Derivation of a cardiac arrest prediction model using ward vital signs*

Abstract

Objective: Rapid response team activation criteria were created using expert opinion and have demonstrated variable accuracy in previous studies. We developed a cardiac arrest risk triage score to predict cardiac arrest and compared it to the Modified Early Warning Score, a commonly cited rapid response team activation criterion.

Design: A retrospective cohort study.

Setting: An academic medical center in the United States.

Patients: All patients hospitalized from November 2008 to January 2011 who had documented ward vital signs were included in the study. These patients were divided into three cohorts: patients who suffered a cardiac arrest on the wards, patients who had a ward to intensive care unit transfer, and patients who had neither of these outcomes (controls).

Interventions: None.

Measurements and main results: Ward vital signs from admission until discharge, intensive care unit transfer, or ward cardiac arrest were extracted from the medical record. Multivariate logistic regression was used to predict cardiac arrest, and the cardiac arrest risk triage score was calculated using the regression coefficients. The model was validated by comparing its accuracy for detecting intensive care unit transfer to the Modified Early Warning Score. Each patient's maximum score prior to cardiac arrest, intensive care unit transfer, or discharge was used to compare the areas under the receiver operating characteristic curves between the two models. Eighty-eight cardiac arrest patients, 2,820 intensive care unit transfers, and 44,519 controls were included in the study. The cardiac arrest risk triage score more accurately predicted cardiac arrest than the Modified Early Warning Score (area under the receiver operating characteristic curve 0.84 vs. 0.76; p = .001). At a specificity of 89.9%, the cardiac arrest risk triage score had a sensitivity of 53.4% compared to 47.7% for the Modified Early Warning Score. The cardiac arrest risk triage score also predicted intensive care unit transfer better than the Modified Early Warning Score (area under the receiver operating characteristic curve 0.71 vs. 0.67; p < .001).

Conclusions: The cardiac arrest risk triage score is simpler and more accurately detected cardiac arrest and intensive care unit transfer than the Modified Early Warning Score. Implementation of this tool may decrease rapid response team resource utilization and provide a better opportunity to improve patient outcomes than the modified early warning score.

Figure 1

Modified Early Warning Score (MEWS) Abbreviations: Unresp, unresponsive; BP, blood pressure

Figure 2

Receiver operating characteristic curves of the CART score and MEWS. Abbreviations: AUC, area under the receiver operating characteristic curve; CART, cardiac arrest risk triage; MEWS, modified early warning score

Figure 3

Cumulative percentage of cardiac arrest patients and percentage of the total population on the hospital wards for different maximum CART score cut-offs. For example, at a cut-off of 23 approximately 35% of cardiac arrest patients and 5% of the total hospitalized population are identified. Abbreviations: CART, cardiac arrest risk triage

Figure 4

Change in CART over time prior to cardiac arrest, ICU transfer, and discharge.* *Time −0.5h= 30 minutes before cardiac arrest, time of last ICU patient vital sign set, or time of last vital sign set in random 48 hours (controls) Abbreviations: CART, cardiac arrest risk triage; CA, cardiac arrest; ICU, intensive care unit; TF, transfer