Comparisons of mortality predictions of mROX, CURB-65, and APACHE II in patients with severe pneumonia: A retrospective cohort study

Abstract

This study investigates the efficacy of the modified respiratory rate oxygenation (mROX) index, the CURB-65 score, their combination, and the Acute Physiology and Chronic Health Evaluation (APACHE) II score in predicting mortality among patients with severe pneumonia over various time frames. This retrospective cohort study analyzed data from patients admitted with severe pneumonia between January 2017 and December 2023. Patient demographics and 7-, 14-, and 28-day mortality outcomes were collected. The mROX, CURB-65, and APACHE II scores were computed upon hospital admission. The receiver operating characteristic (ROC) curve, time-dependent ROC curve, and survival curve analyses were conducted to assess the mortality predictive performance of mROX, CURB-65, and their combination, as well as APACHE II. The study included 140 patients, of whom 100 (71.4%) were male, with a median age of 65.0 years (interquartile range: 24.0). Within 28 days, 91 (65.0%) patients had succumbed. Compared to survivors, deceased patients exhibited higher CURB-65 scores and lower mROX indices. ROC analysis indicated that mROX outperformed CURB-65 and APACHE II in sensitivity, accuracy, and area under the curve (AUC) for predicting 28-day mortality. The combination of mROX and CURB-65 yielded the highest AUC (72.1%), suggesting enhanced mortality prediction accuracy. Time-dependent ROC and AUC analyses demonstrated the superior predictive capability of APACHE II within the initial 7 days post-admission, while mROX and CURB-65, alone or combined, were more effective for predictions beyond 14 days. Kaplan-Meier survival analysis indicated that higher mROX values and lower scores of CURB-65 and the combination of both were associated with reduced mortality risk, whereas APACHE II showed no significant difference in mortality risk. The mROX index, particularly when combined with CURB-65, improves mortality prediction accuracy in severe pneumonia patients beyond 14 days post-admission. The APACHE II score remains a valuable predictor within the first 7 days.

Keywords: Acute Physiology and Chronic Health Evaluation; CURB-65; modified respiratory rate oxygenation index; mortality; prediction model; severe pneumonia.

Figure 1.

Patient enrollment flowchart.

Figure 2.

The receiver operating characteristic curve analyses of different score systems to predict 28-day mortality in patients with severe pneumonia. APACHE II = Acute Physiology and Chronic Health Disease Classification System II, CURB-65 = confusion, urea >7 mM, respiratory rate ≥30 breaths/min, blood pressure <90 mm Hg (systolic) or <60 mm Hg (diastolic), age ≥ 65 years old, mROX = modified respiratory rate and oxygenation, mROX + CURB-65 = mROX score combined with CURB-65 score.

Figure 3.

Time-dependent receiver operating characteristic (ROC) curve analyses of different score systems in predicting 7-, 14-, and 28-day mortality in patients with severe pneumonia. (A) Time-dependent ROC curve of mROX; (B) time-dependent ROC curve of CURB-65 score; (C) time-dependent ROC curve of APACHE II; (D) time-dependent ROC curve of mROX combined with CURB-65 score.

Figure 4.

Different scoring time-dependent AUC curve fitting diagram. APACHE II = Acute Physiology and Chronic Health Disease Classification System II, AUC = area under the curve, CURB-65 = confusion, urea >7 mM, respiratory rate ≥30 breaths/min, blood pressure <90 mm Hg (systolic) or <60 mm Hg (diastolic), age ≥ 65 years old, mROX = modified respiratory rate and oxygenation, mROX + CURB-65 = mROX score combined with CURB-65 score.

Figure 5.

Kaplan–Meier survival curves of mROX at different time points in patients with severe pneumonia. (A) 7-day mortality; (B) 14-day mortality; (C) 28-day mortality. The line shadow represents the 95% confidence interval of the estimate. HR = hazard ratio.

Figure 6.

Kaplan–Meier survival curves of CURB-65 at different time points in patients with severe pneumonia. (A) 7-day mortality; (B) 14-day mortality; (C) 28-day mortality. The line shadow represents the 95% confidence interval of the estimate. HR = hazard ratio.

Figure 7.

Kaplan–Meier survival curves of mROX combined with CURB-65 score at different time points in patients with severe pneumonia. (A) 7-day mortality; (B) 14-day mortality; (C) 28-day mortality. The line shadow represents the 95% confidence interval of the estimate. HR = hazard ratio.

Figure 8.

Kaplan–Meier survival curves of APACHE II score at different time points in patients with severe pneumonia. (A) 7-day mortality; (B) 14-day mortality; (C) 28-day mortality. The line shadow represents the 95% confidence interval of the estimate. HR = hazard ratio.