The American Society of Regional Anesthesia and Pain Medicine's Third Practice Advisory on local anesthetic systemic toxicity is an interim update from its 2010 advisory. The advisory focuses on new information regarding the mechanisms of lipid resuscitation, updated frequency estimates, the preventative role of ultrasound guidance, changes to case presentation patterns, and limited information related to local infiltration anesthesia and liposomal bupivacaine. In addition to emerging information, the advisory updates recommendations pertaining to prevention, recognition, and treatment of local anesthetic systemic toxicity. This interim update summarizes recent scientific findings that have enhanced our understanding of the mechanisms that lead to lipid emulsion reversal of LAST, including rapid partitioning, direct inotropy, and post-conditioning. Since the previous practice advisory, epidemiological data have emerged that suggest a lower frequency of LAST as reported by single institutions and some registries, nevertheless a considerable number of events still occur within the general community. Contemporary case reports suggest a trend toward delayed presentation, which may mirror the increased use of ultrasound guidance (fewer intravascular injections), local infiltration techniques (slower systemic uptake), and continuous local anesthetic infusions. Small patient size and sarcopenia are additional factors that increase potential risk for LAST. An increasing number of reported events occur outside of the traditional hospital setting and involve non-anesthesiologists.

The experimental use of lipid emulsion for local anesthetic toxicity was originally identified in 1998. It was then translated to clinical practice in 2006 and expanded to drugs other than local anesthetics in 2008. Our understanding of lipid resuscitation therapy has progressed considerably since the previous update from the American Society of Regional Anesthesia and Pain Medicine, and the scientific evidence has coalesced around specific discrete mechanisms. Intravenous lipid emulsion therapy provides a multimodal resuscitation benefit that includes both scavenging (eg, the lipid shuttle) and nonscavenging components. The intravascular lipid compartment scavenges drug from organs susceptible to toxicity and accelerates redistribution to organs where drug (eg, bupivacaine) is stored, detoxified, and later excreted. In addition, lipid exerts nonscavenging effects that include postconditioning (via activation of prosurvival kinases) along with cardiotonic and vasoconstrictive benefits. These effects protect tissue from ischemic damage and increase tissue perfusion during recovery from toxicity. Other mechanisms have diminished in favor based on lack of evidence; these include direct effects on channel currents (eg, calcium) and mass-effect overpowering a block in mitochondrial metabolism. In this narrative review, we discuss these proposed mechanisms and address questions left to answer in the field. Further work is needed, but the field has made considerable strides towards understanding the mechanisms.

Background: The objective of this narrative review of local anesthetic systemic toxicity is to provide an update on its prevention, diagnosis, and management. Methods: The authors used a MEDLINE search of human studies, animal studies, and case reports and summarize findings following the American Society of Regional Anesthesia and Pain Medicine practice advisories on local anesthetic systemic toxicity. Results: Between March of 2014 and November of 2016, there were 47 cases of systemic toxicity described. Twenty-two patients (47 percent) were treated with intravenous lipid emulsion and two patients (4.3 percent) died. Seizures were the most common presentation. The spectrum of presenting neurologic and cardiovascular symptoms and signs are broad and can be obscured by perioperative processes. Local anesthetic type, dosage, and volume; site of injection; and patient comorbidities influence the rate of absorption from the site of injection and biodegradation of local anesthetics. Consider discussing appropriate dosages as a component of the surgical “time-out.” A large-volume depot of dilute local anesthetic can take hours before reaching peak plasma levels. Oxygenation, ventilation, and advanced cardiac life support are the first priorities in treatment. Lipid emulsion therapy should be given at the first sign of serious systemic toxicity with an initial bolus dose of 100 ml for adults weighing greater than 70 kg and 1.5 ml/kg for adults weighing less than 70 kg or for children. Conclusion: All physicians who administer local anesthetics should be educated regarding the nature of systemic toxicity and contemporary management algorithms that include lipid emulsion therapy.

Objectives: Bolus infusion of lipid emulsion can reverse cardiac pharmacotoxicity caused by local anesthetics and other lipophilic drugs. The mechanisms of this effect are not completely elucidated. The authors test the hypothesis that lipid emulsion infusion exerts direct, positive inotropic effects. Design: Prospective, randomized animal study. Setting: University research laboratory. Subjects: Adult male Sprague-Dawley rats. Interventions: Rats anesthetized with isoflurane were given intravenous infusions (9 mL/kg over 1 min) of either 20% soybean oil-based emulsion or saline. Measurements and Main Results: Arterial pressure and aortic flow were measured continuously in intact animals. Lipid infusion increased aortic flow and arterial pressure faster and to a greater degree than did the same volume of saline infusion. Isolated rat hearts were studied using an isovolumetric, constant flow, nonrecirculating system. Left ventricular pressure was monitored. The infusion of lipid emulsion in the isolated heart dose-dependently increased rate pressure product, dP/dt, –dP/dt, and myocardial oxygen demand. Conclusions: Lipid emulsion exerts rapid, positive inotropic and positive lusitropic effects in both intact animal and isolated heart models. We hypothesize that this inotropy and the resulting increase in tissue blood flow contribute to the phenomenon of lipid reversal of cardiac toxicity caused by drug overdose.