The ABCs of EWSs: Understanding and Choosing Early Warning Systems

Adverse events on care units, such as cardiac arrest and death, are rarely sudden, and they are often preceded by abnormalities in a patient's vital signs and in other clinical measurements, such as patient observations or diagnostic test results, hours before the event. However, these signs may be missed or not acted on appropriately, even in hospitals with efficient rapid response teams. Historically, clinicians had addressed this risk by manually calculating an early warning score for each patient, based on several clinical measurements. However, the time-consuming nature of performing these calculations, as well as the potential for human error, made this process less than ideal.

Recognizing the need for improvement, in 2007 the U.K. National Institute for Health and Care Excellence recommended that physiologic track-and-trigger systems—also known as clinical decision support tools, early warning scores, early warning scoring systems, or, as this article refers to them, early warning systems (EWSs)—should be used for all adult patients in acute hospital settings, to automate the calculation of early warning scores. And in 2008, the Joint Commission issued National Patient Safety Goal 16 to improve recognition of and response to changes in a patient's condition—further highlighting the need for EWSs.

Currently, there are more than 100 different published EWSs in the clinical literature. Most of these are hospital-specific modifications of the original Early Warning Score developed by Morgan et al. (1997) and have demonstrated various levels of reliability, validity, and usefulness. It is therefore necessary for a hospital to identify an EWS that will accurately track and warn of patient deterioration within the context of the facility's unique patient population and care area needs. This article provides an overview of EWSs and...