Impact of high-flow nasal oxygen therapy in COVID-19 critically ill patients with acute hypoxemic respiratory failure: A prospective observational study

ABSTRACT

Introduction: About 20 to 30% of COVID-19 patients admitted to ICU develop severe ARDS. Tracheal intubation in such patients carries a high risk of complications and mortality.1,2 High-flow nasal oxygen therapy (HFNOT) is an attractive option as it can reduce the requirement of intubation. Objectives: This study aimed to determine the impact of HFNOT on the oxygenation level as well as HFNOT failure. The primary objective was to determine the change in PaO2/FiO2 ratio from baseline to at 1 hour, 6 hours, and 7 days of HFNOT initiation in COVID-19 critically ill patients presenting with acute hypoxemic respiratory failure (AHRF). The secondary objective was to determine the HFNOT failure rate [i.e., the requirement of tracheal intubation or noninvasive ventilation (NIV)]. Materials and methods: After approval from the institutional ethics committee and written informed consent, a prospective observational study was performed over a period of 3 months at the COVID intensive care unit of a government institute-hospital in east India. Adult patients (aged >18 years) with confirmed COVID-positive status (SARS-CoV-2 detected in nasopharyngeal swab by real-time reverse transcription-polymerase chain reaction assay), having AHRF (PaO2/ FiO2 ratio <300) who are not able to maintain saturation above 90% on standard oxygen therapy were included in this study. On the HFNOT device, the initial flow rate and FiO2 were set at 60 L/minute and 100%, respectively. On case record form (CRF), demographic characteristics, vital signs, laboratory tests, and arterial blood gas tests were recorded. ROX index (ratio of SpO2/FiO2 to respiratory rate) was calculated at 2 hours of HFNOT. Continuous variables were reported as mean or median values when appropriate. The intergroup differences were analyzed using Student's t-test or Mann-Whitney U test. The intragroup differences between variables at different time points were analyzed using paired Student's t-test. p ≤ 0.05 was considered statistically significant. Statistical analysis will be performed using SPSS software. Results: A total of 265 patients were screened out of which 256 patients had AHRF. HFNOT was used as first line therapy in 122 patients in which only 108 found to be eligible for study inclusion. Mean age of the patients was 59.7 ± 15.1 years;male patients accounted for majority (79.6%) of HFNOT cohort. Key comorbidities were diabetes mellitus (48.1%) and hypertension (25.9%). Mean PaO2/FiO2 ratio at baseline was 96.8 ± 30.2) which significantly increased at 1 hour (114.8 ± 32.1, p < 0.001) at 6-hours (130.1± 36.5;p < 0.001) and at 7 days (178.7 ± 41.3;p < 0.001) Mean duration of HFNOT was 10.4 ± 4.9 days. Median (with range) APACHE II and SOFA scores were 22 (12-35) and 8 (4-12) respectively. HFNOT failure rate was 27.8%. NIV was used as ceiling respiratory support in 22.2% of HFNOT cohort. Mean ROX index was significantly higher for the patients who successfully continued on HFNOT compared to those who failed (3.4 ± 0.3 vs 2.8+0.3;p < 0.001). Mean admission glucose level, D dimer and IL-6 values were significantly higher in HFNOT failure group compared to HFNOT success group. Overall, 28-day mortality rate in this cohort was 25.9%. About 50% patients receiving HFNOT developed complications in which epistaxis (18.5%) and air hunger (16.7%) were the most common complications. Discussions This study prospectively highlights the significant impact of HFNOT on oxygenation status over time points studied (i.e., at 1 hour, 6 hours, and 7 days). The baseline mean PaO2/FiO2 ratio was <100 (severe ARDS) when HFNOT was initiated. With such a low P/F ratio, HFNOT remarkably outperformed with a success rate of 72.2%. Significant improvement in the P/F ratio may be explained by adequate flow delivery and FiO2 meeting the patients' demand. The main strengths of the study were its prospective nature and large cohort. The main limitation is that being a single-center study, the results from the study need to be cautiously interpreted before extrapolating to patients in differ nt geographical locations. About 50% of patients developed mild complications, such as, epistaxis, air hunger, and abdominal distension;however, one patient also developed spontaneous tension pneumothorax which required immediate intercostal drain tube placement following which, the patient dramatically improved and survived hospital discharge. We observed admission hyperglycemia, high D-dimer value, and IL-6 levels in patients who failed HFNOT. These findings are consistent with other studies.3-5 Conclusion: HFNOT significantly improves oxygenation level in COVID-19 patients developing acute hypoxemic respiratory failure. The HFNOT failure rate was 27.8%.