LAST (Local Anesthetic Systemic Toxicity): A practical update for clinicians

Summary

This video script delves into Local Anesthetic Systemic Toxicity (LAST), a rare but serious complication of local anesthetic use that can lead to severe injury or death. It outlines the evolving clinical presentation of LAST, emphasizing the necessity for vigilance in prevention and the importance of understanding its mechanism. The script also discusses the multimodal antidotal role of lipid emulsion, risk factors, preventive measures, and management strategies, including the crucial steps to take in the event of an LAST episode.

Takeaways

• 🚨 Local anesthetic systemic toxicity (LAST) is a potentially fatal complication of local anesthetic use, with permanent injury or death as possible outcomes.
• 🔍 LAST is an overdose situation that can occur due to accidental intravascular injection or exceeding a patient's toxic threshold.
• 📈 The incidence of LAST is estimated to be between one to two in every thousand nerve blocks, but this number may be higher due to unreported cases.
• 🌐 The presentation of LAST has evolved and can vary, with about half of cases starting with neurologic signs and symptoms, and a quarter with only cardiac signs.
• 👨‍⚕️ The risk of LAST is not limited to a specific site of injection, and vigilance is required to prevent it, especially with the rise of outpatient procedures.
• 💊 The toxic mechanism of LAST involves blockade of sodium channels and mitochondrial poisoning, affecting primarily the heart and brain.
• 🩺 An antidote for LAST is the lipid emulsion, which works by scavenging local anesthetic molecules from the heart and brain, providing an inotropic effect, and improving cardiac output.
• 👶 Certain populations are at higher risk for LAST, including the elderly, infants under six months, pregnant patients, and those with reduced ventricular function or arrhythmias.
• ⚠️ Prevention strategies include being aware of dose limits, using fractional injection techniques, aspirating before injecting, and using epinephrine as a marker for intravascular injection.
• 🔬 Ultrasound guidance is associated with a significantly reduced incidence of LAST, emphasizing its importance in procedural practices.
• 🆘 In the event of LAST, immediate steps include stopping the injection, calling for help, maintaining airway, ventilating the patient, and administering lipid emulsion as the primary treatment.

Q & A

What is Local Anesthetic Systemic Toxicity (LAST)?

LAST is a potentially fatal complication that can occur from the use of local anesthetics, either due to accidental intravascular injection or because the administered dose is too high for the patient, leading to toxic plasma levels.

How common is LAST and what are its historical presentation symptoms?

LAST is considered a rare complication, occurring in approximately one to two in every thousand nerve blocks. Historically, it presented with prodromal symptoms such as numbness around the mouth, metallic taste, and ringing in the ears, followed by agitation, twitching, and seizures as plasma concentrations increased.

How has the understanding of LAST presentation evolved?

Contemporary data shows that not all cases of LAST present with the classic order of symptoms. About half of the cases now present initially with neurologic signs and symptoms, a third with both neurologic and cardiovascular manifestations, and a quarter with only cardiac signs.

Why is it important to remain vigilant about preventing LAST?

Preventing LAST is crucial because the traditional method of catching it early through prodromal symptoms is not reliable. Being vigilant helps in early detection and intervention, which can be life-saving.

What are some changes in where LAST occurs and which professionals are involved?

While the majority of LAST cases still occur in hospitals, there has been an increase in cases in outpatient settings such as urology, cosmetic surgery, and dental offices. The proportion of LAST due to non-anesthesiologists has also increased, partly due to tumescent anesthesia for liposuction.

What is the toxic mechanism of LAST and how does it affect the body?

The toxic mechanism of LAST involves blockade of sodium channels in the heart and CNS, inhibition of other ion channels, and primarily poisoning of the mitochondrial oxidative phosphorylation pathway, leading to metabolic asphyxiation. This results in cardiac and neurotoxicity due to the heart and brain's intolerance to intracellular energy depletion.

How does the lipid emulsion work as an antidote for LAST?

Lipid emulsion works multimodally, primarily by scavenging lipid-soluble local anesthetic molecules from the heart and brain, reducing their concentration at ion channels, and providing fatty acid substrate for poisoned mitochondria. It also has a volume effect that helps generate cardiac output.

Which patient populations may be at higher risk for LAST?

Populations at higher risk for LAST include the extremes of age (elderly with cardiac comorbidities and infants under six months with immature hepatic pathways), pregnant patients with reduced plasma binding proteins, and patients with reduced ventricular function or pre-existing arrhythmias.

What preventive strategies can be employed to reduce the risk of LAST?

Strategies include being conscious of published dose limits, using the lowest effective dose, fractional injection with pauses, aspirating before injecting, using epinephrine as a marker for intravascular injection, and utilizing ultrasound guidance for blocks.

What are the special considerations for managing LAST in the case of a cardiac arrest?

In a cardiac arrest due to LAST, standard ACLS should be followed with modifications: avoid using high doses of epinephrine or vasopressin, and do not use lidocaine to treat arrhythmias. Chest compressions are key to improve coronary perfusion with lipid emulsion.

What steps should be taken if LAST is suspected during a procedure?

If LAST is suspected, immediately stop injecting the local anesthetic, call for help, prepare a lipid emulsion kit, maintain the airway, and if necessary, ventilate the patient. Administer benzodiazepines for seizures and start the lipid emulsion as soon as possible.