The people who can’t go numb at the dentist’s
June 3, 2021 9:24 PM   Subscribe

Some people are resistant to local anaesthetic, meaning they must endure dental and medical procedures without such pain relief. And we’re only beginning to understand why.
posted by aniola (63 comments total) 28 users marked this as a favorite
 
Anaesthetic doesn't work well for me at the dentist's office. It's one reason I'm so excited about silver diamine fluoride!

Anyway, it's neat to see they're studying this.
posted by aniola at 9:36 PM on June 3, 2021 [2 favorites]


This is interesting to me, in that I have found that no over-the-counter NSAID pain killers work on me except for naproxen, and also acetaminophen doesn't do much for me either. I went for years taking aspirin or ibuprofen or whatever and thinking "well, it kept the pain from getting worse, I guess???", but then naproxen came along and I was all "oh wow, no more pain! is this what people have been getting from those other pills all along?"

I think we don't know nearly enough about pain and haven't really even begun to explore it or understand it even to the level of a standard model, let alone beginning to grok the outliers.
posted by hippybear at 9:38 PM on June 3, 2021 [20 favorites]


yeah, I always burn through novacaine and it's ilk apparently way faster than most dentists anticipate. I try and warn them and inevitably somewhere about halfway through a procedure I need to raise my hand
posted by drewbage1847 at 10:33 PM on June 3, 2021 [6 favorites]


I wonder if there's anything in common with the people who wake up from anesthesia mid-surgery? Like, there are expected reactions to substances, but humans are all unique and we don't all do the things the same way.
posted by hippybear at 10:48 PM on June 3, 2021 [4 favorites]


(Derail: For the last few times at the dentist, for routine fillings, I've asked to do it with no anaesthetic. And since what I hate the most about the dentist is the two hours of numb mouth afterwards, the little bit of pain involved has been totally worth it. The unpleasant grinding and vibration of the drill is still there, but that's there anyway, even with anaesthetic, so the experience doesn't change much. NB: Not recommended for root canals.)
posted by clawsoon at 10:53 PM on June 3, 2021 [2 favorites]


Unless you keep going to dentists and saying "my tooth really hurts" and they (rightly, I think?) say "let's wait and see, we wouldn't want to do a root canal if we don't have to, and eventually the tooth stops hurting, and then they don't anaesthetize you and it really truly doesn't hurt in the slightest because the nerve has completely rotted away. In that case, it's fine to forgo the anaesthetic.
posted by aniola at 10:59 PM on June 3, 2021 [1 favorite]




I've had a couple of people giving me a local disbelieve that I was in pain and say something like, "OK, tell me each time you feel something." Me: "Now ... now ... now." Them: "Uh ... you should not have felt any of that." Probably just by coincidence, I did gain consciousness under general anesthesia once as a child--I couldn't move or feel anything, but I could hear for a little while and was able to tell the doctor something they'd said that I shouldn't have known (basically they had an inconsequential "oops" moment, but I had questions that sure got their attention). I've had general anesthesia since then with no issue though.
posted by Wobbuffet at 11:10 PM on June 3, 2021 [2 favorites]


Really interesting. Luckily I'm not totally resistant likes those in the article, and I've had the same dentist for 20 years who has learned from experience to give me three times the normal number of shots and to wait twice as long for them to take effect before starting any procedures. Apparently my roots and nerves endings are just much longer than average - the same reason my wisdom teeth were removed in the hospital under general anaesthetic and even then they left one in as the roots had wrapped around a branch of my trigeminal nerve. I'd rather have a numb mouth / face for 6 hours than worry that the freezing will wear off during the drilling.
posted by acroyear at 11:11 PM on June 3, 2021 [6 favorites]


I think I'm the "nerves in my mouth are located in unusual spots" case from the article. A couple of times I've gone in for dental work and the anaesthetic just didn't take that day, but usually they figure it out after a few tries and it's fine. I just leave extra slack on my calendar if I know I'll have to have it done in case it takes longer than they expect. But once I did have to just go home without getting my tooth fixed and try again the following week. Local anesthesia is weird.
posted by potrzebie at 11:12 PM on June 3, 2021 [2 favorites]


I remember reading somewhere that this also applies to people who are going through labor.
posted by aniola at 11:19 PM on June 3, 2021 [1 favorite]


For what it's worth, I've had an epidural done for one of my childbirths and it worked like a charm. I was numb as fuck, immediately, and stayed that way for as long as the needle was in my spine. But yeah I guess it's the same or at least similar stuff - a friend of mine is deathly allergic to novacaine and was surprised to learn she'd have to use alternate anesthesia for childbirth if she wanted it.
posted by potrzebie at 11:36 PM on June 3, 2021


My father and I both have a similar issue at the dentist's - the local anaesthetic doesn't kick in till much, much later than it should. Usually really kicks in in the car on the way home, after getting two shots in the chair because the first one didn't seem to be doing much.
posted by stillnocturnal at 11:42 PM on June 3, 2021 [2 favorites]


Novocaine didn't work for me when I was a child, or maybe I just had a bad dentist who didn't know where to inject it.

