If you've ever had general anesthesia, you may have had a rough time sleeping afterward.

And that’s a big deal, because rest is … kind of necessary for healing up  from whatever surgery you just had. It would make sense to blame the  sleeplessness on post-op pain, bright hospital lights, or nurses  constantly stopping by to poke and prod.

But there’s more to it. Scientists have learned that  general anesthesia somehow resets your entire internal clock,  throwing off your circadian rhythm. When you mess with that clock, you  mess with just about everything your body does … digestion, disease  prevention, and of course, sleep.

But general anesthesia isn’t going anywhere. So we have to figure out how the  thing that’s sometimes referred to as “putting you to sleep” keeps  you from doing just that. [♪ INTRO] The body’s circadian rhythm is  biologically hardwired to align with the rising and setting of the  sun, the seasons, and other factors. And we really need to keep this clock on  track, because it runs the schedule for all of our organs and cells to keep doing their  thing hour after hour and day after day.

A complex molecular mechanism runs this clock. It involves a bunch of  different molecules that wax and wane throughout the body at regular intervals. These substances interact with  each other and the environment.

You can think of them like a  bunch of molecular metronomes, each with different factors  controlling their different tempos. Studies are shedding light on how  these metronomes fit together. But one thing is clear: they are finicky.

Circadian patterns are sensitive  to travel and shift work, and to common substances,  like caffeine and alcohol. They’re also sensitive to elements of the hospital environment, including medications. General anesthesia gets attention because it’s one of the strongest of these disruptors.

Being put under is so disruptive  that some post-op patients experience cognitive dysfunction, high blood  pressure, and heart problems. More than ten genes are thought to govern the molecular mechanisms of your internal clock. Different genes are switched on  during different parts of the rhythmic process in practically all  of the body’s organs and tissues.

And in terms of anatomy, a big focus  for scientists is a cluster of cells in the brain’s hypothalamus called the  suprachiasmatic nucleus, or SCN. It’s like a master synchronizer  responsible for setting and tweaking the rhythms of gene activity  in various tissues throughout the body. General anesthesia, especially the  components that make people unconscious, seems to mess with this synchronization.

One way they do this is by interacting with the receptors in the SCN that are also  activated by regular exposure to light. When light enters through the retina  and reaches neurons in the brain, it sends molecular signals, and that syncs up all the molecular metronomes throughout the body. Studies have found that while  general anesthesia is making someone lose consciousness, it basically  chucks a wrench into those signals, throwing off the clock’s calibration.

Ultimately, it’s like general anesthesia  is causing a form of artificial jet lag in which someone skips forward without  their clock catching up to them. We also hear a lot about how the hormone melatonin helps regulate our sleep-wake cycles. Multiple studies have found decreased  melatonin production in post-op patients.

So yeah, clearly, general anesthesia is doing various things to mess with our daily  rhythms and our much-needed rest. There is good news, though. While researchers continue to unravel  the human clock and its disruptors, they’re also looking into ways to reduce the circadian fallout from general anesthesia.

One promising area of research  is what’s called chronotherapy, which is an umbrella term for timing  a treatment with the circadian rhythm. Doctors are already using this  approach in multiple settings, including the timing of chemotherapy for cancer. Researchers are also looking into  whether the timing of surgery can affect sleep and healing.

One study, published in the  Annals of Medicine in 2023, looked at over 28,000 non-cardiac  surgeries that required general anesthesia at a hospital in China between 2016 and 2021. It found that patients who had  surgery in the afternoon had faster recovery times in the  post-anesthesia care unit. Also, since light is a big part  of setting sleep-wake cycles, it makes sense to tap into light  therapy, or exposing people to strategically-timed bright lights, to  realign the circadian rhythm after surgery.

The lack of light at appropriate  times is also important. A big challenge, though, is keeping a  person’s environment very dark at night while allowing the nurses  to see what they’re doing. More studies will help tease out  exactly how and when to use light to improve recovery and sleep when  undergoing general anesthesia.

There’s also potential for everything  from using sleep masks and ear plugs, to administering melatonin to  make up for low post-op levels. So there you have it! General anesthesia is one of  the culprits behind poor sleep and the all-around off-ness  that follows major surgery.

But it’s good to know that  solutions are on the way, and bioscience isn’t sleeping on the job. This video was inspired by The Inner  Clock, a new book by Lynne Peeples. It’s all about circadian  rhythms, and the surprising number of ways they affect our lives.

If you’d like to check it out,  head to the SciShow Bookshop page. And thank you to the Alfred P. Sloan  Foundation for making this video possible. [♪ OUTRO]