Posts tagged #local anesthetic

Hand Nerve Blocks

**Written by:** Aldo Gonzalez, MD (NUEM ‘23) **Edited by:** Jason Chodakowski, MD (NUEM '20)
**Expert Commentary by**: Mike Macias, MD

Hand Nerve Blocks

Nerve blocks are the use of anesthetics to anesthetize an area by injecting directly around the nerve that innervates a certain area. It is useful when there is a large area to provide anesthesia, the area might get distorted by local infiltration and make it difficult to close the tissue, or the distribution of the area to be anesthetized is well-suited to a nerve block.

Indications

Nerve blocks of the median, ulnar, radial, and digital nerves are useful for injuries of the hand including fractures, lacerations, and burns.

Contraindication

Overlying infection
Previous allergic reaction to anesthetic

Anesthetics

Landmark versus Ultrasound guidance

Ultrasound guidance is preferred given the ability to visualize the desired nerve and proper instillation of the anesthetic around the nerve. On ultrasound nerves are circular or triangular hyperechoic structures with hypoechoic structures within. Often described as having a “honeycomb” appearance as seen in the image of the median nerve below.

Materials

Ultrasound with Linear Transducer
Probe Cover
Sterile Ultrasound Gel
Anesthetic
10 cc syringe
18 gauge needle (to draw medication)
25-27 gauge needle at least 1.5 in in length
Antiseptic Solution (ex. Chlorhexidine)
Towel

Positioning

The patient can be either supine or seated with their arm slightly abducted and rested on a flat surface. Their elbow can be flexed with the wrist supinated and in slight extension. A rolled towel can be used for patient comfort and help in maintaining slight extension.

Figure 1: Nerves, arteries, and muscles of the human forearm

Radial Nerve Block

The superficial radial nerve travels between the flexor carpi radialis and the radial artery on anterior (volar) and lateral (radial) aspect of the forearm. Near the wrist the radial nerve splits into the medial and lateral branch of the superficial radial nerve. The block of this nerve should be performed at the mid-forearm to distal third of the forearm before the nerve splits. The nerve may be difficult to see at the distal forearm so instead it can be found proximally and followed distally. A lateral (radial) approach of the forearm provides the most direct route to the nerve.

Ulnar Nerve Block

At the distal forearm the ulnar nerve runs on the medial (ulnar) and anterior (volar) aspect of the forearm between the flexor carpi ulnaris tendon and the ulnar artery. The ulnar nerve lies in very close proximity to the ulnar artery in the distal forearm and increases the risk of accidental intravascular injection. It is safer to identify the ulnar nerve distally and the follow the artery and nerve proximally. Around the proximal third of the forearm the ulnar artery dives deeper and separates from the ulnar nerve. This provides a safer target. A medial (ulnar) approach of the forearm provides the most direct route to the nerve.

Median Nerve Block

At the mid to distal forearm the median nerve runs in the middle of the anterior (volar) aspect of the forearm between the flexor digitorum superficialis and flexor digitorum profundus muscles/tendons. Near the wrist the nerve can be difficult to appreciate due to all the tendons of the anterior compartment of the arm. The nerve can be best appreciated at the mid-forearm. A lateral (radial) or medial (ulnar) approach can be used for in-plane technique or a mid-line approach using out-of-plane technique. Be mindful to avoid accidentally puncturing the radial or ulnar artery If using an in-plane technique with a lateral or medial approach.

Figure 5: Demonstration of a median nerve block using a median (ulnar) approach with in-plane ultrasound technique on a patient’s right hand. Median nerve (yellow line) and ultrasound probe location (blue line).

Figure 6: Demonstration of a median nerve block using a lateral (radial) approach with in-plane ultrasound technique on a patient’s right hand. Median nerve (yellow line) and ultrasound probe location (blue line).

Steps for Ultrasound-Guided Nerve Block

Document a neurological exam prior starting the procedure
Select the nerve or nerves best suited to achieve best anesthesia for the injury
Use the linear transducer to visualize the nerve prior beginning the procedure
Plan an approach and select the best site
Draw up anesthetic in the 10 cc syringe with an 18 G needle
Replace 18 G needle with 25-27 G needle
Use antiseptic solution to prepare the skin
Dawn sterile gloves
Cover transducer in sterile cover
Use ultrasound to visualize the nerve and confirm approach
Insert the needle into the skin
Advance the needle using in-plane or out-of-plane technique
Come close to the nerve but do not puncture the nerve
Draw back to confirm not with-in a vessel
Deliver 5mL of anesthetic
The nerve will become enveloped in hypoechoic anesthetic and peel away from the fascia of nearby muscles
Withdraw the needle.
Wait 3-5 minutes until patient is fully anesthetized

