Effects of high-flow nasal cannula therapy on oxygenation, lung volumes and CO₂ removal in critically ill hypoxemic patients: preliminary results

Introduction

High-flow nasal cannula (HFNC) is increasingly proposed as respiratory support for hypoxemic non-intubated acute respiratory failure patients. Clinically, HFNC therapy decreases dyspnea, improves patient's comfort, improves oxygenation and enhances clearance of upper airway secretions [1]. We present preliminary results from a clinical study aimed at measuring the effects of HFNC on gas exchange, lung volumes and inspiratory effort in hypoxemic non-intubated critically ill patients.

Methods

We performed a prospective randomized cross-over study on hypoxemic non-intubated patients (PaO₂/FiO₂ ≤300 mmHg) admitted to the ICU of the San Gerardo Hospital and prescribed to receive oxygen by facial mask. We delivered the same air/oxygen mix by HFNC (Optiflow; Fisher & Paykel Healthcare, Auckland, New Zealand) and facial mask (20 minutes per step). Continuous recordings of regional lung volumes by EIT (Pulmovista 500; Drager Medical GmbH, Lubeck, Germany) and of inspiratory effort by esophageal pressure (Pes) were obtained and analyzed offline by dedicated software.

Results

We enrolled 15 patients (10 male), age 57 ± 16 years. Compared with standard facial mask, HFNC significantly improved PaO₂/FiO₂ (199 ± 60 vs. 150 ± 46, P < 0.001) and end-expiratory lung impedance (corresponding to aeration) (866 ± 568 au vs. baseline, P < 0.001). Moreover, HFNC decreased the respiratory rate (22 ± 5 bpm vs. 20 ± 5 bpm, P < 0.001), as well as negative Pes swings (ΔPes 8.3 ± 5 mmHg vs. 6.6 ± 1 mmHg, P < 0.01) and corrected minute ventilation (that is, actual MV × actual PaCO₂ / 40 mmHg) (49,887 ± 16,176 au vs. 41,811 ± 14,042 au, P < 0.001). Finally, central venous pressure increased (6 ± 5 mmHg vs. 4 ± 5 mmHg, P < 0.01), possibly indicating positive end-expiratory pressure effect.

Conclusion

In non-intubated hypoxemic critically ill patients, HFNC improves oxygenation and end-expiratory aeration; moreover, HFNC reduces the inspiratory effort and the minute ventilation needed to maintain normal arterial CO₂ tension.