More than one in four elderly Americans lacked the capacity to make their own medical care decisions at the end of life in a study of published in the New England Journal of Medicine.

Those who had done advance directives—including living wills or durable powers of attorney for health care—received the care they wanted most of the time, says the lead author, Dr. Maria Silveira, physician scientist at the VA Ann Arbor Healthcare System's Clinical Management Research. Silveira also is an assistant professor of internal medicine at the University of Michigan.

"Prior to our study, no one knew how many elderly adults might need others to make complex medical decisions on their behalf at the end of life," she says. "Our research shows that a substantial number of older adults need someone else to make decisions about whether aggressive, limited, or comfort care should be provided at the end of life."

Silveira says, "This study underscores the need to prepare oneself and one's family for the often emotional and difficult medical decisions that can arise at the end of life. It also suggests that the time spent to craft a living will and appoint a durable power of attorney for health care can be worthwhile."

Advance directives usually document patients' wishes for life-sustaining treatment in a living will, as well as their choice of a proxy decision-maker in a durable power of attorney for health care. Advance directives are sanctioned in all 50 states and can be completed for free without the aid of an attorney.

Still, "There is a lot of myth and misunderstanding about advance directives," Silveira says.

For example, many people don't understand that advance directives are used only when patients can't make medical care decisions for themselves, and they can be revoked by the patient at any time, either in writing or orally. Advance directives frequently are confused with wills and durable powers of attorney, which have no bearing on medical care decisions.

Of the more than 3,700 people studied, 61 percent had advance directives. Of those, more than 90 percent requested either limited or comfort care at the end of life.

Among those who needed decisions made, but couldn't make them themselves, 83 percent who had requested limited care and 97 percent who had requested comfort care received the care that was in line with their wishes, Silveira says.

The study subjects were elderly Americans living at home or in facilities across the U.S. who died between 2000 and 2006 and participated in the Health and Retirement Study, a national longitudinal study conducted at the University of Michigan's Institute for Social Research and funded by the National Institute on Aging.

"Folks with a living will or durable power of attorney for health care were less likely to die in a hospital or to get aggressive care—but that is what most of them wanted," she says.

One interesting finding suggests the importance of having both a living will and an appointed surrogate decision-maker. The study showed that among the handful of subjects who indicated a preference for aggressive care, half didn't receive it.

"Given this, some might conclude that advance directives are used to deny wanted health care, but our study showed that a preference for aggressive care had a very strong association with receiving such care, when compared to those who did not state a preference for it," Silveira says.

"It's just that at the end of life, aggressive treatment is often not an option; limited care and comfort care are always an option," she says.

Silveira says many patients expect their physicians to start the conversation about end of life care and advance directives, and that physicians should be supported in their attempts to do so.

The recent effort to provide Medicare reimbursement for periodic end-of-life discussions was a good start, she says.

"The health-care system should ensure that providers have the time, space, and reimbursement to conduct the complex and time-consuming discussions necessary to plan appropriately for the end of life. Most elderly patients want and expect this," she says.