Pneumonia scoring systems for severe COVID-19: which one is better

This single-center, retrospective observational clinical study was approved by the Ethics Committee of the General Hospital of central theater command of PLA (2020–008-1). A total of 53 cases of severe novel coronavirus pneumonia were confirmed in the General Hospital of central theater command of People’s Liberation Army between 1, January 2020 and 4, March 2020 (Fig. 1).

The inclusion criteria for the study were as follows: (1) All patients were confirmed positively by SARS-CoV-2 nucleic acid RT-PCR (Ct value ≤ 38.0, BGI, Shenzhen, China) using specimens derived from oropharyngeal swabs or sputum, prior to or during the hospitalization; and (2) Patients with the severe form of the disease were categorized based on the 7th edition of the Chinese National Health Commission, which included meeting any of the following criteria: (1) shortness of breath, respiratory rate ≥ 30 beats/min; (2) oxygen saturation ≤ 93% in the resting state; (3) arterial blood oxygen partial pressure (PaO₂)/oxygen concentration (FiO₂) ≤ 300 mmHg (1 mmHg = 0.133 kPa); and (4) lung images showing obvious progress of lesions > 50% within 24–48 h.

The exclusion criteria for the study were as follows: (1) Age < 18 years; (2) Patients with definite diagnosis of cancer; (3) Long-term hospitalization ≥ 3 m before death; (4) Presence of unconsciousness before admission; and (5) Patients receiving renal replacement therapy.

Data related to demography, underlying comorbidities, symptoms, physical and radiological findings, laboratory values, and respiratory and physiologic parameters of the subjects while receiving mechanical ventilation were collected from electronic and paper medical records. We used a positive bacterial culture of blood and sputum samples as the criteria for bacterial growth. The APACHE II, MuLBSTA, and CURB-65 scores were calculated for different treatment time points, and the predictive power of each score for treatment with clinical respiratory support and respective mortality risk was compared.

High-flow oxygen inhalation, noninvasive ventilator support, and invasive ventilator support were used as the three treatment methods. The APACHE II, MuLBSTA, and CURB-65 scoring systems were used to calculate the patient scores at each time point. The area under the receiver operating characteristic (ROC) curve was used to calculate the hierarchical boundary values of each scoring model for each treatment method [6]. The sensitivity and specificity of all the values were calculated, and the difference in area under ROC curve (AUROC) of each scoring model for the same treatment was compared. The patients were divided into high-flow oxygen inhalation group, noninvasive ventilator support group, and invasive ventilator support group. They were also categorized into death and non-death groups. The categorization was based on the severity of the patient's condition and the outcome. The APACHE II, MuLBSTA, and CURB-65 scores for the high-flow oxygen inhalation, noninvasive ventilator support, and invasive ventilation support groups prior to intubation were recorded. Further, the APACHE II, MuLBSTA, and CURB-65 scores in the death group were recorded on the day of death.

The MuLBSTA score was recorded based on the following [5]: multilobular infiltration (5 points), lymphocytes ≤ 0.8*109/L (4 points), bacterial infection (4 points), acute smokers (3 points) or quitters (2 points), hypertension (2 points), age ≥ 60 years (2 points), maximum 22 points.The CURB-65 score was recorded based on the following[2]: consciousness disorder (1 point), blood urea nitrogen > 7 mmol/L (1 point), respiratory frequency ≥ 30 beats/min (1 point), systolic blood pressure < 90 mmHg or diastolic blood pressure ≤ 60 mmHg (1 point), age ≥ 65 years (1 point), maximum 4 points. APACHE II score system is now widely used in the intensive care unit (ICU). APACHE II score system includes a 12-point acute physiology score (including Temperature, Heart rate, Breathing rate, Blood pressure, Oxygen partial pressure, PH, K⁺, Na⁺, Creatinine, HCT, WBC and Consciousness), Age point, and Chronic health evaluation. The higher the score, the more serious the condition [3, 4].

Software Package for Social Sciences (IBM SPSS 25.0) was used for statistical analysis. Dates were described with median and range of continuous variables as well as frequency and percentage of categorical variables. The performance of each scoring system was evaluated by measuring the AUROC. Further, the χ² test was used to calculate sensitivity and specificity. The different scoring models used different ROC curve areas for comparison.

Out of the 53 patients, 27 patients in the high-flow nasal catheter oxygen therapy group were cured and discharged. The remaining 26 patients underwent noninvasive ventilator support. Out of these, 20 patients further underwent endotracheal intubation; however, 16 patients could not be cured and eventually died. One of the patients who died had only received noninvasive ventilator treatment but not endotracheal intubation. The median time from onset to admission was 7 days, onset to noninvasive ventilator support was 12 days, onset to invasive ventilator support was 20 days, onset to death was 25 days, and onset to discharge was 35 days. The other demographic characteristics are listed in Table 1.

The frequency (number of patients) of high-flow oxygen inhalation group, noninvasive ventilation support group, and invasive ventilation support group in CURB score 0, 1, 2, 3, 4, in APACHE II score 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, 17, 19, 20, 21 and in MuLBSTA score 2, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18 are separately shown in Figs. 2, 3, and 4.

In terms of the cut-off values of CURB-65, 1.5 points was used for noninvasive ventilator support, 2.5 points for invasive ventilator support and mortality. In terms of the cut-off values of APACHE II, 9.5 points was used for noninvasive ventilator support, 12.5 points for invasive ventilator support and 11.5 points for mortality. In terms of the cut-off values of MuLBSTA, 8.5 points was used for noninvasive ventilator support, 10.5 points for invasive ventilator support and 13.5 points for mortality. These have been listed in Table 2.

On evaluating the three scoring models for noninvasive ventilator support, the area under the ROC curve of the APACHE II scoring model was identified to be the largest and statistically different from that of the MuLBSTA and CURB-65 models (P = 0.0046 and 0.0059, respectively). Further, no statistical difference was identified between the MuLBSTA and CURB-65 models (P = 0.9369). The assessment of the need for invasive ventilator support revealed that the AUROC of the APACHE II scoring model was the largest, statistically different from the CURB-65 scoring model (P = 0.0372), and identical with the MuLBSTA scoring model (P = 0.2708). When assessing mortality, the AUROC of the MuLBSTA scoring model was identified to be the largest, which was statistically different from CURB-65 (P = 0.0021). However, no difference was noted with APACHE II (P = 0.0549). These findings are listed in Table 3 and shown in Figs. 5, 6, and 7.

On evaluating the individual risk factors in each model for death in patients with COVID-19, bacterial coinfection and age ≥ 60 years from MuLBSTA scoring model, breathing rate ≥ 30/min and age ≥ 65 years from CURB-65 scoring model were considered to be statistically different (P < 0.05); On evaluating the individual risk factors in each model for intubation in patients with COVID-19, breathing rate ≥ 30/min from CURB-65 scoring model were considered to be statistically different (P < 0.05). All other individual risk factors from the three scoring models had no statistical differences. These have been listed in Tables 4 and 5.