Cardiac arrest means simply that the heart has stopped beating. Without that constant thumping in our chests, the 10 or so pints of blood that usually circulate through arteries and veins stop flowing — and bad things start to happen, fast. The lungs are not delivering fresh oxygen. Metabolic waste products pile up. The blood turns dangerously acidic. If circulation isn't restored within four or five minutes, the brain shuts down completely and permanently. That's the definition of death.
Enter cardiopulmonary resuscitation (CPR), to keep the person alive until they can be treated in a hospital. Rapid chest compressions push blood through the body. They must be done quickly (100 times per minute, according to guidelines) because they're no match for the pumping power of the heart, which normally beats about 70 times per minute if you're resting. The ventilations, or puffs into the mouth (2 for every 15 compressions), are meant to resupply the blood with oxygen. Although there's less oxygen in expired air than in the atmosphere (16% versus 21%), the difference isn't important in an emergency.
Some research suggests that, when done correctly, CPR more than doubles your chances of surviving a cardiac arrest outside the hospital. The gloomy "on the other hand" is that those chances aren't very good. The statistics vary tremendously, but studies in large cities have found that only about 1 in 20 people who have a cardiac arrest outside of the hospital survive — even if they receive CPR.
The advent of the automated external defibrillator (AED) has added another wrinkle. AEDs analyze the activity of the heart and if it has developed a lethal rhythm (it's fibrillating) or is not beating at all, the machine delivers an electric shock to jolt it back into a normal beat. In 2005 the FDA started allowing the sale of AEDs without a prescription. The price is about $1,500.
So, when someone collapses from what seems to be cardiac arrest, should you do CPR or, if there is one nearby, run and get an AED? So far, there's no consensus.
Two studies published in the Journal of the American Medical Association in January 2005 have suggested one reason for CPR's low batting average: It isn't being done correctly, even by trained professionals. That doesn't bode well for the efforts of laypeople.
The first study included 176 adult cardiac arrest patients from three hospitals, in Stockholm, London, and Akershus (a county outside of Oslo). Paramedics or nurse anesthetists gave the patients CPR on the way to the emergency room. The ambulances carried equipment that measured the depth and frequency of chest compressions and the number of ventilations. The main finding: Chest compressions weren't given 48% of the time when the patients' hearts weren't beating. The compressions were also too shallow — less than the recommended 1½–2 inches "deep."
The other study involved 67 cardiac arrest patients given CPR by doctors or nurses at the University of Chicago Hospitals between December 2002 and April 2004. Using special monitoring equipment, the researchers divided the first five minutes of CPR into 30-second intervals. The compression rate was too slow during 28% of those intervals, and 40% of the compressions were too shallow. Professionals didn't get the ventilations right, either. During 60% of the 30-second intervals, patients were hyperventilated.
Dr. John Tobias Nagurney, an emergency department doctor at Massachusetts General Hospital and member of the Health Letter's editorial board, notes that brief interruptions in CPR are unavoidable, at least in the hospital, as doctors put in intravenous lines, check for a pulse, and perform other procedures. Keep in mind that although these studies have shown departures from guidelines, they haven't taken the next step and proved that those departures result in bad outcomes.
One solution is to improve CPR training, so doctors and emergency service workers get the message about keeping up with chest compressions and not hyperventilating patients. But research has shown that CPR training starts to "wear off" in just a few months.
Some have high hopes for computer-guided CPR that will give audio prompts: The compression rate is too slow; the ventilation rate is too fast; and so on. Early attempts at automating the chest compressions failed, but now there are improved devices that wrap around the patient and squeeze the chest at the appropriate time. It isn't clear, though, how much fire departments and ambulance companies will want to spend on this equipment.
Changing CPR is another possibility. Some experts are suggesting that ventilations — particularly in out-of-hospital cardiac arrests — may not be worth doing because they get in the way of the chest compressions. Studies have identified chest compressions as the critical element during the first few minutes. In most circumstances people can survive for four to five minutes (longer if the body temperature is low) without having their blood reoxygenated.
Dr. Mickey Eisenberg at the University of Washington, a leading expert on CPR, thinks the jury is still out. The success in Seattle depended on quick response times by the fire department, he says, asking "What happens to the patient after four or five minutes" if there's no ventilation? Dr. Eisenberg is undertaking a compression-only CPR study in suburban Seattle. One possibility is keeping the ventilations but cutting the rate down to, say, once or twice every 100 compressions.
Every five years, CPR experts from around the world gather to review the science, but individual "resuscitation councils" decide how to translate scientific findings into practical guidelines. In this country, the American Heart Association (AHA) serves as the resuscitation council. The expert meeting was held in January 2005 in Dallas, but its conclusions are being kept under wraps until November 2005, when they'll be published in Circulation. The AHA is following up with new guidelines in December 2005.
The AED presents a tough choice. On one hand, it's theoretically better than CPR because it can restart the heart, whereas CPR is merely a stopgap. A study published in 2004 in the New England Journal of Medicine found that a defibrillator-CPR combination improved the survival rate over CPR alone (23% versus 14%). On the other hand, if you run around looking for an AED while neglecting CPR, you could lose valuable lifesaving minutes.
June 2005 Update