MCW Researchers Identify Steps to Improve CPR Survival

The figures are startling, even if you've heard them before:

• Every year in the US, more than a million people suffer heart attacks.
• About half of these people - 515,000 of them - die as a result.
• More than 250,000 of these coronary heart disease deaths occur without the victim ever reaching a hospital.

A heart attack occurs when the supply of blood and oxygen to an area of heart muscle is blocked, usually by a clot in a coronary artery. Often, this blockage leads to arrhythmia, an irregular heartbeat that causes a severe decrease in the pumping function of the heart and can result in sudden death. If the blockage is not treated within a few hours, the affected heart muscle will die and be replaced by scar tissue.

Emergency personnel can often stop arrhythmias with emergency CPR (cardiopulmonary resuscitation), defibrillation (electrical shock), and prompt advanced cardiac life support procedures. If care is sought soon enough, blood flow in the blocked artery can be restored in time to prevent permanent damage to the heart.

Now, in a first-of-its-kind study, researchers at the Medical College of Wisconsin have identified steps to improve survival rates of cardiac patients being resuscitated by paramedics.

"Despite widespread cardiopulmonary resuscitation (CPR) training, survival rates after cardiac arrest remain dismal," says lead investigator Tom P. Aufderheide, MD, Professor of Emergency Medicine at the Medical College of Wisconsin. "The overall survival rate in the United States from cardiac arrest is about five percent." Dr. Aufderheide practices at the Level 1 Trauma Center at Froedtert Hospital, a major teaching affiliate of the Medical College.

Dr. Aufderheide and his colleagues found that despite seemingly adequate training, ambulance crews giving CPR exceeded the American Heart Association's recommendation of 12 to 15 breaths per minute when treating cardiac arrest victims.

"Excessive ventilation may be contributing to poor outcome in these patients," Dr. Aufderheide.

Examining data from seven patients in an observational study, the researchers found the average maximum ventilation rate was 37 breaths per minute, roughly 250% to 300% greater than the rate the American Heart Association recommends. After a CPR retraining program was instituted, the average ventilation rate for six additional patients dropped to 22 breaths per minute, still higher than the recommended number.

Dr. Aufderheide explained that the chest is compressed during CPR. This increases pressure in the chest forcing blood out of the heart and into the rest of the body. When the compression is relieved, on the upstroke, the chest is allowed to expand creating a slight vacuum inside. This vacuum is essential to allow the venous blood to return to the heart. Extra ventilations decrease return of the blood to the heart.

"Excessive ventilations decrease the amount of blood flowing in and out of the heart, and that significantly decreases the effectiveness of CPR." Dr. Aufderheide says.

Subsequent to their observation of the 13 patients, the researchers found in animal studies that similar excessive ventilation rates resulted in significantly increased chest pressure and marked decreased blood flow and survival rates from cardiac arrest.

"All professional rescuers, including EMTs, nurses, doctors, respiratory therapists, and anyone else who does CPR as part of their profession-need to get this message: Do not hyperventilate when performing CPR," he said.

To prevent excessive ventilations, Dr. Aufderheide suggests intensive retraining and the use of a system that flashes a light every five seconds to let rescuers know when to deliver the next breath of oxygen, helping them keep the number of breaths delivered to approximately 12 per minute.

Although the small study focused on cardiac arrests in only one city, Milwaukee, the researchers strongly believe that this could occur nationwide. As a result of their findings, the authors urge that all hospitals and emergency medical services assess whether hyperventilation is a problem in their units. If it is, they suggest reducing ventilation during CPR to 12 breaths a minute.

These findings have significant implications not only for clinical practice, but also for CPR guidelines, CPR training programs, the development of future biomedical devices, and quality assurance for professional resuscitation teams.

The study, funded by the National Heart, Lung, and Blood Institute with additional assistance from Advanced Circulatory Systems, was reported April 5 in Circulation: Journal of the American Heart Association.

This article includes information from the National Heart, Lung and Blood Institute and the Centers for Disease Control and Prevention.

For more information on this topic, see the HealthLink articles Calculate Your Risk of Coronary Heart Disease and Calculate Your LDL Cholesterol Goal Level.

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.