Accuracy of the National Early Warning Score version 2 (NEWS2) in predicting need for time-critical treatment: Retrospective observational cohort study

Background Initial emergency department (ED) assessment can use early warning scores to identify and prioritise patients who need time-critical treatment. We aimed to determine the accuracy of the National Early Warning Score version 2 (NEWS2) for predicting the need for time-critical treatment. Methods We undertook a single centre retrospective observational cohort study. We randomly selected 4000 adults who attended a tertiary hospital ED in 2022 and had NEWS2 routinely recorded on electronic patient records. The first NEWS2 score and vital signs were extracted from electronic records. Research nurses selected cases that received a potentially time-critical treatment. Two independent clinical experts then determined whether time-critical treatment was or should have been received, using an expert consensus derived list of interventions. We used receiver operating characteristic (ROC) analysis and calculated sensitivity and specified at pre-defined thresholds to evaluate the accuracy of NEWS2 for predicting need for time-critical intervention. Results After excluding ten patients who received their intervention before NEWS2 recording, 164/3990 (4.1%) needed time-critical treatment and 71/3990 (1.8%) died within seven days. NEWS2 predicted need for time-critical treatment with a c-statistic of 0.807 (95% confidence interval 0.765 to 0.849) and death within seven days with a c-statistic of 0.865 (0.813, 0.917). NEWS2>4 predicted need for time-critical treatment with sensitivity of 0.518 (0.442, 0.593) and positive predictive value of 0.258 (0.213, 0.307). Patients needing emergency surgery, antibiotics for open fractures, insulin infusion, or manipulation of limb-threatening injuries frequently had NEWS2≤4. Patients with NEWS2>4 who did not need time-critical treatment frequently scored three points on NEWS2 for their respiratory rate, conscious level, or receiving supplemental oxygen. Conclusion NEWS2 has limited accuracy for predicting need for time-critical treatment. We have identified time-critical interventions that frequently have low NEWS2 scores and NEWS2 parameters than may overestimate need for time-critical intervention.