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, SaO2, Temperature, Blood pressure, Heart rate, AVPU response) and one other observation.
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The basis of an EWS
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).
The ideal EWS
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.
Early Warning Score variations
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).
These include:
Leeds Teaching Hospitals Trust (LTHT), England 2011
(accurate as of February 2011)
Wellington Hospital, New Zealand 2012
(accurate as of January 2012)
This matrix links the MEWS with a coloured band that corresponds to that on the observation chart. This not only provides visual cues to deterioration but also makes it easier to assign a score once the colours are learned.
This system also demonstrates 'single parameter' triggering whereby an extreme deterioration results in a mandatory MET call which ensures immediate attendance by a Medical Emergency Team to the bedside of the sickest patients.
National Early Warning Score, UK
In the UK, the Royal College of Physicians has introduced a national early warning score (NEWS) to replace local or regional scores. The NEWS score is the largest national EWS effort to date, but still remains problematic in the UK due to its lack of universal implementation ability (it has exclusion criteria) and it has yet to have its retrospective validation study published.
Sundsvall Regional Hospital, Sweden
The following parameters are used to estimate MEWS at Sundsvall Regional Hospital, Sweden:
Following are guidelines for re-estimating MEWS: