Effects of asymmetric nasal high flow cannula on carbon dioxide in hypercapnic patients: a randomized crossover physiological pilot study.

Introduction and Objectives: Nasal high flow (NHF) therapy is an established form of non-invasive respiratory support, used in both acute and chronic care. A new high-flow nasal cannula with asymmetric prongs has recently been approved, but its clinical benefits remain undefined, especially for patients with Chronic Obstructive Pulmonary Disease (COPD). This doctoral thesis explores potential mechanisms through which NHF may benefit stable COPD patients, based on current literature. Additionally, it presents a physiological study comparing two nasal cannulas (asymmetric vs. standard) in hypercapnic COPD patients conducted at the Respiratory and Critical Care Unit, IRCCS Azienda Ospedaliero Universitaria di Bologna (CODUET Study). Patients and Methods: A single-center, prospective, crossover, randomized study was conducted to evaluate the effects of two different nasal interfaces (asymmetric vs. standard) on partial pressure of carbon dioxide (PaCO2) levels in 20 hypercapnic COPD patients recovering from acute severe exacerbations. Inclusion criteria were COPD patients with FEV1/FVC < 70% and persistent hypercapnia (PaCO2 > 50 mmHg and pH > 7.35). Each patient underwent two 90-minute trials of NHF with either the asymmetric or standard nasal cannula, with a 60-minute washout period between treatments. Results: Both the asymmetric and standard NHF interfaces effectively reduced PaCO2 levels, with similar outcomes in diaphragm activity, dyspnea, and patient comfort. However, the asymmetric NHF cannula was notably more effective in reducing dead space ventilation and improving ventilatory efficiency, particularly in more severe COPD patients with baseline PaCO2 ≥ 65 mmHg. Conclusions: While the overall clinical benefit of NHF remains unclear, the study suggests potential advantages of NHF, particularly the asymmetric cannula, in reducing dead space and improving ventilatory efficiency in COPD patients with severe hypercapnia. Both cannulas performed similarly in reducing PaCO2 and improving patient comfort, but the asymmetric design may offer specific benefits for patients with advanced disease.