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Local Anesthetic Systemic Toxicity (LAST) Under Anesthesia

Practice Essentials

Local anesthetic systemic toxicity (LAST) is a rare but serious critical event. Minimizing the risk of LAST, recognizing it early when it occurs, and initiating prompt treatment are imperative for safe use of perioperative local anesthetics.

Anesthesiologists must be vigilant for signs and symptoms of impending LAST, which include cardiovascular and neurologic toxicity. General anesthesia or deep sedation may obscure the initial warning signs, and sudden severe hemodynamic instability or seizures may be presenting symptoms.

If systemic toxicity is suspected, immediately call for help. Initiate hemodynamic support according to Advanced Cardiac Life Support (ACLS) protocols, but exclude calcium-channel blockers, beta blockers, and lidocaine. Administer benzodiazepines for seizure prophylaxis or cessation, and support the airway as necessary.

Intravenous (IV) lipid emulsion 20% (Intralipid; Fresenius Kabi, Uppsala, Sweden) is definitive therapy for severe LAST. The initial bolus dose is followed by continuous infusion until 10 minutes after return of spontaneous circulation (ROSC), with subsequent intensive care unit (ICU) monitoring for 12 hours in case of recurrence.

In patients with severe cardiac toxicity, prolonged resuscitation, full cardiopulmonary support on extracorporeal membrane oxygenation (ECMO) or cardiopulmonary bypass (CPB), or both may be necessary, particularly in cases of bupivacaine toxicity.

Other complications of local anesthetic use include neural toxicity, allergic reactions, and metabolic abnormalities, including methemoglobinemia (not covered in this article).

Key points for minimizing risk of LAST include the following:

Use the minimum effective dose for every patient (ie, the lowest effective volume at the lowest appropriate concentration)

Perform incremental injections with aspiration (eg, 3- to 5-mL aliquots every 30-45 seconds) 

Consider addition of intravascular markers (eg, epinephrine, fentanyl)

Be aware of patient populations at higher risk for LAST – Neonates and infants (< 4 months); geriatric patients; patients with underlying arrhythmias or cardiac disease; and patients with impaired hepatic, renal, or metabolic systems

Know which techniques carry a higher risk of LAST – Intercostal and IV regional techniques have the highest potential rates of systemic absorption; alternative techniques should be considered in patients at high risk for toxicity

Perform close monitoring for 30 minutes after injection of a local anesthetic in patients receiving potentially toxic doses of the anesthetic

Key points for recognizing LAST include the following:

Signs and symptoms of LAST may be cardiovascular or neurologic

Generally, symptoms can be categorized as typical (mild symptoms followed by severe) or atypical and can range from mild to severe

Initial neurologic symptoms in the excitatory phase include perioral numbness, a metallic taste, tinnitus, and agitation, followed by seizures, and ultimately neurologic depression with respiratory arrest, coma, or both

Cardiovascular symptoms may include an initial hypertensive and tachycardic excitatory phase with ventricular arrhythmias, as well as subsequent cardiac depression with bradycardia, myocardial depression, conduction block, asystole, and cardiac arrest

Atypical presentations are common and include initial cardiac toxicity with arrhythmias (notably with bupivacaine toxicity), heart block, and/or asystole without preceding central nervous system (CNS) signs

Patients may also initially present with seizures or with simultaneous severe neurologic and cardiovascular toxicity

Patients may present with mixed pictures, particularly when under deep sedation or general anesthesia

Key points for treating LAST include the following:

Prompt initiation of ACLS, IV lipid emulsion administration, and advanced hemodynamic support are the cornerstones of therapy for established LAST

Primary physiologic goals are to maintain coronary and cerebral perfusion, to stop or prevent seizures, to reverse hypoxia, and to treat acidosis

If cardiac arrest occurs, commence ACLS with the following modifications: (1) Do not administer calcium channel blockers or beta blockers, because these drugs may potentiate LAST-induced conduction block; (2) consider smaller initial doses of epinephrine (10-100 μg IV bolus in adults); (3) vasopressin may be used safely (minimal risk of dysrhythmias that may occur with epinephrine); and (4) amiodarone is the preferred first-line agent to treat malignant arrhythmias (do not use local anesthetics or phenytoin)

Administration of lipid emulsion 20% should be initiated with a 1.5 mL/kg IV bolus followed by IV infusion at 0.25 mL/kg/min (patients < 70 kg) or with a 100 mL bolus followed by infusion of 200-250 mL over 15-20 minutes (patients >70 kg), which is continued until 10 minutes after ROSC; the bolus may be repeated once or twice and the infusion rate doubled if cardiovascular collapse persists; total dose should not exceed 12 mL/kg

In cases of refractory cardiac arrest, mechanical circulatory support with CPB or ECMO may be required until toxicity subsides

Checklist for treatment of LAST is available from the American Society of Regional Anesthesia and Pain Medicine

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