References

Drake, R., Vogl, A. W., & Mitchell, A. W. (2015). Gray's Anatomy for Students (3rd ed.): Elsevier.
Farag, E., Mounir-Soliman, L., & Brown, D. L. (2017). Brown’s Atlas of Regional Anesthesia (5th ed.): Elsevier.
Gray, H. (2000). Gray's Anatomy of the Human Body. 20th edition. Retrieved from https://www.bartleby.com/107/
Harmon, D., Barrett, J., Loughnane, F., Finucane, B. T., & Shorten, G. (2010). Peripheral Nerve Blocks and Peri-Operative Pain Relief (2nd ed.): Elsevier.
Pester, J. M., & Varacallo, M. (2019). Ulnar Nerve Block Techniques. In StatPearls [Internet]: StatPearls Publishing.
Roberts, J. R., Custalow, C. B., & Thomsen, T. W. (2019). Roberts and Hedges' clinical procedures in emergency medicine and acute care (7th ed.): Elsevier.
Waldman, S. D. (2016). Atlas of Pain Management Injection Techniques E-Book (4th ed.): Elsevier.
Waldman, S. D. (2021). Atlas of Interventional Pain Management E-Book (5th ed.): Elsevier.

Expert Commentary

Thank you Drs. Gonzalez and Chodakowski for the excellent post on forearm nerve blocks! This is an important skill that definitely improves the care of our patients, especially since hand injuries are such a common emergency department presentation. This is especially true for injuries that are difficult to anesthetize using traditional local injection such as dog bites, burns, abscesses, large lacerations, and fractures of the hand. I’d like to dive a little deeper into a few aspects of forearm nerve blocks:

Ultrasound guidance

I think that the days of a landmark based approach to the majority of nerve blocks are gone with the widespread availability of ultrasound and its superiority with respect to block success and reduced complications. So if you have it, use it!

Which nerve to block?

Once you have made the commitment to block one forearm nerve, it doesn’t require much additional time or effort to block a second or even a third! Often, hand injuries will span several nerve distributions so make sure you are providing adequate anesthesia. Here is a quick way to think of it:

Major hand injury (ie burn, multiple hand fractures): Triple block
Injury to radial aspect of hand or digits 1-4: Radial + median nerve block
Injury to ulnar aspect of hand or 5th digit (ie Boxer’s fracture): Ulnar nerve block

It is important to remember that forearm nerve blocks do not provide anesthesia to the volar forearm or wrist and therefore will not be adequate for distal radius fracture reduction. In this case, an above the elbow Radial nerve block should be performed.

Which local anesthetic should I use?

It’s always important to consider what the goals of your local anesthetic are when determining which one to use. If you are performing a quick procedure, the shorter the better such as lidocaine. If you are providing prolonged pain management such as with a burn, bupivicaine is a better choice. I tend to prefer lidocaine + epinephrine (duration of acton 2-2.5 hours) for most of my hand injuries. Why? In a busy emergency department managing many patients at a time, the initial block and the procedure you plan on performing (ie lac repair, fracture reduction, etc) do not always happen simultaneously (ie patient may still need x-ray, irrigation, ring removal, etc). Using lidocaine + epinephrine will allow you to provide immediate pain relief for your patient but give you time to do other tasks before the patient is ready for the procedure

Positioning

As with any procedure, the set up is extremely important. You nicely described positioning earlier but I just want to highlight a couple additional points. Make sure your patient is comfortable and your ultrasound screen is in-line with your procedure. You don’t want to be turning your head away from your block to look at the screen. For the median and radial nerve block, the patient’s arm should be supinated and resting on a hard flat surface. Both nerves can then be approached using an in-plane technique from the radial aspect of the arm. The ulnar nerve can be cumbersome to get to with this same patient positioning so I recommend abducting the shoulder to about 90 degrees and placing the arm on a Mayo stand next to the patient. This will allow an in-plane approach from the ulnar aspect of the arm. I have also found this positioning technique helpful for the ulnar nerve block.

Procedural Tips

I wanted to end with a couple of important procedural pearls I have learned during my experience with performing these blocks:

Perform a pre-block exam! Always make sure to perform and document a full neurological exam of the hand before you block any nerve. This is important because you want to make sure you know if any sensory or motor changes are present before your perform the block otherwise if a neurological deficit is noted after, it makes it difficult to tell if the block caused the new symptom (you can always wait until the anesthetic wears off but it may be awhile if you used bupivicaine).

