Rationale: Early warning system (EWS) scores are used by hospital care teams to recognize early signs of clinical deterioration and trigger more intensive care.
Objective: To systematically review the evidence on the ability of early warning system scores to predict a patient's risk of clinical deterioration and the impact of early warning system implementation on health outcomes and resource utilization.
Methods: We searched the MEDLINE, CINAHL, and Cochrane Central Register of Controlled Trials databases through May 2014. We included English-language studies of early warning system scores used with adults admitted to medical or surgical wards. We abstracted study characteristics, including population, setting, sample size, duration, and criteria used for early warning system scoring. For predictive ability, the primary outcomes were modeled for discrimination on 48-hour mortality, cardiac arrest, or pulmonary arrest. Outcomes for the impact of early warning system implementation included 30-day mortality, cardiovascular events, use of vasopressors, respiratory failure, days on ventilator, and resource utilization. We assessed study quality using a modified Quality in Prognosis Studies assessment tool where applicable.
Measurements and main results: Of 11,183 citations studies reviewed, one controlled trial and 20 observational studies of 13 unique models met our inclusion criteria. In eight studies, researchers addressed the predictive ability of early warning system tools and found a strong predictive value for death (area under the receiver operating characteristic curve [AUROC], 0.88-0.93) and cardiac arrest (AUROC, 0.74-0.86) within 48 hours. In 13 studies (one controlled trial and 12 pre-post observational studies), researchers addressed the impact on health outcomes and resource utilization and had mixed results. The one controlled trial was of good quality, and the researchers found no difference in mortality, transfers to the ICU, or length of hospital stay. The pre-post designs of the remaining studies have significant methodological limitations, resulting in insufficient evidence to draw conclusions.
Conclusions: Early warning system scores perform well for prediction of cardiac arrest and death within 48 hours, although the impact on health outcomes and resource utilization remains uncertain, owing to methodological limitations. Efforts to assess performance and effectiveness more rigorously will be needed as early warning system use becomes more widespread.
Keywords: clinical deterioration; early warning systems; systematic review.