Track & trigger warning systems

Physiological track and trigger warning systems for identifying at-risk patients on the ward: a systematic review

What was this review about?

Physiological track and trigger warning systems have been developed for use outside critical care areas with the objective of ensuring timely recognition of deteriorating patients. These track and trigger systems use periodic observation of basic vital signs (heart rate, blood pressure, etc.) together with pre-determined criteria for requesting the attendance of more experienced staff, usually the critical care outreach service.

This review looked for papers that described the use of a track and trigger system or were concerned with the testing or development of track and trigger systems. In addition, all NHS acute hospitals in England with critical care facilities were contacted to identify available datasets on track and trigger systems.

The aims of this work were:

  • to describe published track and trigger systems 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 track and trigger system for timely recognition of critically ill patients.

This systematic review was part of the Evaluation of outreach services in critical care.

What did the review find? 

The review identified 36 eligible papers providing detailed descriptions of 25 distinct physiological track and trigger warning systems. Fifteen eligible datasets were received, each on a different track and trigger system, only one of which had been identified in the review.

A wide variety of track and trigger systems 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 track and trigger system.

The authors recommended that physiological track and trigger warning systems should be used as an adjunct to clinical judgement.


  • Authors: Gao H, McDonnell A, Harrison DA, Moore T, Adam S, Daly K, Esmonde L, Goldhill DR, Parry GJ, Rashidian A, Subbe CP, Harvey S Title: Systematic review and evaluation of physiological track and trigger warning systems for identifying at risk patients on the ward Publication: Intensive Care Medicine Journal website PubMed citation

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