Whether one, two, three or more volunteer responders rush to help when someone experiences cardiac arrest affects how likely a bystander is to carry out defibrillation. The results may be important for calibrating the algorithms that alert volunteer responders when required.
Several countries have established volunteer (or citizen) responder programmes in which an emergency call reporting cardiac arrest automatically triggers an alert to several volunteer responders that someone needs help.
However, different countries alert different numbers of volunteer responders, which also means that different numbers of volunteers reach the location before an ambulance arrives.
A new study shows that whether the emergency services activate one, two, three or more volunteer responders does matter. The more volunteers who respond, the greater the likelihood that a bystander will carry out defibrillation before an ambulance arrives.
The new research results can be useful in calibrating the algorithms that transmit the alerts to the volunteer responders.
“A country with an ambition to try to resuscitate a certain proportion of people experiencing out-of-hospital cardiac arrest through defibrillation can use our data to see how many alerts should be sent to volunteer responders. They can also determine how many alerts to send to increase the number of volunteers who respond and how this affects the likelihood of a bystander carrying out defibrillation or administering cardiopulmonary resuscitation,” explains a researcher behind the study, Mads Gregers, doctor and PhD fellow, Copenhagen University Hospitals – Copenhagen Emergency Medical Services.
The research has been published in the Journal of the American College of Cardiology.
150,000 volunteer responders in Denmark
The study was based on data from the volunteer responder programme in Denmark, which has 150,000 registered volunteers.
When an emergency call is received about a possible out-of-hospital cardiac arrest, 20 alerts are sent to volunteer responders located within 5 kilometres of the of the incident. For every five volunteers accepting an alert, four are sent to get a defibrillator and one is sent directly to the location of the incident.
Past research has shown that a volunteer responder arriving at a cardiac arrest increases the chances of bystander cardiopulmonary resuscitation (CPR) and defibrillation before an ambulance arrives.
30% of volunteer responders accept an alert
In the new study, Mads Gregers and colleagues wanted to determine the effect of not just one but several volunteer responders arriving in connection with an out-of-hospital cardiac arrest.
For this purpose, the researchers investigated 906 out-of-hospital cardiac arrests from the Capital Region of Denmark and the Central Denmark Region, two of Denmark’s five administrative regions. The data on the proportions receiving CPR and defibrillation were obtained from the Danish Cardiac Arrest Registry, and the volunteer responders received a questionnaire 90 minutes after receiving an alert. They said whether they arrived before an ambulance, whether CPR was given and whether defibrillation was applied.
The results show that the number of volunteer responders who were alerted was linearly correlated with the number of volunteers who accepted an alert and rushed to help and that the number of volunteers who accepted an alert was linearly correlated with the number of volunteers who arrived before an ambulance.
The survey showed that 30% of the volunteer responders accepted an alert, which means an average of between six and seven volunteers rushing to get a defibrillator or directly to the location of the incident.
“None of these results are surprising, but they show how many alerts should be sent to get a certain number of volunteer responders to respond to the alert and a certain number of volunteers to reach the incident before an ambulance,” says Mads Gregers.
He elaborates that the programme in Denmark started by sending 10 alerts but increased this to 20 to ensure that at least one volunteer responder accepts the alert.
Several volunteer responders are better than one
The results also show that the number of volunteer responders arriving at the incident before an ambulance affects whether life-saving first aid is administered.
If no volunteer responder arrives, the probability that a bystander will carry out CPR is about 75–78%; this increases to 95% if a volunteer arrives, but more volunteer arriving provides no additional gain.
Mads Gregers says that 95% is a high percentage and difficult to improve on. The use of defibrillation, however, depends on the number of volunteer responders who arrive before an ambulance.
If one volunteer responder arrives, the probability of bystander defibrillation increases by a factor of two versus no volunteer arriving before an ambulance. The probability increases by a factor of 2.88 for two volunteers and 4 for three volunteers.
According to Mads Gregers, these results are interesting because they provide data that can be used in calibrating the algorithms that send alerts to the volunteer responders.
“Sending more alerts is beneficial for increasing the proportion of CPR and defibrillation of people with cardiac arrest carried out by bystanders. Conversely, this must be weighed with how many volunteer responders should be disturbed with alerts. Different countries activate different numbers of volunteer responders, and these data can help them to adjust the number needed in each country,” explains Mads Gregers.
Major study will document the effect of the volunteer responder programme
The researchers also investigated whether the number of volunteer responders was associated with the probability of a person experiencing cardiac arrest being alive 30 days later. However, the study was not geared for this, and the results also showed that this did not make any difference.
Nevertheless, an upcoming study in which Mads Gregers is also involved may elucidate whether the volunteer responder programme only affects whether resuscitation is attempted among people experiencing out-of-hospital cardiac arrest or whether this also affects their survival.
“We are conducting the first randomised controlled trial in the world with a survival endpoint in which some cardiac arrests activate volunteer responders and others do not. This should provide results on how much the volunteer responder programmes around the world affect survival,” he concludes.
