Local anesthetic systemic toxicity: signs and management

Local anesthesia is part of the routine in many orofacial harmonization (HOF) procedures, from topical cream to infiltrative block. Most patients have no problem at all, and the safety of this use rests on small volumes and short pauses. Even so, local anesthetic systemic toxicity (known by its acronym, LAST) exists, and it is an emergency. This text gathers what the professional needs to recognize and how to prepare, at a review level.

It is not a care protocol and does not replace life support training. Doses, drugs and emergency procedures are covered in specific training and follow the rules of your professional council. The content presented is meant to organize your reasoning.

What is LAST?

It is the set of manifestations caused by high levels of local anesthetic in the blood. This can happen through:

1. Accidental intravascular injection, which delivers the anesthetic directly into the circulation.
2. Excessive total dose, adding up all applications during the procedure.
3. Rapid absorption in highly vascularized areas or from use over large areas of mucosa and skin.
4. Patient factors that change metabolism and elimination.

The anesthetic blocks sodium channels in nerves, but in excess in the circulation it also acts on the brain and the heart. That is why the picture is typically neurological and, in severe cases, cardiovascular.

What are the signs?

Signs evolve in variable ways and do not always follow an order. The classic description lists central nervous system signs first.

A few details matter in practice:

• The patient's complaint is usually the first warning. Any report of a metallic taste, ringing in the ears or numbness around the mouth right after anesthesia should be taken seriously.
• Signs can be immediate (intravascular injection) or delayed (progressive absorption, up to tens of minutes later).
• The presentation can be atypical, with cardiac symptoms before neurological ones, or with subtle signs.

Telling LAST apart from a vasovagal episode, anxiety, an allergic reaction or a primary seizure is difficult. That is why the possibility should be on the mind of anyone who administers anesthetic. See also vasovagal syncope in the clinic, panic attack in the clinic and anaphylaxis in the HOF clinic.

Who is at higher risk?

Some factors raise the chance of problems, or their severity:

• Liver disease (reduced metabolism of some anesthetics).
• Heart disease and use of certain antiarrhythmics.
• Kidney disease.
• Advanced age, pregnancy and low body weight.
• Low plasma protein, which changes the free fraction of the drug.
• Drug interactions that interfere with metabolism.
• Concurrent use of several sources of anesthetic (topical, infiltrative, block).

The medical history in HOF should screen for these conditions. In patients at higher risk, the anesthetic plan may be adjusted, and the professional decides case by case. See also local anesthesia in HOF: overview and topical anesthetics: composition and risks.

How to prevent it

Prevention rests on simple habits:

1. Know the total dose of the anesthetic used and add up all sources.
2. Record product, concentration and volume in the patient record.
3. Respect the limits set by the manufacturer and the literature, which vary by product and by patient.
4. Inject slowly and in small fractions, watching the patient.
5. Consider aspiration before injection according to the professional's approach and the technique used, remembering that the absence of blood return does not guarantee a vessel was not reached.
6. Talk to the patient during the injection, to catch complaints early.
7. Do not leave the patient alone in the minutes after anesthesia.
8. Be careful with large areas of topical anesthetic, especially on broken skin or under occlusion.

What to do if you suspect it

In general terms, the reasoning is that of a clinical emergency, and every clinic should have a plan and training:

1. Stop administering anesthetic.
2. Call for help: activate emergency services and the team.
3. Maintain the airway and ventilation, with oxygen if available.
4. Monitor vital signs and level of consciousness.
5. Treat seizures and instability according to training, with appropriate drugs and maneuvers.
6. Follow the emergency protocol of the facility and the guidance of the ambulance service.
7. Inform the emergency team about the anesthetic, the dose and the time, since there are specific treatments that depend on this information.

These steps describe the reasoning and do not replace life support training. To organize the clinic, see emergency kit for the HOF clinic, AED in the clinic and seizure in the clinic.

Preparing the clinic

A prepared clinic recognizes the event sooner and responds better. Items that deserve attention:

• Regular training of the whole team in basic life support.
• A written emergency plan, with defined roles: who calls, who monitors, who takes notes.
• Available equipment: oxygen, bag-valve mask, suction, access to an AED and an emergency medication kit.
• Emergency phone number in plain sight and an agreed transfer route.
• Periodic drills, because the memory of old training fades.
• Recording the event and reviewing it afterward, even for near misses, in line with the idea of a near miss.

The topic also connects with the safety time-out before injecting: checking allergies, dose and emergency equipment before the first injection is part of the preparation.

Timeline of a hypothetical event

Communicating with the patient and documenting

Faced with a complication like this, honest communication is part of the care: explain what happened, what is being done and what comes next. Afterward, record times, doses, signs, actions and the outcome in the patient record, and assess whether reporting is needed, according to adverse event reporting in Notivisa (Anvisa's reporting system in Brazil).

Where Harmy fits

Harmy does not deal with anesthesia or emergencies. It helps with visual planning by volume, before the procedure. Having the plan settled and shown to the patient at the consultation can help reduce the need for rushed decisions in the chair.

Quick review

Local anesthetic systemic toxicity is rare and serious. The professional who knows it, calculates the total dose, watches the patient and keeps the clinic prepared lowers both the chance of it happening and the harm if it does.