Neuro: 8:00 - 9:00 Scribe: David Davis

Neuro: 8:00 - 9:00 Scribe: David Davis Friday, January 22, 2009 Proof: Molly Clark Dr. Eleazer Selecting Local Anesthetics Page 1 of 6 I. Selecting the Best Anesthetics – Intro [S1] a. Most important lecture of your life. It will be the balance point on which every patient judges you. If you fail to make your patients comfortable, you will forever be known as Dr. Dumb Ass. To achieve the title of Dr. Good, it requires a lot more expertise. b. Pilots are judged by their landings. If you can’t get your patients comfortable and at the outset of their treatment, they are going to judge you. II. Goal [S2] a. Our goal today is to talk about some principles of local anesthesia that will help us make our patients comfortable. We will talk about some dull and boring stuff, but important, in neuroanatomy and pharmacology. b. There isn’t just one anesthetic. There are many and given different patient scenarios, your local anesthetic will vary. If someone asks what local anesthetic do you use, your answer should be that it depends on the clinical situation. c. It is true that teeth with inflamed pulps are much harder to get numb. There are a lot of reasons. Nerves from the periphery to the brain open up pathways and the brain becomes much more attentive in that one area. d. That makes sense doesn’t it? If you have a splinter in your finger, everything that finger does is more tender. e. Teeth with no pulpal inflammation, teeth that are generally treated with a filling, one little shot was enough. When the tooth was hot and the pulp inflamed, it took 3 times as much. One cartridge was lidocaine was enough 95% of the time in the uninflammed pulpal teeth. 60% of the time for the other way around. III. What is it worth to be 5 or 10% better? [S3] IV. 5% better can save time[S4] V. Hot teeth are harder to numb [S5] a. It is true that teeth with inflamed pulps are much harder to get numb. There are a lot of reasons. Nerves from the periphery to the brain open up pathways and the brain becomes much more attentive in that one area. b. That makes sense doesn’t it? If you have a splinter in your finger, everything that finger does is more tender. c. Teeth with no pulpal inflammation, teeth that are generally treated with a filling, one little shot was enough. When the tooth was hot and the pulp inflamed, it took 3 times as much. One cartridge was lidocaine was enough 95% of the time in the uninflammed pulpal teeth. 60% of the time for the other way around. VI. Anesthesia is relative [S6] a. In the old days, we thought of local anesthetic as a switch but now we know much more about it. The first thing to go is cold perception. That is a misnomer for what we do in teeth because of the raw, naked nerve endings in teeth. b. The principle here is that it is a relative sort of thing. If you can get a little better anesthesia, then it might be enough for that given clinical situation. c. Get the concept that small differences make a huge difference in the overall result in the patient’s lack of perception in pain during your procedure. d. You will not be 100% effective. If you know all of the tricks, you can be about 95% effective. e. Remember, time is money. When you miss a block, not only do you lose your patient’s confidence, you are time. It costs about 200 bucks an hour in a dental practice just to pay overhead. VII. Clinical Tip – If “numb tooth responds to cold…. [S7] a. One way to see if your anesthetic worked is to challenge that tooth with cold. You put cold on the tooth and it isn’t numb yet, we are going to have to do something more. VIII. Outline [S8] a. What I want to talk about today and I doubt that I get through it all, is these four things. IX. 1. History [S9] a. Here is the history slide and I kind of like history. Maybe, it’s because I am old. The first local anesthetic that was used was used by a general surgeon to himself. He used a great topical anesthetic, cocaine. b. He injected cocaine into his own pterygomandibular space. He must have had a raging tooth ache because the local anesthetic needles back in the 1800’s were dull and big. If they sterilized them at all, they sterilized them in boiling water. They were probably just bouncing around in there and they could have gotten a bur on them. c. Cocaine wasn’t so good because it caused tissue sloughing and it caused all of these systemic reactions that you read and hear about in the newspaper. d. Cocaine wasn’t the best local anesthetic as an injection. e. A German chemist came over and invented Novocain. Chemically, it is very similar to cocaine. f. Novocain