Follow the arteries! Sometimes it can be tricky to find the ulnar and radial nerves. The easiest method is to always start distally at the wrist. Both the radial and ulnar nerves run with their paired artery so if you start here and slide proximally, you should see the nerve split away from the artery around the mid forearm. Block them here!
Target the fascial plane! The key to an effective forearm nerve block is “bathing” the nerve in anesthetic. You will want to see spread of the anesthetic around the nerve in a crescent shape, full circumferential spread is not needed. Since these nerves run in the fascial plane the goal is to get your needle tip into this plane to deposit anesthetic. There is never a need to actually touch the nerve so avoid this by aiming for the fascia and not the nerve.
Protect the hand! After you perform a forearm nerve block be sure to communicate with nursing, consultants, and the patient regarding what block was performed and how long the effects will last. If a long acting agent was used such as bupivicaine, the hand should be splinted or arm placed in a sling and instructions provided to patient regarding care at home if they are being discharged.

Thank you again for providing this excellent piece on forearm nerve blocks. I cannot stress enough how essential I think these blocks are to the toolkit of the modern emergency physician. I promise you once you add these to your practice your patient’s will thank you!

Michael Macias, MD

Global Ultrasound Director, Emergent Medical Associates

Clinical Ultrasound Director, SoCal MEC Residency Programs

How To Cite This Post:

[Peer-Reviewed, Web Publication] Gonzalez, A. Chodakowski, J. (2021, Nov 29). Hand Nerve Blocks. [NUEM Blog. Expert Commentary by Macias, M]. Retrieved from http://www.nuemblog.com/blog/hand-nerve-blocks

Lipid Emulsion Therapy for Local Anesthetic Systemic Toxicity

Written by: Dana Loke, MD (NUEM ‘20) Edited by: Jim Kenny, MD (NUEM ‘18) Expert Commentary by: Patrick Lank, MD, MS — **Written by:** Dana Loke, MD (NUEM ‘20) **Edited by:** Jim Kenny, MD (NUEM ‘18) **Expert Commentary by**: Patrick Lank, MD, MS

Local anesthetic systemic toxicity (LAST) is a feared complication of local anesthetic use. Current estimates of LAST toxicity in adults range from 7.5 to 20 per 10,000 peripheral nerve blocks and 4 per 10,000 epidurals.[1] Although rare, this complication can be fatal. Unfortunately, many physicians are unaware of the toxic dose of local anesthetics and are unable to recognize the signs and symptoms of this toxicity.[2] For this reason and the fact that local anesthetic toxicity is rare, by the time this syndrome is identified, patients are often in cardiac arrest or peri-arrest. Thankfully, lipid emulsion such as Intralipid is a safe and effective therapy used to treat LAST.

How does lipid emulsion therapy work?

Lipid emulsion therapy is an intravenous therapy that binds lipophilic toxins and therefore reverses their toxicity. There are several brand name lipid emulsion therapies, however Intralipid, a soy-based lipid emulsion that contains long-chain triglycerides, is the most commonly used (Figure 1).[3] The ability of lipid emulsion therapy to counteract the toxic effects of local anesthetics was discovered in 1998 by Weinberg et al when it was incidentally found that lab rats pre-treated with an infusion of lipids could withstand larger doses of bupivacaine before arresting.[4] The rats were also more easily resuscitated if given lipid emulsion therapy.[1] These findings were subsequently confirmed in other laboratories and clinical systemic analyses.[5] Once studied more directly, it was found that intralipid acts as a “sink” by creating a lipid compartment within the plasma that attracts lipophilic compounds, such as local anesthetics, into the lipid sink, which is separate from the aqueous phase of the plasma.[1]

Figure 1: Composition of Various Brands of Lipid Emulsions[1] — **Figure 1**: Composition of Various Brands of Lipid Emulsions[1]

How does LAST manifest?

Toxicity is a rare but potentially lethal side effect of local anesthetic. However, since patients often present without any knowledge that they were administered toxic doses of local anesthetic, it is important that the EM physician be cognizant of the signs of this toxicity. Symptoms typically start after a toxic dose of local anesthetic is administered or if local anesthetic is inadvertently administered directly into a vessel instead of subcutaneously (Figure 2). Onset of LAST is typically 30 seconds to 60 minutes after administration of the anesthetic but more often than not occurs within 1-5 minutes.[6]

Figure 2: Maximum Doses and Durations of Various Local Anesthetics[9] — **Figure 2**: Maximum Doses and Durations of Various Local Anesthetics[9]

Symptoms of LAST can vary, however there are 5 general ways in which LAST presents.[6] One or all of these manifestations may be present.

