Increasing the time spent administering CPR to cardiac arrest patients won't increase their chances of survival, researchers said Wednesday, putting to rest one of the raging debates in emergency medicine. "Our study definitively shows that there is no advantage to a longer period of initial CPR," said Dr Ian Stiell, a senior scientist at the Ottawa Hospital Research Institute (OHRI), one of the entities leading the study. Paramedics and firefighters traditionally have provided only brief CPR while readying a defibrillator to jolt the heart into restarting. But some experts over the years have said that a longer period of initial cardio-pulmonary resuscitation -- for up to three minutes -- may help increase a cardiac arrest patient's odds of survival. The scientists in the study, which also involved the University of Ottawa and the Resuscitation Outcomes Consortium (ROC), said the new research settles the question once and for all. "I think it is better to be on the safe side and stick with the traditional shorter initial CPR approach," Stiell said. The study found that increasing the time that paramedics and firefighters administer cardiopulmonary resuscitation (CPR) from one to three minutes provides no additional benefit. The results, published in the New England Journal of Medicine, analyzed medical data gleaned from some 10,000 US patients. The researchers said that prompt CPR can increase blood flow to the brain and keep the body alive for a short time, but for patients with certain cardiac rhythms, the heart can only be restarted by providing electrical shocks with a defibrillator. Paramedics and firefighters across Canada and the United States were randomly divided into groups and instructed to provide 30 to 60 seconds of initial CPR or three minutes of initial CPR. Part way through the study, the groups were switched. An analysis of the results found that survival tended to decrease as the length of initial paramedic CPR increased in patients who also received bystander CPR and had a heart rhythm amenable to defibrillation. Every year, more than 350,000 people in Canada and the United States suffer a sudden cardiac arrest, and less than 10 per cent survive, medical experts said.