was a sorry anesthetic. It didn’t work very well. It had some toxicity problems but not as bad as cocaine. It wasn’t very effective at stopping nerve conduction. g. A few years before I become a baby boomer, it wasn’t until then that we received lidocaine. It has stood the test of time and it is a wonderful anesthetic. It isn’t the only one in that category. Neuro: 8:00 - 9:00 Scribe: David Davis Friday, January 22, 2009 Proof: Molly Clark Dr. Eleazer Selecting Local Anesthetics Page 2 of 6 h. Practically speaking, we are dealing with the five bottom drugs on this list (lidocaine, carbocaine, citanest, septocaine, and marcaine) for injection. Each has its distinct advantages. X. 2. Neuroanatomy [S10] a. Let’s talk about neuroanatomy. Remember, it is a depolarization effect. b. There is a marching front of depolarization and is about 70 millivolts. It leaps from one to the other. This happens until you have a myelinated nerve and that is a little different. c. It leaps from one sodium channel to another. In a myelinated nerve, most of the sodium channels that persist gravitate to breaks between the myelin called the Nodes of Ranvier. d. We also deal with potassium channels which are kind of the opposite of sodium channels. e. We deal with calcium channels and these are important for treating heart and blood pressure conditions and they might have an effect on our local anesthetic. f. You can think of the sodium channel as a gate and there is a pump inside the nerve cell that pumps the sodium out until the depolarization wave comes on and in a step wise fashion, these sodium channels allow sodium from the periphery to rush into the nerve cell and it goes from the beginning of the nerve, or from the middle of the nerve, to its terminus to a synapse or ultimately to the brain. It is kind of important. g. In face of inflammation, the nerve endings can proliferate in a matter of hours. Furthermore, along the trunk of the nerve, signals can be conducted either upward or downward. XI. Nerve Transmission [S11] XII. Diagram of Needle and Nerve [S12] a. I made this little crude drawing and here we are injecting local anesthetic through the mucus membrane to form a puddle in the tissues. Think of the schematically. b. The only way to receive a local anesthetic is in the ionized form. It isn’t possible to sell it to you in the base form. We inject the ionized form and in the tissues, it dissociates into the base and it turns out that is the only way that it can cross the nerve membrane. c. Once it gets inside the nerve, it has to undergo another reaction back into the ionized form and it physically blocks the sodium channel or changes a molecule at the sodium channel to make it impermeable. d. So, you don’t have that depolarization wave. Pretty much, it just stops. e. Maybe a little sneaks through, and that is where we can use intellects to figure out what works for a particular patient. f. Now, this is the henderson-hasselbalch equation and so is this. That is pH dependent. What do you think the pH is with a localized abscess? What do you think the pH is with a normal patient? What about the individual variability when dealing with these? Can’t really give an answer. XIII.Cell Membrane [S13] a. Here is a schematic of what a sodium channel might look like and the protein next to it kind of squeezes it out, but remember, inside the nerve is the only way that the local anesthetic can access the sodium channel. b. This is made from an actual drawing through the nerve membrane. (Hydrophilic, hydrophobic, hydrophobic, hydrophilic). c. Some kind of a channel, a passageway. We are now learning that there are lots and lots of those specific channels and passageways. Some of those things attach to the outside, stick proteins through the hole and act as a switch to make a cell do one thing or another. d. In our situation, we are only worried about whether the sodium goes through the channel or doesn’t. e. There are nine different kinds of sodium channels. Two of them don’t respond very well to local anesthetics. XIV. Latest News [S14] XV. Local Anesthesia is NOT all or nothing [S15] a. Here are a couple of graphs. They are pretty important. If local anesthesia were an all or none phenomenon, there would be a vertical component. There would be a horizontal and a straight vertical and that would be where your nerves would be on or off. b. That isn’t what this graph shows. This graph shows that it is a gradual change. If we can get more change, we are going to do better. The patient history can give you an awful lot of information. The patient can tell you that they have