Block Party: Local Regional Anesthesia in the ER

Josh Cruz, DVM, discusses the use of local and regional blocks in the emergency room, when to use specific blocks, as well as important cautions and considerations to keep in mind.

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If pain control was a party, the opioids, NSAIDs, and neuromodulating therapies would be the most glamorous and gregarious attendees. But sometimes a very effective member of the party is the often forgot wallflower, the local, or regional block. Regional anesthesia, or local blocks, is an essential component to managing pain in a wide variety of our patients in the emergency and critical care setting. Of course, the primary goal of these blocks is to provide a relief from current painful stimuli, or to prevent the sensation of pain caused by our own intervention. A local block’s use, however, extends beyond this simple classification. Allowing for the minimization of other analgesics and sedatives, ease of administration with minimal risk, and overall cost effectiveness, makes local anesthesia one of the more interesting and useful characters at this party.


Understanding basic nerve anatomy and physiology is essential for understanding how local anesthesia works. Ultimately, rapid changes to an electrical gradient across nerve membranes allows for transmission of various signals (pain, sensation, motor) through nerve fibers. These action potentials of electrical energy are typically managed by sodium gated channels. Local blocks utilize these channels to inhibit propagation of nerve signals, hence, anesthesia. At greater doses of blockade, not only pain sensation but motor function may be inhibited. While the basic function is similar among local anesthetics, there are many local anesthetics that vary in duration and strength of action, positive/negative side effects, and motor and sensory blockade. Lidocaine and bupivacaine are the most notable and widely used sodium channel blockers in the ER/ICU setting, and will be the focus of this article.


Many regional anesthesia dose variations and recipes involving lidocaine/bupivacaine have been described in veterinary medicine. Combining both shorter acting lidocaine with longer acting bupivacaine is often used. Mixing local blocks with sodium bicarbonate, in an attempt to minimize patient discomfort and increase onset of anesthesia is still controversial. Mixing with a vasoconstrictor (epinephrine) has also been used to prolong duration of analgesia, but may alter regional pH limiting clinical benefit. Opioids, alpha-2 agonists, and NMDA antagonists (ketamine) have also been used in conjunction with sodium channel blockade to achieve regional anesthesia. Ultimately it is difficult to determine the effectiveness and benefit of adjunctive mixtures to the primary sodium channel blockage anesthetics. Often in the emergency setting, keeping it simple is often the best. Patient selection and reason for anesthesia should help guide your choice but there is nothing wrong with one drug selection for local blocks.


Various complications exist with performing local blocks. These complications are usually rare. With appropriate dose, technique, and patient selection, complications become insignificant. Systemic absorption and subsequent side effects to the cardiovascular and central nervous systems are definitely possible, but using appropriate drug volumes and understanding species difference should help prevent this complication. Injection at any site that may already be compromised from severe trauma or infection should not be performed. Moving the injection site further up the neurologic pathway, or increasing the circumference of the block, may be reasonable options assuming safety of injection and dosage is still appropriate. Hemorrhage is always a concern, but understanding landmarks, knowing rough location of major vessels, and aspirating back prior to injection will help prevent this complication. Also having a good understanding of patient systemic health is essential (e.g. coagulation parameters, drug sensitivities, and concurrent medications). Reconsider performing local anesthesia on patients with coagulopathies and thrombocytopathies. Nerve trauma is of course possible, but less likely in the majority of blocks performed in the ER.


Local Block Techniques

The following are four of my favorite, and most commonly used local blocks. This is meant to be a quick guideline, for more in depth anatomy and description, other resources should be consulted. The techniques described below are by no means meant to be all inclusive. Dental, topical, intraarticular, testicular, ring, epidural, and brachial plexus (all-time favorite) blocks are all useful, but usually used preemptively prior to more advanced surgery or painful stimuli, and not as practical in the ER setting. As with all blocks, calculating total doses prior to injection, site preparation (clip/scrub), aseptic technique (sterile gloves, needles), and aspirating prior to injection is essential.


Incisional Line Block

The most commonly used block in the ER. One of the biggest perceived failures of this block is its failure to work adequately. Ensuring accurate dosage and allowing time to pass (>5 minutes) is essential. Most traumatic wounds requiring regional anesthesia typically also require thorough hair clipping, cleaning, and flushing. Usually by performing a local block prior to final wound cleaning, but well before induced injury, you are able to give enough time to allow complete anesthesia to occur. Also remember to block those areas not near wound site but near areas of future pain (i.e. drain placement).


Sacrococcygeal Block

While typically associated with male feline urinary catheter placement, any procedure in which caudal pudendal and tail anesthesia is required could make use of this block. This block is only recently described and further investigation into its effectiveness is warranted. However, it has been used effectively, and for some cases, allowing catheterization without use of general anesthesia in even clinically stable patients. Because of this, assuming the patient already has systemic analgesia and sedation, a sacrococcygeal block is attempted on the majority of my patients. Depending on block’s effectiveness, you can either move on towards catheterization or general anesthesia if needed.


Retro-bulbar Block

In the ER setting, the retro-bulbar block is typically performed prior to enucleation post traumatic proptosis. Patient selection is essential in deciding whether to perform this block, and controversy still exists regarding the preferred technique and overall effectiveness. Traumatized anatomy, increased vagal tone, and unseen bacterial contamination may lead to increased procedural risks. Also due its location, the risk for injury and systemic/CNS absorption is higher. Regardless, this block can still be used to good effect and should be considered.


Interpleural/intercostal Block

An easy, an often underutilized option for analgesia in critical patients suffering from pancreatitis, painful pleural space disease, or diaphragmatic disease is the interpleural/intercostal block. Many patients already on systemic multimodal analgesia that still exhibit refractory pain may see dramatic benefit from these blocks.  For most of the pain expected in these patients, initial administration of lidocaine, followed by bupivacaine should be performed.


Hopefully after reading this, if you are new to local blocks you will more comfortable performing these various techniques. If you are already well versed in local blocks, let this be a gentle reminder. Ultimately, I like to think that if it is painful and I can get close to or around the nerves responsible for the pain with a needle, regional anesthesia should considered. Remember, sometimes even the wallflower has something to add. After all, everyone is invited to a block party.






Incisional Line

Lidocaine 2%

   2-4 mg/kg

Bupivacaine 0.5%:  

   1-2 mg/kg

25 or 22 gauge needle

Dilute with saline as needed for volume, or 0.3mls of sodium bicarbonate per 10 mls.


Lidocaine 2%: 0.25-0.5 mls

25 gauge needle inserted 30-45 degrees into most mobile joint caudal to sacrum

Sacrococcygeal joint or first 2 coccygeal joints are acceptable. Feel for “pop”


Lidocaine 2%: 1-2mls

22 gauge 1.5 inch needle. Bent at middle 20 degrees, inserted at midline or just lateral to midline under inferior eyelid.

Aim slightly dorsally and nasally after initial insertion about 1-2 cm. Feel for “pop”

Interpleural Intercostal

Lidocaine 2%: 1.5mls/kg, followed by bupivacaine 0.5%: 1.5mls/kg

Injected at midline of thorax at middle of 9th rib space. 25 to 22 gauge needle in small patients. 22 gauge 1.5 inch needle for larger patients

Block can be instilled into chest tubes, but will likely need saline as flush down tube

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