A Simplified Protocol for Intralipid Administration in the ED

Ultrasound-guided nerve blocks (UGNBs) are becoming more common in emergency medicine practice. These techniques allow the modern emergency physician to deliver targeted pain control in conjunction with using lower doses of other analgesics. Recently, numerous Emergency Department (ED) groups have demonstrated the efficacy of UGNBs for pain control with a low rate of complications.^1-3 This cohort study included data from the National Ultrasound-Guided Nerve Block Registry, a retrospective multicenter observational registry encompassing procedures performed in 11 EDs in the US from January 1, 2022, to December 31, 2023, of adult patients who underwent a UGNB. The primary outcome of this study was complication rates associated with ED-performed UGNBs recorded in the National Ultrasound-Guided Nerve Block Registry from January 1, 2022, to December 31, 2023. The secondary outcome was patient pain scores of ED-based UGNBs. Data for all adult patients who underwent an ED-based UGNB at each site were recorded. The volume of UGNB at each site, as well as procedural outcomes (including complications. Even with these encouraging data, local anesthetics can be toxic, and the larger doses of anesthetics associated with UGNBs increase the risk of toxicity. Any clinician administering local anesthetics, especially in large doses, should be aware of the prevention, diagnosis, and treatment of local anesthetic systemic toxicity (LAST). Departments should create a clear policy outlining the dosing and administration of the antidote (20% intralipid solution) in the event of this rare, but dangerous, complication. Our goal is not to performan exhaustive review of LAST, but rather define a simplified collaborative process to establish a protocol that we have implemented in our ED.⁴

What is Local Anesthetic Systemic Toxicity (LAST) and how to detect it?

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Local anesthetic systemic toxicity is a serious, life-threatening complication of local anesthetic use with both cardiovascular and central nervous system (CNS) manifestations.^4-6 Toxicity is thought to be the result of local anesthetic binding to sodium channels within the myocardium and/or the thalamocortical neurons in the brain, although potassium and calcium channel blockade may also play a role. While LAST may occur with any route of administration, the vast majority of cases occur as a result of regional anesthesia.^7,8 Anesthesiology and ED studies drawing on registries and case reports estimate an incidence of 0.04-1.8 major LAST events (cardiac arrest or seizures) per 1,000 peripheral nerve blocks.^8,9 The frequency of minor LAST events (e.g., perioral paresthesias, tinnitus, dizziness, metallic taste) is less clear, as cases may be unrecognized and unreported. Unfortunately, the presentation and progression of LAST does not follow a simple pathway and clinicians must be aware of early/minor symptoms. (Table 1)

Previously, it was thought that LAST only occurs when anesthetic was administered inadvertently into a vein or artery; however, rapid vascular absorption from an acute hematoma or highly vascular plane blocks has been reported as the source in numerous cases.^10,11 Direct vascular injection generally causes symptoms within 5 minutes, but systemic absorption from injection sites causes a more delayed, gradual onset of symptoms, sometimes more than an hour after injection. For this reason, we recommend continued cardiac monitoring of patients for at least 60 minutes following the vast majority of UGNBS.⁷

Key safety point: Based on our 15-year experience performing UGNBs, we have observed cases of suspected early LAST with thoracic fascial plane blocks and hematoma blocks (including erector spinae plane, serratus anterior, and sternal hematoma blocks). After calculating the maximum accepted dose of anesthetic and drawing up less, we believe that clinicians should take more time to perform these blocks by waiting 30 seconds to 2 minutes between each 3-5 ml. aliquot of anesthetic injection. During the pauses, clinicians should monitor the patient’s vital signs and inquire about symptoms to enable early detection of toxicity. We recognize that pausing between anesthetic injections should be standard for all UGNBs, but feel special attention should be paid when placing local anesthetic in highly vascular regions in close proximity to the heart.

Treatment Protocol

Early recognition and treatment of LAST is critical. The cornerstone of treatment is intravenous lipid emulsion, which is believed to draw lipophilic local anesthetic from sensitive tissues, like the brain and heart, into the bloodstream and act as a “lipid sink,” binding and inactivating local anesthetic.⁴ We highly recommend that a simplified protocol for intralipid administration be discussed and practiced by clinicians performing UGNBs, clinical administrators, and hospital pharmacists far in advance of the first block performed in the ED. As with all critical, time-sensitive, and uncommon procedures (like cricothyrotomy and thoracotomy), a simplified pathway reduces cognitive load during stressful events.