I remember one time when I was getting a filling and told him (as I always did) that I could still feel things. He said it should be getting numb soon and started work. When I told him that it really, really hurt he said he was too far into it to stop. I remember that I tightly squished two fingers of one hand in the fist of the other hand so hard, that after it was all over, those two fingers were completely numb for 24 hours. I thought I was going to lose the feeling in those fingers forever.

For some reason, novocaine seemed to work when I became an adult, though it makes me feel nauseous. I had a root canal by a dentist who was considered a novocaine artist. After he gave me the injection I could feel all around the tooth and panicked. But the one tooth was numb, so he said don't worry. He actually managed to make just a single tooth numb--so numb that I didn't feel the root canal. That's a little off topic but I'm amazed to this day and am glad novocaine now works.

(Yes I had an incredible sugar addiction as a child and as a result have had lots of teeth problems).
posted by eye of newt at 1:07 AM on June 4, 2021 [4 favorites]


Once upon a time, on one of those Technologies to Come magazine shows (interactive CD-ROMs, wave of the future!), I saw a segment on electronic anesthesia. The idea being that nerve pain is just electrical signals, so if you can locate the nerve and flood it with artificial 'white noise', you block the pain. Great for dental purposes, since you hit a switch to turn it on and off, rather than being numb-faced and drooly for hours. Something akin to a TENS muscle stimulation device, but for nerves.
I assume, since I haven't heard anything come of it since, that this doesn't actually work so simply?
posted by bartleby at 1:27 AM on June 4, 2021 [1 favorite]


'Some of her patients have told her that their doctor or dentist simply won’t believe them when they say “local anaesthetic doesn’t work on me”.'
Ehlers-Danloss Syndrome affects 8 times more women than men, of course medical professionals are ignoring its effects.
posted by howfar at 1:48 AM on June 4, 2021 [38 favorites]


Something akin to a TENS muscle stimulation device, but for nerves.

That is a TENS device. Sadly they only work to a limited extent for a limited range of issues, which confirms your understanding and estimate of the problem: that the basic theory is sound, but nociception is a complex and inconveniently robust process. I think this is what one would expect of the sensory process with the most fundamental role in keeping us alive from minute to minute.
posted by howfar at 1:58 AM on June 4, 2021 [2 favorites]


Combo of "nerves in unusual places" and dental phobia is fun. Did you know that up to the mid-90s, pediatric dentistry in Poland didn't use any pain relief at all because "kids don't feel pain"?

I've been going to the same dentist for 20 years now. Thankfully she's very good generally, but most of all she knows how to make sure I don't feel a thing. I had an appointment with another guy in the same clinic once while she was on leave and ended up just going "stop" because after four different injections I could still feel everything.
posted by I claim sanctuary at 3:26 AM on June 4, 2021 [3 favorites]


When I was a kid I never got novocaine at the dentist — not because I could endure the pain, but for some reason the drilling etc. never hurt. I have no idea why.

I wonder if that would still be true today but I'm afraid to try, and also I doubt any dentist these days would even let me try.
posted by Ampersand692 at 3:59 AM on June 4, 2021


I had this issue when I was twenty years old and had a lengthy surgery to repair/reconstruct my nose that I’d broken rather badly as a young toddler pulling myself into a stand. Being a singer I didn’t want to risk damage from intubation, so I elected to do it with local. Big mistake. I must have been pumped full of every member of the “-caine” family and still the area never got numb. I felt everything and can still recall the lengthy surgery with surprising clarity, including all the peeling, breaking and especially the pain. F+++++ would not do again. I do have a nice nose that works properly, though.
posted by slkinsey at 4:19 AM on June 4, 2021 [2 favorites]


I once had to have a wisdom tooth extracted without anesthetic. They had to break it in place and pull out two sections separately. I literally screamed and almost ripped the arms off the chair. They called it "surgery" but I called it "interrogation by Jack Bauer."

The last time I went in for a filling, they damaged a nerve with the anesthetic and my tongue has been partially numb ever since. It was "mostly recovered" after about two weeks but not quite there after a couple of months -- a weird and mildly unpleasant sensation, not recommended.
posted by Foosnark at 4:56 AM on June 4, 2021


Anesthesia works for me but doesn't last as long as expected. I've woken up during surgery and regained feeling in the middle of dental work so I'm always careful to make sure my doctors and dentists are aware of this before they start.
posted by tommasz at 5:43 AM on June 4, 2021


I'm also resistant to local anesthetic, which makes dental surgery an adventure. Every time I go to a new dentist, I have to re-prove my condition to them, which involves an escalating series of "well can you feel THIS?" jabs after the second and third novocaine shots. (Spoiler: yes, I can feel it, because I just told you it's not numb) It's annoying, but I understand why they do it: claiming resistance to local anesthetic is classic opiate-seeking behavior, and if I'm a new patient, they don't know what my deal is.

