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They might save the life of one of the city's growing number of tourists.
Rob Atkinson, of Macandrew Bay, works as a nurse in New Zealand and Australia.
He expects a potential spike in medical emergencies on Otago Peninsula when contractors finish a multimillion-dollar roading project and more tourists descend on the area.
"With that influx of people comes an increased risk.''
International visitor arrivals to New Zealand are expected to jump 37% in the next six year, Ministry of Business, Innovation and Employment figures show.
Otago Peninsula Trust marketing manager Sophie Barker said she believed more than 500,000 tourists - domestic and international - visited the peninsula this year.
More visitors had taken tours at the centre this year than in any previous year.
She expected an increase in tourist numbers visiting the peninsula to be in line with the ministry's forecast.
To prepare for the influx, Mr Atkinson wants people on the peninsula with first-aid training to register for the GoodSAM (Smartphone Activated Medics) app.
The free app was developed in England and has been implemented by ambulance services around the world including St John in New Zealand.
People who know how to perform cardiopulmonary resuscitation (CPR) and use an automated external defibrillator (AED) and were prepared to voluntarily respond to a patient suspected to be in cardiac arrest could register as a responder and download the app on their phone.
If a GoodSAM responder was within 1000m of a suspected cardiac arrest, they would receive an alert on their phone giving them the opportunity to respond.
The app also shows responders the location of the incident and the known closest AED.
Outcomes from cardiac arrest were best when the patient received resuscitation and defibrillation within the first three minutes, he said.
The community had a responsibility to help provide the best level of emergency care available.
"If it's something as simple as doing CPR or keeping someone's airway open, then so be it.''
St John coastal Otago territory manager Doug Third said the number of emergency ambulance callouts in the greater Dunedin area had remained stable in the last three years, with a slight decrease this year.
St John medical director Dr Tony Smith said St John embedded the GoodSAM app into its emergency ambulance dispatch systems in April.
"The more people who download the app, the more coverage we will achieve across New Zealand, and the more likely we are to improve outcomes from cardiac arrest.''
In the past five years, bystander use of AEDs had increased from 3.9% to 5.1%, he said. The introduction of the GoodSAM app was part of the reason for the positive result, he said.
• To sign up to be a GoodSAM responder, go to www.goodsamapp.org/regResponder.
Who is Rob Atkinson?
Works on a roster of six weeks on and six weeks off as a remote area nurse in Alice Springs, central Australia.
In his six weeks off, he returns home to Dunedin and works on an on-call roster as a prime (primary response in medical emergencies) nurse in Central Otago from Friday afternoons to Monday mornings.