Physiologic Effects of High Flow Nasal Cannula Compared to Conventional Oxygen Therapy Postextubation: A Randomized Crossover Study

Rationale: High flow nasal cannula (HFNC) has been shown to generate several physiological which would be responsible forreducing weaning failure rates. However, there are not many physiological studies focused on the post-extubationstage.Objective: To determine the physiological effects of HFNC in the post-extubation period.Methods:Prospective randomizedcrossover study in the post-extubation period of patients with acute respiratory failure (ARF), which was approved by the HealthSciences Scientific Ethics Committee of Pontificia Universidad Católica de Chile. Critically ill patients connected to mechanicalventilation (MV) more than 48 hours, with PaO2/FiO2 <300 mmHg, and in whom the physician planned to perform a spontaneousventilation test (SBT) were included. After obtaining consent informed a catheter with an esophageal and gastric balloon andelectrodes to record the electrical activity of the diaphragm (EAdi) were installed. Moreover, an electrical impedance tomography(EIT) around the chest was connected, arterial and venous blood gases were recorded, in addition to the usual clinical signs.After extubation, the patients were connected to HFNC set at 50 L/min for one hour and conventional oxygen therapy (venturimask) for one hour in a random sequence.Results:Nine patients (6 men) aged 60.7 ± 10.0 years were included. Patients wereconnected to MV for 6.6 ± 3.2 days. Compared with conventional oxygen therapy, HFNC significantly reduces the respiratoryeffort observed by a reduction of esophageal pressure swings (ΔPes)(p= 0.006) and pressure-time product (PTPes) (p= 0.047)of 30% and 27%, respectively. In the HFNC period, the end-expiratory lung impedance (p< 0.001) and dynamic lung compliance(VT/ΔPes) (p= 0.041) was significantly higher. However, no differences were observed in tidal volume (p= 0.255), electricalactivity of the diaphragm (ΔEAdi) (p= 0.104), Neuro-ventilatory efficiency (p= 0.262), and respiratory rate (RR) (p= 0.299)compared to the period of conventional oxygen therapy. Finally, the PaO2 / FiO2 ratio was also higher in the HFNC period (p =0.029).Conclusion:The use of HFNC in the post-extubation period in patients with acute respiratory failure reduces work ofbreathing and is capable of increasing end-expiratory lung volume, dynamic compliance, and gas exchange.