Modified early warning score
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The Modified early warning score (MEWS) is a simple guide used by hospital nursing & medical staff as well as emergency medical services to quickly determine the degree of illness of a patient. It is based on data derived from four physiological readings (systolic blood pressure, heart rate, respiratory rate, body temperature) and one observation (level of consciousness, AVPU). The resulting observations are compared to a normal range to generate a single composite score as follows:
|Systolic BP||<45%||30%||15% down||Normal for patient||15% up||30%||>45%|
|Heart rate (BPM)||—||<40||41-50||51-100||101-110||111-129||>130|
|Respiratory rate (RPM)||—||<9||—||9-14||15-20||21-29||>30|
Different MEWS systems are in use worldwide; either the parameters scored vary or the weighting of the scores for worsening deterioration are changed. 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.
Within hospitals, the MEWS 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).
Some examples of MEWS systems currently in use are shown below:
Leeds Teaching Hospitals Trust (LTHT), England 2011
(accurate as of February 2011)
|Systolic BP||<45%||<30%||15% down||Normal for patient||15% up||30% up||>45%|
|Heart rate (BPM)||<30||<40||41-50||51-100||101-110||111-130||>130|
|Respiratory rate (RPM)||<8||—||8-11||12-20||21-25||26-30||>30|
|Oxygen Saturations (%)||<85||>85||>90||>95||—||—||—|
|Respiratory Support||CPAP BiPAP||>60%||O2||Nil||—||—||—|
|Urine Output (mls)||<80||80-119||120-200||>200||>800||—||—|
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.
- Subbe C.P., Kruger M., Gemmel L. - "Validation of a modified Early Warning Score in medical admissions." Quarterly Journal of Medicine 2001; 94; 521-6
- Brown, H. (2010). Graded Response Observation Chart (Leeds Teaching Hospitals Trust - Revision date: November 2012)