Characteristics and Outcomes of Patients With COVID-19 Treated With High-flow Nasal Oxygen and Awake-prone Position

A subset of patients with COVID-19 develops acute respiratory failure and acute respiratory distress syndrome (ARDS) (1). The use of invasive mechanical ventilation for the treatment of these conditions is associated with high mortality rates (2,3). The use of high-flow nasal oxygen therapy (HFNO) and awake prone position (AW-PP) could to decrease the need for endotracheal intubation and other adverse clinical outcomes (4-6).

The aim of this study is to evaluate the clinical results of the simultaneous application of high-flow nasal oxygen therapy HFNO and awake-prone position in a cohort of patients with severe respiratory failure secondary to COVID-19 on relevant clinical outcomes, and to assess risk factors of treatment failure defined as requirement of invasive mechanical ventilation.

Objective. To evaluate the clinical results of the simultaneous application of high-flow nasal oxygen therapy HFNO and awake-prone position in a cohort of patients with severe respiratory failure secondary to COVID-19 on relevant clinical outcomes, and to assess risk factors of treatment failure defined as requirement of invasive mechanical ventilation.

Design: Prospective multicenter cohort study conducted at 5 ICUs of 5 centers in Argentina. The Internal Review Board from the 5 centers approved the study including waived informed consent. The interventions carried out were part of the usual practice at each center and confidentiality of participants was guaranteed.

Population. Patients older than 18 years admitted to the ICU with a confirmed diagnosis of COVID-19 (real-time PCR) and receiving HFNO for at least 4 hours. Patients received HFNO when any of the following criteria were present: a) peripheral oxygen saturation (SpO2) \< 92% with oxygen \> 4 liters/minute; b) increased work of breathing with use of accessory respiratory muscles, and a respiratory rate \> 30/min; c) partial pressure of oxygen /Fraction of inspired oxygen (PaO2/FiO2ratio) \< 200 mmHg. Patients with respiratory failure secondary to a different etiology, decreased level of consciousness, presence of shock requiring vasopressors, immediate need for intubation, use of positive-pressure ventilation prior to HFNO, and with do-not intubate orders were excluded.

Procedures.Immediately after admission to the ICU, the inclusion criteria regarding oxygenation and/or work of breathing are checked. Then a high-flow nasal cannula sized according to the nares size is placed, and connected to a specific device for the provision of high-flow O2. The initial flow is 50-70 L/min, with the fraction of inspired oxygen (FiO2) necessary to obtain an SpO2 \> 92%. No maximum FiO2 limits is established. Once therapy with HFNO is started, participants are encouraged and assisted by the health-care team to rotate from supine to prone position for as long as possible, taking breaks for personal hygiene and eating. No maximum time limits for prone position are established. Patients who tolerated HFNO for the next 4 hours are included in the study. These interventions are maintained during the study period until one of the following criteria was met: maintenance of SpO2 \> 92% with FiO2 ≤ 40%, and flow ≤ 40 L/min for a period \> 12 hours in the supine position; or endotracheal intubation. Analgesic drugs (opioids, paracetamol) or light sedation (dexmedetomidine) was allowed and indicated according to the criteria of the health-care team.

Variables and measurements. The following variables are collected: demographics (age, sex, body mass index \[BMI\]), comorbidities, severity scores upon ICU admission (APACHE II and SOFA), chronology of the disease (time from the onset of symptoms to hospital admission and ICU admission), vital signs, laboratory parameters, Respiratory rate Oxygenation index (ROX index) \[7\] , and chest computed tomography score (CT score) determined as the sum of lung involvement, ranging from 0 -no involvement- to 25 -maximum involvement \[8\].

Exposure: The main exposure of this study was awake prone positioning. The investigators will evaluate the number and proportion of patients who tolerate and cannot tolerate the prone position. For those who tolerate the prone position, the investigators record information on the number of hours in prone, and the number of days in prone position per patient. Additionally the following data is recorded: a) the predominant position adopted by the patient, defined as the position in which the patient spent most h/day, i.e., prone, lateral or supine position; b) the average number of h/day in that position; and c) the number of days of exposure to said position for a period of ≥ 6 h/day (AW-PP).

The primary outcome is defined as the receipt of endotracheal intubation. The decision to intubate was based on the criteria of the attending health-care team. However, intubation is recommended for anyone meeting the following criteria: deterioration of neurologic status, hemodynamic instability, or if two or more of the following criteria were met: decline in oxygen saturation with SpO2 \< 90% for more than 5 minutes (not explained by technical failures), lack of improvement in the signs of respiratory muscle fatigue, impossibility to control airway secretions and respiratory acidosis with log10 hydrogen ion concentration (pH) \< 7.30 \[9\]. Secondary outcome: hospital mortality. Secondary clinical outcomes: ICU and hospital length of stay, time to endotracheal intubation, and severe complications related to AW-PP.

Statistical analysis. The dynamics of the pandemic and the number of patients admitted to ICUs cannot be predicted. As many patients as possible were consecutively recruited without a predefined sample size (estimated 600).

Descriptive statistics will be used to describe the baseline characteristics of the patients. Categorical data will be presented as absolute frequency (n) and percentage (%) and continuous data as mean ± standard deviation (SD) or median and interquartile range (IR), respectively, as appropriate. Categorical variables will be compared by chi-square test (with Yates correction) or Fisher's exact tests, as appropriate. Continuous quantitative variables will be compared using the unpaired t-test or the Mann-Whitney test for normally and non-normally distributed variables, respectively. Each test will be two-tailed and a value of p\<0.05 will be considered statistically significant. All analyses will be performed with STATA version 15.1.

Eligibility Criteria:
Inclusion Criteria:

* Older than 17 years, admitted to the ICU
* Confirmed diagnosis of COVID-19 (real-time PCR)
* Receiving HFNO for at least 4 hours. Patients received HFNO when any of the following criteria were present: peripheral oxygen saturation (SpO2) \< 92% with oxygen \> 4 liters/minute; increased work of breathing with use of accessory respiratory muscles, and a respiratory rate \> 30/min; PaO2/FiO2ratio \< 200 mmHg.

Exclusion Criteria:

* Patients with respiratory failure secondary to a different etiology,
* Decreased level of consciousness,
* Presence of shock requiring vasopressors,
* Immediate need for intubation.
* Use of positive-pressure ventilation prior to HFNO, and f) with do-not intubate orders.