The odds of surviving cardiac arrest after getting CPR in a hospital are slim and have not improved in more than a decade, a big Medicare study concludes.

Only about 18 percent of such patients live long enough to leave the hospital, researchers found. Blacks fared worse than whites – a disparity only partly explained by more of them being treated in hospitals that did a poorer job of CPR. Results were published in today’s New England Journal of Medicine.

Dr. Lance Becker, a University of Pennsylvania emergency medicine specialist and an American Heart Association spokesman, called the findings “grim” and “a wake-up call that we need to redouble our efforts” to find better ways to treat cardiac arrest.

It occurs when the heart quivers or stops beating entirely, because of a heart attack, a sudden heart rhythm problem, a drug overdose or other cause.

CPR, rhythmic chest compressions, can help maintain blood pressure and flow until more advanced treatments can be tried. Those might involve using a defibrillator to shock the heart back into a normal rhythm. Big strides have been made getting bystanders to do cardiopulmonary resuscitation and to use defibrillators, but the new study suggests that less improvement is occurring in the nation’s hospitals.

Researchers led by Dr. William Ehlenbach at the University of Washington analyzed the care of 433,985 Medicare patients treated from 1992 through 2005 around the United States.

Survival odds did not substantially change over time, they found. Blacks had survival rates about one-quarter lower than whites. Men, older patients, and people admitted from nursing homes also had lower survival rates after CPR.