For many, the next step in a diagnosis involves a scan, like a CT or M.R.I. But many extremely heavy people cannot fit in the scanners, which, depending on the model, typically have weight limits of 350 to 450 pounds.

Scanners that can handle very heavy people are manufactured, but one national survey found that at least 90 percent of emergency rooms did not have them. Even four in five community hospitals that were deemed bariatric surgery centers of excellence lacked scanners that could handle very heavy people. Yet CT or M.R.I. imaging is needed to evaluate patients with a variety of ailments, including trauma, acute abdominal pain, lung blood clots and strokes.

When an obese patient cannot fit in a scanner, doctors may just give up. Some use X-rays to scan, hoping for the best. Others resort to more extreme measures. Dr. Kahan said another doctor had sent one of his patients to a zoo for a scan. She was so humiliated that she declined requests for an interview.

Photo

Patty Nece of Alexandria, Va., saw a doctor who attributed her hip pain to obesity without examining her, she said. She later learned she had progressive scoliosis, a condition not caused by obesity. Credit Lexey Swall for The New York Times

Problems do not end with a diagnosis. With treatments, uncertainties continue to abound.

In cancer, for example, obese patients tend to have worse outcomes and a higher risk of death — a difference that holds for every type of cancer.

The disease of obesity might exacerbate cancer, said Dr. Clifford Hudis, the chief executive officer of the American Society of Clinical Oncology.

But, he added, another reason for poor outcomes in obese cancer patients is almost certainly that medical care is compromised. Drug doses are usually based on standard body sizes or surface areas. The definition of a standard size, Dr. Hudis said, is often based on data involving people from decades ago, when the average person was thinner.

For fat people, that might lead to underdosing for some drugs, but it is hard to know without studying specific drug effects in heavier people, and such studies are generally not done. Without that data, if someone does not respond to a cancer drug, it is impossible to know whether the dose was wrong or the patient’s tumor was just resisting the drug.

One of the most frequent medical problems in obese patients is arthritis of the hip or knee. It is so common, in fact, that most patients arriving at orthopedists’ offices in agonizing pain from hip or knee arthritis are obese. But many orthopedists will not offer surgery unless the patients first lose weight, said Dr. Adolph J. Yates Jr., an orthopedics professor at the University of Pittsburgh School of Medicine.

“There are offices that will screen by phone,” Dr. Yates said. “They will ask for weight and height and tell patients before they see them that they can’t help them.”

But how well grounded are those weight limits?

“There is a perception among some surgeons that it is more difficult, and certainly some felt it was an added risk,” to operate on very obese people, Dr. Yates said. He was a member of a committee that reviewed the risks and benefits of joint replacement in obese patients for the American Association of Hip and Knee Surgeons. The group concluded that heavy patients should first be counseled to lose weight because a lower weight reduces stress on the joints and can alleviate pain without surgery.

But there should not be blanket refusals to operate on fat people, the committee wrote. Those with a body mass index over 40 — like a 5-foot-5-inch woman weighing 250 pounds or a 6-foot man weighing 300 — and who cannot lose weight should be informed that their risks are greater, but they should not be categorically dismissed, the group concluded.

Hospitals Wary of Penalties

Dr. Yates said he had successfully operated on people with body mass indexes as high as 45. What is behind the refusals to operate, he said, is that doctors and hospitals have become risk-averse because they fear their ratings will fall if too many patients have complications.

A lower score can mean reductions in reimbursements by Medicare. Poor results can also lead to penalties for hospitals and, eventually, doctors.

A recent survey of more than 700 hip and knee surgeons confirmed Dr. Yates’s impressions. Sixty-two percent said they used body mass index scores as cutoffs for requiring weight loss before offering surgery. But there was no consistency in the figures they picked.

“The numbers were all over the map,” Dr. Yates said. And 42 percent who picked a body mass index cutoff said they had done so because they were worried about their performance score or that of their hospital.

“It’s very common to pick an arbitrary B.M.I. number and say, ‘That is the number we won’t go above,’” Dr. Yates said. Yet a person with an index of, say, 41 might be healthy and active, he said, but in terrible pain from arthritis. A knee replacement could be life transforming.

“It’s a zero-sum game, with everyone trying to have the lowest-risk patient,” Dr. Yates said. “Patients who may be at a marginally higher risk may be treated as a class instead of individuals. That is the definition of discrimination.”

Surgery involves anesthesia, of course, giving rise to another issue.

There are no requirements for drug makers to figure out appropriate doses for obese patients. Only a few medical experts, like Dr. Hendrikus Lemmens, a professor of anesthesiology at Stanford University, have tried to provide answers.

His group looked at several drugs: propofol, which puts people to sleep before they get general anesthesia; succinylcholine, used to relax muscles in the windpipe when a breathing tube must be inserted; and anesthetic gases.

Propofol doses, Dr. Lemmens found, should be based on lean body weight — the weight of the body minus its fat. Using total body weight, as is routine for normal-weight people, would result in an overdose for obese patients, he said. But succinylcholine doses should be based on total body weight, he determined, and the dosing of anesthetic gases is not significantly affected by obesity.

As for regional anesthetics, he said, “There are very few data, but they probably should be dosed according to lean body weight.”

“Bad outcomes because of inappropriate dosing do occur,” said Dr. Lemmens, who added that 20 to 30 percent of all obese patients in intensive care after surgery were there because of anesthetic complications. Given the uncertainties about anesthetic doses for the obese, Dr. Lemmens said, he suspects that a significant number of them had inappropriate dosing.

Yet for many fat people, the questions about appropriate medical care are beside the point because they stay away from doctors.

“I have avoided going to a doctor at all,” said Sarai Walker, the author of “Dietland,” a novel. “That is very common with fat people. No matter what the problem is, the doctor will blame it on fat and will tell you to lose weight.”

“Do you think I don’t know I am fat?” she added.

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