Changes in Lung Aeration and Inspiratory Effort With and Without Awake Prone

Changes in Lung Aeration and Inspiratory Effort During High-Flow Nasal Oxygen and Non-Invasive Mechanical Ventilation With and Without Awake Prone

The investigators aimed to investigate the ventilation homogeneity and transpulmonary pressure during treatments of High-flow nasal cannula(HFNC) and (CPAP) on supine and prone position for COVID-19 or non-COVID-19 patients with acute hypoxemic respiratory failure (AHRF).

Awake prone positioning (APP) for non-intubated patients has been reported to improve oxygenation for patients with acute hypoxemic respiratory failure (AHRF),particularly for patients with COVID-19 induced AHRF, APP has been shown to decrease the need of intubation.Similarly, APP with helmet continuous positive airway pressure (CPAP) enables a reduction in the work of breathing and an improvement in oxygenation and sensation of dyspnea in COVID-19-associated acute respiratory distress syndrome (ARDS). Moreover, among intubated patients with ARDS assessed by electro-impedance tomography (EIT), prone positioning was found to reduce alveolar overdistention and collapse, resulting in improvement of ventilation homogeneity.However, the effects of APP on the ventilation homogeneity and work of breathing for non-COVID-19 patients with AHRF remain unknown. High-flow nasal cannula (HFNC) has been proven to improve oxygenation and reduce intubation rate for patients with AHRF in multiple meta-analyses,and has been recommended to treat AHRF in several recently published guidelines.CPAP provides consistent level of positive end-expiratory pressure (PEEP), in comparison to variable level of PEEP generated by HFNC, thus CPAP was reported to have greater improvement of oxygenation than HFNC in 20 patients with AHRF, more importantly, they found that among patients who avoided intubation, the extent of oxygenation improvement was greater with HFNC+APP than with NIV+APP, in contrast, for patients who were intubated, the extent of oxygenation improvement was greater with NIV+APP than with HFNC+APP.This raised the concerns of the self-inflicted lung injury (SILI) generated by heterogenous aeration and large swings of transpulmonary pressure. Thus, the investigators aimed to investigate the ventilation homogeneity and transpulmonary pressure during treatments of HFNC and CPAP on supine and prone.

HFNC flow at 60 L/min or maximum tolerable flow at supine position HFNC flow at 60 L/min or maximum tolerable flow at prone position CPAP with full face mask at 10 cmH2O at supine position CPAP with full face mask at 10 cmH2O at prone position MC at supine position MC at prone position

The differences in lung homogeneity (global inhomogeneity index) during HFNC therapy at 60 L/min or maximum tolerable flow at supine and awake prone position

The differences in lung homogeneity (global inhomogeneity index) during CPAP with full face mask at 8 cmH2O at supine and awake prone position

the differences in WOB during HFNC therapy at 60 L/min or maximum tolerable flow at supine and awake prone position

Inclusion Criteria: adult patients (18-90 years) who have acute hypoxemic respiratory failure, requiring FIO2 > 0.4 to maintain SpO2 at 90-95% during HFNC at 50 L/min Exclusion Criteria: patients who need immediate intubation; refuse to participate in the study; unable to communicate; have contraindication to place the esophageal catheter; unable to use EIT, such as open-chest surgery with chest tube placement; have contraindication for prone positioning, including pregnant, post-abdomen surgery within a week; hypercapnic respiratory failure.