Predictive Factors of Oxygen Therapy Failure in Patients with COVID-19 in the Emergency Department

Abstract

Background

Most patients with coronavirus disease 2019 (COVID-19) pneumonia require oxygen therapy, including standard oxygen therapy and a high-flow nasal cannula (HFNC), in the Emergency Department (ED), and some patients develop respiratory failure. In the COVID-19 pandemic, the intensive care unit (ICU) was overburdening. Therefore, prioritizing patients who require intensive care is important. This study aimed to find predictors and develop a model to predict patients at risk of requiring an invasive mechanical ventilator (IMV) in the ED.

Methods

We performed a retrospective, single-center, observational study. Patients aged ≥18 years who were diagnosed with COVID-19 and required oxygen therapy in the ED were enrolled. Cox regression and Harrell’s C-statistic were used to identifying predictors of requiring IMV. The predictive model was developed by calculated coefficients and the ventilator-free survival probability. The predictive model was internally validated using the bootstrapping method.

Results

We enrolled 333 patients, and 97 (29.1%) had required IMV. Most 66 (68.0%) failure cases were initial oxygen therapy with HFNC. Respiratory rate-oxygenation (ROX) index, interleukin-6 (IL-6) concentrations ≥20 pg/mL, the SOFA (Sequential Organ Failure Assessment) score without a respiratory score, and the patient’s age were independent risk factors of requiring IMV. These factors were used to develop the predictive model. ROX index and the predictive model at 2 hours showed a good performance to predict oxygen therapy failure; the c-statistic was 0.814 (95% confidence level [CI] 0.767–0.861) and 0.901 (95% CI 0.873–0.928), respectively. ROX index ≤5.1 and the predictive model score ≥8 indicated a high probability of requiring IMV.

Conclusion

The COVID-19 pandemic was limited resources, ROX index, IL-6 ≥20 pg/mL, the SOFA score without a respiratory score, and the patient’s age can be used to predict oxygen therapy failure. Moreover, the predictive model is good at discriminating patients at risk of requiring IMV and close monitoring.

Keywords:

• coronavirus disease 2019
• COVID-19
• oxygen therapy
• respiratory rate-oxygenation index
• ROX index
• predictive model

Abbreviations

AUROC, Area under the receiver operating characteristic curve; CI, Confidence level; COVID-19, Coronavirus disease 2019; CRP, C-reactive protein; ED, Emergency Department; FiO_2, The inspired oxygen fraction; HFNC, High-flow nasal cannula; ICU, intensive care unit; IL-6, Interleukin-6; IMV, invasive mechanical ventilation; IQR, interquartile range; IVMP, intravenous methylprednisolone; LDH, lactate dehydrogenase; PF ratio, Ratio of the partial pressure of arterial oxygen (PaO₂ in mmHg) to inspired oxygen fraction (FiO₂); ROX, Respiratory rate-oxygenation; SD, Standard deviation; SOFA, Sequential Organ Failure Assessment.

Data Sharing Statement

The datasets analyzed in this study are not publicly available owing to privacy issues but are available from the corresponding author upon reasonable request.

Ethical Approval

The study was approved by the Ethics Committee of Ramathibodi Hospital, Mahidol University. (COA. MURA2021/679). The ethics committee did not require consent because our study is based on hospital registry data, and reviewing the medical record is the reason for the waiver and a statement covering patient data confidentiality and compliance according to the Declaration of Helsinki. All patient data were treated with confidentiality by the Declaration of Helsinki.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors declare that they have no competing interests.