Background: Cardiac arrest is the leading cause of mortality in Canada, and the overall survival rate for out-of-hospital cardiac arrest rarely exceeds 5%. Survivors have a quality of life similar to the general population. While bystander CPR can increase survival for cardiac arrest victims up to four times, bystander CPR rates remain low in Canada (15%). Many Canadian urban communities offer 9-1-1 dispatch-assisted CPR instructions to callers reporting a victim in cardiac arrest. Some evidence suggests that agonal breathing can be misinterpreted as a sign of life by Dispatch Officers, resulting in the inappropriate withholding of dispatch-assisted CPR instructions. Dispatch-assisted CPR instructions are recommended by the International Guidelines on Emergency Cardiovascular Care, but their ability to improve cardiac arrest survival remains unclear according to a systematic review of the literature. Objectives: The overall goal of this study is to better understand the factors leading to successful dispatch-assisted CPR instructions and to ultimately save more lives of cardiac arrest patients. Specific objectives are to: 1) Determine the ability of 9-1-1 dispatchers to make the diagnosis of cardiac arrest over the phone; 2) Quantify the frequency and impact of perceived agonal breathing on cardiac arrest diagnosis; 3) Measure the frequency with which dispatch-assisted CPR instructions can be successfully completed in out-of-hospital cardiac arrest cases; and 4) Measure the impact of dispatch-assisted CPR instructions on bystander CPR and survival rates for out-of-hospital cardiac arrest. Methods: We will conduct a before-after, prospective cohort study that evaluates 9-1-1 call reporting for out-of-hospital cardiac arrest victims. The study will take place in 19 urban communities in Ontario providing dispatch-assisted CPR instructions since April 1st 2004. The study population will include all 9-1-1 callers reporting out-of-hospital cardiac arrests for which resuscitation was attempted in patients 16-years or older.

The dispatch center protocol consists of establishing the nature of the emergency before initiating the appropriate level of response; this includes asking standardized questions to determine if cardiac arrest is present. The Dispatch Officer then offers CPR instructions over the telephone while emergency response vehicles are on their way to the location. Standardized data collection tools will be used to extract information from: 9-1-1 call recordings, paramedic patient care reports, base hospital records, fire medical records, and hospital medical records. All participating centers already combine information from various sources in a cardiac arrest registry. The following information will be collected: confirmation of cardiac arrest status by the Dispatch Officer, presence of apparent agonal breathing, CPR instructions offered to the 9-1-1 callers, factors influencing the ability of 9-1-1 callers to perform CPR including their proximity to the victim�s location and their emotional receptiveness to instructions, the time interval between the call to 9-1-1 and the initiation of CPR by the bystander. Measurements will include the accuracy of cardiac arrest diagnosis, the frequency of perceived agonal breathing during cardiac arrest, 9-1-1 caller�s ability to receive instructions and initiate CPR, bystander CPR rates, and survival to hospital discharge. Data analysis for Objective #1 will include sensitivity, specificity and receiver operating characteristic curve; Objectives #2 and #3 will be analyzed using descriptive statistics; and for Objective #4 univariate, stepwise logistic regression, and time series analysis will be performed to control for trends over time and variables otherwise associated with bystander CPR and survival rates in 6000 arrest victims.