a really hard time getting numb and you should pay attention. XVI. A delta/C Fibers [S16] a. In the pulp, we have two different kinds of nerves. That is a little bit of a misnomer because we actually have more than that. We have the A delta fibers. Those predominate in the peripheral pulp. They are myelin coated. There sodium channels tend to be grouped at the Nodes of Ranvier where the myelin sheath has a natural break. That is the only place that our local anesthetic can go to work. i. Here is a key for your practice. The A delta nerves have their nerve endings in the peripheral pulp. The characteristics pains that a patient experiences from A delta fibers are sharp, lancinating pains. Neuro: 8:00 - 9:00 Scribe: David Davis Friday, January 22, 2009 Proof: Molly Clark Dr. Eleazer Selecting Local Anesthetics Page 3 of 6 Transmission speed of the A delta fibers are much faster. Well, they are all pretty fast. A patient can’t tell the difference, but a patient can tell what a sharp, lancinating and brief pain is. That is characteristic of fibers in the peripheral pulp being jangled. When your patient says to you when I drink something cold, I get this sharp pain. It doesn’t last long, but it really bugs me. That is caused by exposed dentin. Brushing can aggravate that. There are some things that we can do to help those patients. Most of them don’t have to have a root canal. If you do a root canal on one of them, you probably aren’t going to solve the problem. A root canal will remove the nerve function from the tooth but it is “killing a fly with a sledge hammer.” b. Let’s contrast that with a patient that comes in with a dull throbbing pain. “I hear my heart beat all night.” They have this throbbing all night. Well, those are the C fibers. They don’t have a myelin sheath. They predominate in the core of the pulp. When those C fibers are the predominant ones being jangled, that patient’s symptoms of dull, throbbing pain are telling you this pulp is going to die. The sooner you do something about it, the sooner that the patient is going to like you. In fact, if you catch it before it gets infected; your chances of a root canal being successful go up by about 10 percent. c. There it is. A dull, throbbing pain equals a deep inflammation in the pulp. You should extract a tooth or do a root canal. XVII. Clinical Tip: Dull Throbbing Pain [S17] XVIII. Bad News – C Fibers more resistant [S18] a. C fibers are hard to numb. It isn’t intuitive. They are just harder to numb. b. Two or three times the local anesthetic concentration. Those are laboratory studies where they dissect out frog nerves and put them in a chamber. They measure concentrations and make nice graphs. All of those are very helpful to us as clinicians. XIX. 5,000 Nerves in IAN at our target [S19] a. One day, I thought it would be cool to try and figure out how many nerve fibers I had to anesthetize when I did a classic inferior alveolar nerve block. I researched it because I am a nerd. I wanted to know. b. I came up with the answer of about 5,000 nerve fibers. Turns out that this is way low. c. In reality, there can be as many as 3,500 in a single rooted premolar. XX. Fibers Peel Off as They Go [S20] a. There is a principle. Generally, fibers on the periphery of the nerve where we are injecting – those branch off and go to the molars so the mantle or peripheral fibers branch off and go to the molars. b. The core fibers go to the chin. You start reading studies about how teeth respond to regular nerve blocks, you will find out that the lower anterior teeth are really hard to numb, at least with the nerve block (the way that we do it). c. The nerves aren’t really nice and round. They aren’t even really yellow. They don’t always run where they usually run. Sometimes, you will have a patient that instead of having a round nerve, it will be a ribbon shape. It will branch and split off and do some crazy things. d. Sometimes, you will get a renegade nerve. XXI. Clinical Tip – Molars get numb first [S21] a. Here is the principle of it. As the nerve fiber gets smaller, you are left with the core fibers. Arguably, they are in the middle of the bundle and arguably, it is just tougher to get the local anesthetic to diffuse that deeply. That is just a conceptual picture that I have in my mind. I would say to the average clinician that when the chin starts to get numb, the molars have pretty much been numb. XXII. Dysesthesia [S22] a. Sometimes, things go wrong. Sometimes, the patient gets numb and doesn’t wake up. That is where you don’t want your patient to go home and look at the telephone book. You want