May 4, 2007

reperfusion and apoptosis: or, everything you know about CPR is wrong

Scientists are discovering that it's not lack of oxygen that kills heart cells; it's the return of oxygen into the cell that causes apoptosis. Newsweek explains the implications:
With this realization came another: that standard emergency-room procedure has it exactly backward. When someone collapses on the street of cardiac arrest, if he's lucky he will receive immediate CPR, maintaining circulation until he can be revived in the hospital. But the rest will have gone 10 or 15 minutes or more without a heartbeat by the time they reach the emergency department. And then what happens? "We give them oxygen," Becker says. "We jolt the heart with the paddles, we pump in epinephrine to force it to beat, so it's taking up more oxygen." Blood-starved heart muscle is suddenly flooded with oxygen, precisely the situation that leads to cell death. Instead, Becker says, we should aim to reduce oxygen uptake, slow metabolism and adjust the blood chemistry for gradual and safe reperfusion.

Researchers are still working out how best to do this. A study at four hospitals, published last year by the University of California, showed a remarkable rate of success in treating sudden cardiac arrest with an approach that involved, among other things, a "cardioplegic" blood infusion to keep the heart in a state of suspended animation. Patients were put on a heart-lung bypass machine to maintain circulation to the brain until the heart could be safely restarted. The study involved just 34 patients, but 80 percent of them were discharged from the hospital alive. In one study of traditional methods, the figure was about 15 percent.
It's also been discovered recently that mouth-to-mouth resuscitation is actually counterproductive. The linked article doesn't make the connection, but the new understanding of reperfusion might explain why chest compressions alone are better than traditional CPR.

Happy Friday!


Mike Kretzler said...

I think your title overstates. You mention that CPR (at least the chest compressions) are valuable to patients, in that they prevent the heart from losing oxygen, therefore avoid the problems that arise from standard emergency room actions.

Jim Anderson said...

You'll pardon this English teacher's purposeful use of hyperbole. It's important to get people's attention on this vital matter: the top Google hit for "CPR" is still putting out the same ol' same ol' about mouth-to-mouth.