About 1-3 hours of that time is taken to get the patient under general anesthesia. This may involve placing monitors for blood pressure management and big catheters for blood transfusions and administering drugs. The patient has to be put to sleep and the breathing tube placed. At the end of the surgery the patient has to wake up from the drugs and the breathing tube taken out (if this is planned).
A significant portion of the time is then spent after making the incision(s) dissecting down to the area of interest for the surgery. This may involve various different teams. For example if we were removing a tumor from the thoracic spinal cord this may involve cardiothoracic surgeons to help us get into the chest to get in front of the spine. Getting good exposure to the site of surgery is as important as the ability to do the surgery itself.
Once the area of interest is exposed the delicate part of the surgery might take place. If we are taking out a tumor from a delicate area of the brain or near the spinal cord, just chipping away at the tumor and taking small blood vessels to cut blood flow to the tumor may take 12 hours itself.
Now this is the part where complications may happen intraoperatively that if not addressed right then and there can cause serious issues. Sometimes a significant amount of time can be spent correcting these iatrogenically caused issues. These are where all the “routine” complications that are common with the surgery can be addressed. For example if we are doing spine surgery and we unintentionally cut into the covering over the spinal cord (the dura) then it may add hours to try to repair the tear under the microscope.
After part of the surgery sometimes the surgeon wants some interval imaging to see where they are at with the goals of surgery. The incision may temporarily be closed and the patient might go to an MRI to see if there is any residual tumor (if it is a brain tumor) or perhaps an angiogram procedure to see if the vascular lesion is all gone (if say we were clipping multiple aneurysm). Afterwards the patient might return to the operating room for final closure. Maybe this could take an hour or two.
If there is more work to be done it is possible you may need to do 12 more hours of work to get the last piece of tumor out or ligate the blood vessels you have to go complete the surgery. Maybe after this the surgeon might elect to go get ANOTHER MRI or angiogram to confirm that they are truly done with the goals they intended to achieve. It is possible that they send a piece of the tumor to the pathologists so they can freeze it and section it and get the diagnosis back to the surgeon so they can decide whether they need to respect the entire tumor or if they can leave some behind. This may take up to an hour.
Next is the closure of the surgical site. Depending on how deep they are inside the body this could take hours. If another type of surgeon helped expose the surgical site, often they come back in to surgery to help close the site.
At the end of the surgery, depending on what type of surgery it is and what the expected recovery of the patient is, it is possible the patient may get other surgeries done during the same general anesthesia session. For example if we take a huge tumor out of the brainstem area and we expect the patient to have significant swallowing issues due to disruption of the nerves that control swallowing, maybe they will need a stomach tube (gastric tube) to be fed through a tube in the future, or even a tracheostomy (breathing tube) so that they can recover postoperatively. This can take 4+ hours.
All in all this can add up to 36 hours but it is truly rare to go that long (at least in neurosurgery). If you are going to do that we usually like to stage the surgery over two different surgical episodes. For example if you have a giant tumor in your spine and you need the tumor removed from the spine from the front and screws and rods placed from the back you might do the back part on the first day, let the patient recover a little bit and then take them back for the front part.
And yeah the surgeons have breaks. The residents will go for breaks while the attending operates and vice versa. Multiple attendings will give each other breaks. The anesthesiologists will switch out multiple times. The longest surgery I’ve been in lasted around 36 hours. As a resident in that surgery I watched the metro train which is outside the OR window go by at least a hundred times.