That said, I'm also a dude who advocates pretty well for himself, and I'm not completely immune to the stuff like the woman in the article. Having had the novocaine wear off mid-drilling, I don't envy anyone the experience of dental work without anesthetic.
posted by Mayor West at 5:45 AM on June 4, 2021 [4 favorites]


Once upon a time, on one of those Technologies to Come magazine shows (interactive CD-ROMs, wave of the future!), I saw a segment on electronic anesthesia. The idea being that nerve pain is just electrical signals, so if you can locate the nerve and flood it with artificial 'white noise', you block the pain. Great for dental purposes, since you hit a switch to turn it on and off, rather than being numb-faced and drooly for hours. Something akin to a TENS muscle stimulation device, but for nerves.

I assume, since I haven't heard anything come of it since, that this doesn't actually work so simply?

It actually does exist - I was at the dentist earlier this week and rather than giving novacane, they used this wand-like thing called a 'synapse dental pain eraser' that they rub on your gums for about 30 seconds. The hygienist told me it interrupts the nerve signals for 24-48 hours, and I then proceeded to have a deep scaling done with zero (zero) pain or discomfort. Definitely legit amazing.
posted by Fidel Cashflow at 6:22 AM on June 4, 2021 [14 favorites]


"claiming resistance to local anesthetic is classic opiate-seeking behavior" this isn't directed at you, Mayor West, but this kind of nonsense is why the war on drugs is so silly.

It doesn't make any sense to claim that you are resistant to local anesthesia as a path to drugs, because what, they're going to shoot you full of horse to drill a tooth? Maybe in a Victorian novel or something, but not in the 21st century.

It's the reason I dread going to the doctor - they make decisions based on ludicrous stereotypes and have the power to enforce it and through their notes impose it on you for as long as you are in that medical system.
posted by winna at 6:23 AM on June 4, 2021 [13 favorites]


> Novocaine didn't work for me when I was a child, or maybe I just had a bad dentist who didn't know where to inject it.

I had four back teeth go abscess over the year before I turned six in 1972. I was an Army brat, close enough to Post that Army dentists pulled them for me. It was traumatizing hell that took me over forty years to get fully over. (It was only about three years ago it finally dawned on my that a five-year-old with rotten teeth had bad parents, not bad hygiene, but that's another story.) I was put under for other teeth to be removed as an older child, and throughout my teenaged and young adult years, my "routine" fillings were without anesthetic.

I've read somewhere since that Novocain doesn't work well with abscesses because something something acidic environment. Dunno. My dental health is better now than it's ever been, and I'm past my issues, but it still takes me more to get numb when there's something to do.
posted by phrits at 6:40 AM on June 4, 2021 [5 favorites]


"I think until there’s that level of proof about it, it’s going to be very difficult to get doctors to accept it."

Doctors have beliefs.
posted by villard at 6:45 AM on June 4, 2021 [2 favorites]


My sister and my father are of the “novacaine doesn’t work on me” variety. I have the dental story where I remember as a child, hearing my sister tell the dentist over and over that she could still feel the dentists drill, and being told she was just being difficult. My mother was there, I think, but I honestly don’t remember if she did anything. Just hearing it was traumatizing to me.

The weird thing: my mother and I are super sensitive to novacaine. Like above and beyond normal. Doctors never believe until they see how numb, how quickly. They’ll tell me “you should be getting numb soon” and I am often saying “doc, I’m not just already numb, my whole face is frozen”.

I’ve always wondered if they are the same genetic pathway, just different switches on or off.
posted by [insert clever name here] at 6:59 AM on June 4, 2021 [2 favorites]


Gas, baby, gas. Novocaine, yes, but supplemented with gas. I only use dentists who use it — and generously.
posted by lometogo at 7:04 AM on June 4, 2021 [6 favorites]


I had a wisdom tooth removed a while back. It was an extremely easy extraction, and I still needed multiple shots of novocaine. My theory was that I was keyed up and anxious, which was causing the 'caine to wear off. I've got another surgery coming up in the next year that'll require a local, and now I'm curious how well it'll work on me.
posted by SansPoint at 8:55 AM on June 4, 2021


I wonder if there's anything in common with the people who wake up from anesthesia mid-surgery?

My limited understanding is that this kind of anesthetic operates (heh) in a different way, but I'm sure someone here knows more and not sure that means there's nothing in common.

I'm somewhat resistant to local anesthetic myself, although thankfully so far that just means a double-dose rather than dealing with too much pain. Interested in digging into this.
posted by aspersioncast at 9:02 AM on June 4, 2021 [1 favorite]


It's the reason I dread going to the doctor - they make decisions based on ludicrous stereotypes and have the power to enforce it and through their notes impose it on you for as long as you are in that medical system.

BRB, hiring a skywriter.

