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Pause between CPR, defibrillation can be deadly: study

Student Olivia Frierson presses contact pads from an AED machine onto a CPR mannequin during a CPR training class at Shaker Heights High School in Shaker Heights, Ohio on Monday, Jan. 10, 2011.

Amy Sancetta/Associated Press/Amy Sancetta/Associated Press

Urgent memo to paramedics: Do not pause between CPR and defibrillation because doing so can be deadly.

That is the key message to be taken from a new Canadian study that shows for every five-second delay between pumping the heart manually and shocking it back into action, a patient's chances of surviving cardiac arrest plummet by almost 18 per cent.

The research, published in Tuesday's edition of the medical journal Circulation, indicates that minimizing the brief period it takes to move from cardiopulmonary resuscitation to administering an electric shock with a defibrillator is a key predictor for survival.

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"If your preshock pause is over 20 seconds, the chances of surviving to reach a hospital, be treated and be discharged are 53 per cent less than if the pause is less than 10 seconds," said Sheldon Cheskes, medical director of the Sunnybrook Osler Centre for Prehospital Care in Brampton, Ont., and lead author of the study. "Those seconds matter."

He said he hopes the findings will encourage paramedics to move more quickly. In particular, he said, using defibrillators in manual mode halves the delay. Dr. Cheskes said that manufacturers of lifesaving equipment also need to update software to ensure that the time required to analyze a patient's heart rhythm and charge the defibrillator before delivering a shock is minimal.

The new study is based on data from 815 people who suffered out-of-hospital cardiac arrest between 2005 and 2007 across Canada and the United States. Their average age was 64, and 80 per cent were men.

All of the people included in the research suffered either ventricular fibrillation (abnormal heart rhythm) or pulseless ventricular tachycardia (no effective cardiac output), conditions that can be reversed with an electric shock. They were treated promptly – paramedics arrived, on average, in less than six minutes – and received CPR and defibrillation. The patients received at least one shock but required, on average, five jolts to restart their heart.

Dr. Cheskes and his colleagues in the research group known as the Resuscitation Outcomes Consortium found the time that passed between stopping CPR and defibrillation ranged from 0 to 107 seconds. The median time required for the transition was 22 seconds.

The researchers found that when the pause was less than 20 seconds, 32.6 per cent of patients survived; between 20 and 39 seconds, the survival rate was 31.9 per cent. But when the pause exceeded 40 seconds, the survival rate fell to 20.3 per cent.

"If you minimize interruptions, you maximize survival," Dr. Cheskes said. He stressed, however, that the study focused on just one element in a chain of events that needs to occur when a person suffers cardiac arrest.

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"We looked at the work of paramedics but don't forget that without bystander CPR – people doing CPR before the paramedics arrive – very few people survive," Dr. Cheskes said. "Any delay in blood flow to the brain is detrimental for survival."

In 2010, new CPR guidelines were published that urge people to push hard and fast – at least 100 compressions a minute. While assisting with breathing (mouth-to-mouth in common parlance) is still important, it is considered secondary because it discouraged many people from intervening.

In addition to chest compressions, people are urged to call 911 and ask for another bystander to locate a public access defibrillator. PADs are automated and will not "shock" a patient unless there is no heart rhythm.

In the new study, in 52 per cent of cases, a bystander performed CPR before paramedics arrived, but a PAD was used in fewer than 1 per cent of cases.

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