Scottish Out-of-Hospital Cardiac Arrest data linkage project: initial results

This report presents the initial results of the Scottish Out-of-Hospital Cardiac Arrest data linkage project (OHCA data linkage project).

Initial results of the Scottish out-of-hospital cardiac arrest data linkage project

Interpretation of results and comparisons

Box 1

The Utstein Template

In June 1990, an international multidisciplinary meeting held at the Utstein Abbey in Norway has led to the development of uniform terms and definitions for out-of-hospital resuscitation. The ultimate goal of this 'Utstein style' was to improve health care and quality improvement through better understanding of the epidemiology of cardiac arrest and enable comparisons within and between systems and countries.

An important part of the Utstein style is a standardised template for reporting outcomes for OHCA [15] . Based on this template OHCA cases can be classified in different groups based on characteristics of the OHCA case and circumstances (such as resuscitation attempted or not, initial heart rhythm, witnessed or not).

One of the groups which can be identified using this Utstein standardised template is the Utstein comparator group. This group is formed by OHCA cases who are most likely to survive (presenting with shockable heart rhythms, have witnessed arrests and where prompt bystander CPR is started). Outcomes within Utstein comparator group are increasingly used by researchers and registries to standardise the reporting of OHCA. This enables comparisons between geographical regions in terms of system efficacy and short-term and long-term outcomes [11] .

This report presents initial results of the Scottish OHCA data linkage project. This innovative work has linked complex datasets for the first time in order to report on OHCA in Scotland. As such, the results should be treated as provisional while the data and methodology are still in development. Throughout the report interpretations of the figures are given, and any assumptions are explained, with additional detail in the ' methods and assumptions' section of this report. Our results are compared, where possible, with data from other OHCA registries and academic publications.

We have taken this approach as international commentators have suggested that a large part of the variation in published OHCA outcomes may be due to the use of a broad range of population and outcome definitions [11], [15], [16]. This problem was recognised some time ago and led to the introduction of specific guidelines for the uniform reporting on OHCA outcomes in 1991; the Utstein Template [15] . These definitions can be used to help identify a more homogeneous and comparable cohort of OHCA cases (see Box 1 above for a description of the Utstein criteria). International registries and research groups often report survival percentages based on these criteria. To enable comparability this report includes results based on the Utstein comparator group.

Defining the cohort; identifying people who had an OHCA

Our findings are based on a dataset including information about OHCA patients of all ages in Scotland between the 1 January 2011 until the launch of the National Strategy for OHCA for Scotland on the 28 March 2015 [2] . OHCA due to traumatic causes, including hanging and drowning, are not included in our study cohort. All other cases of OHCA where resuscitation was attempted by the SAS are included.

Of the 14,895 people in Scotland who had an OHCA between the 1 January 2011 and the 28 March 2015 where resuscitation was attempted, 75.7% are included in the dataset. For the other 24.3%, data linkage was not possible because of missing personal identifiers ( see Figure 14 in the 'methodology' section for further information about the data linkage). All analysis is based on the OHCA cases which could be linked with other data sources (including survival outcome) unless otherwise specified. Importantly, this means it is likely that incidences and other absolute estimates will be underestimates of the true values. Future analysis is planned to investigate this assumption in more detail.

Box 2

What's the difference between a 'heart attack' and 'cardiac arrest'?

A heart attack is a sudden interruption to the blood supply to part of the heart muscle. It is likely to cause chest pain and permanent damage to the heart. The heart is still sending blood around the body and the person remains conscious and is still breathing.

A cardiac arrest occurs when the heart suddenly stops pumping blood around the body. Someone who is having a cardiac arrest will suddenly lose consciousness and will stop breathing or stop breathing normally. Unless immediately treated by CPR this always leads to death within minutes.

A person having a heart attack is at high risk of experiencing a cardiac arrest.

Both a heart attack and a cardiac arrest are life-threatening medical emergencies and require immediate medical help. Call 999 if you think you are having a heart attack or if you witness someone having a cardiac arrest.



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