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First-year medical residents, aka interns, basically live at the hospital. I know this mainly from watching Scrubs, but also from talking to fledgling MDs in real life. Interns' schedules surely make a 9-5 job seem like a side gig. Can they safely work the long hours required of them? Maybe. Medical residents' hours, and how best to regulate them, is the subject of ongoing debate and research. A new study published in the journal Sleep, for instance, found that interns who work "extended" overnight shifts — that's 28 hours in a row — are underslept and less alert than needle-wielding medical professionals ought to be. By alternating overnight shifts with days off, study authors suggested, interns might be able to get enough rest and sustain the sharp cognitive skills they need to furnish quality care. 

It's important to point out that intern work hours are regulated by national guidelines. The Accreditation Council for Graduate Medical Education first imposed limits on residency training program schedules in 2003: Interns were to work no more than 80 hours per week and 24 hours in a row. The limits were a while in the making — efforts to reform residents' schedules first gained momentum in the '80s, after a woman named Libby Zion died in an NYC emergency room from an adverse drug reaction. The hospital chalked up Zion's death to misfortune, but her parents blamed the hospital. They believed that Zion died at the hands of unsupervised, inexperienced doctors who made a preventable error while manning the ER in the middle of the night.

In 2011, the Accreditation Council updated the rules, imposing a 16-hour limit on shifts (but keeping the 80-hour week). Then, earlier this year, they reversed their position somewhat. Starting in July, all residents (including first-years) will be able to work for up to 28 consecutive hours (that includes 24 hours on-call plus four hours to handle paperwork and any residual patient-care needs). 

Shorter shifts didn't appear to reduce stress or improve patient care.

There's arguably a good reason for removing the 16-hour cap. The elimination of "extended" overnight shifts in 2011 was intended to prevent interns from burning out and making mistakes. But shorter shifts didn't appear to reduce stress or improve patient care. A few studies instead found that high-stake errors were most likely to happen during shift turnovers, when doctors handed off their caseloads to colleagues who weren't familiar with patients. Disjointed schedules, according to this line of thought, impedes high-quality care more than bleary-eyed interns do. But not everyone accepts this line of thought or believes that interns can handle the grind of working from 7am to 1pm the following day. Plenty of critics, including the American Medical Student Association, argue that doctors-in-training need safeguards against unduly long shifts. 

For the current study, researchers at the University of Pennsylvania analyzed morning alertness levels and sleep habits for 224 interns and upper-level residents working in internal medicine and oncology in the University of Pennsylvania Health System. Data collection took place over a two-year period, from 2009 to 2011. That means researchers conducted the study before the 16-hour rule took effect. (That also means that the Accreditation Council's most recent policy change, taking effect in July of this year, will usher in resident work hours that resemble those in the study.)

To participate, interns and residents had to keep sleep diaries, use actigraphy trackers (e.g., fitbits) and take a 3-minute alertness test every workday morning for a month. Because the study involved residents and interns working at different hospitals in two different specialties, participants were on a few different schedules. 

Participating interns worked about six days a week with a 28-hour overnight shift every fourth night. That means they worked a full day and then continued working from 5pm through the next day. Upper-level residents worked from 7am or 8pm to either 5pm or 8pm on weekdays. They also rotated to cover weekend shifts. "Night float" residents worked weekday night shifts for a week (or so) at a time. This way, when residents weren't on night-float duty, they didn't have to work any weekday overnights. (This is a fairly typical schedule.)

To keep interns thinking sharper around the clock, researchers recommended implementing a 3-hour "protected sleep period" in the middle of overnight shifts.

Researchers used data from sleep diaries and actigraphy trackers to see how much participants slept in a 24-hour period (on average). Naps were factored in to this estimate. Researchers also measured participants' alertness levels in the morning, both after nights spent on call and in bed. 

They found that residents who either didn't work extended overnight shifts (28-hour ones) or only worked them sporadically averaged more than seven hours of sleep per night. So they weren't sleep-deprived by clinical standards. Interns who worked extended shifts, by comparison, averaged 15-17 minutes less sleep, putting them under the 7-hour threshold for healthy sleep. This seemingly small difference matters, said researchers, writing that "the extra sleep observed in residents may be crucial to sustain a higher level of alertness and performance."

Interns were also significantly less alert in the morning when they'd been up all night. (They're human, it turns out.) Researchers pointed out a few ways to make up for their sleep loss and mental fog. Interns would have averaged enough sleep, researchers wrote, if they had a day off for every extended shift they worked. Additionally, to keep interns thinking sharper around the clock, researchers recommended implementing a 3-hour "protected sleep period" in the middle of overnight shifts. But, a chunk of those three hours should be used as a buffer to prevent interns from working in a groggy, just-woke-up state. 

Of course, the big question is: Would the study bear out the same way if the 16-hour cap were in place? Maybe. The cap protects against double shifts, but not overnight shifts. And it requires interns to transition between a night-shift and day-shift schedule more frequently, making it hard for their bodies to settle into any stable sleep-and-wake groove. 

The study highlights the challenges of designing a schedule that leads to the best possible care for patients and the least possible stress for doctors. Ultimately, there will always be doctors, nurses and other hospital workers working the night shift. Hopefully, we'll keep improving their schedules so they don't burn out in the process.