I'm lucky enough not to be one of those EDS people who doesn't respond to local anesthetics at all, but it takes a lot more and a lot longer to properly numb me up. Fortunately the dentists I've seen don't seem to think that I'm asking for more injections in my mouth for funsies. They're mostly baffled but willing. Doctors are the ones who think pain is invented by neurotic ladies, ime, dentists have mostly been fine.
(Drug seeking behaviour? I'm asking for more novocaine, not opiates. They don't really help with nerve pain anyway).
It's true about abscesses making it harder to numb the area, though, which is how I got to have a root canal without anaesthesia that one time. The abscess already hurt so much I kind of didn't care, though.
posted by BlueNorther at 9:11 AM on June 4, 2021 [5 favorites]


Is it weird that it doesn't work only in certain areas? I've had some miserable dental experiences because I had problems getting numb enough for upper work. I told my (new) dentist this and she basically told me to buckle my seatbelt for some recent crown work. She must've injected me 4 or 5 times in the same area. I didn't feel a thing for hours, but then it all flushed out at once.
posted by jquinby at 9:21 AM on June 4, 2021


I also wonder if it's similar to waking up from anesthesia... terrifying. There's a creepy movie about that.

I've also heard of former/current opioid addicts being resistant to several forms of pain management.
posted by jumanjinight at 11:04 AM on June 4, 2021


Local anesthesia is basically useless for my brother. They figured that out when he needed some minor knee surgery. Multiple rounds of shots but each time they'd cut he'd scream. This led to some scans and examinations being done which had rather surprising results. The doctors involved suggested that he may have been twins that never really separated. He's always had an amazing metabolism, he was a great competitive swimmer and diver with astonishing lung volume and also able to sober up quickly after drinking. Now we know why: he's got 4 kidneys (and they told him he shouldn't donate any) a nearly double-sized liver, huge lungs, a big but healthy heart. So, in his case, his body just processes local anesthetics very quickly. It's kind of like a super power.

But I don't think it's the whole story either because I most definitely don't have extra organs but I also seem to process things more quickly than normal. I once had eye surgery with local anesthetic plus one of those substances where you're not out cold but completely out of it and can't move any muscles. Except it started to wear off too fast and my eye twitched right as they were pulling out, which caused a misalignment of a tiny flap they had cut in my cornea. So I suspect there's some genetic component involved as well where, regardless of the twin thing, we're both just processing stuff a little faster to start with.
posted by Hairy Lobster at 11:43 AM on June 4, 2021 [11 favorites]


Jquinby, I just had a dentist tell me that there is a major nerve in the jaw that can be more easily reached, but it isn’t the same with the upper teeth. So that tracks.
posted by Monday at 2:09 PM on June 4, 2021 [1 favorite]


It’s lidocaine, not novocaine. Nobody uses novocaine anymore. You’re not allergic to the anesthetic. It’s the vasoconstrictor in the shot. This is used to attempt to restrict the local anesthetic to remain as local as possible. I worked at a dental school and helped to prepare classes on how lidocaine works and on lidocaine toxicity. Some people here talk about requesting more shots. There is a limit, based on body weight. A local anesthetic is not local. It eventually percolates throughout your whole body. Too much and you stop breathing, not dead, just not breathing. If the dentist has a respirator in the office, they can keep you ventilated until the lidocaine is cleared out and you start breathing again. If not then RIP.

The lidocaine works by blocking the sodium channels along the nerve. This essentially stops the action potential on the nerve, no current, so to speak, and thus no signal is transmitted down the nerve. Eventually the lidocaine molecule is freed from the sodium channel and everything is back to normal. Meanwhile, tetrodotoxin works in a similar way, it blocks the sodium channel too. But permanently. No recovery. This is the chemical in puffer fish, AKA fugu, that gives that tingle to your tongue in the sushi restaurant, as long as they know how to prepare it. And according to Wade Davis, in his book, The Serpent and the Rainbow, it was used to make zombies in Haiti.

Anatomy… The nerve that feeds into your lower teeth is inside the jaw bone. To reach it, the dentist directs the needle through a small hole, foramen, back on the inside behind your molars. Dentists have been taught for years where to aim to get closest to the nerve. At the dental school I worked at, a physical anthropologist managed the anatomy lab. He was curious about this anatomical description. When the general anatomy class was over and he had 18 cadavers to examine, he did precise dissections in that region to see where the nerve actually was. Guess what! It was all over the place back there. He invited the faculty dentists who teach local anesthesia to see for themselves what the reality actually was. They were surprised. So the procedure as taught wasn’t really right. Some of you who have problems getting your lower teeth numb could be outliers on where your nerve lies in the bone. Your dentist is just missing it.
posted by njohnson23 at 2:42 PM on June 4, 2021 [15 favorites]


Oh yes. Anaesthetic definitely spreads throughout the whole body. I had a dentist who got into a heated argument with another customer (about pain med seeking) while I was in the chair. She did a single round of "how 'bout now?" and then must have gotten tired of it or something. She roughly jabbed me so full of so much anaesthetic all at once that afterwards I had to sit at the restaurant across the street for a while and try to eat something because my heartbeat was out of control. That jab permanently damaged my nerve (which maybe wasn't where she was expecting it).
posted by aniola at 2:55 PM on June 4, 2021


I wonder if there's anything in common with the people who wake up from anesthesia mid-surgery?

