Elsevier

Resuscitation

Volume 79, Issue 1, October 2008, Pages 11-21
Resuscitation

Clinical paper
A review, and performance evaluation, of single-parameter “track and trigger” systems

https://doi.org/10.1016/j.resuscitation.2008.05.004Get rights and content

Summary

Objectives

There is no up-to-date literature review of physiologically-based, single-parameter weighted “track and trigger” systems (SPTTS) and little data on their sensitivity and specificity to predict adverse outcomes. The aim of this study was to describe the SPTTS in clinical use and measure their sensitivity and specificity when using admission vital signs data for predicting in-hospital mortality.

Materials and methods

We performed a systematic review of the literature to describe the SPTTS, their components and their differences. We measured their sensitivity and specificity for predicting in-hospital mortality when using a database of 9987 admission vital signs datasets.

Results

We identified 39 unique classes of SPTTS, of which 30 were evaluated. There was considerable variation in the physiological variables used, together with significant variation in the physiological values used to trigger a medical emergency or critical care outreach team. There was marked variation in sensitivity (7.3–52.8%), specificity (69.1–98.1%), positive predictive values (13.5–26.1%), negative predictive values (92.1–94.2%) and the potential number of calls triggered (234–3271).

Conclusions

There is a wide range of unique, but very similar, SPTTS in clinical use. Although specificities were high, sensitivities were too low to provide institutions with confidence that these SPTTS could identify patients at risk of in-hospital death using admission vital signs. Institutions may wish to consider these data when selecting which, if any, single-parameter track and trigger systems to introduce.

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.

References (97)

  • C. Crispin et al.

    Nurses’ responses to acute severe illness

    Aust Crit Care

    (1998)
  • M.I. Foraida et al.

    Improving the utilization of medical crisis teams (Condition C) at an urban tertiary care hospital

    J Crit Care

    (2003)
  • D.R. Goldhill et al.

    Intensive care outreach services

    Curr Anaesth Crit Care

    (2002)
  • A.L. Green et al.

    An evaluation of an early warning clinical marker referral tool

    Intensive Crit Care Nurs

    (2006)
  • G.A. Harrison et al.

    The prevalence of recordings of the signs of critical conditions and emergency responses in hospital wards—the SOCCER study

    Resuscitation

    (2005)
  • G.A. Harrison et al.

    Combinations of early signs of critical illness predict in-hospital death-The SOCCER Study (signs of critical conditions and emergency responses)

    Resuscitation

    (2006)
  • K. Hillman et al.

    A clinical model for Health Services Research—the Medical Emergency Team

    J Crit Care

    (2003)
  • T. Jacques et al.

    Signs of critical conditions and emergency responses (SOCCER): a model for predicting adverse events in the inpatient setting

    Resuscitation

    (2006)
  • D. Jones et al.

    Long-term effect of a Medical Emergency Team on mortality in a teaching hospital

    Resuscitation

    (2007)
  • D. Jones et al.

    Using an MET service to manage an acute thromboembolic stroke

    Comm J Qual Patient Saf

    (2006)
  • J. Kause et al.

    A comparison of antecedents to cardiac arrests, deaths and emergency intensive care admissions in Australia and New Zealand, and the United Kingdom—the ACADEMIA study

    Resuscitation

    (2004)
  • G. Kenward et al.

    Evaluation of a medical emergency team one year after implementation

    Resuscitation

    (2004)
  • M. Parr et al.

    Predicting inhospital cardiac arrest

    Resuscitation

    (1998)
  • M.J. Parr et al.

    The Medical Emergency Team: 12 month analysis of reasons for activation, immediate outcome and not-for-resuscitation orders

    Resuscitation

    (2001)
  • J. Ranse

    Cardiac arrest: can the in-hospital chain of survival be improved?

    Australasian Emerg Nurs J

    (2006)
  • Y. Salamonson et al.

    The evolutionary process of Medical Emergency Team (MET) implementation: reduction in unanticipated ICU transfers

    Resuscitation

    (2001)
  • A.F. Smith et al.

    Can some in-hospital cardio-respiratory arrests be prevented? A prospective survey

    Resuscitation

    (1998)
  • S. Tolchin et al.

    Eliminating preventable death at Ascension Health

    Comm J Qual Patient Saf

    (2007)
  • D.R. Goldhill et al.

    Physiological abnormalities in early warning scores are related to mortality in adult inpatients

    Br J Anaesth

    (2004)
  • G.B. Smith et al.

    Review and performance evaluation of aggregate weighted ‘track and trigger’ systems

    Resuscitation

    (2008)
  • M.A. DeVita et al.

    Findings of the first consensus conference on medical emergency teams

    Crit Care Med

    (2006)
  • A.D. Baxter

    Critical care outreach comes to Canada

    CMAJ

    (2006)
  • D.R. Goldhill et al.

    The patient-at-risk team: identifying and managing seriously ill ward patients

    Anaesthesia

    (1999)
  • Department of Health and NHS Modernisation Agency. The National Outreach Report. London: Department of Health;...
  • A. Lee et al.

    The Medical Emergency Team

    Anaesth Intensive Care

    (1995)
  • D. Bright et al.

    Clinical review: outreach—a strategy for improving the care of the acutely ill hospitalized patient

    Crit Care

    (2004)
  • H. Gao 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)
  • L. Esmonde et al.

    Investigating the effectiveness of critical care outreach services: a systematic review

    Intensive Care Med

    (2006)
  • A. Aneman et al.

    Medical emergency teams: a role for expanding intensive care?

    Acta Anaesthesiol Scand

    (2006)
  • S. Parissopoulos et al.

    Critical care outreach and the use of early warning scoring systems; a literature review

    ICUs Nurs Web J

    (2005)
  • B.D. Winters et al.

    Rapid response systems: a systematic review

    Crit Care Med

    (2007)
  • F. McArthur-Rouse

    Critical care outreach services and early warning scoring systems: a review of the literature

    J Adv Nurs

    (2001)
  • McGaughey J, Alderdice F, Fowler R, Kapila A, Moutray M. Outreach and Early Warning Systems (EWS) for the prevention of...
  • Intensive Care Society. Guidelines for the Introduction of Outreach Services. London: Intensive Care Society;...
  • Department of Health. Comprehensive critical care. A review of adult critical care services. London: Department of...
  • Royal College of Physicians of London. The interface between acute general medicine and critical care. Report of a...
  • Audit Commission. Critical to success: the place of efficient and effective critical care services within the acute...
  • Department of Health. The nursing contribution to the provision of comprehensive critical care for adults: a strategic...
  • Cited by (140)

    View all citing articles on Scopus

    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.

    View full text