A Systematic Review: Early Warning System Scores
Early warning system (EWS) scores are tools used by hospital care teams to recognize the early signs of clinical deterioration in patients in order to initiate early intervention and management, such as increasing nursing attention, informing the provider, or activating a rapid response or medical emergency team. These tools involve assigning a numeric value to several physiologic parameters (e.g., blood pressure, heart rate, oxygen saturation, level of consciousness) to derive a composite score that is used to identify a patient at risk. Therefore, the purpose of EWS scores is to assist with timely and appropriate management of deteriorating patients on general hospital wards.
This is potentially a significant topic for the VA healthcare system, as the Portland, Oregon VAMC has implemented a Modified Early Warning System (MEWS), and there are plans to implement this nationally. Thus, this evidence review will be used by the Office of Nursing Services Clinical Practice Programs ICU Workgroup to develop guidelines for the development and implementation of EWS scores at facilities within the VA system – and it will be used to identify gaps in evidence that warrant further research. The VA Evidence-Based Synthesis Program located in Portland, OR reviewed the literature from database inception through April 2013. After applying inclusion/exclusion criteria, 17 articles were used to provide the Summary, which is followed by key questions and answers that offer more detailed information.
Six observational studies tested in large urban hospitals in developed countries found a strong predictive value for death and cardiac arrest within 48 hours. Eleven observational cohort studies, with historical controls, provided evidence on the impact of EWS implementation, but were insufficient to draw firm conclusions due to methodological limitations. Overall, results suggest that current early warning system scores perform well for predicting cardiac arrest and death within 48 hours; however, the impact on health outcomes and utilization of resources remains uncertain. Efforts to more rigorously assess their performance and effectiveness are needed, as use becomes more widespread.
Key Question #1
In adult patients admitted to the general medicine or surgical wards, what is the predictive value of EWS scores for patient health outcomes within 48 hours of data collection, including short-term mortality (all cause or disease specific), and cardiac arrest? And which factors contribute to the predictive ability of EWS scores, and does predictive ability vary with specific subgroups of patients?
Six observational studies that met study criteria reported the predictive values of four distinct models of early warning system scores within 48 hours of measurement. Findings show:
- In general, the early warning system scores appeared to have strong predictive ability for cardiac arrest and mortality as judged by the 'area under the receiver operator characteristic curve' (AUROC).
- Patients with favorable EWS scores were very unlikely to suffer cardiac arrest or death within 48 hours. However, most patients with unfavorable scores also did not have these outcomes. These findings suggest that many patients would be triaged to higher levels of care without a large decrease in the number of patients suffering cardiac arrest or death, if these EWS scores were to be used in practice.
- The evidence is insufficient to determine if one system is superior to another – or to determine which factors contribute most to the models' predictive ability.
Key Question #2a
What is the impact of using Early Warning Systems on patient health outcomes including 30-day mortality, cardiovascular events, use of vasopressors, number of ventilator days, and respiratory failure?
- Six studies addressed the effects of EWS implementation on mortality. Four studies found a decrease in overall mortality after implementation of an EWS, but only one study found this to be statistically significant.
- Three studies met inclusion criteria and found mixed results. One study found that the proportion of cardiac arrest calls per adult admission decreased. A second study found no difference in cardiac arrests in the low- and high-risk groups, but did find an increase in cardiac arrests in moderate-risk patients (EWS scores 3-4). A final study found no difference in cardiac arrests after EWS implementation.
No studies that met inclusion criteria addressed the effects of Early Warning Scoring systems on the use of vasopressors, number of ventilator days, or respiratory failure.
Key Question #2b
What is the impact of EWS on resource utilization including but not limited to admissions to the intensive care unit (ICU), length of hospital stay, and use of Rapid Response Teams (RRT)?
Overall, studies evaluating the impact of EWS on the use of resources were limited by study designs. Results suggest that the use of staffing, including nursing care and rapid response teams, will increase; however, the effect on the length of hospital or ICU stay remains uncertain. Specific findings include:
Intensive Care Unit (ICU) Admission
- Four studies evaluated the impact of the EWS on the number of admissions to the ICU. Two studies found a significant increase in the number of ICU admissions after implementing EWS, while two other studies found no difference in the length of ICU stay.
Length of Hospital Stay
- Three studies evaluated the impact on length of hospital stay before and after implementing an early warning system and found mixed results. One study found no difference in the length of hospital stay; another study found a significant decrease; while the third study compared 4 months before and 4 months after implementation and showed an increase in length of hospital stay from 4.0 days to 4.8 days.
Use of Rapid Response and Code Teams
- Four studies evaluated the impact of EWS on rapid response and code teams, and all found at least a 50% increase in the number of rapid response or ICU liaison team calls.
- The impact of nursing was not well studied. However, one study found that the number of observations and clinical attention by nursing increased with the use of the EWS, with greater attention for EWS scores >5.
The major gaps in research identified by this review relate to the limitations of the evidence base. Future studies that are randomized trials, with more rigorous adherence to methodological standards for observational studies, are needed to inform clinical practice and policy. Standardization of cut-offs to trigger a response and standardization of responses would improve the applicability of study findings. Decisions about defining other aspects of patient populations, interventions, comparators, outcomes, study timing and duration, and study settings should be guided by clinical practice, expertise, and factors most relevant to stakeholders, including patients, clinicians, and policymakers.
A Cyberseminar session on this ESP Report will be held at a future date. To register, go to the HSR&D Cyberseminar web page.
This report is a product of VA/HSR&D's Quality Enhancement Research Initiative's (QUERI) Evidence-Based Synthesis Program (ESP), which was established to provide timely and accurate synthesis of targeted healthcare topics of particular importance to VA managers and policymakers — and to disseminate these reports throughout VA.
Smith MEB, Chiovaro J, O'Neil M, Kansagara D, Quinones A, Freeman M, Motu'apuaka M, Slatore CG. Early Warning Scoring Systems: A Systematic Review. VA-ESP Project #05-225; 2013
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