We read with interest the article by Dr. Jang and colleagues1 on the ability of disease severity scores to predict more rapid clinical deterioration in severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infected patients. Of the three scoring systems analyzed, the National Early Warning Score (NEWS) measured at the time of hospital admission was best able to predict critical outcome, defined in this study as admission to the intensive care unit (ICU) or death, with critically ill patients defined similarly. We believe that these definitions should be modified.
These definitions of critical outcome and critically ill patients would result in a target group with heterogeneous characteristics, including not only patients with severe coronavirus disease 2019 (COVID-19) but patients with other conditions. The outbreak of COVID-19 may result in a selection bias, as some critically ill patients may not be admitted to the ICU because of a shortage of ICU beds. Actually, some critical patients using high flow oxygen were in the general ward, and some elderly patients who died from conditions other than COVID-19 were not actively treated and had do-not-resuscitate (DNR) orders.
In addition, these definitions of critical outcomes and critically ill patients do not include timing. Admission to the ICU care and death was assumed to occur within 28 days after initial hospitalization because 28-day mortality rates were measured. In another study evaluating the National Early Warning Score 2 (NEWS2) in 3,869 patients, the primary outcome was defined as patient status 14 days after symptom onset, with patients categorized as those who were transferred to the ICU or died (WHO-COVID-19 Outcomes Scale scores of 6–8) and those who were not transferred and did not die (scores of 3–5) within a specific time after symptom onset.2
Third, the definitions of critical outcomes and critically ill patients cited by Jang et al. were too broad. We found it unusual that the definition of critical outcome did not include acute respiratory distress syndrome or respiratory failure. A study showing an association between hypoxemia and mortality in 140 COVID-19 patients defined disease severity according to proposed Chinese guidelines for COVID-19 associated pneumonia.3 In that study, critical outcome was defined as COVID-19 associated pneumonia along with a requirement for intubation due to respiratory failure, shock, or multiple organ dysfunction requiring ICU admission.
Therefore, in this paper, we believe that critical outcomes and critical patients should be defined more specifically and accurately, and in reference to time of evaluation.
The study by Jang et al. was important, showing that NEWS can predict the progression of COVID-19 patients to ICU care or death. Several components of NEWS, including hypoxemia, oxygen saturation, and respiratory rate, are therefore important factors predicting whether or not COVID-19 patients will progress to critical condition. Our findings, in a tertiary hospital located in the same area as the hospital described in the study by Jang et al., were similar. Of 131 patients aged ≥ 18 years who were hospitalized for COVID-19, 13 patients (9.9%), all of whom were hospitalized for hypoxemia, were admitted to the ICU. Five patients (3.8%) died within 28 days, with all having DNR orders. Of these five patients, only one was admitted to the ICU, whereas the other four died while on high flow oxygen therapy in the general ward because there was no room in the ICU. As the outbreak progressed rapidly, admission to the ICU was very difficult. Of the 13 patients admitted to the ICU, three (23.1%) showed slow improvements in hypoxemia while on high flow oxygen therapy, but did not require a ventilator. In addition, of the 118 patients in the general ward, 12 (10.2%) used more than 40% of fraction of inspired oxygen (FiO2) in the ward. NEWS scores at the time of hospitalization differed significantly in non-critical and critical patients (2.6 ± 2.6 vs. 8.2 ± 3.3, P < 0.001). Although there was no between-group difference in blood pressure, respiratory rate, and body temperature, oxygen saturation (P < 0.001) and supplemental oxygen (P = 0.001) differed significantly. That is, blood pressure, body temperature, and respiratory rate at the time of hospitalization did not significantly differ between critical and non-critical COVID-19 patients.
We fully agree with Jang et al. that severe COVID-19 infection is accompanied frequently by silent hypoxemia. Therefore, oxygen saturation may be reduced despite comfortable breathing, making it necessary to continuously monitor oxygen saturation by pulse oximetry. Our patients who required ventilator therapy were characterized by ‘rapid desaturation,’ with a median time from desaturation to application of maximum FiO2 being only 7.5 hours (interquartile range, 3.5–15.3 hours).
As mentioned in the limitations of the paper by Jang et al., the inability to perform arterial blood gas analysis in many patients with COVID-19 prevented measurements of their arterial oxygen pressure (PaO2). It was therefore difficult to analyze the ability of SOFA and PaO2/FiO2 (PF ratio) to predict the likelihood of critical illness. Because of this, we suggest using an alternative to oxygen saturation/FiO2 (SF ratio).4
In conclusion, exacerbation of hypoxia and reduction in saturation, as well as the NEWS scale, are important predictors of outcome in patients with COVID-19.
Footnotes
Disclosure: The authors have no potential conflicts of interest to disclose.
- Conceptualization: Kim EJ, Hong HL.
- Data curation: Kim EJ, Hong HL.
- Formal analysis: Kim EJ, Hong HL.
- Investigation: Kim EJ, Hong HL.
- Methodology: Kim EJ, Hong HL.
- Project administration: Kim EJ, Hong HL.
- Resources: Kim EJ, Hong HL.
- Software: Kim EJ, Hong HL.
- Supervision: Kim EJ, Hong HL.
- Visualization: Kim EJ.
- Writing - original draft: Kim EJ.
- Writing - review & editing: Hong HL.
References
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