Emergency Health Services

Stroke Ambulance Key Performance Indicators

The following document provides information on the methodology used to create the cohort for patients arriving at the emergency department (ED) via ambulance due to strokes or ST Elevation Myocardial Infarction (STEMI) and the calculation of the 30-day risk adjusted mortality rate post ED visit.

Stroke/Transient Ischemic Attack (TIA)


Stroke: Rapidly developing clinical signs of focal (at times global) disturbance of cerebral function, lasting more than 24 hours or leading to death, with no apparent cause other than that of vascular origin1.  

Stroke types included in cohort:

  • TIA: Transient ischemic attack, or ‘mini-stroke’; an episode of temporary and focal cerebral dysfunction of vascular origin, variable in duration, commonly lasting from 2 to 15 minutes but occasionally lasting as long as a day (24 hours), which leaves no persistent neurological deficit. 
    ICD-10-CA codes: G450, G451, G452, G453, G458, G459

  • Ischemic stroke: Stroke caused by the interruption of blood flow to the brain due to a blockage or constriction of the arteries that supply it.
    ICD-10-CA codes: I63, I64, H340, H341
  • Hemorrhagic stroke:  Stroke caused by the interruption of blood flow to the brain due to uncontrolled bleeding in the brain.
    ICD-10-CA codes: I60, I61, I62

Stroke Methodology :

The database used to create the stroke cohort is the National Ambulatory Care Reporting System (NACRS); the diagram below is based on cases from 2013/14 to 2015/16.

NACRS identified
stroke/TIA visits

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All visits reported in NACRS database between April 1, 2013 and March 31, 2016 where one of the diagnoses was TIA, ischemic stroke or hemorrhagic stroke. 

Eligible visits

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Adult Ontario patients with a valid health card number

Excludes: (total=3,059)

  • Patients 18 and under or missing age (n=360)
  • Unknown gender (n=5)
  • Non-Ontario patients (n=2,656)
  • Patients without a valid health card (n=38 )

Treated in ED as
main problem

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ED visits for adults with a main problem of stroke or TIA 

Excludes: (total=19,983)

  • Visits not treated in the ED (n=1,181)
  • Urgent care center visits (n=1,826)
  • Visits where stroke is not the main problem (n=16,696)
  • Palliative care coded on ED visits (n=280)

Initial visit

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ED to ED transfers (n=8,422) based on the following criteria:

  1. Any ED visit within 6 hours of a previous ED visit;
  2. Any ED visit within 12 hours of a previous ED visit where either the previous ED visit hospital transfer to number matches to second visit hospital number OR the hospital from type or to type is ambulatory care.
  3. Any ED visits within 24 hours where the previous ED visit hospital number matches the hospital from number of the second visit.

Final Cohort: Arrival via Ambulance


  • Patients that did not arrive via ambulance (n=51,029)

Mortality Rate

The mortality rate is created by linking the stroke cohort to Health Analytics Branch’s internal death file. The death file uses several administrative databases (Discharge Abstract Database, National Ambulatory Care Reporting System, Ontario Mental Health Reporting System, Continuing Care Reporting System, OHIP Claims, and Registered Person Database) to determine Ontario resident’s date of death. The stroke cohort is linked to the death file to determine the 30-day mortality rate post registration date of the ED visit.

Risk Adjustment Factors

When comparing outcomes across regions or over time, it is important to account for differences in patient characteristics. Risk adjustment is a method used to control for patient characteristics that may affect health care outcomes and improves comparability after the pre-existing influence of patient population is removed.  Therefore, risk adjustment allows for fair comparison of performance between the populations such as LHINs.

The selected risk factors were identified based on a literature review, clinical evidence and expert group consultations using the principles of appropriateness, viability (i.e., sufficient number of events) and data availability. The risk adjustments for the stroke 30-day mortality rate control for:

  • Fiscal year
  • Fiscal quarter
  • Age
  • Sex
  • Stroke type
  • Charlson comorbidity index 
  • Previous inpatient admissions
  • Atrial fibrillation
  • Previous stroke/TIA
  • History of coronary artery disease
  • Diabetes
  • Peripheral vascular disease
  • Hypertension
  • Hyperlipidemia
  • Arrival by ambulance

Confidence Limit

A confidence interval (CI) reflects the uncertainty surrounding the risk-adjusted mortality ratio. In the analyses presented in this document, the CI indicates that the true value of the risk-adjusted mortality ratio falls between the upper and lower confidence limits 19 times out of 20. The narrower a CI, the more one can be confident in the value of the risk-adjusted mortality ratio.

Reporting Period

The reporting period is based on three years of pooled data. The data is scheduled to be updated annually based on three years of pooled data.

For more information, please contact:
Health Analytics Branch

 1 Ontario Stroke Evaluation Report 2014, On Target for Stroke Prevention and Care, ICES.

For More Information

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