Fewer intensive care patients are dying in U.S. hospitals, but not much is known about survival rates for discharged patients.

Columbia University's Dr. Hannah Wunsch led a three year study of a random sample of Medicare patients older than 65 who were treated in intensive care units in 2003.

Wunsch: "We found that the risk for patients who have been in the ICU really was concentrated in a few select groups, including those who required mechanical ventilation and those who were discharged to skilled care facilities."

The study found the death rate within three years of hospital discharge for patients who were on ventilators in the ICU was 5% higher than that for the control group.

The findings were published in the Journal of the American Medical Association.