Buffered Local Anaesthetic: Difference between revisions
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The administration of local anaesthetic can be painful. There are many factors that increase influence pain. These are needle insertion, pH of the solution, temperature of the solution, and pressure from fluid distension. | The administration of local anaesthetic can be painful. There are many factors that increase influence pain. These are needle insertion, pH of the solution, temperature of the solution, and pressure from fluid distension. In the US, many doctors routinely buffer their lidocaine as an evidence based way to reduce patient discomfort. In the authors experience, it is relatively unknown in New Zealand and this low usage rate is believed to be based on cultural factors rather than the evidence. | ||
[[Lidocaine]] is a weakly basic amid and is unstable at its pH of 7.9. It is therefore prepared in acidic formulations to increase stability and shelf life, with a resultant pH of 4. | ==Pharmacological Basis== | ||
[[Lidocaine]] is a weakly basic amid and is unstable at its pH of 7.9. It is therefore prepared in acidic formulations to increase stability and shelf life, with a resultant pH of 2.5-4.0. This acidity, which is 1000 times more acidic than physiological pH, can cause tissue irritation with a stinging or burning pain. | |||
In addition, raising the pH increases the amount of the non-ionized (active) form, and reduces the charged hydrophilic (non-active) form. The active form readily permeates the nerve membrane, and at the physiological pH, there are 2,500 more of the active form than at a pH of 3.8. With non-buffered lidocaine, the body has to first naturally buffer the solution which causes a longer duration of burning.<ref name="vent"/> | |||
When sodium bicarbonate is mixed with an acidic lidocaine solution, water and carbon dioxide are formed. CO₂ has an independent direct local anaesthetic effect, and it enhances the action of lidocaine. CO₂ directly deactivates the nerve axon, and indirectly increases the anaesthetic effect by changing its electrical charge. | |||
A common mixture is | ==Evidence== | ||
There have been many studies that have looked at buffering lidocaine with sodium bicarbonate to reduce its acidity. Sodium bicarbonate is safely metabolised by the kidneys. A Cochrane review in 2010 included 23 studies, and found that increasing the pH of lidocaine decreased pain with infiltration. Parallel group studies include 2 independent groups receiving different treatments, whereas in crossover trials, each patient receives both treatments. The difference was -1.98 on a 0 to 10 scale in the cross-over studies, and -0.98 in the parallel group studies. There was a greater decrease in pain when the injectate contained adrenaline. Patients also preferred buffered lidocaine. It was safe with no adverse events or toxicity. Buffering also does not reduce the anaesthetic effect.<ref>{{#pmid:21154371}}</ref> | |||
A common mixture is 9:1 of 1% lidocaine and 8.4% sodium bicarbonate. It can also be used with adrenaline. Various other ratios have been used (10:1 - 5:1). More recently an RCT of 48 participants found that a 3:1 mixing ratio was significantly less painful than a 9:1 ratio. Median numerical pain ratings where 2.0 for 3:1, 3.0 for 9:1, 4.5 for unbuffered, and 6.0 for normal saline. While both a 9:1 and 3:1 solution effectively neutralises the pH, it is thought that the extra CO₂ that is produced in the 3:1 could explain the extra analgesic effect. In the 48 participants, one person had a deep subcutaneous nodule that disappeared after two months, and five people had local tenderness for 1-2 days.{{#pmid:31958526|vent}} | |||
==References== | ==References== | ||
Revision as of 22:14, 13 April 2021
The administration of local anaesthetic can be painful. There are many factors that increase influence pain. These are needle insertion, pH of the solution, temperature of the solution, and pressure from fluid distension. In the US, many doctors routinely buffer their lidocaine as an evidence based way to reduce patient discomfort. In the authors experience, it is relatively unknown in New Zealand and this low usage rate is believed to be based on cultural factors rather than the evidence.
Pharmacological Basis
Lidocaine is a weakly basic amid and is unstable at its pH of 7.9. It is therefore prepared in acidic formulations to increase stability and shelf life, with a resultant pH of 2.5-4.0. This acidity, which is 1000 times more acidic than physiological pH, can cause tissue irritation with a stinging or burning pain.
In addition, raising the pH increases the amount of the non-ionized (active) form, and reduces the charged hydrophilic (non-active) form. The active form readily permeates the nerve membrane, and at the physiological pH, there are 2,500 more of the active form than at a pH of 3.8. With non-buffered lidocaine, the body has to first naturally buffer the solution which causes a longer duration of burning.[1]
When sodium bicarbonate is mixed with an acidic lidocaine solution, water and carbon dioxide are formed. CO₂ has an independent direct local anaesthetic effect, and it enhances the action of lidocaine. CO₂ directly deactivates the nerve axon, and indirectly increases the anaesthetic effect by changing its electrical charge.
Evidence
There have been many studies that have looked at buffering lidocaine with sodium bicarbonate to reduce its acidity. Sodium bicarbonate is safely metabolised by the kidneys. A Cochrane review in 2010 included 23 studies, and found that increasing the pH of lidocaine decreased pain with infiltration. Parallel group studies include 2 independent groups receiving different treatments, whereas in crossover trials, each patient receives both treatments. The difference was -1.98 on a 0 to 10 scale in the cross-over studies, and -0.98 in the parallel group studies. There was a greater decrease in pain when the injectate contained adrenaline. Patients also preferred buffered lidocaine. It was safe with no adverse events or toxicity. Buffering also does not reduce the anaesthetic effect.[2]
A common mixture is 9:1 of 1% lidocaine and 8.4% sodium bicarbonate. It can also be used with adrenaline. Various other ratios have been used (10:1 - 5:1). More recently an RCT of 48 participants found that a 3:1 mixing ratio was significantly less painful than a 9:1 ratio. Median numerical pain ratings where 2.0 for 3:1, 3.0 for 9:1, 4.5 for unbuffered, and 6.0 for normal saline. While both a 9:1 and 3:1 solution effectively neutralises the pH, it is thought that the extra CO₂ that is produced in the 3:1 could explain the extra analgesic effect. In the 48 participants, one person had a deep subcutaneous nodule that disappeared after two months, and five people had local tenderness for 1-2 days.[1]
References
- ↑ 1.0 1.1 Vent et al.. Buffered lidocaine 1%/epinephrine 1:100,000 with sodium bicarbonate (sodium hydrogen carbonate) in a 3:1 ratio is less painful than a 9:1 ratio: A double-blind, randomized, placebo-controlled, crossover trial. Journal of the American Academy of Dermatology 2020. 83:159-165. PMID: 31958526. DOI.
- ↑ Cepeda et al.. Adjusting the pH of lidocaine for reducing pain on injection. The Cochrane database of systematic reviews 2010. CD006581. PMID: 21154371. DOI.
Literature Review
Literature Review
- Reviews from the last 7 years: review articles, free review articles, systematic reviews, meta-analyses, NCBI Bookshelf
- Articles from all years: PubMed search, Google Scholar search.
- TRIP Database: clinical publications about evidence-based medicine.
- Other Wikis: Radiopaedia, Wikipedia Search, Wikipedia I Feel Lucky, Orthobullets,
