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When Charles Thompson of Greenville, S.C., checked into the hospital one July morning in 2011, he expected a standard colonoscopy.

He never anticipated how wrong things would go.

Partway through, a doctor emerged from the operating room to tell Thompson’s wife, Ann, that there had been complications: His colon may have been punctured. He needed emergency surgery.

Thompson, now 61, almost died on the operating table after experiencing cardiac distress. His right coronary artery required multiple stents. He also relies on a pacemaker.

“He’s not the same as before,” said Ann Thompson, 62. “Our whole lifestyle changed — now all we do is sit at home and go to church. And that’s because he’s scared of dying.”

When things like this happen, questions arise: Who’s responsible? If treatment makes things worse — meaning that a patient needs more care than expected — who pays?

It depends.

Despite provisions in the 2010 health law that put added emphasis on quality of care, entering the hospital still carries risk. Whether because of mistakes, infections or plain bad luck, those who go in don’t always come out better.

More than 400,000 Americans die annually in part because of avoidable medical errors, according to a 2013 estimate published in the Journal of Patient Safety. In 2008, the most recent year studied, medical errors cost the country $19.5 billion, most of which was spent on extra care and medication, according to another report.

If a problem such as Thompson’s stemmed from negligence, a malpractice lawsuit may be an option. But lawyers who collect only when there’s a settlement or a victory may not take on a case unless it’s exceptionally clear that the doctor or hospital was at fault.

That creates a Catch-22, said John Goldberg, a professor at Harvard Law School and an expert in tort law. “We’ll never know if something has happened because of malpractice,” he said, “because it’s not financially viable to bring a lawsuit.” That leaves the patient responsible for extra costs.

Ann and Charles Thompson maintain that he experienced an avoidable error. The hospital denied wrongdoing, she said, but the physician’s notes indicated they had been advised of the risks of the procedure, including injury to the colon. The Thompsons tried pursuing a lawsuit but couldn’t find a lawyer who would take the case. The hospital and the doctor declined to comment, with the hospital citing patient privacy laws.

Because of his heart problem, which led to the loss of his specialized driver’s license, Thompson lost his truck-driving job. He lost the health insurance he had through his job, depriving him of help in paying for follow-up care. The couple paid close to $600,000 out of pocket, depleting their life savings. They struggled to pay other bills until Thompson was awarded disability benefits, his wife said.

“You would expect if [health-care providers] make the mistake, they would make you whole,” said Leah Binder, president of the Leapfrog Group, a nonprofit organization that grades hospitals on their record of preventing errors, injuries, accidents and infections. “But that is not what happens. In health care, you pay and you pay and you pay.”

There’s no single rule for how hospitals handle the cost of care when patients have bad outcomes and fault is disputed, said Nancy Foster, vice president of quality and patient safety at the American Hospital Association.

Some hospitals have rules requiring that a patient be told right away if something happened that shouldn’t have and, to the best of the institution’s knowledge, why. Typically, those rules stipulate that if the hospital finds that it erred, the necessary follow-up care is free. Hospitals may not have an obvious financial interest in admitting guilt, though research suggests that patients are less likely to sue when hospitals are transparent about medical mishaps.

“If the [need for further] care was preventable, we’re waiving bills,” said David Mayer, vice president of quality and safety for MedStar Health, which operates 10 hospitals in the Baltimore/Washington area.

Virginia’s Inova Health System has a similar policy, said spokeswoman Tracy Connell.

Most hospitals don’t have such rules, said Julia Hallisy, a patient safety advocate from California. That may change: A number of professional and safety groups are urging more hospitals to adopt them. Supporters include the American College of Obstetricians and Gynecologists, the American Medical Association, Leapfrog, the National Quality Forum and the Joint Commission, which accredits many health-care organizations. The federal Agency for Healthcare Research and Quality is also on board.

But even when they tell patients that something went wrong, hospitals may say it was unavoidable. Then, patients often pay for the consequences, directly or through their insurance.

Determining error can be straightforward, Mayer said, in such instances as misdiagnosis or operating on the patient’s left leg when his problem was with his right leg.

Other times, providers follow correct procedures but things go wrong. Then, hospitals can deny culpability. “Some things happen, and it’s hard to tell if it could truly have been avoided,” Binder said.

If hospitals don’t agree to pay for unexpected care, employers might push them to do so because absorbing such costs might eat into the firm’s profits.

On average, a privately insured patient cost about $39,000 more — $56,000 vs. $17,000 — in hospital bills when surgery led to complications than when it did not, according to a 2013 study in the Journal of the American Medical Association.

People with employer-based insurance — 147 million Americans this year — who have experienced complications or otherwise gotten worse while in the hospital should contact their benefits offices, especially if they can show hospital error, Binder said.

If that doesn’t pan out, insurance plans may step in.

When insurers add hospitals to their networks, they sometimes stipulate how to handle certain errors. For some mistakes, the hospital may provide necessary follow-up care for free, part of a “bundled payment,” said Clare Krusing, a spokeswoman for America’s Health Insurance Plans, a trade group. For that to apply, complications must clearly stem from bad treatment.

In other situations, patients can complain through the insurer, which should work with the hospital to determine who’s responsible.

Patients, Krusing said, shouldn’t pay for what’s out of their control.

And if the hospital doesn’t provide financial assistance, insurance should cover these unexpected expenses once the patient has met his or her deductible.

“Patients don’t normally think about these issues — and who would? They don’t think of any of these issues until they’re right in the middle of it,” patient safety advocate Hallisy said. “At that moment, they’re completely shocked and overwhelmed to think that this is how this works.”

This article was produced by Kaiser Health News, an editorially independent program of the Kaiser Family Foundation.