Why is it so hard to tell chronically ill patients that further treatment is futile — that it might erode their quality of life without making a difference in their life expectancy?

Surgeons do it indirectly when they declare a patient “inoperable,” a determination of futility that people generally accept, maybe because the harm of ineffective surgery is so obvious that it can’t be avoided.

But a physician dealing with patients who have advanced chronic diseases doesn’t have such clear-cut negative certainties to rely on, especially when patients make such broad inquiries as “Doctor, isn’t there anything else that you can do — that might possibly help?” In many cases the answer is, technically, “yes,” when practically speaking it is “no, not really.”

Such treatment will give the impression that something is being done, but it will not have curative or even significant results that simultaneously improves quality while prolonging life. The most widely recognized example of futile treatment that makes this distinction is tube feeding a brain-dead patient.

Lawrence J. Schneiderman, a co-founder of the ethics committee at the University of California at San Diego Medical Center, defined medical futility as the unacceptably low “likelihood of achieving an effect that the patient has the capacity to appreciate as a benefit.

Schneiderman has decades of experience as a leading voice discussing the ethics of medical futility. But every clinical physician dealing with chronic illnesses will experience medically futile situations on a regular basis.

Some years ago, in my second-to-last year of medical practice, I was called to the emergency room to see a 56-year-old man with progressive metastatic colon cancer, which was causing uncontrollable diarrhea and other serious gastrointestinal distress. He was receiving IV fluids for dehydration, and I was on call for one of the several gastroenterologists who, in failed efforts to heal him, had ordered multiple cycles of tests and treatments.

I reviewed his X-rays and the multiple failed treatments. Typical for advanced colon cancer, he had several metastases in his liver and a large mass in his colon. Atypically, his pelvis was also filled with a large tumor and that was the cause of some of his worst distress.

I knew there was no effective medical treatment for his symptoms and no surgical cure for his disease. Palliative surgery was his only option to control the incontinence and the pain it was causing, yet he was emotionally unwilling and too physically weak for a colostomy.

And yet for weeks he had wasted time with clinic visits because his gastrointestinal specialists fragmented his care, focusing only on this horrible symptom. Nobody had looked at him as a whole being. No one had told him that he was terminally ill. No one had told him that his symptoms might be reduced by palliative care but could not be eliminated. When I tried to explain that to him, it appeared to fall on deaf ears.

I was haunted by this and disappointed with myself for days. Had I overstepped my role as a stand-in emergency room consultant? Perhaps. But a week later, he appeared in my office, acknowledged what I had said and asked to be introduced to hospice care.

The American Medical Association has long encouraged all health-care institutions to adopt policies and physicians to adopt practices that recognize the futility of treating certain extreme situations and advanced diseases. (This is exemplified by but is not limited to patients in a persistent vegetative state. )

Yet there remains a powerful resistance, shared by doctors, patients and family members, to recognizing treatments as ineffective when dealing with chronic illnesses such as advanced congestive heart failure, severe dementia and unresponsive cancer, as in the patient I described.

This resistance locks chronically ill patients, most of whom are elderly, into a test-and-treat cycle of hospitalization, convalescence and deterioration even as it’s clear the end is near and the cycle is only making their final days terrible. This is when they would be better served by end-of-life palliative care that is designed to control symptoms while maximizing comfort, dignity and family contact.

The challenge is to accurately recognize the time for palliative care and, subsequently, hospice care. Fortunately, scientific work has been done on this subject. In two articles, one dealing with cancer and another dealing with other chronic diseases, Shelley Salpeter, a Stanford University geriatrics and palliative-care doctor, and colleagues documented clinical conditions that predicted a six-month mortality independent of whether aggressive treatment or palliative care was used.

For example, a patient with advanced heart failure who is older than 70, is dependent on others for three or more activities of daily living, has been hospitalized four times overall or twice within two months for recurrent fluid overload, and has another chronic illness (such as diabetes, dementia, lung disease, liver disease or cancer) will have a median survival of less than six months, regardless of the treatments used.

Identifying conditions that give patients a median survival of six months no matter what aggressive interventions are tried seems a good step toward ending ineffective and often painful end-of-life medical care.

Hippocrates did not teach physicians to prolong life at any cost. He did teach physicians “to refuse to treat those who are overmastered by their diseases, realizing that in such cases medicine is powerless.”

As a doctor who has encountered many very sick patients, many of whom will recover but some who I know will not, I am sure that futile treatment is cruel and wrong. Yet treatment, frequently overtreatment, is both the default position and the path of least resistance in our health-care system. Physicians must recognize and help patients understand that endless treatment eventually becomes cruelly ineffective but that palliative care is never futile.

Harrington is a retired gastroenterologist and the author of “At Peace: Choosing a Good Death After a Long Life.”