I think that local anesthesia prevents nerves from transmitting pain (and other) information at all, whereas general anesthesia blocks the information transmission so one's brain never processes the pain. In my case, local anesthesia works fine, but I'm one of those folks who has woken up mid-surgery while allegedly incapacitated by general anesthesia. They had to try alternate medications to keep me under and also tied my hands down because I kept "trying to help." Waking up only to find myself in restraints and intubated was terrifying, and I remember a lot, unfortunately. I've only had general anesthesia that one time, but if I ever need it again I hope the anesthesiologist doesn't decide that I'm exaggerating.
posted by carmicha at 3:08 PM on June 4, 2021 [1 favorite]


"Some of her patients have told her that their doctor or dentist simply won’t believe them when they say “local anaesthetic doesn’t work on me” .... a real change in practitioners’ perceptions will probably only come about when a large, formal study confirms the existence of the phenomenon in a sizeable sample of patients."

**Screams**

Why does it have to be so frickin' hard for them to believe the things their patients are telling them about their own bodies in which they live?
posted by penguin pie at 3:18 PM on June 4, 2021 [7 favorites]


"yeah, I always burn through novacaine and it's ilk apparently way faster than most dentists anticipate."

My husband does too, he typically need three shots for a procedure most people only need one for, it doesn't fully numb him, and it's always worn off by the time he leaves the office. (He thought it was hilarious when I came home with my mouth still numb.)

"I've had a couple of people giving me a local disbelieve that I was in pain and say something like, "OK, tell me each time you feel something." Me: "Now ... now ... now." Them: "Uh ... you should not have felt any of that.""

Yeah, every time I've had anesthetic the anesthesiologist has given me a normal amount and then we're still staring at each other because I am a redhead which they can literally SEE and every anesthesiologist will TELL you "redheads need more anesthesia" and yet every single time they seem surprised when the thing they just told me turns out to be true. I can't even imagine what people who don't have a visible "I need extra anesthetic!" marker have to go through.

"Did you know that up to the mid-90s, pediatric dentistry in Poland didn't use any pain relief at all because "kids don't feel pain"?"

The idea that babies (in particular) didn't feel pain was common medical "knowledge" until, gosh, the mid-1970s? And lots of doctors still believed it in the 90s. (I think partly it was a motivated belief because anesthesia is hard to get right in babies, so telling yourself babies don't feel pain is easier than "we have to do this surgery but can't safely anesthetize this baby.") It's used in a lot of medical ethics textbooks to talk about assumptions and received wisdom.
posted by Eyebrows McGee at 3:47 PM on June 4, 2021 [6 favorites]


Recovering alcoholics are another group that general anesthetics don't work well on. I tell them every time, it seems like most docs have heard of this, some haven't. I recall giving an oral surgeon a play-by play of what he did when he was done, and also recall my amazement at how long and skinny the needle was that they were using to give me a chest biopsy. That last, I felt no pain, it was like watching it happen on youtube or something.
posted by rudd135 at 4:35 PM on June 4, 2021


Why does it have to be so frickin' hard for them to believe the things their patients are telling them about their own bodies in which they live?

I don't know. Twice in the last five years I have had incidents where drs/dentists didn't believe that lidocaine takes significantly more shots to take effect, and would wear off significantly faster. First time I wasn't believed was for a muscle biopsy. As the doctor was cutting the skin I told him I could feel it, he re-injected and kept cutting. It felt like every layer down would need a new re-numbing. When he reached muscle, I had to stop him because I could feel the biopsy grabber tool. He asked me if "I'm sure it's not just pressure I feel?" I know the difference between pressure and pain! But then he said it would be over quickly and continued grabbing with the tool. I almost broke the poor nurse's hand, I think she realized earlier I was in pain and held mine. I'm not a hand-holdy person

Second time was for my first ever root canal. Warned the new dentist it would take more than usual, she said something like "we'll see" and I got well numbed for the drilling. But then for the fitting (same day appt), she used a burst of air on the tooth stump to check for numbness and I almost bolted out of the chair. It took three more rounds of numbing, then checking, for it to finally be numb. Both incidents are seared in my mind.

