Two years ago, when my father was dying of dementia, my siblings and I faced a terrible dilemma: Whose wishes for his medical treatment were we to honor? Those of my father back when he was a healthy, highly functioning geneticist? Or those of the simpler, weakened man my father had become?

It was a predicament that has led me to rethink my views on advance directives for end-of-life care.

At the time, my father’s health had been in decline for several months. His appetite had been steadily decreasing, he’d been losing weight, and he often had to wear a diaper because he couldn’t always make it to the bathroom in time. Now he had taken a rapid downturn over the course of a week, and he had stopped eating and conversing.

Thinking he might be dehydrated, my older brother and I, both doctors, started to give him fluids through an IV at home. It didn’t help. We were faced with the awful choice of whether to remove the IV and withdraw medical care.

Some years back, in 2004, my father had written a letter to my brother saying that if he or my mother were to get “very sick,” neither would want extraordinary measures taken to keep them alive. “We want to live only if we have a meaningful life,” he wrote. In keeping with my father’s directive, formulated when he was “of sound mind,” my brother said we should stop the IV fluids and let my father die peacefully.

I had misgivings. It was true that life in a state of dementia would not have seemed meaningful to my father in 2004. The scientist in him would not have wanted to live without an intellectual existence.

But despite his weakened state, my father didn’t seem unhappy. Over the course of his illness, he’d never expressed a sincere wish to die. What was meaningful to my father in 2004 was very different from what had become meaningful to him in the past few months, when watching TV, spending time with his caregiver and children, and even just eating a spoonful of ice cream had clearly given him genuine pleasure.

It was possible to view those pleasures as simple, childlike, somehow beneath my father. But wasn’t this man before me also my father? Why not continue the IV fluids, I thought, and maybe try giving him some antibiotics?

This is a conundrum that in one form or another many families are facing. At the hospital system where I work, almost half of the 600 or so ethics consultations performed last year dealt with various disagreements over advance directives. “It is a daily occurrence,” Renee McLeod-Sordjan, the head of our bioethics service, told me.

The sort of problem my siblings and I faced will only increase as the population ages. The number of Americans estimated to have Alzheimer’s or related forms of dementia is more than six million today and is projected to double in about 25 years. Many older Americans will have advance directives like my father’s. And in many cases those directives will seem to contradict their current desires.

Courts have generally ruled that an advance directive should be prioritized as an expression of the will of a person when he is presumably independent and rational and has the time and the presence of mind to reflect on what he wants. However, isn’t that also a kind of bias that risks lowering the moral standing of the patient in later years? A person’s current wishes, even if formed in a state of cognitive impairment, must count for something. As a son, how do you withhold lifesaving treatment from your demented father who, through gestures and utterances, seemingly expresses a desire to live?

My brother often said that my father was living a life of “plus-minus,” by which he meant that it basically added up to zero. In my darkest moments, I believed this too. But perhaps we were suffering over our father’s condition more than he was. His world had shrunk, but so too had his desires, his perspective, his expectations of what constituted a worthwhile existence. The man who’d craved recognition and respect more than anything else no longer seemed to care about those fickle rewards.

To my brother, our father was no longer the person he once was. To me, he was still the same person, just a changed one.

In the end, after much debate, my brother, in conjunction with a hospice nurse, made the final call to honor my father’s advance directive, which is the goal in palliative care. We stopped the IV fluids and did not start antibiotics. Our father died at home a few days later.

I continue to struggle with the question of what caregivers should do in this situation. Perhaps a family dispute such as ours might be avoided if an advance directive were to explicitly state that the contrary wishes of a “future self” should not be heeded, though this still would not resolve the ethical dilemma.

Though courts may disagree, I no longer believe that advance directives should strictly be followed in every situation. They are often vaguely worded and may poorly predict future attitudes and feelings. To me, it seems that a contemporaneous desire to live, even in a person with dementia, must be taken seriously, despite what that person might have previously written. We recognize that minds evolve and people change in every sphere of human life.

Families and caregivers should weigh both past and present wishes in deciding what is in an incapacitated patient’s best interests. This would be best accomplished by a surrogate in tune with the patient’s wishes and how he has evolved — in most cases, a loved one chosen by the patient in advance. Ideally social norms will one day reflect this.

As I learned on the journey through my father’s illness, contentment with life can be compatible with cognitive dysfunction — along with the prerogative to change one’s mind about the care one wants at life’s end.