succeeded on HFNC therapy, while all patients with obesity hypoventilation syndrome failed on HFNC (p-value = 0.009 and p-value = 0.046 respectively). In the HFNC success group, statistically significant improvements were found between the initial and follow-up excursion (p-value = 0.008) and between the initial and follow-up thickening fraction (p-value = 0.021). Conclusion HFNC outcomes in type 2 respiratory failure are influenced by multiple factors, especially the diversity of underlying etiologies and disease processes. Diaphragmatic ultrasound parameters, including excursion and thickening fraction measured before initiation of high-flow nasal cannula (HFNC), were not sufficient on their own to predict the outcome of HFNC therapy in patients with type 2 respiratory failure. Following successful HFNC therapy, significant improvement was observed in diaphragmatic parameters, including excursion and thickening fraction.