My mom had the same experience with all of her c-sections. She never got fully numb, and all four were very traumatic for her, especially when they didn't tell her right away that my sister's neck was wrapped around the cord and she died before they could do anything about it. I always thought, oh, well that was in the 80s, medicine has come aways. Guess not.
posted by lizjohn at 4:40 PM on June 4, 2021 [2 favorites]


I used to not understand why they would numb/check/numb/check/numb/check until the above-mentioned impatient dentist. Now I understand, but I no longer need to be anaesthetized for cavities since I discovered silver diamine fluoride, they just paint it on!
posted by aniola at 5:06 PM on June 4, 2021


My dad had a procedure to surgically clean his carotid arteries. The paralytic worked but the anesthesia did not. It was bad my friends.
posted by Gadgetenvy at 6:44 PM on June 4, 2021 [1 favorite]


I don't really understand the bit about sodium channels. What do sodium channels have to do with nerves?
posted by aniola at 8:15 PM on June 4, 2021


Extremely simplified, sodium channels in your cells' membranes is how cells can transmit electrical signals one to the next, which is basically how a nerve cell sends a signal from your finger up your arm to your spine and into your brain, that makes you go "FUCK! A papercut!" If you block the sodium channel (which is how local anesthetics seem to work), your angry finger nerve is like "OMG SEND THIS PAPERCUT MESSAGE TO THE BRAIN" and the next nerve up is like "Oh, sorry dude, we're off duty and not sending any messages, sodium channels closed here." (And vice versa, the brain messages are not going to the finger, so you can't move it while it's numbed.)

You have to understand a lot about cell membranes and microelectricity and proteins and cations and stuff to understand the actual thing, which I do not. But when my doctor friend was explaining to me how epidurals work before my C-section and I was like "so it's like ... cells using salt water (or, like, salt cytoplasm or something) to conduct electricity, or not conduct it, to send signals?" she was like, "Yeah, close enough." (But I think they use individual sodium ions, not "salt water," but I get how salt water conducts electricity better than fresh so that made it clearer for me.)
posted by Eyebrows McGee at 8:58 PM on June 4, 2021 [3 favorites]


I'm sure someone else can answer this more fully, but I understand that the ionized sodium is a way for electrons to be passed along, which is sort of the "electricity" that we understand to exist in the nervous system.
posted by hippybear at 9:02 PM on June 4, 2021


As I said....
posted by hippybear at 9:03 PM on June 4, 2021


This is certainly an interesting read. I've long had the problem of needing way more local than they think I need, and I've had it start to wear out partway thru. I remember getting a set of partially impacted wisdom teeth scooped out and by the end, I was just crying in pain but told them to just finish it so I could be done. I made it to the end and then just vomited.
I've since gotten better at controlling my breathing and enduring the pain when it doesn't kick in much or wears out.
The two best dental experiences I had involved nitrous. Even tho I could feel the local wearing off I just didn't care? In fact, I thought it was hilarious almost.
posted by MrBobaFett at 10:25 PM on June 4, 2021


There is a limit, based on body weight. A local anesthetic is not local. It eventually percolates throughout your whole body. Too much and you stop breathing, not dead, just not breathing. If the dentist has a respirator in the office, they can keep you ventilated until the lidocaine is cleared out and you start breathing again. If not then RIP.

Local anesthetics as sodium channel blockers are sometimes used deliberately for their effect on the electrical activity of the heart (i.e. to halt arrhythmias) so I’m pretty sure it’s not just breathing that can be impacted in overdose.
posted by atoxyl at 10:42 PM on June 4, 2021


I wonder if nitrous oxide would work for these people? I always had terrible lingering pain in my gums from the numbing injections and started only using gas for all my dental procedures, including a root canal (which amazed my dentist). With nitrous, I can still sorta feel that there is pain, but I just don't care. Too painy? Breathe deeper and all is bearable. I'm bummed that only a very few dentists have it as a option. Another great thing is no recovery time is needed. Stop the gas and your head clears quickly and no horrible numb face.
posted by a humble nudibranch at 11:43 PM on June 4, 2021 [2 favorites]


I ran into this last week when I was looking up something else about nitrous, but it has a weird side effect:
Nitrous oxide has been used for more than 150 years and has been given to several billion patients. It justifiably remains a popular anaesthetic agent because it is inexpensive, analgesic, and extremely short acting. It reduces the need of maintenance anaesthetic, which has more significance when ventilators with larger fresh airflows are used. However, intestinal distension by nitrous oxide has been reported at least since the 1960’s (1), and it is well established that nitrous oxide inflates closed, gas-filled spaces (2).

Nitrous oxide will move into air-filled cavities in the body that normally contain nitrogen; so as nitrous oxide transfers from the blood into the space, nitrogen transfers out. However, nitrous oxide is 34 times more soluble than nitrogen in blood. Thus, substantial quantities of nitrous oxide leave the blood and enter the bowel, but not much nitrogen can leave the bowel to enter the blood. The result is that during exposure to nitrous oxide, like in other compliant spaces, the volume of gas in the bowel increases. The amount of the increase depends on the alveolar partial pressure of nitrous oxide, the intestinal blood flow, and the duration of nitrous oxide administration.
Dental surgery probably doesn't last long enough for this to manifest significantly, and the partial pressure of nitrous in the lungs may also be too low anyway, but it's interesting we don't see anything like it with oxygen -- or at least I don't think we do.
posted by jamjam at 12:40 AM on June 5, 2021 [2 favorites]


I've had dental surgery (wisdom teeth out) under nitrous, done right it's quite weird, your sort of standing over there watching what's going on .... but then turn it off, sober up right away, nip out for a pee, then back under for the rest of the process.

