Evaluating High-Flow Nasal Oxygen in Adult Critical Care: A Systematic Review of Its Clinical Effectiveness and Risks Compared to Conventional Oxygen and Intubation Strategies

Abstract

High-flow nasal oxygen (HFNO) is increasingly utilised as a non-invasive ventilation method in critical care populations. Use has increased in particular for individuals experiencing acute respiratory failure (ARF) and acute respiratory distress syndrome (ARDS). Over the last decade increasing numbers of studies examining HFNO efficacy have been published, including RCTs such as FLORALI (Frat, et al, 2015) and HiFlo (Perkins et al, 2022) observational studies and expert opinions. Despite the increase in use and study there are still gaps in the literature. On the one hand, there is general consensus that HFNO enhances oxygenation, diminishes respiratory effort, and increases patient comfort; however, the effect on mortality is still uncertain (Frat et al., 2015; Azoulay et al., 2018; Ospina-Tascón et al., 2021; Perkins et al., 2022; Li et al., 2022; Helviz and Einav, 2018). This systematic review therefore, assesses the efficacy and constraints of HFNO in adult ICU patients experiencing ARF and ARDS with a view to understanding where the disconnect may be in clinical presentation and outcomes. Employing Cochrane-compliant methodology, studies selected were dated between 2015 to 2025, which were evaluated according to stringent PICO criteria. This work therefore concentrates on ICU patients aged 18 and older undergoing HFNO in comparison to standard oxygen therapy or non-invasive ventilation methods such as CPAP and non-rebreather mask NIV. Thematic analysis concentrated on mortality outcomes, intubation rates, and secondary complications. Findings illustrate that HFNO consistently lowered intubation rates and enhanced physiological markers in patients with moderate ARDS (PaO₂/FiO₂ 150–300 mmHg); however, it did not show a statistically significant decrease in mortality in the majority of studies. A significant gap recognised pertains to the influence of patient comorbidities. Adverse outcomes were prevalent in studies exhibiting greater comorbidity burdens; however, limited trials have investigated this phenomenon comprehensively. This thesis posits that the profiling of comorbidities and the implementation of structured escalation protocols are crucial for optimising the advantages of HFNO while mitigating potential risks. To address this, I propose the implementation of a novel hypothetical COMBO-FLO score, integrating comorbidity burden (e.g., Charlson Index) with dynamic physiological markers (e.g., ROX index) to predict HFNO failure risk and escalation pathways. This evidence-based approach aims to optimise patient selection and reduce delayed intubation harms and prevent mortality in high-risk ICU populations