SGEM#307: Buff up the lido for the local anesthetic

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Date: October 29th, 2020

Guest Skeptic: Martha Roberts is a critical and emergency care, triple-certified nurse practitioner currently living and working in Sacramento, California. She is the host of EM Bootcamp in Las Vegas, as well as a usual speaker and faculty member for The Center for Continuing Medical Education (CCME). She writes a blog called The Procedural Pause for Emergency Medicine News and is the lead content editor and director for the video series soon to be included in Roberts & Hedges‘ Clinical Procedures in Emergency Medicine.

Reference: Vent et al. Buffered lidocaine 1%, epinephrine 1:100,000 with sodium bicarbonate (hydrogencarbonate) in a 3:1 ratio is less painful than a 9:1 ratio: A double-blind, randomized, placebo-controlled, crossover trial. JAAD (2020)

Case: A 35-year-old female arrives to the emergency department with a 3 cm laceration to the palmar surface of her left forearm sustained by a clean kitchen knife while emptying the dishwasher. The patient reports a fear of needles and has concerns about locally anaesthetizing the area because, “I got stitches on my arm once before and that shot burned like crazy”! The patient asks the practitioner if there is any chance, she can get a shot that “burns less” than her last one.

Background: We have covered wound care a number of times on the SGEM. This has included some myth busing way back in SGEM#9 called Who Let the Dogs Out.

That episode busted five myths about simple wound care in the Emergency Department:

Patients Priorities: Infection is not usually the #1 priority for patients. For non-facial wounds it is function and for facial wounds it is cosmetic. This is in contrast to the clinicians’ #1 priority that is usually infection.
Dilution Solution: You do not need some fancy solution (sterile water, normal saline, etc) to clean a wound. Tap water is usually fine.
Sterile Gloves: You do not need sterile gloves for simple wound treatment. Non-sterile gloves are fine. Save the sterile gloves for sterile procedures (ex. lumbar punctures).
Epinephrine in Local Anesthetics: This will not make the tip of things fall off (nose, fingers, toes, etc). Epinephrine containing local anesthetics can be used without the fear of an appendage falling off.
All Simple Lacerations Need Sutures: Simple hand lacerations less than 2cm don’t need sutures. Glue can be used in many other areas including criss-crossing hair for scalp lacerations.

Other SGEM episodes on wound care include:

SGEM#63: Goldfinger (More Dogma of Wound Care)
- This episode looked at how long do you have to close a wound. The bottom line was that there is no good evidence to show that there is an association between infection and time from injury to repair.

SGEM#156: Working at the Abscess Wash
- The question from that episode was: does irrigation of a cutaneous abscess after incision and drainage reduce the need for further intervention? Answer: Irrigation of a cutaneous abscess after an initial incision and drainage is probably not necessary.

SGEM#164: Cuts Like a Knife – But you Might Also Need Antibiotics for Uncomplicated Skin Abscesses.
- SGEM Bottom Line: The addition of TMP/SMX to the treatment of uncomplicated cutaneous abscesses represents an opportunity for shared decision-making.

The issue of buffering lidocaine was covered on SGEM #13. This episode briefly reviewed a Cochrane SRMA that looked at buffering 9ml of 1% or 2% lidocaine with 1ml of 8.4% sodium bicarbonate (Cepeda et al 2010).

The SRMA of buffering lidocaine contained 23 studies with 8 of the 23 studies having moderate to high risk of bias. The SGEM bottom line was that patients might appreciate the extra effort of buffering the lidocaine.

Interestingly, this Cochrane Review was withdrawn from publication in 2015. The reason provided was that the review was no longer compliant with the Cochrane Commercial Sponsorship Policy. The non-conflicted authors have decided not to update the review.

Clinical Question: Does buffering lidocaine with sodium bicarbonate make local anesthetic less painful?

Reference: Vent et al. Buffered lidocaine 1%, epinephrine 1:100’000 with sodium bicarbonate (hydrogencarbonate) in a 3:1 ratio is less painful than a 9:1 ratio: A double-blind, randomized, placebo-controlled, crossover trial. JAAD (2020)

Population: Healthy volunteers age 18-75 years of age
- Exclusions: Hypersensitivity or allergies to local anesthetics of the amide type or to auxiliary substances such as sulfites, pregnant, damaged skin on the arms, or inability to give informed consent.
Intervention: IMP (investigational medicinal products) were injected 5cm distal from the cubital fossa
- IMP1: 1% lidocaine with epinephrine plus sodium bicarbonate in a 3:1 mixing ratio
- IMP2: 1% lidocaine with epinephrine plus sodium bicarbonate in a 9:1 mixing ratio
- IMP3: 1% lidocaine with epinephrine
Comparison: Placebo of 0.9% sodium chloride (IMP4)
Outcomes:
- Primary Outcome: Pain during infiltration on a numerical rating scale (0-10, with 0=no pain and 10=unacceptable pain)
- Secondary Outcomes: Patient comfort during infiltration (four categorical terms: desirable, acceptable, less acceptable or unacceptable) and duration of local anesthesia (30-minute intervals up to 3 hours) using a standardized laser stimulus (numbness yes or no?)

