Recently a client commissioned me to look at the potential cognitive impacts of general anesthesia. I was surprised to find out that it’s not obvious general anesthesia does more damage than spinal or local anesthesia, and my guess is most but not all of the damage is done by the illness or surgery themselves.
Caveats and difficulties
I’m not a doctor. The following represents something like 5 hours of work, which obviously is not enough time to process even a fraction of the literature. I was focused on the dangers of median uses of anesthesia, where nothing goes obviously wrong and the anesthesiologist considers it a success; I didn’t even attempt to look at the rate of accidents, which can be pretty severe. My friend’s dad’s life was ruined by a fungal contaminant in a spinal injection. And of course, people die from excess general anesthesia. But for this post I only looked at damage done by routine anesthetic usage.
Like all client research, this was tailored to a particular person’s needs and budget, and shouldn’t be considered a general-purpose survey.
It’s pretty hard to tease out the difference between damage done by anesthesia, damage done by whatever necessitated the surgery, and damage done by having your body ripped open and bits moved around. Bodies hate that sort of thing. The few RCTs that exist by necessity focus on a narrow range of minimally invasive surgeries for which there exists a choice in type of anesthesia, and animal studies tended to focus on developing animals rather than adults. Even for procedures where multiple types are possible, patients tend to be pretty opinionated about what they want; one paper even announced they’d given up on reaching their sample size goal because recruiting was too hard.
Studies also often focused on cognition within a few hours of surgery (when people are still at the hospital to test). I think that’s less likely to be “damage” and more likely to be “it’s still wearing off” or “I’m sorry, I just had minor surgery and you want me to take an IQ test?”. This made me throw out a lot of studies.
Few if any of the papers attempted to control for post-operative condition or pain med usage, which seems like an enormous oversight to me.
My overall take home is that:
- Little or nothing that necessitates surgery is good for cognition and that needs to be factored into assessments.
- Surgery itself is enormously stressful, physically and emotionally, and that stress impairs cognition, sometimes in lasting ways. This includes procedures that are not cutting new holes in you, like kidney stone treatments, although presumably it’s worse for open heart surgery.
- Probably there are additional effects from anesthesia. At least general and spinal, maybe including local. On priors I still believe general and spinal are worse on a purely physical level.
- Probably a lot of whatever damage there is heals in most people, although people who need surgery are already under heavy load and will be the worst at healing.
- There may be treatments that can prevent damage but they’re still in rodent trials right now.
- I also believe that being awake and aware during surgery can be emotionally traumatic, and trauma is also bad for cognition, so include that in your math.
- But I’m not trustworthy on this, seeing as I was terrorized by a series of dentists and now can’t get myself through simple teeth cleaning without some sort of bribe, a human to guard me from the bad dentist monster, and a sedative.
I didn’t rigorously track correlational studies, but my sense was they tended to show faster recovery from local and spinal anesthetic, relative to general, presumably because milder cases get milder anesthesia even when the procedures use the same billing code. Additionally a lot of studies were given too soon after surgery, which I don’t expect to predict long term damage
In the few studies that randomly assigned patients to spinal, local, or general anesthesia, and surveyed at least 7 days out, it’s really hard to pick a winner.
Incidence of postoperative cognitive dysfunction after general or spinal anaesthesia for extracorporeal shock wave lithotripsy tries really hard to claim that spinal and general anesthetic are equally damaging to cognition, despite finding a 3x higher rate of cognitive issues after general anesthestic. I showed this paper to my statistician father and he gave a rant I wish I had recorded because it would make me famous in the right corner of Twitter. Hell hath no fury like a statistician forced to read a medical paper. He agreed with me that 19.6% (the rate of complications in the spinal group) was much larger than 6.8% (rate of complications in the general group), but dismissed that as merely a felony next to the war crimes against statistics they committed by using the wrong test for statistical significance.
Two meta-analyses both find a small difference in favor of spinal over general, with confidence intervals that overlap no-difference. One found spinal to be ~5% better (26 studies), the other 50% (but only 5 studies, so still overlapping with 0). The latter analysis is tiny in part because it is restricted to tests within a week of surgery. The analysis that looked also failed to find improvements from using local anesthetic.
On the other hand, animal studies of anesthesia without surgery regularly show impairment, although they can’t agree if post-anesthesia animals start off worse but catch up, or start off the same but fall behind. Also they found other medications could mediate the effects. I summarize the animal results in this spreadsheet. These are effect sizes we would clearly notice in humans so I assume they’re using much more anesthetic (although they claim it’s proportionate) or the animals, primarily rodents, are much more sensitive. Also the studies tended to be within days of anesthesia application, removing a chance to heal.
The original commission was to investigate kidney stone treatments, and what I can say there is that the general medical site UpToDate is pretty good. Every claim I investigated checked out and I didn’t find anything at all established that they didn’t.
Thank you to Claire Zabel for commissioning the research and encouraging me to share the findings, and to my Patreon patrons for supporting the public write-up.