Valenzuela would have to take anti-viral medications that would make her nauseated for weeks. And she’d have to explain to her husband that she may have contracted a life-long disease.

“We were going to start trying to have kids soon,” she says, choking up, “and so that would make it complicated for us.”

That’s what she was thinking about when she finally left the hospital at 4 in the morning.

“I found my car and I was backing out,” she says. “And I mixed up the gas and the brake. I've never done that before, but I backed right into a concrete pole.”

Mistakes like these led medical experts at the Institute of Medicine to issue a recommendation in 2009 that residents' work shifts be capped at 16 hours. Until then, they were allowed to work up to 28 hours. After a year-long review of the scientific literature, the Institute concluded that human performance begins to decline after 16 hours, and the risk of medical errors and car accidents goes up.

So, in 2011, the Accreditation Council for Graduate Medical Education made a rule, saying first-year doctors could only work a maximum of 16 hours per shift.

But this year, the council reversed itself, and starting this summer, new doctors can again work up to 28 hours in a row.

“I think the majority of patients in the United States expect that their physician will be available to them whether it's daytime, nighttime, Saturday or Sunday,” says Dr. Rowen Zetterman, co-chair of the task force that reviewed and changed the rule.

Patient and resident groups wanted to keep the 16-hour rule, Zetterman says. But senior doctors argued that long hours come with the profession. They complained that the shift limits cut into the time they had for teaching in the hospital, compromising the educational integrity of the residency.

“You ask residents a question and they'll say, ‘’I'm just covering, I don't know those things.’ That drives the more senior physicians batty,” says Adams Dudley, a pulmonologist and professor at UCSF School of Medicine. “The perception is they don't know what they're doing as well because they spend less time at the hospital.”

Physicians grouse that residents don’t seem as invested in the work when shift limits are in effect, he says, because they’re more focused on handing off their patients to others, rather then seeing them through the cycle of illness.

“Because they leave, they don't see the evolution of things, and they don't know the patients as well,” Dudley says. “If you're told you must pay attention to leaving, you have to detach yourself from the patient.”

Surgical residents complained about this, too.

“They would be in the middle of an operation that they felt like they were learning from, and they would hit the end of their 16 hours and be told that they had to leave the operation and go home,” Zetterman says.

This hurt morale on the health care team, he says, as other doctors watched first-year residents clock out when they had to stay, and raised patient-safety concerns.

“Let's say your copilot kept coming and going throughout the flight and, then was gone. Didn't come back for the remainder that flight,” Zetterman says. “It seems to me that would be disruptive.”

It’s unclear what’s riskier for patients: more frequent hand-offs between doctors, or doctors that are just exhausted. Most studies show little or no change in patient outcomes after shift limits were put in place, suggesting mistakes and miscommunications that resulted from transitions in care offset any gains made from reducing doctor fatigue.

If that's the case, Dr. Josie Valenzuela believes there should be more focus on residents’ well-being, in addition to patients. And while the shift limit was extended to 28 hours in the regulatory, other rules require residency programs to provide more support for residents who feel burned out, stressed, or depressed, including 24/7 access to a mental health professional.

Valenzuela is in her last year of residency now. She says she was lucky after that accidental cut. After nearly a year of periodic checks, she's been officially declared negative for HIV and hepatitis C. Next year, she and her husband plan to have a baby.