Like many I've also done it recreationally, it's quite a different, rather more extreme experience than the carefully controlled dental experience. It can also be quite dangerous ... I've lost a friend to it, don't EVER use a plastic bag, you can pass out and suffocate ... use a balloon so it will just go pffffbpt if you go too far
posted by mbo at 3:10 AM on June 5, 2021


Interesting!! I frequently get the 'wrong' nerves numbed when Novocain is injected; so I've always believed my wires were crossed somehow. I wish I knew what was going on in there.
posted by I_Love_Bananas at 3:59 AM on June 5, 2021


This comment is an anecdote based only on my experience with dental anaesthetic as a person with relatively normal reaction to anaesthetics (ie, it works). So not really related to the article, just the general discussion about dental anaesthetics.

As a kid, I had a lot of dental work and would often required multiple doses and longer than usual wait before the anaesthetics kicked in.

During one of these experiences the dentist asked if I had had anything to eat recently because the anaesthetics tended to work better on a full stomach.

Lightbulb! I was a kid, in school, who rarely ate lunch. And my dentist appointments were always after school. So I typically wouldn't have had anything to eat or drink since before school.

In my experience, if I eat before an appointment, the anaesthetics work better, quicker, and with the "normal" dose.

I don't know why or how it matters. I've mentioned it to other dentists and no one was familiar with the idea. So again, aside from being suggested by that one dentist, this is anecdotal.

But it's simple enough. And it helps avoid post-dentist hunger. The kind of hunger that results in me attempting to shove hastily bought mcdonald fries into my now completely numb face hole. And mostly biting my own cheeks and lips.

Again, anecdotal, so take this with a grain of sodium ions.
posted by alikins at 3:02 PM on June 5, 2021 [2 favorites]


Agreed, eating first does help some with the post-anaesthetic jitters. I always eat before going to the dentist after a dentist told me to once. Including I ate before my above-mentioned story. I can only imagine if I hadn't.
posted by aniola at 3:17 PM on June 5, 2021 [1 favorite]


I have a very high metabolism. I tell dentists the anaesthetic won't work as well or last as long because of my metabolism, but I don't really know what that even means other than that I'm skinny and get hungry easier than other people. I'm just handwaving to get them to believe me, but could there be something to it?
posted by aniola at 3:19 PM on June 5, 2021


Good post and comments! I happen to know a little about this subject, so thought I would weigh in. First off, it helps to understand how nerves work and how local anesthetics keep them from functioning. Although nerves are often compared to electrical wires, the analogy breaks down pretty rapidly under close examination. Nerves (and many other cells) actively pump certain ions out and others in to create an electrical potential across their cell membrane. In general, sodium, potassium, and calcium are the main ions involved with this process, with chloride ions playing a smaller role. And it doesn't just apply to neurons, but similar processes occur in other cells, including muscle cells, cardiac conduction tissue (which is why local anesthetics are also antiarrhythmic drugs) and some secretory cells. When exposed to the appropriate stimulus, the nerve will change the electrical potential across a portion of its membrane, which will trigger sodium channels in nearby regions of the neuron to open, flood the interior of the cell with sodium ions, and change the electrical potential of the membrane adjacent to the where the original stimulus was applied. This in turn opens sodium channels further down the neuron, and the process repeats over and over again down the length of the nerve cell; this is called an action potential. There are a lot of other details that come into play at times (such as the size of the neuron and myelinization), but this is not the place for a neurophysiology lecture.

Given that background, the way local anesthetics work is to insert themselves into those sodium channels and plug them up, bringing the action potential to a screeching halt and stopping the nerve from carrying out whatever function it is supposed to. And it has long been recognized that different types of nerves within the same patient respond differently to local anesthetics. This is why, for example, anesthesiologists will use a local anesthetic for labor epidurals that is less likely to affect motor neurons and cardiac conduction tissue, making it both safer and less uncomfortable for the patient.