CNS (excitement) – an early manifestation of LAST that often begins with confusion or slurred speech but may include subjective symptoms like metallic taste in the mouth, tinnitus, oral numbness, dizziness, lightheadedness, or visual or auditory disturbances. If not treated promptly, these symptoms often progress to seizures, syncope, coma, respiratory depression, or cardiovascular collapse.

Cardiovascular – often preceded by CNS symptoms but not always. May include hypertension, tachycardia or bradycardia, arrhythmias, and asystole. Depressed contractility of the heart then leads to progressive hypotension and ultimately cardiac arrest.
Hematologic – methemoglobinemia, cyanosis
Allergic – urticaria, rash, and rarely anaphylaxis
Local tissue response – numbness, paresthesia

The EM physician should maintain a high level of suspicion should a patient present after a same day surgery or procedure with any constellation of these symptoms.

How is lipid emulsion therapy administered?

Once LAST is recognized, the EM physician should immediately consider giving lipid emulsion therapy. An initial dose of 20% lipid emulsion at 1.5 ml/kg or a 100 ml bolus can be administered over a few minutes. This can be repeated after 5 minutes for 2 or more times for persistent hemodynamic instability. The bolus(es) should immediately be followed by a continuous infusion at 0.25-0.5 ml/kg/min.[3] The infusion should run for a minimum of 10 minutes after return of hemodynamic stability, however there are documented reports of recurrent systemic toxicity even after this. For this reason, patients should be admitted for at least 12 hours for observation and additional doses of intralipid as needed for rebound symptoms or hemodynamic compromise.[3] Consultation with your facility’s poison center is also crucial to further guide management.

Efficacy

In terms of efficacy, case reports and systemic analyses have found that lipid emulsion therapy:

Can reverse both neurologic and cardiac toxicity [5]
Leads to significantly higher rates of ROSC compared to saline controls in animal models [5]
Is more effective for witnessed events (for example, brief down time for patients that arrest)5
Is often effective in patients in which epinephrine, vasopressin, and antiarrhythmic medications did not work

Both hypoxia and acidosis worsen the toxicity of local anesthetics and may inhibit lipid emulsion therapy, so it is imperative that oxygenation and acid-base status are optimized when lipid emulsion therapy is needed.[3, 5]

Contraindications, Complications, and Special Populations

There are no absolute contraindications to intravenous lipid emulsion therapy and no clinically significant complications documented in the literature. The benefits of lipid emulsion therapy will often outweigh any potential risks in patients with LAST, especially if hemodynamically unstable or coding.

Potential complications of lipid emulsion therapy are mainly related to hypersensitivity. Patients allergic to soybean protein or eggs theoretically may develop allergic or anaphylactic reactions. These reactions should be treated like all other allergic or anaphylactic reactions: with anti-histamines, steroids, and epinephrine as needed. Additionally, there are reported cases of hyperamylasemia however no documented progression to clinical pancreatitis.[3] There are also case reports of extreme lipemia, however even a patient that was inadvertently given 2 L of 20% lipid emulsion did not develop any cardiopulmonary complications.[5] The lipemia however did interfere with standard laboratory tests.[5]

Intralipid is safe in pregnancy and has documented use for treating LAST in term pregnancy.[7] Furthermore, it has documented uncomplicated use in pediatric and neonatal patients.[3, 8]

Key Points

Systemic toxicity is a rare but potentially fatal complication of local anesthetic use.
Lipid emulsion therapy such as Intralipid mitigates the toxic effects of local anesthetics and can reverse both neurologic and cardiac toxicity.
LAST may manifest initially with CNS symptoms but can progress to seizure, respiratory depression, coma, and cardiovascular collapse.
An initial bolus of 1.5 ml/kg or 100 ml 20% lipid emulsion followed by an infusion starting at 0.25 ml/kg/min is crucial to reverse toxicity and prevent recurrence.
Hypoxia and acidosis both worsen LAST and may inhibit lipid emulsion therapy.
Patients should be admitted in order to monitor for recurrent toxicity.
There are no contraindications to and minimal side effects of lipid emulsion therapy.

Expert Commentary

Thank you both for the above thorough review of local anesthetic systemic toxicity (LAST) from the emergency physician perspective! I only want to add a few points to consider when learning more about LAST.

