Derivation and Validation of a Novel Severity Scoring System for Pneumonia at Intensive Care Unit Admission

Abstract

Background: Severity stratification scores developed in intensive care units (ICUs) are used in interventional studies to identify the most critically ill. Studies that evaluate accuracy of these scores in ICU patients admitted with pneumonia are lacking. This study aims to determine performance of severity scores as predictors of mortality in critically ill patients admitted with pneumonia.

Methods: Prospective cohort study in a general ICU in Brazil. ICU severity scores (Simplified Acute Physiology Score 3 [SAPS 3] and Sepsis-Related Organ Failure Assessment [qSOFA]), prognostic scores of pneumonia (CURB-65 [confusion, urea, respiratory rate, blood pressure, age] and CRB-65 [confusion, respiratory rate, blood pressure, age]), and clinical and epidemiological variables in the first 6 hours of hospitalization were analyzed.

Results: Two hundred patients were included between 2015 and 2018, with a median age of 81 years (interquartile range, 67-90 years) and female predominance (52%), primarily admitted from the emergency department (65%) with community-acquired pneumonia (CAP, 80.5%). SAPS 3, CURB-65, CRB-65,and qSOFA all exhibited poor performance in predicting mortality. Multivariate regression identified variables independently associated with mortality that were used to develop a novel pneumonia-specific ICU severity score (Pneumonia Shock score) that outperformed SAPS 3, CURB-65, and CRB-65. The Shock score was validated in an external multicenter cohort of critically ill patients admitted with CAP.

Conclusions: We created a parsimonious score that accurately identifies patients with pneumonia at highest risk of ICU death. These findings are critical to accurately stratify patients with severe pneumonia in therapeutic trials that aim to reduce mortality.

Keywords: intensive care unit; mortality; pneumonia; severity scores.

Figure 1.

Patient flowchart of discovery and validation cohort. A total of 2401 patients were initially admitted to the intensive care unit in the discovery cohort between August 2015 to July 2018, of which 200 met inclusion criteria. In the validation cohort, 405 patients were initially included from the Community-Acquired Pneumonia Organization dataset, of which 43 had incomplete data, resulting in 362 patients included in the final analysis. Abbreviations: CAPO, Community-acquired Pneumonia Organization; ICU, intensive care unit.

Figure 2.

Adjusted and unadjusted multivariate regression model for intensive care unit mortality. Univariate analysis yielded unadjusted odds of death. Multivariate regression adjusted for differences in baseline characteristics (variables of P < .1 identified in univariate analysis). *Documented inspired oxygen percentage or assumed fraction of inspired oxygen (FiO2) ≥ 30% undergoing mechanical ventilation. Abbreviations: CI, confidence interval; FiO₂, fraction of inspired oxygen; WBC, white blood cell.

Figure 3.

Performance of Pneumonia Shock score in the discovery cohort. Receiver operating characteristic curve analysis to determine accuracy of the Pneumonia Shock score in predicting intensive care unit death. Abbreviations: AUC, area under the receiver operating characteristic curve; CI, confidence interval; Sens., sensitivity; Spec., specificity.

Figure 4.

Comparisons of discriminate function of pneumonia scores, intensive care unit (ICU) scores, and the Pneumonia Shock score in the discovery and validation cohort. Receiver operating characteristic (ROC) curve analysis to determine score accuracy in prediction of ICU death. A, The Pneumonia Shock score outperformed the Simplified Acute Physiology Score 3 (SAPS 3), the quick Sequential Organ Failure Assessment (qSOFA), and CURB-65 (confusion, urea, respiratory rate, blood pressure, age) and CRB-65 (confusion, respiratory rate, blood pressure, age), as well as in prediction of mortality in the discovery cohort. P values refer to comparisons of area under the ROC curve (AUC) of the Pneumonia Shock score with the severity models analyzed in the discovery cohort. B, In the validation cohort, the Shock score performed equally well with comparable discriminate function. The Pneumonia Shock score was significantly superior to all severity models analyzed in the validation cohort, with P values referring to AUC comparisons.