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 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 perform an 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.^5,7 For this reason, we recommend continued cardiac monitoring of patients for at least 60 minutes following the vast majority of UGNBs.⁷