In cases of suspected LAST, there is no clearly defined point at which intralipid should be administered. In patients with late symptoms (seizure, altered mental status, dysthymias, cardiac collapse, etc.), the pathway is obvious and intralipid should be administered immediately. In patients with possible early symptoms, the decision can be challenging however, based on our experience, we recommend frequent and careful monitoring, with immediate administration of intralipid if symptoms progress.

In addition to early intralipid, seizures should be treated with benzodiazepines and standard Advanced Cardiac Life Support (ACLS) guidelines should be followed for arrhythmias and cardiac arrest, with some notable modifications. Smaller doses of epinephrine are recommended (start at <1mcg/kg). Local anesthetics, beta blockers, calcium channel blockers, and vasopressin should not be used.

Highland ED Protocol for Intralipid Administration

Because LAST is a very rare (and stressful) event, we have developed a simplified process for our clinicians. As part of our departmental protocol, all patients receiving USGNBs must have functional intravenous access and be placed on a cardiac monitor prior to starting the procedure. Also, the patient must be kept on a continuous cardiac monitor for 60 minutes after the block has been completed. UGNBs distal to the elbow or knee (forearm and tibial nerve blocks specifically) that require volumes less than 10ml of anesthetic can be performed without continuous monitoring.

Figure 1. Click to enlarge.

Intralipid solution is readily accessible in our ED, stored in a clearly marked box within the ED block cart and in two automated medication dispensing systems. The ED block cart, which contains all block supplies, including 250 ml. of intralipid, is brought to the patient’s bedside for all UGNBs. In conjunction with pharmacy colleagues, we developed a simplified protocol for the administration of intralipid based on the American Society of Regional Anesthesia (ASRA) guidelines, with all supplies and instructions located inside the block cart. The “Open-Pull-Push” technique was created for the initial bolus of intralipid. First, the clinician “opens” the box and removes all the supplies (Figure 1). The clinician then “pulls” a full ml. syringe of intralipid through the filter (to reduce large particulate matter) (Figure 2). A 50 ml. intralipid “push” is then rapidly administered through the preexisting IV, with this process repeated. a second time in rapid succession for a total dose of 100 mL (Figure 3). If the patient remains unstable, this 100mL bolus can be repeated one more time using the contents of the initial bag.

Figure 2. Click to enlarge.

After administering the initial boluses of intralipid (100mL x2), start the patient on an infusion of 0.25 ml/kg/min. If the patient continues to remain unstable, the infusion can be increased to 0.5 mL/kg/min. In this way, intralipid administration is simplified to a bolus, which is repeated if hemodynamic stability is not achieved, followed by an infusion dose, which is doubled if hemodynamic stability is still not achieved. Once hemodynamic stability is achieved, continue the infusion for at least 15 minutes. The intralipid drip should be made and ready to administer while the clinician is stabilizing the patient with intralipid boluses and ACLS. A laminated information sheet attached to the cart details the ASRA guidelines, which include details on intralipid administration, treatment of seizures, hypotension, and arrhythmias. We recommend conducting simulated. cases of LAST in the department, so physicians are familiar with the pathway and the equipment.

Figure 3. Click to enlarge.

Summary

Optimal pain control in the ED is a growing field that relies on clinicians learning how to use novel agents (ketamine, nitrous, etc.) as well as UGNBs, With this expansion of knowledge, clinicians must be aware of complications from these novel agents and procedures. For UGNBs, clinicians must be vigilant about patient selection, preparation, and detection of complications. The possibility of LAST should be considered in every case, with proper monitoring and intravenous access. and simple pathways must be in place for antidote delivery. Each ED group should meet with their pharmacy colleagues to ensure there is a clearly defined process for immediate intralipid access and administration during a LAST episode. Stocking our ED block cart with all the supplies to deliver intralipid and our “Open-Pull-Push” technique comes from our desire to ensure all providers have a simplified plan. Aspiration of intralipid through a filter with a large bore needle, and rapid administration should be a learned pathway for all clinicians performing UGNBs in the ED. Like other uncommon procedures, simulated practice will reduce confusion and error in the event of LAST.

Dr. Nagdev is an attending physician Highland Hospital/Alameda Health System.

Dr. Moore is an attending physician Highland Hospital/Alameda Health System.

Dr. Martin is an attending physician Highland Hospital/Alameda Health System.

Dr. Howell is an attending physician Highland Hospital/Alameda Health System.

Dr. Chilstrom is clinical faculty of emergency medicine, Los Angeles General Medical Center.

References

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