Without going into too much detail, there has been a lot of research done to figure out exactly how lipids aide in the treatment of patients with severe LAST. The lipid sink model is wonderfully understandable and explains many of the clinical and laboratory we see (e.g., a greater decrease in free serum concentration of more lipophilic local anesthetics). However, there are some other models and theories to be aware of. One I am fascinated by is the “lipid shuttle.” Fundamentally, this describes the phenomenon that lipid therapy will decrease the concentration of local anesthetic at sites of toxicity (i.e., heart and CNS) and increase its concentration in the liver. So instead of lipids acting only as a “sink” to remove a toxin from free availability, it is helping mobilize the toxin to an area where it can go through the process of elimination from the body. Additionally, there are wonderful biochemical explanations (e.g., fatty acid supply, inhibition of nitric oxide release, reversal of mitochondrial dysfunction) to the positive cardiovascular effects seen after lipid treatment in LAST. All of these explanations, it seems, combine to contribute to the hemodynamic response seen in LAST.

Second, I would like to point your readers towards a resource that may help them work through the mechanics of administering lipid rescue therapy in LAST – lipidrescue.org. On that website, one can find links to various protocols, compilations of prior research done on the topic, and much more background on the science of the treatment than I provided above.

Third, in the emergency department, I think you are correct in saying that the most likely source of LAST we would see would come from outpatient surgery centers. A few other clinical scenarios to be aware of would include the following: ingestion of local anesthetics – mostly benzonatate (Tessalon); non-surgical outpatient aesthetic offices that may use topical anesthetics; inappropriate and excessive home use of local anesthetics for pain relief.

Finally, a very brief comment on the use of lipid rescue therapy in non-LAST toxic exposures although that was not the subject of your post. While lipid rescue therapy for LAST has a remarkable record of being effective, that is not yet the case with its use in other toxic exposures. A list of the side effects of lipid rescue therapy includes but is not limited to ARDS, pancreatitis, infection, and significant laboratory interference. While in the setting of severe LAST, the risk: benefit often favors administering lipid rescue, this may not be the case in the setting of non-LAST exposures. For those non-LAST cases (as well as with LAST cases) in which you are wondering if lipid rescue would be appropriate, I would strongly recommend you call your regional poison center to discuss further focused therapy.

Patrick Lank, MD, MS

Assistant Professor of Emergency Medicine

Medical Toxicologist

Department of Emergency Medicine

How To Cite This Post:

[Peer-Reviewed, Web Publication] Loke D, Kenny J. (2020, July 20). Lipid Emulsion Therapy for Local Anesthetic Systemic Toxicity. Expert Commentary by Lank P. Retrieved from http://www.nuemblog.com/blog/lipid-emulsion-therapy

References

1. Manavi, M. (201). Lipid infusion as a treatment for local anesthetic toxicity: a literature review. AANA Journal, 78(1), 69-78.

2. Cooper, B.R., Moll, T., & Griffiths, J.R. (2010) Local anaesthetic toxicity: are we prepared for the consequences in the Emergency Department. J Emerg Med, 27(8), 599.

3. Mercado, P. & Weinberg, G.L. (2011). Local anesthetic systemic toxicity: prevention and treatment. Anesthesiology Clin, 29(2), 233-242.

4. Weinberg, G.L., VadeBancouer, T., Ramarju, G.A., Garcia-Amaro, M.F., & Cwik, M.J. (1998). Pretreatment or resuscitation with a lipid infusion shifts the dose-response to bupivacaine-induced asystole in rats. Anesthesiology, 88(4), 1071-5.

5. Weinberg, G.L. (2012). Lipid emulsion infusion: resuscitation for local anesthetic and other drug overdose. Anesthesiology, 117(1), 180-7.

6. Wadlund, D. (2017). Local anesthetic systemic toxicity. ARON Journal, 106(5), 367-77.

7. Dun-Chi Lin, J., Sivanesan, E., Horlocker, T.T., & Missair, A. (2017). Two for one: a case report of intravenous lipid emulsion to treat local anesthetic systemic toxicity in term pregnancy. A&A Case Reports, 8(9), 235-7.

8. Shah, S., Gopalakrishnan, S., Apuya, J., Shah, S., & Martin, T. (2009). Use of intralipid in an infant with impending cardiovascular collapse due to local anesthetic toxicity. J Anesth, 23(3), 439-441.

9. “Missouri Society of Health-System Pharmacists - Overview of Management of Local Anesthetic Systemic Toxicity (LAST) Based on Updated 2017/18 ASRA Practice Guidelines.”

Posted on July 20, 2020 by NUEM Blog and filed under Toxicology and tagged lipid emulsion therapy toxicology emergency medicine local anesthetic.

The Best Agent For Digital Nerve Blocks

Explore the evidence behind previously held beliefs regarding local anesthetic use in digital nerve blocks.