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The use of buffering agents in local anesthetics
Getting patients numb is one of my most favorite things to do. I know I am one of those weirdo’s but we all have our “thang”. But there are a few things about giving local that I don’t necessarily care for. Like seeing the patient flinch, pull back, and moan in pain because it burns or stings while the injection is happening. And I get frustrated with how long it can take some patients to get really numb.
I don’t think I am the only one who feels this way either. I’m often asked about ways to help increase our patients comfort with anesthetic or for tips on achieving profound anesthesia in a timely manner.
As we know, the pain of getting numb is often the reason why patients, and some clinicians, choose to avoid the needle. There are very few people who want to feel pain or be the cause of it, especially in the dental setting. Then we as clinicians have the other “pain”, which is feeling the loss of time as we wait to see if the injection worked.
Well, my friends, there is one solution for both questions. And that is using a buffering agent.
To understand why buffering is useful, first we need to dive into some of the pharmacology of local anesthetics.
One reason patients feel pain with anesthesia is due to the acidity of the solution. In general, local anesthetic solutions have an acidic pH of 4 or less. And some are even as low as a pH of 3.0, similar to a lemon. Have you ever had lemon juice come across a papercut or scratch on your hand? I have, and yeah it STINGS!
So when it enters the neutral 7.0 pH of the oral tissues, our patients can feel that same sensation. If you haven’t noticed, when you look at the anesthetic cartridge label you will see these three little letters, HCL. That stands for hydrochloric acid. HCL is important because it allows the anesthetic to be water soluble, so we can inject the fluid. But it is like the name says acidic. You will see that on every cartridge if it’s a plain anesthetic or not. Adding vasoconstrictor to our anesthetic solution, makes it even more so.
Vaso’s are wonderful for our anesthetic solution. They keep the blood vessels constricted limiting how much can enter the blood stream. This is a great safety feature for our patients, and it also keeps our patient numb for a longer period. The drawback is in order to keep the vasoconstrictor stable and extend the shelf life of anesthetic solutions another acidic item is added, Sodium Metabisulfite. Making an already acidic solution even more so. This is why anesthetics with vasoconstrictor really have the “ouch” factor.
Now that I’ve reviewed why the sting of the shot is present, now lets dive into what needs to happen for our anesthetic solution to work on the nerve. And it is related to the pH of the solution.
Without getting to “sciencey” it’s important to know that the anesthetic molecule has two major components, a neutral base and hydrogen ion, which work together to stop the flow of neural communication. In order for the anesthetic to work, it needs to break apart creating a free neutral (lipid loving) base and a hydrogen ion. This allows the base to enter the nerve axon. Once the base is inside the cell it will attach to another free floating hydrogen ion and reform the active molecule. This reformed molecule will block the sodium channel pump in the nerve cell wall. If the pump is blocked, the word about pain happening won’t get out. So, we have disrupted the pain signaling response by stopping the communication.
Ok…back to the hydrogen ion. It is the free-floating hydrogen ions which already exist in the anesthetic solution that cause the stinging sensation of the injection and slow down the anesthetics capability to enter the nerve cell to stop the pain response. Increasing the onset time of the anesthetic solution. If there are a lot of hydrogen ions, then the base has a harder time staying single long enough to enter the nerve cell.
I said earlier that the current answer to these problems is the use of buffering agents. Buffering solution is primarily made of sodium bicarbonate. This basic salt counteracts the acidic salts of the anesthetic. It raises the pH of the anesthetic solution closer to the body’s natural pH of 7.4. Now the sting of the solution is gone. As a bonus, it allows the anesthetic molecules to enter the nerve cell at a quicker more efficient rate. All because those free-floating hydrogen ions are now hooking up with the sodium bicarbonate solution. This in turn reduces the time needed for profound anesthesia. Within just a couple of minutes you know if your patient is ready for treatment.
At the time of this writing there are two different companies who provide buffering solution options to the dental office. There are even some clinicians who choose to create their own solution. Which is better? Well, that my friend is a discussion for a different time.
It doesn’t matter the reason for the injection. If it’s for restorative, hygiene therapy, or extractions this is something, as oral health clinicians, we should consider incorporating into our pain management set-up. It may not make the injection process the exciting event of the year, but our patients will appreciate the comfort it brings, and we will enjoy the extra time to provide quality treatment to our patients.
Now go out there and HIT YOUR BEST SHOT!
Cheers,
Tina
Plus, if you want more Anesthesia information and get CE credit for it to head to https://teachertina.thinkific.com/