So how do you get local anesthetic to the nerves you want to block? It generally involves an injection. If only a small area on the skin needs to be numbed (for suturing a small to medium laceration, for example) injecting the anesthetic all around the area will usually (more on the "usually" later) numb it up and allow the procedure to be done painlessly. This is easy, but an inefficient way to deliver the drug, so for larger procedures one has two deliver the drug directly to the nerve. This can mean giving a shot directly adjacent to a peripheral nerve (giving a shot directly into the nerve can injure it, resulting in permanent or semipermanent anesthesia). Finding that nerve can be done in many different ways, including knowing where the nerve should be, eliciting a tingling sensation (paresthesia) when you touch the nerve with the needle, using a special needle and electrical device to stimulate the nerve when you get close to it, and/or using ultrasound to directly visualize the nerve and needle as you perform the block. Almost any nerve that can be reached with a needle can be blocked this way, from the nerves to the fingers and toes, to nerves supplying and entire arm or leg, to nerve roots coming out of the spinal canal (epidural anesthesia) to the spinal cord itself (spinal anesthesia). Given that these techniques all rely on local anesthetic remaining in a specific part of the body for a while, much of the duration of these blocks depends on how long the anesthetic remains in proximity to the nerve. Diffusion away from the nerve relies in large part on blood flow, so vasoconstricting drugs like epinephrine are often added to local anesthetics. This has the added affect of reducing bleeding at the site of the procedure, but also can be responsible for untoward side effects such as heart racing and anxiety, which can be misinterpreted as an allergic reaction.

Sounds pretty straightforward, but what can go wrong? Many things. Obviously, the person performing the block can just miss the intended nerves. Or come close enough to obtain a partial block. The volume or concentration of local anesthetic used may not be enough for a given block in a given patient. In the context of the original post, nerves commonly blocked for dentistry are branches of the facial nerve that have very well defined courses through the skull and so are generally easy to find and block based on anatomy, although that is not foolproof. (I have had a few failed dental blocks myself.) And as others have mentioned, field blocks often fail in the setting of an inflamed setting such as an abscess. This is because the pharmacologically active form of local anesthetics (and many other drugs) is a free base; but the more stable form that is easier to manufacture, transport, and store is a salt. At acid pH the salt won't dissociate and the drug won't work.

So, to get back to the topic of the post, in my 30 some odd years in anesthesia I have heard many people say that "local anesthetics don't work on me." Without more detail though, I have no idea what that means. What local anesthetics in what setting? What was the person trying to accomplish with them? How skilled were they at whatever block they were trying to perform? Lots of reasons for local anesthetics to not work other than a congenital insensitivity. Having said that, it makes perfect sense that different patients may have sodium channels that interact differently with local anesthetics. Many, even most, drugs exert their effects through interactions with proteins DNA replication is such that these proteins may have small mutations that don't make a difference in their normal function, but do make a difference in how they interact with drugs. The concept of pharmacogenomics is based on this. So it makes perfect sense that (to use an example from above) that someone may have a version of cyclooxygenase that is inhibited by naproxen, but not so well by ibuprofen. And it also makes sense that some people have sodium channels that respond differently than expected to local anesthetics. Which is a good reason to have a variety of drugs available to try. Local anesthetics can be divided into two chemical groups, esters and amides. This is taken into account when dealing with patients who are allergic to a particular local anesthetic. But it would be worth seeing how patients with the described mutation respond to anesthetics from a different class. Lots of potential avenues for inquiry there. I expect to see more on this topic in the future.

I also have a few thoughts on some of the comments regarding other anesthetic drugs that were mentioned above, but since I'm already headed into Treaty of Westphalia territory here, I think I'll stop.
posted by TedW at 5:47 PM on June 6, 2021 [6 favorites]


Some of us are still are reading the comments down here, TedW, and if you have the time and inclination, I'd love to hear to more.
posted by mollweide at 6:13 PM on June 6, 2021 [1 favorite]


I'd love to hear to more.

Me too.

Given that these techniques all rely on local anesthetic remaining in a specific part of the body for a while, much of the duration of these blocks depends on how long the anesthetic remains in proximity to the nerve. Diffusion away from the nerve relies in large part on blood flow, so vasoconstricting drugs like epinephrine are often added to local anesthetics. This has the added affect of reducing bleeding at the site of the procedure, but also can be responsible for untoward side effects such as heart racing and anxiety, which can be misinterpreted as an allergic reaction.

I think this could be the key reason people with Ehlers Danlos Syndrome make up the majority of the population with resistance to local anesthetic, because the leading theory for the significant proportion of people with EDS who have Orthostatic Intolerance (they get dizzy when they stand up, among other things), is that vasoconstriction fails due to overly compliant blood vessels.
posted by jamjam at 8:09 PM on June 6, 2021 [2 favorites]


That is very tidy.
posted by aniola at 8:32 AM on June 7, 2021


fwiw...
Anesthesia Doesn't Simply Turn Off the Brain – It Dramatically Changes and Controls Its Rhythms - "Simultaneous measurement of neural rhythms and spikes across five brain areas reveals how propofol induces unconsciousness... Conscious functions, such as perception and cognition, depend on coordinated brain communication, in particular between the thalamus and the brain's surface regions, or cortex, in a variety of frequency bands ranging from 4 to 100 hertz. Propofol, the study shows, seems to bring coordination among the thalamus and cortical regions down to frequencies around just 1 hertz."
posted by kliuless at 11:08 PM on June 7, 2021


« Older Harvey Katz AKA Athens Boys Choir   |   Best Practices for Outlook Newer »


This thread has been archived and is closed to new comments