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In Defense of Early Warning Scores
- Richard J M Morgan, Margaret M. Wright (14 August 2007)
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Early warning scores: a homogeneous score for a heterogenous population?
- Carolyn Johnston (25 June 2007)
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Richard J M Morgan, Consultant in Anaesthesia & Critical Care Blackpool Victoria Hospital, Margaret M. Wright
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Whilst we acknowledge the valuable recent contribution made in relation to physiological scoring by Duckitt and colleagues (1), it is with some concern that we read the final conclusions in the accompanying British Journal of Anaesthesia Editorial (June 2007) entitled ‘A warning on early warning-scores!’ by Cuthbertson and Smith (2). As co-developers of the first Early Warning Scoring System (EWS), based on aggregate weighted scoring of physiological variables (3), we must re-emphasise that EWS was designed solely to secure the timely presence of skilled clinical help by the bedside of those patients exhibiting physiological signs compatible with established or impending critical illness. The original EWS was not presented as a predictor of outcome. The overall clinical course for most critically ill patients is punctuated by multiple potential confounding influences (4) making such attempts at final outcome prediction, on the basis of early routine standard bedside observations, an unrealistic expectation. Whilst the Medical Emergency team (MET) calling criteria (5) do represent a form of physiological tracking,they do not include the assignment of weighted numerical values to the degree of deviation of given physiological parameters from agreed normal ranges, nor do they utilize any form of numerical score or score trigger value at which skilled help is summoned to the bedside. By the early 2000’s EWS had become synonymous with a wide range of variations from the original including some non-aggregate weighted scoring systems. In order to address this particular ambiguity in terminology the National Outreach Forum (NorF) adopted the phrase ‘Physiological Track and Trigger System’ in 2003 (6). ‘Physiological Track and Trigger System’, as a descriptive, accommodates all systems which include calling criteria based on any form of physiological tracking, together with a threshold at which mandatory assistance is summoned. Cuthberston & Smith cite the recent publication by Gao, McDonnell & Harrision et al (7), and quote the authors as concluding that ‘there was little evidence of reliability, validity and utility’ in relation to current scoring systems, and that the sensitivity of such systems was ‘poor’. Gao et al based their conclusions on use of the composite outcome measure of death, admission to critical care, ‘do not attempt resuscitation’ or cardiopulmonary resuscitation. As far as we are aware, data available to Gao and colleagues afforded them no estimate of the number of patients whose clinical course was positively influenced through the use of early warning scoring at ward level and who, as a result, were not admitted to critical care and did not suffer cardiac arrest or death. Application of the aforementioned composite end point describes final patient outcome, not only as a reflection of a given physiological track & trigger system, but also as a reflection of the nature of the accompanying response algorithm, in addition to all other confounding variations in subsequent clinical management. The work currently underway by Smith et al (8) may lead to a greater degree of accuracy in the tracking of physiological parameters through the use of electronic data capture and analysis against a track and trigger algorithm. Whilst such electronic data capture helps offset human error in the calculation of physiology scores, the work in question is still in its developmental stage and the relevant practical tools are not likely to be available to the majority of healthcare professionals in even the near future. Cuthbertson and Smith also imply that the routine application of physiological track and trigger scoring to all acute patients generates a significant additional workload. Work in the late 1990’s confirmed that the application of an aggregate weighted scoring system, with calculation of a total score, took only 30 seconds to complete (personal communication). The time taken to complete an aggregate score is now significantly less with improved hard copy ward observation charts incorporating EWS principles in their primary design. Physiological track & trigger can be applied to all acute patients with minimal extra effort for significant potential gain. Routine measurement of ‘basic observations’ to assist in assessment of the severity of a patient’s illness and their clinical progress has been a mainstay of medical and nursing practice for decades. Indeed it has been a form of implicit physiological tracking but without an explicit ‘trigger’. Early Warning Scoring (EWS) represents a simple refinement to the completion of basic observations by the assignment of weighted values to time honored physiological parameters according to their degree of deviation from the norm. A total score is then calculated and executive action initiated at an agreed trigger threshold. This trigger threshold is used to mandate inexperienced nursing or medical staff in calling for immediate more experienced help. The process enables the implementation of prompt, appropriate customized management plans. These plans are often very simple in the early stages of physiological deterioration but at other times significantly more complex and resource intensive. Such tailored individual patient management clearly represents high quality care. It is notable that the National Institute for Clinical Excellence (NICE), in its recent (July 2007) definitive guidance on ‘Acutely ill patients in hospital’ (9) recommend, as a priority, that ‘physiological track and trigger systems should be used to monitor all patients in acute hospital settings’. This priority recommendation echoes an exactly similar priority recommendation made by the National Confidential Enquiry into Patient Outcome and Death (NCEPOD) in 2005 in their publication entitled ‘An Acute Problem’ (10). In many acute hospitals in England the current use of track and trigger scoring systems facilitates the prompt summoning of skilled help to the bedside. We remain convinced that this process enables the ‘high-quality clinical assessment and judgement by appropriately skilled and experienced personnel’, as applauded by Cuthbertson and Smith in their closing comments, to be applied in more timely fashion than might otherwise have been the case. Richard J M Morgan FRCA Victoria Hospital Blackpool Margaret M Wright FRCA James Paget Hospital Great Yarmouth References: 1.Duckitt R, Buxton-Thomas R, Walker J, et al. Worthing physiological scoring system:derivation and validation of a physiological early warning system for medical admissions. An observational, population-based single- centre study. Br J Anaesth 2007; 98: 769-74 2.Cuthbertson B H, Smith GB, A warning on early warning scores! Br J Anaesth 2007; 98: 704-6 3.Morgan RJM,Williams F,Wright MM, An early warning scoring system for detecting developing critical illness. Clinical Intensive Care 1997; 8: 100 4.Morgan RJM, Outreach critical care – cash for no questions? Correspondence Br J Anaesth 2003; 90 (5): 699 - 700 5.Buist MD, Moore GE, Bernard SA et al. Effects of a medical emergency team on reduction of incidence of and Mortality from unexpected cardiac arrests in hospital: preliminary study. BMJ 2002; 324: 387-390 6.NHS Modernisation Agency 2003, Progress in Developing Services – Critical Care Outreach 7.Gao H, McDonnell A, Harrison DA et al, Systematic review and evaluation of physiological track and trigger warning systems for identifying at-risk patients on the ward. Intensive Care Med 2007; 33: 667 -79 8.Smith GB, Prytherch DR, Schmidt P, et al. Hospital wide physiological surveillance – a new approach to the early identification and management of the sick patient. Resuscitation 2006 ; 71:19-28 9.NICE clinical guideline 50, July 2007: ‘Acutely ill patients in hospital' 10.NCEPOD 2005 Report: ‘An Acute Problem?’ Conflict of Interest:None declared |
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Carolyn Johnston
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Editor, I read with interest the paper by Duckitt at al (1) describing their novel physiological scoring system. Through their hard and skilful work, the authors have produced a scoring system which they were able to show to be superior to the pre-existing early warning system in that hospital. Evidence of such a validated scoring system lends credence to those who point to the theoretical benefits of early warning scores (EWS). However, the failure to demonstrate the benefits of EWS across hospitals in the MERIT trial (2) and others (3) casts doubt on the ability of such systems to save lives. Your editorial addresses these issues and the choices of observations to be included in an ideal scoring system. I would argue that no such ideal system exists. The variables involved are too heterogeneous to apply one system nationally or internationally. Duckitt et al validated their system in their own general hospital with their own data set. I suggest that the Worthing physiological scoring system may not be beneficial if applied to my district general hospital in Birmingham or those in Cardiff, Belfast or Sydney. The scores aim to work within the constraints of the workings of a hospital. If care was ideal, there would be no need for EWS- at risk patients would be flagged up the traditional systems i.e. the interpretation of regular observations by medical and nursing staff. EWS represent the best attempts to deal with the constraints of the system- mainly the number of skilled staff for an increasingly dependent patient population. EWS are therefore a compromise and as such need to reflect the particular problems of that population (both the patient and medical/nursing populations). For example, the score attributed to pyrexia on a surgical ward may not be equal to that on a coronary care unit. Ventilatory frequency may be a more important finding in populations where diseases like TB are more common. All clinicians know some wards are able to take and interpret observations more frequently and accurately than other wards. Any scoring system needs to work within the limitations of the hospital in which it is applied. This interpretation explains why the MERIT trial and others have not been able to show benefit across many centres, whilst Duckitt et al are able to show the Worthing scoring system works in their own centre. Perhaps the future is the generation of scoring systems individually tailored to particular hospitals. I look forward to the publication of ongoing trial data of the application of the Worthing score and perhaps other scoring systems from the Inverness score to the Plymouth score and everything in between. (1) Duckitt R, Buxton-Thomas R, Walker J, et al. The Worthing Physiological Scoring System: derivation and validation of a physiological early warning system for medical admissions. Observational population based single-centre study. Br J Anaesth (2007) 98:770–75. (2) Hillman K, Chen J, Cretikos M, et al. Introduction of the medical emergency team (MET) system: a cluster-randomised controlled trial. Lancet (2005) 365:2091–7 (3) Gao H, McDonnell A, Harrison DA, et al. Systematic review and evaluation of physiological track and trigger warning systems for identifying at-risk patients on the ward. Intensive Care Med (2007) 33:667–79 Conflict of Interest:None declared |
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