to inform your patient that there is a certain risk of this, but the likelihood is strong that you will recover in a matter of weeks. I want you to come back and see me once a week so that we can plot your progress. That is where making a little drawing of where the numb area is. b. Don’t lose touch with those patients. You will have a patient that will not wake up all of the way. It will happen. It is one of the risks that you assume. XXIII. Lingual nerve is easy target [S23] a. The nerve that is most often affected by damage is the lingual nerve. Why is that? b. Well, it has fewer fascicles to it and probably, a little bit of damage to a nerve with a lot of fascicles on it might even go unnoticed. This isn’t the case for the lingual nerve. How can you tell if your needle has penetrated the lingual nerve? i. Well, the patient feels an electric shock in the distribution of that nerve – in their tongue. It turns out that local anesthetics cause a lot of damage. They are not nice chemicals. XXIV. Clinical Tip – Drawing of numb area [S24] XXV. Local Anesthetics are Myotoxic and Neurotoxic [S25] Neuro: 8:00 - 9:00 Scribe: David Davis Friday, January 22, 2009 Proof: Molly Clark Dr. Eleazer Selecting Local Anesthetics Page 4 of 6 a. They, themselves, are myotoxic and neurotoxic. If you inject it into a muscle, you will kill part of that muscle and that patient will have trismus. That patient will not be able to open well and have pain. Those patients need to be treated with warm compresses, reassurance, and muscle stretching exercises. It is so much better to not inject into the muscles. b. The ones that you inject into the nerve – most will recover. Some won’t. Using the stronger, higher concentrations of local anesthetics increases the risk. How can you tell that you are in a nerve? The electric shock feel. XXVI. Clinical Tips – Do NOT [S26] a. If the patient feels an electric shock, don’t inject right there. Furthermore, don’t use that needle that is dull. When you touch bone with a needle, you have bent over the tip of it. Just put a new needle on. If you inadvertently pass the needle through the nerve and if you did it with a sharp needle, the damage would be less. b. If you have to push hard, you might be in a muscle. Don’t inject there either. Avoid these risks rather than addressing them after the fact. Don’t inject where they feel the shock, don’t push hard and do use a sharp needle. XXVII. Nodes of Ranvier [S27] a. Nodes of Ranvier – we talked about them and I took a little trip back to nerd-ville one day and tried to decide how long that myelin section is. What is the spacing or intervals between the nodes of Ranvier? It turns out that it is hard to find that information. i. The best information that I can get says that it is about 3 millimeters. b. That means that I want to inject and make a puddle of anesthetic so I can get at least three of those nodes. That means about 10 millimeters. I would really like to get a bit more. c. I want to have the best odds that I can get. XXVIII. Nodes of Ranvier [S28] a. I made this little drawing that illustrates that – I was pretty bored one night. It gives you the concept that there are spaces between the nodes where your anesthetic can get to. b. It also gives you the concept that the myelin may act like an insulation on an electric wire and protect that current inside the wire. Yes, it does have those little breaks and those are the only things that give me an advantage as a clinician – those nodes of Ranvier. c. XXIX. Clinical Tip – Need at least 3 Nodes [S29] a. More is better. If you were rabbit hunting with a shotgun, would you wait until the rabbit was halfway into his hole before shooting or would you shoot the rabbit when you had the entire pattern of the shot around the rabbit? It is pretty easy to say that you would like as much of an opportunity to hit the rabbit as you could, right? b. You wouldn’t want to be following this rabbit with this potential, round pattern and now he is halfway into his hole. Half of the shot goes into the ground. I am trying to bathe as great of length of nerve that I can. c. If you inject right where the nerve (inferior alveolar nerve) goes into the mandibular canal, then you have changed your odds a bit. It is probably a good idea to do what they do in the Air Force – aim high. Shoot for your main target a little above of where that hole is. XXX. Bathe More Nerve [S30] a. These are frog nerves or squid nerves in the laboratory. They basically bathed different lengths of nerve and measured how much of the voltage they apply on one end passes the nerve block. b. That