ABSTRACT
Background: Management of acute respiratory distress in patients with COVID-19 has changed over the course of the pandemic. The impact of length of time on High Flow Nasal Cannula (HFNC) prior to mechanical ventilation is unknown. Methods: This is a multi-center retrospective chart review of COVID-positive hospitalized patients, who received mechanical ventilation from March 2020- October 2021. The primary outcome variable was survival to discharge, variables collated included patient demographics, vital signs, comorbidities, including the Charlson comorbidity index (CCI), as well as critical care therapeutic and diagnostic interventions. Results: All COVID-19 positive patients, with respiratory failure who underwent mechanical ventilation across study sites were included (N=709), of which 318 (45%) were accrued in March-May 2020. Patients had an average age of 62 (SD=15) years, majority male (67%), and an average CCI of 3.65 (SD=3.11). The unadjusted mortality for mechanically ventilated patients in our cohort was 56% (n=397). 169 (54%) of the remaining 312 were discharged home. Mortality varied over the study period, with the highest noted Nov 1st 2020 - Jan.31st 2021 (N=141, 69.8%) compared to other time periods (47-53%, p<0.0001). Notably at this time patients had the longest duration of pre-intubation high-flow oxygen support (mean 6.3 days vs. 4.2 days overall), the highest rate of Non-Invasiave Positive Pressure Ventilation (NIPPV) utilization (49% vs. 33% overall) and the lowest PaO2 to FiO2 ratio (mean 125 vs. 139 overall) (p<0.01). Duration of HFNC was independently associated with a higher risk of post-intubation mortality: OR (95% CI) = 3.1 (1.8-5.4) for 3-7 days, 7.2 (3.8-13.7) for ≥8 days (reference: 1-2 days) (p<0.0001) (accounting for age, gender, BMI and CCI). Furthermore, the magnitude of this association was found to vary between age groups: for 3-7 days duration (ref: 1-2 days), OR = 4.8 (1.9 - 12.1) in ≥65 years old vs. 2.1 (1.0 - 4.6) in <65 years old. Notably, at 8 days or more of HFNC, the association with age was reversed for ≥8 days duration (ref: 1-2 days): OR = 5.3 (2.0 - 13.9) in ≥65 years old vs. 8.6 (3.7 - 20.0) for <65 years old. Conclusion: The prolonged use of high flow oxygenation prior to mechanical intubation increased the risk of mortality, particularly in young patients use of HFNC for 8 days or more was associated with significantly higher mortality.