Are track and trigger systems linked to rates of in-hospital cardiac arrest?

Use of the National Early Warning Score (NEWS) to monitor adults in hospital is associated with reduced risk of having a cardiac arrest while in hospital. Using an electronic rather than paper-based system is also linked to reduced risk.

Many patients who die from a cardiac arrest while in hospital show signs of deterioration beforehand that aren’t identified or acted upon. Several interventions aimed at reducing these avoidable deaths have been introduced in the NHS. These include NEWS, a national track and trigger system introduced in England in 2012. This NIHR-funded study investigated which of these interventions have the most impact

The study was not able to take into account other changes to policy and practice that took place at the same time. This means that the results can only show associations, rather than causation, and more research is needed. Nevertheless, the findings support the use of track and trigger electronic systems.


Why was this study needed?

Acutely ill patients admitted to hospital are at risk of their health deteriorating, which can sometimes lead to in-hospital cardiac arrest. Hospitals deal with about 20,000 arrests in England each year. Approximately 85% of these patients die in hospital. Some of those deaths could be avoided with better monitoring of patients and better responses to signs of deterioration.

In 2000, the Department of Health recommended several interventions that aimed to decrease avoidable deaths and improve standards of care. These included track and trigger systems (see Definitions), nurse-led outreach teams, and structured handover tools. These are all components of a rapid response system.

However, data from the National Cardiac Arrest Audit shows that there is still wide variation in cardiac arrest rates and survival around the country.

This study aimed to investigate which interventions have the most impact on rates and outcomes, by assessing differences in how interventions have been implemented in practice.


What did this study do?

This was a mixed-methods study. Qualitative interviews were undertaken with 60 staff from 13 hospitals, to identify key components of interventions, processes and contextual factors. The results, along with a systematic review, were used to design an organisational survey which was carried out in 171 hospitals. Data from the survey was combined with other national data sources such as clinical activity data. Cross-sectional interrupted time-series, and difference-in-difference analyses were carried out. These examined links between variations in services and in-hospital cardiac arrest rates and survival in 106 hospitals before and after some major service changes were introduced.

The study was limited by relying on survey respondents’ memory when investigating changes over time. It was also unable to take into consideration other policy and practice changes that were taking place at the same time.


What did it find?

  • In-hospital cardiac arrests fell by 6.4% per year and survival increased by 5% per year from October 2009 to March 2015 according to 13,059,865 hospital admissions, with 32,364 patients having 34,202 arrests.
  • National Early Warning Score (NEWS) was introduced in 2012 and was being used by 70% of NHS hospitals by 2015. The use of NEWS was associated with an additional 8.4% decrease in arrests.
  • By 2015, a third of hospitals were using electronic track and trigger systems, rather than paper-based ones.  Switching from paper to electronic systems was associated with an additional 7.6% decrease in arrests.
  • Outreach teams have been increasingly adopted in the NHS since 2000. They have an overarching role of clinical care for critically ill patients on the ward, end-of-life decision-making, and education and quality assurance. However, there are big differences in the way they’ve been implemented in the NHS, in terms of team composition, hours, autonomy, and education or improvement activities. Outreach teams didn’t appear to have an impact on arrests over time.


What does current guidance say on this issue?

NICE’s 2007 guideline on recognising and responding to deterioration in acutely ill adults in hospital says that physiological track and trigger systems should be used to monitor all adult patients in acute hospital settings. It says that trigger thresholds should be set locally and that a graded response strategy to the trigger should be agreed.

The guideline currently does not recommend a specific track and trigger system. However, in February 2019, NICE announced that the guideline will be amended to state that the early warning score NEWS2 has been endorsed by NHS England. The first version, NEWS1, is already endorsed in Scotland and Wales.


What are the implications?

Electronic track and trigger systems, NEWS in particular, are linked to lower in-hospital cardiac arrest rates. However, this study wasn’t able to identify which aspects of the interventions have the most impact, or whether other external factors influenced the associations.

Variation in arrest rates still exists, which may be due to differences in the ways that hospitals have implemented these rapid response systems. This research should help those implementing track and trigger systems and other elements of rapid response systems to better understand the issues so that the number of avoidable deaths in hospital is reduced.


Citation and Funding

Hogan H, Hutchings A, Wulff J et al. Interventions to reduce mortality from in-hospital cardiac arrest: a mixed-methods study. Health Serv Deliv Res. 2019;7(2).

This project was funded by the NIHR Health Services and Delivery Research Programme (project number 12/178/18).



NICE. Acutely ill adults in hospital: recognising and responding to deterioration. CG50. London: National Institute for Health and Care Excellence; 2007.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre



Track and trigger systems are a way of recording standard observations (such as heart rate, respiratory rate, blood pressure, oxygen saturation, temperature and level of consciousness) and converting these into a score.

Different scores trigger different responses, ranging from increasing the frequency of observations and alerting the nurse in charge, to an emergency call to a critical care team with advanced airway management and resuscitation skills.


Expert commentary

In-hospital cardiac arrests are, in the majority of cases, predictable and potentially preventable with robust systems which recognise and respond to the deteriorating patient. This enables an early decision about appropriateness of escalation of care. 

From this large analysis of 106 UK hospitals, the two most effective interventions to reduce cardiac arrests appear to be standardising recognition of the deteriorating patient by adoption of NEWS, and electronic monitoring systems to improve reliability. It is less clear which response interventions are the most effective; with no clear evidence favouring outreach teams over ward-based staff. However, this risks oversimplification as typically outreach teams are involved in improving the entire process.

In-hospital cardiac arrests often represent a failure of process. In 2015, less than 30% of these hospitals utilised an electronic system to improve reliability. This must be a catalyst for change.

Dr Dan Beckett, Consultant Acute Physician, Unscheduled Care Clinical Lead, NHS Forth Valley

The commentator declares no conflicting interests