Chapter 61: Local Anesthetic Systemic Toxicity

BACKGROUND

• Incidence of local anesthetic systemic toxicity (LAST) after peripheral nerve blocks is higher than after epidural anesthesia.

• Ultrasound-guided peripheral nerve block is associated with lower incidence of LAST (Odds ratio 0.23).¹

• Use of epinephrine in local anesthetics decreases its systemic absorption.

• In 1998, Dr. Guy Weinberg first observed that pretreatment or resuscitation with a lipid infusion shifts the dose-response curve to the right in a rat model of bupivacaine-induced asystole.²

• In 2006, the first case was reported of the successful use of a 20% lipid emulsion (intralipid) in a patient after LAST-induced prolong cardiac arrest.³

• Since then, lipid emulsion has been used successfully in lipophilic drug overdoses, such as tricyclic antidepressants, bupropion, verapamil, diltiazem, caffeine, and olanzapine.

RISK FACTORS

• Unrecognized intravascular epidural catheter

• Extremes of age

• Nerve block site

• Patient-related factors: cardiac, renal, and hepatic diseases

• Multiple procedures: such as labor analgesia to cesarean section, or regional block after cesarean section

• Multiple routes of administration: local infiltration, irrigation, neuraxial, nerve blocks, and lidocaine patch

• Repeated use of local anesthetics for infiltration

MECHANISM OF LIPID EMULSION (FIG. 61-1)

Mechanism of Lipid Emulsion⁴

• Lipid sink

• Metabolic effect: increases fatty acid uptake by mitochondria

• Membrane effect: stabilizes the membranes

• Cytoprotection: via activation of Protein kinase B (PKB), also known as Akt pathway

DIAGNOSIS

The signs, symptoms, and timing of LAST are unpredictable and can be subtle. Wide range of symptoms include:

• Mental status change including coma and convulsions.

• Cardiovascular instability to cardiac arrest.

• Be vigilant. Early diagnosis is the key for successful resuscitation.

TREATMENT

• The LAST Checklist from the American Society of Regional Anesthesia and Pain Medicine (ASRA) summarizes the workflow of resuscitation of LAST and the use of lipid emulsion (Fig. 61-2).⁵

• Data are inconsistent regarding whether lipid emulsion is effective to resuscitate the patients with LAST due to lidocaine overdose. The lipid administration proved to be safe; the author would recommend using lipid emulsion to treat lidocaine-induced LAST.

• Important note for resuscitation: Use smaller than normal dose of epinephrine in the Advanced Cardiovascular Life Support (ACLS). Avoid beta blockers, calcium channel blockers, and vasopressin.

REFERENCES