Early warning score

An early warning score (EWS) is a guide used by medical services to quickly determine the degree of illness of a patient. It is based on the six cardinal vital signs (respiratory rate, oxygen saturation, temperature, blood pressure, pulse/heart rate, AVPU response) and one other observation.

The resulting observations are compared to a normal range to generate a single composite score, for instance based on the following diagram:

A score of five or more is statistically linked to increased likelihood of death or admission to an intensive care unit.

Within hospitals, the EWS is used as part of a "track-and-trigger" system whereby an increasing score produces an escalated response varying from increasing the frequency of patient's observations (for a low score) up to urgent review by a rapid response or Medical Emergency Team (MET call).

Throughout the world the EWS is based on the principle that clinical deterioration can be seen through changes in multiple physiological measurements, as well as large changes within a single variable. However, the scale is calibrated to different populations and sometimes expanded to include additional parameters, specific to different parts of the world. The parameters scored may vary, as well as the weighting of the scores for worsening deterioration. Some systems also assign scores to other parameters including urine output, oxygen saturation, flow rate of oxygen administration and pain scores.

There is a lack of consensus on what constitutes the 'ideal' early warning score system. Comparing different systems in clinical use shows variation in which parameters are scored and how those scores are assigned to differing levels of deterioration. There is however some evidence that certain parameters are better at predicting which patients will die within 24 hours than others. This has led to a call in several countries for the development of a national early warning score that would allow a standardised approach to assessing and responding to deteriorating patients.

A range of Early Warning Scores have been developed in response to the needs of specific patient types (e.g. PEWS for children) or to support local best practice (NEWS in the UK).

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