Before being deployed overseas for the Iraq War in 2003, Army reservist Don Morrison filled out military forms that gave instructions about where to send his body and possessions if he were killed.

“I thought, wow, this is mortality right in your face,” Morrison, now 70, recalled.

With his attention keenly focused on how things might end badly, Morrison asked his lawyer to draw up an “advance directive” to describe what medical care he did and did not want if he were unable to make his own decisions.

One document, typically called a living will, spelled out Morrison’s preferences for life-sustaining medical treatment, such as ventilators and feeding tubes. The other, called a health care proxy or health care power of attorney, named a friend to make treatment decisions for him if he were to become incapacitated.

Not everyone is as motivated to tackle these issues. Even though advance directives have been promoted for nearly 50 years, only about a third of U.S. adults have them, according to a recent study.

People with chronic illnesses were only slightly more likely than healthy individuals to document their wishes.

For the analysis, published in the July issue of Health Affairs, researchers reviewed 150 studies published from 2011 to 2016 that reported on the proportion of adults who completed advance directives, focusing on living wills and health care power-of-attorney documents.

Of nearly 800,000 people on whom the studies reported, 36.7 percent completed some kind of advance directive. Of those, 29.3 percent completed living wills, 33.4 percent health care proxies and 32.2 percent were “undefined,” meaning the type of advance directive wasn’t specified or combined the two.

People older than 65 were significantly more likely to complete any type of advance directive than younger ones, 45.6 percent vs. 31.6 percent. But the difference between people who were healthy and those who were sick was much smaller, 32.7 percent compared with 38.2 percent.

The Medicare program began reimbursing physicians in January 2016 for counseling beneficiaries about advance-care planning.

This study doesn’t incorporate any data from those changes. Rather, it can serve as a benchmark to gauge improvement, said Dr. Katherine Courtright, an instructor of medicine in pulmonary and critical care at the University of Pennsylvania. She is the study’s senior author.

There are many reasons that people are reluctant to sign a living will. State forms vary, but they generally ask people to spell out what medical intervention they want under various circumstances.

“Many people don’t sign advance directives because they worry they’re not going to get any care if they say they don’t want [cardiopulmonary resuscitation],” said Courtright. “It becomes this very scary document that says, ‘Let me die.’”

Living wills also don’t account for the fact that people’s wishes may change over time, said Dr. Diane Meier, a geriatrician and the director of the New York-based Center to Advance Palliative Care.

“In some ways, the public’s lack of excitement about this is related to the reality that it’s very hard to make decisions about the kind of care you want in the future when you don’t know what that will be like,” Meier said.

Sometimes as patients age and develop medical problems they’re more willing to undergo treatments they might have rejected when they were younger and healthier, Meier said.

“People generally want to live as well as they can for as long as they can,” Meier said. If that means going on a ventilator for a few days in order to get over a bout of pneumonia, for example, many may want to do that.

But if their living will says they don’t want to be put on a ventilator, medical staff may feel bound to honor their wishes. Or not. Although living wills are legal documents, medical staff and family members or loved ones can reinterpret them.

“At the moment, I’m very healthy,” Morrison said. If he were to become ill or have a serious accident, he said, he’d want to weigh life-saving interventions against the quality of life he could expect afterward. “If it were an end-of-life scenario, I don’t want to resuscitated,” he said.

If someone’s wishes change, the documents can be changed. There’s no need to involve a lawyer in creating or revising advance directives, but they generally must be witnessed and may have to be notarized.

Although living wills can be tricky, experts have no reservations about recommending that people have a health care proxy. Some even suggest, for example, that naming someone for that role should be a routine task that’s part of applying for a driver’s license.

“Treatment directives of any kind all assume we can anticipate the future with accuracy,” said Meier. “I think that’s an illusion. What needs to happen is a recognition that decisions need to be made in real time and in context.”

That’s where the health care proxy comes in. Just naming someone isn’t enough, though. To be effective, people need to have conversations with their proxy and other loved ones to talk about their values and what matters to them at the end of life.

They may tell their health care proxy that they want to die at home, for example, or that being mobile or able to communicate with their family is very important, said Jon Radulovic, a vice president at the National Hospice and Palliative Care Organization.

Some may opt to forgo painful interventions to extend their lives in favor of care that keeps them comfortable and maintains the best quality of life for the time that remains.

“The most important thing is to have the conversation with the people that you love around the kitchen table and to have it early,” said Ellen Goodman, a Pulitzer Prize-winning writer who founded The Conversation Project, which provides tools to help people have conversations about end-of-life issues.

Morrison said he’s talked with his health care proxy about his wishes. The conversation wasn’t difficult, he said. Rather than spell out precisely what he wants done under what circumstances, Morrison is leaving most of the decisions to his health care proxy, if he can’t make his own choices.

Morrison said he’s glad he’s put his wishes down on paper. “I think that’s very important to have,” he said. “It may not be a disease that I get, it may be a terrible accident. And that’s when [not knowing someone’s wishes] becomes a crisis.”

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KHN’s coverage related to aging & improving care of older adults is supported by The John A. Hartford Foundation.

KFF Health News' coverage of aging and long-term care issues is supported in part by The SCAN Foundation.