Clinical paperA review, and performance evaluation, of single-parameter “track and trigger” systems☆
Introduction
Many hospitals have introduced rapid response systems (RRS) to facilitate the early identification of deteriorating adult patients and the delivery of enhanced care to the patient's bedside.1, 2, 3, 4, 5 Most RRSs use a set of predetermined, largely objective, “calling criteria” as indicators of the need to call for more expert help. These sets of calling criteria, also known as “track and trigger” systems, can be categorised as single-parameter systems, multiple-parameter systems, aggregate weighted scoring systems or combination systems.6 The simplest of these – the single-parameter systems – was first described in 19957 when it consisted of a range of specific conditions (e.g., pulmonary oedema), physiological/pathological abnormalities (e.g., pulse rate <40 or >120 beats min−1) and the loose criterion “any time urgent help is required”. The occurrence of one of more of these criteria is used as an indication to call for help. In the original description, the assistance took the form of a medical emergency team (MET).7 In the UK, the response is often provided by a critical care outreach team (CCOT).6, 8, 9 The original MET calling criteria7 have been modified by many others, often with only subtle changes to the physiological trigger points. Generally, the inclusion of calling criteria variables and their trigger points are solely based on expert clinical opinion and intuition.
There is little data regarding the function of single-parameter track and trigger systems (SPTTSs) to predict specific clinical outcomes and there is no clear indication of which is the best. Previous limited analysis of such systems suggests that they have acceptable specificities and negative predictive values, but low sensitivities and positive predictive values.10 The rationale for using a SPTTS is that an extreme physiological value heralds an adverse outcome (e.g., cardiac arrest, unanticipated ICU admission, death). However, a major barrier to the evaluation of this relationship has been the intermittent nature of most ward-based monitoring and the lack of completeness of the vital signs datasets. As part of a stepwise approach to analysing the relationship between the components of SPTTS and adverse clinical outcomes, this study was designed to review the published SPTTS and evaluate their ability to discriminate between survivors and non-survivors of hospital admission using a large, vital signs database collected in a standardised manner from unselected, medical patients admitted to hospital as an emergency.
Section snippets
Method
Prior to starting the study, we obtained local research ethics committee approval. We performed a comprehensive review of the published literature to identify the most commonly described SPTTSs. This included reviewing existing review articles, consensus guidelines and the reports of key UK healthcare organizations,2, 6, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 and performing electronic searches using Dialog Datastar® (The Thompson Corporation) and PubMed (National Library of
Results
From our literature search, we identified 75 publications1, 3, 4, 7, 13, 15, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93 which described a total of 80 SPTTSs (Table 1). 41 SPTTSs were excluded because they duplicated systems that had been described in earlier
Discussion
Abnormal physiology is associated with adverse events such as cardiac arrest, unanticipated ICU admission and in-hospital death.31, 34, 59, 61, 76, 94 However, research investigating the ability of physiologically-based, track and trigger systems to identify general hospital patients who will suffer an adverse event is sparse. A previous review of the components of one type of track and trigger system – the aggregate weighted track and trigger systems (AWTTS)95 – has shown a lack of consistency
Conclusions
In conclusion, our review of the literature has demonstrated considerable variation in the physiological variables used in single-parameter track and trigger systems, together with significant variation in the physiological values used to trigger a medical emergency or critical care outreach team. These differences lead to marked variations in the performance of the respective systems when using initial vital signs data for predicting in-hospital mortality. The systems evaluated in our study
Conflict of interest
The electronic vital signs data gathering system used in this study, VitalPAC™, is a collaborative development of The Learning Clinic Ltd. and Portsmouth Hospitals NHS Trust. Dr. Paul Schmidt and the wives of both Professor Smith and Dr. Prytherch are creditors of The Learning Clinic Ltd.
Acknowledgements
The authors would like to acknowledge the co-operation of the nursing and medical staff of the Medical Assessment Unit of Portsmouth Hospitals NHS Trust.
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A Spanish translated version of the summary of this article appears as Appendix in the final online version at doi:10.1016/j.resuscitation.2008.05.004.