Authors’ Conclusions: “Lido/Epi-NaHCO3 mixtures effectively reduce burning pain during infiltration. The 3:1 mixing ratio is significantly less painful than the 9:1 ratio. Reported findings are of high practical relevance given the extensive use of local anesthesia today.”

Quality Checklist for Randomized Clinical Trials:

The study population included or focused on those in the emergency department. No
The patients were adequately randomized. Yes
The randomization process was concealed. Yes
The patients were analyzed in the groups to which they were randomized. Yes
The study patients were recruited consecutively (i.e. no selection bias). Unsure
The patients in both groups were similar with respect to prognostic factors. Unsure
All participants (patients, clinicians, outcome assessors) were unaware of group allocation. Unsure
All groups were treated equally except for the intervention. Yes
Follow-up was complete (i.e. at least 80% for both groups). Yes
All patient-important outcomes were considered. Yes
The treatment effect was large enough and precise enough to be clinically significant. Unsure

Key Results: They enrolled 48 healthy volunteers, 21 males and 27 females aged 21-62 with a mean age of 31 years.

Buffering lidocaine made injections less painful

Primary Outcome: Pain during infiltration
- IMP1 (3:1 mixture) was less painful than IMP2 (9:1 mixture)
- IMP3 (unbuffered) was more painful than IMP1 or IMP2
- IMP4 (placebo) was more painful than IMP1-3
Secondary Outcomes:
- Patient Comfort Discomfort During Infiltration: IMP1 (3:1 mixture) had the least reported discomfort and IMP4 (placebo group) reported the most discomfort.
- Duration of Local Anesthetic: Laser-induced pain was absent in the injection areas for IMP1-3 (intervention groups) between 5 minutes and 3 hours after infiltration but not for IMP4 (placebo)

1) External Validity: These healthy volunteers with a mean age of 31 years may not represent the patients we see for simple wound repairs in the emergency department. We do not know any details about the volunteers except their age and self-identified gender. The study was also conducted in Germany. Cultural and social factors can play a role in the perception of acute and chronic pain (Peacock and Patel 2018, MM Free 2002 and MM Free 2012).

2) Blinding: Local anesthetic hurts. If the patients were aware of the hypothesis (buffering lidocaine to minimize pain), this could have biased the subjective self-reporting for the primary outcome to have a larger effect size.

3) Sample Size: This was a relatively small study with only 48 volunteers. Are the results large enough (3 points on an NRS value) and precise enough (no 95% CI were provided for the point estimates) to be clinically relevant?

4) Shelf-Life: We stock large bottles of sodium bicarbonate and would usually only require a small amount to buffer the amount of lidocaine needed to treat a single patient. This could lead to a great deal of waste. Sodium bicarbonate is not expensive but take a small number and multiply it by a big number (number of simple wound repairs done per day) can end up being a large number. One way around that would be to mix-up a larger amount at the start of a shift. However, the stability of the buffered lidocaine-sodium bicarbonate solution is limited. It would be great if a stable commercial product was available in the <10ml solutions we typically require.

5) Alternatives: There are other methods that can be used to minimize the pain of local anesthetic injection. Those includes but are not limited to L.E.T. (lidocaine, epinephrine and tetracaine) used topically.

Comment on Authors’ Conclusion Compared to SGEM Conclusion: We agree that buffering lidocaine with sodium bicarbonate decreases pain during infiltration and that a 3:1 mixture is better than a 9:1 mixture. We are not as sure of the “high” practical relevance due to the issues mentioned in nerdy point #4.

SGEM Bottom Line: Consider buffering your lidocaine with a 3:1 sodium bicarbonate mixture to decrease the discomfort of local anesthetic infiltration.

Case Resolution: You inform her that there is a way to make the local injection burn less. You mix up your 1% lidocaine in a 3:1 mixture with sodium bicarbonate. She leaves very happy with post-suture instructions.

Clinical Application: If the patient expresses fears about the anesthetic injection, buffering the lidocaine may be a suitable option. The practical aspects of how sodium bicarbonate comes (volume) and short shelf life limit the generalizability to use in all patients at this time.

Martha Roberts

What Do I Tell My Patient? I want to make sure you are all numbed up around your cut. This will make it easier for you and for me to do the stitches. I know the “freezing” can really burn and this can be scary for many people. I can buffer the injection with something called bicarb. Mixing it with the lidocaine can help lessen the burn and pain from injection.

Keener Kontest: Last weeks’ winner was Dr. Steven Stelts from New Zealand. A back-to-back win. He knew the Simon Personal Communicatorwas produced by IBM in 1992, went on sale in 1993 and is widely credited as the first smartphone.

Listen to the SGEM podcast to hear this weeks’ question. Send your answer to TheSGEM@gmail.com with “keener” in the subject line. The first correct answer will receive a cool skeptical prize.