The more times a paramedic has witnessed or participated in treating cardiac arrest outside the hospital, the greater the next patient's odds of survival, according to a study from Australia.

"Cardiac arrest is a leading cause of death worldwide," said lead author Kylie Dyson of the school of public health and preventive medicine at Monash University in Melbourne.

"Ambulance Victoria attend approximately 5,000 cardiac arrests a year," Dyson said. "Due to the large service area and workforce, individual paramedics only treat around two cardiac arrests a year."

The researchers matched data from a cardiac arrest registry to an ambulance employment database for the years 2003 to 2012 in Victoria, Australia. They tallied each time a paramedic responding to a cardiac arrest had responded in the previous three years to one where resuscitation was attempted.

During the study period, more than 4,000 paramedics worked in the area and there were more than 48,000 out of hospital cardiac arrests, with resuscitation attempts in 44 percent of cases.

Half of the paramedics had been exposed to at least two cardiac arrests per year, while half had less experience; 11 percent of the paramedics had not been exposed to any cardiac arrest cases.

Half of treating paramedics who attempted to resuscitate an out of hospital cardiac arrest victim had responded to at least 11 cardiac arrests outside hospitals over the preceding three years.

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About 7 percent of patients treated by paramedics who had experienced six or fewer cardiac arrests over the previous three years survived. That compared to 12 percent of those treated by paramedics who had responded to between seven and 11 cardiac arrests.

When treated by paramedics who had responded to up to 17 previous cardiac arrests or more, 14 to 17 percent of patients survived, according to the results published January 26 in Circulation: Cardiovascular Quality and Outcomes.

"Paramedics attend about 5,000 cardiac arrests every year across the state," said Anthony Carlyon, acting general manager for emergency operations for Ambulance Victoria, who was not part of the new study.

"Our cardiac arrest results are very impressive, with our survival rates among the world's best," Carlyon told Reuters Health in a statement. "About 30 percent of people whose heart is in a shockable rhythm survive, which is a 10-fold increase compared to survival rates in 1995."

Following a review, Ambulance Victoria is significantly increasing the number of hours dedicated to training for all paramedics annually, Carlyon added.

Resuscitation skills are complex and difficult to perform, and deteriorate rapidly over time for all professions, including doctors, nurses and paramedics, Dyson said.

"Our study indicates that paramedics may need six-monthly exposure or training to prevent skill decay and improve survival," Dyson told Reuters Health by email. "The results of our study are likely to have implications for other settings and other healthcare professionals as well."

In the Netherlands, paramedics are retrained in cardiac arrest every five years, said Dr. Jocelyn Berdowski of the Academic Medical Center University of Amsterdam.

"Preparing a resuscitation attempt on a real person is very different than practicing on a mannequin," Berdowski, who was not part of the new study, told Reuters Health by email. "My advice would be to take a refresher course (at least) once a year, and train realistic scenarios."

There's no way to increase actual paramedic exposure to cardiac arrest, but organizations could try formal debriefing after every cardiac arrest to ensure that paramedics learn from every case they treat, Dyson said.

"In addition to actual exposure, we could simulate cardiac arrest to give paramedics more opportunity to practice their skills," Dyson said.