clearly says that more nerve equals better nerve conduction blockage. The numbers are relative but the principle is the same. XXXI. Gow Gates – View from the Cervical Spine [S31] a. Here is a clear skull. b. I wrote it wrong. It is the foramen ovales. The spacing between the foramen ovales and the spacing between the mandibular canal entrances are substantially different. c. Think of those green pipe cleaners as the inferior alveolar nerve. d. That isn’t exactly the right anatomy but the principle is that in the pterygomandibular space, the nerve doesn’t hug the bone and all of a sudden translate horizontally. e. If you are going to inject high, you aren’t right at the bone. How can you tell where the bone is? The best way is to touch it with a needle. Now, you have made it a cookie cutter. Life isn’t perfect. That is a good reason to put a new needle on. XXXII. Pharmacology [S32] a. Let’s talk about some principles of pharmacology. b. pH – If you inject a more acidic solution, it will hurt more. I am trying to get a rapport going with a patient that I have never seen before. Neuro: 8:00 - 9:00 Scribe: David Davis Friday, January 22, 2009 Proof: Molly Clark Dr. Eleazer Selecting Local Anesthetics Page 5 of 6 c. pKa is great though because it tells us about the dissociation of different anesthetics. Those are the two keys there. d. Lipid solubility talks about how well a local anesthetic will diffuse into the tissue. e. Protein binding gives us some idea of how long the local anesthetic will linger in the tissues. f. There is the concept of toxicity. Someone will ask you what is the maximum number of cartridges of local anesthetic that you can give the patient. The answer is that it depends. g. My challenge for your guys is to read the little fine print that comes with the local anesthetic. h. I would love for you to read that package insert. It will say the same thing on all of the local anesthetics. It will say that it is a CNS depressant. These CNS depressants can cause respiratory depression, can cause anaphylactic reactions. That is a really good reason for us to not allow dental hygienists to give injections. i. They don’t have the background that you guys have and they are not equipped to deal with emergencies. XXXIII. pH [S33] a. pH is scientific notation. It is an abbreviation. It is easy for us to lose sight of that. Because it is an abbreviation, a little difference in number can make a huge difference. Would you rather be in an earthquake of magnitude of 6 on the Richter scale or would you rather be in one of 7? Let’s take 6 because it isn’t one number, it is a 10-fold difference. A pH of 7 is 10 times more basic than a pH of 6/ b. When we start thinking about the pHs of our local anesthetics, little numbers make a lot of difference. XXXIV. pH is a logarithm [S34] XXXV. On the Richter Scale….. [S35] XXXVI. In the logarithmic systems…. [S36] XXXVII.Clinical Tip – Less Acidic Anesthetic [S37] a. I will tell you that I love Citanest as my first shot because it has a pH that is closest to the natural pH of the tissue. That is just a fact. b. You can inject an acidic solution so slowly that it is essentially painless. I, however, am not that patient of a guy. I can’t sit there for two minutes with a needle in there easing it in there drop by drop. I need an advantage and I need the pH to be a good one. XXXVIII. Plain Citanest pH = 6.0 – 7.0 [S38] a. Any anesthetic with a vasoconstrictor in it has to be acidified as a way of stabilizing that vasoconstrictor such as epinephrine. The fine print will say that the pH of citanest with no vasoconstrictor varies from 6.0 to 7.0. They do that simply for the FDA. Every time that I have measured it, it has been 6.5. Anytime that I measure carbocaine with no vasoconstrictor, the pH has been 5.3. They hit it right in the middle. b. So, let me have the most favorable local anesthetic solution for my first shot. c. It also turns out that carbocaine without a vasoconstrictor is in 3 percent concentration while whereas citanest is in 4. I am assuming liability of that patient not waking up if I inject into the wrong place. d. I use the patient as a mixing vessel. It is my goal here to convey to you that there isn’t one anesthetic here that you can buy. e. You should have, maybe, all five of them at your disposal because different patient situations will vary. XXXIX. pKa [S39] a. So, pKa – that is the pH at which 50 percent is in the ion form and 50 percent is in the base form. We talked about that earlier. b. Every chemical has this pKa. We can’t change it. We can use it to decide which one we want. c. Let’s say that for the average patient, the tissue pH is 7.4. 