Effects of asymmetric nasal high-flow cannula on carbon dioxide in hypercapnic patients: A randomised crossover physiological pilot study.

Nasal high flow (NHF) therapy is an established form of non invasive respiratory support used in acute and chronic care. Recently, a new high flow nasal cannula with asymmetric prongs was approved for clinical use. The clinical benefits of the new cannula have not yet been defined and no evidence are available on the use of asymmetric NHF support in patient with Chronic Obstructive Pulmonary Disease (COPD). We conducted a single-centre, prospective, physiologic, crossover, randomised study to investigate the effects on partial pressure of carbon dioxide (PaCO²) levels of two different nasal cannula ("asymmetric" vs "standard" nasal interface) in 20 COPD hypercapnic patients. All patients were recovering from an acute exacerbation that required hospitalisation and had persistent hypercapnia, despite having attained a stable pH. After enrolment, two 90-min trials with the asymmetric nasal high flow interface (Optiflow + Duet, Fisher & Paykel Healthcare Ltd., New Zealand) or the standard interface (Optiflow, Fisher & Paykel Healthcare Ltd., New Zealand) were randomly applied and a washout period of 60 min between the two treatments was performed for minimising the carryover effect. Study results suggested that the asymmetrical cannula did not significantly decrease PaCO² compared with the standard cannula. Similar performances were also observed in terms of diaphragm activity, dyspnoea and patient's comfort. Interestingly, asymmetric NHF cannula performed significantly better in reducing the dead space ventilation and increasing the ventilatory efficiency in more advanced COPD patients with more severe hypercapnia higher baseline PaCO² values (PaCO² ≥ 65 mmHg at baseline).   .