Systematic Review

Intensive Care Medicine

, Volume 33, Issue 4, pp 667-679

First online:

Systematic review and evaluation of physiological track and trigger warning systems for identifying at-risk patients on the ward

  • Haiyan GaoAffiliated withIntensive Care National Audit & Research Centre
  • , Ann McDonnellAffiliated withFaculty of Health and Wellbeing, Sheffield Hallam University
  • , David A. HarrisonAffiliated withIntensive Care National Audit & Research Centre Email author 
  • , Tracey MooreAffiliated withSchool of Nursing and Midwifery, University of Sheffield
  • , Sheila AdamAffiliated withIntensive Care Unit, University College Hospital
  • , Kathleen DalyAffiliated withIntensive Care Unit, St. Thomas’ Hospital
  • , Lisa EsmondeAffiliated withSchool of Healthcare, University of Leeds
  • , David R. GoldhillAffiliated withAnaesthetics, Royal National Orthopaedic Hospital
  • , Gareth J. ParryAffiliated withQuality Measurement & Analysis, Children’s Hospital Boston
    • , Arash RashidianAffiliated withDepartment of Public Health and Policy, London School of Hygiene & Tropical Medicine
    • , Christian P SubbeAffiliated withIntensive Care National Audit & Research CentreThoracic Medicine, Wrexham Maelor Hospital
    • , Sheila HarveyAffiliated withIntensive Care National Audit & Research Centre

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Physiological track and trigger warning systems (TTs) are used to identify patients outside critical care areas at risk of deterioration and to alert a senior clinician, Critical Care Outreach Service, or equivalent. The aims of this work were: to describe published TTs and the extent to which each has been developed according to established procedures; to review the published evidence and available data on the reliability, validity and utility of existing systems; and to identify the best TT for timely recognition of critically ill patients.

Design and setting

Systematic review of studies identified from electronic, citation and hand searching, and expert informants. Cohort study of data from 31 acute hospitals in England and Wales.

Measurements and results

Thirty-six papers were identified describing 25 distinct TTs. Thirty-one papers described the use of a TT, and five were studies examining the development or testing of TTs. None of the studies met all methodological quality standards. For the cohort study, outcome was measured by a composite of death, admission to critical care, ‘do not attempt resuscitation’ or cardiopulmonary resuscitation. Fifteen datasets met pre-defined quality criteria. Sensitivities and positive predictive values were low, with median (quartiles) of 43.3 (25.4–69.2) and 36.7 (29.3–43.8), respectively.


A wide variety of TTs were in use, with little evidence of reliability, validity and utility. Sensitivity was poor, which might be due in part to the nature of the physiology monitored or to the choice of trigger threshold. Available data were insufficient to identify the best TT.


Systematic review Critical care Critical illness Scoring systems