7.4 is a good average but it isn’t accurate for every patient. d. There are some medical conditions where the tissue pH changes. Patients can walk around with some degree of acidosis. Those patients are going to come see us so I need to know about their medical history. XL. Ideal [S40] a. Let’s just say that the ideal tissue pH is 7.4 and the anesthetic’s (I’m sorry that is a misprint – the pKa would be 7.4), but in reality, all together this is what we get. XLI. Reality [S41] a. Carbocaine wins the race as the most favorable pKa – 7.6. We can’t change it. b. Everyone loves septocaine because it is great in diffusion. It has great lipid solubility. c. Good ole lidocaine, xylocaine, with a pKa of 7.9 - pretty good. d. Citanest – it is just the same as xylocaine. Why do I like it better? For its pH. So, my first shot is going to be citanest plain, with no vasoconstrictor. My second shot is going to be carbocaine with a vasoconstrictor. Carbocaine with a vasoconstrictor is going to be 2 percent. Marcaine – wonderful, long lasting anesthetic. Protein binding – hangs in the tissue for a long period of time. It also has some lingering nerve function decrease when the feeling seems to wake up. If you are doing a painful procedure, a final injection of Marcaine might not be a bad idea. It might be great. Neuro: 8:00 - 9:00 Scribe: David Davis Friday, January 22, 2009 Proof: Molly Clark Dr. Eleazer Selecting Local Anesthetics Page 6 of 6 e. There is poor Novocain. Its pKa is 9.1. No wonder it is such a sorry anesthetic. XLII. Normal Tissue pH [S42] a. Let’s take a concept here. We are really injecting 10 to the 23 ions in a cartridge. b. Let’s just say that we are injecting just a thousand ions. It undergoes this henderson-hasselbalch equation at 25 percent dissociation at this pH situation. You get 250 bases and those go through the nerve membrane where they undergo another dissociation back and you guys have to help me out with the henderson-hasselbalch equation because I don’t know if that is 75 percent or 25 percent. It doesn’t really matter. The principle is that it has to go under another henderson-hasselbalch equation so we are losing ground. c. You inject 1,000 – you only have about 188 ready to go to work for you in a normal tissue pH with plain xylocaine. XLIII. Carbocaine wins [S43] a. Carbocaine at 40 percent dissociation gives me 400 instead of 250 so I will wind up with 240 instead of 188. b. Most of the time I can get by with lidocaine. Sometimes, I need a little bit of an advantage and that is why I like carbocaine as my second injection, XLIV. Clinical Tip – Select anesthetic with lowest pKa [S44] XLV. Acidic Tissue [S45] a. Now, let’s throw in an acidic environment and the world changes drastically. b. Local anesthetic injected into tissue acidosis such as you get with an abscess means that the anesthetic effect is horrible. It is almost nonexistent. c. Because of this henderson-hasselbalch equation and that is in a tissue with a pH of 6, it often goes to 4. d. It is hard to do less than 10. 1 percent dissociation. XLVI. Clinical Tip – Use BLOCK anesthesia [S46] a. The last thing I will leave you with. The concept there and maybe you want to read some more of the handout, the concept that I will leave you with is that if you are dealing with an abscess, you need to use block anesthesia. b. Never inject into an abscess. Make sure that it says you injected peripherally to the abscess in your chart notes. c. You are not going to get good anesthesia that way. Your best chance is with a block anesthesia. d. That is a whole new topic and we might get to that another day and that is why you learn gross anatomy. e. There is a lot more to know about anesthesia. It is what makes or breaks you in practice. f. If you are a dentist, you have to start the game. You have to win them over by getting them numb and getting them comfortable. Sometimes, that requires more than just a local anesthetic, but it always requires a careful history. i. How do you deal with anesthesia? Do you ever have any problems? ii. If yes, you need to ask a lot more questions. Is it an allergic reaction? If so, to which ingredient? Is it a toxicity reaction? That doesn’t have to be dose related especially anaphylaxis. g. Truism of medicine is that your patient will tell you what you want to know, but it might take them a while. You have to be a careful listener to figure out what they are saying. Getting to know your patient is an important part of practice.

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