A rare complication that can occur within a few minutes after getting local anesthetics is called local anesthetic systemic toxicity (LAST). Typically, it is a medical emergency that causes problems with the nervous system and heart. Fortunately, LAST is treatable, especially when doctors quickly diagnose it.
In other words, LAST occurs as a complication of local anesthetic medicines. It may cause central nervous system problems, but in some cases, it may affect the cardiovascular system and cause irregular heart rhythms (also called arrhythmias). Typically, local anesthetics work by temporarily blocking the peripheral nerves from sending pain signals to the brain. Usually, physicians use them to numb a specific area of the body for different procedures.
What Are The Symptoms of LAST?
In most cases, this complication causes problems with the central nervous system (including the brain and spinal cord). Check some primary symptoms of LAST below:
- Agitation
- Confusion
- Seizures
- Numbness around the mouth
- Auditory changes (including tinnitus)
- A metallic taste in the mouth
- Dysarthria (slurred speech)
- Hallucinations
- Abnormal eye movement
However, LAST may also cause cardiovascular problems and the following symptoms. These include:
- Hypotension (low blood pressure)
- Bradycardia (slow heart rate)
- Tachycardia (fast heart rate)
- Arrhythmia (irregular heart rhythm)
- Cardiac arrest (including failure of the heart’s electrical system)
- Ventricular fibrillation (VFib)
Without immediate treatment, LAST may progress to coma. Commonly, doctors look for LAST signs before giving you a local anesthetic, especially if they know about your risk factors.
Causes and Risk Factors
While the most common cause of LAST is an accidental injection of local anesthetic into a blood vessel, it may also occur due to other forms of medicines. Examples include:
- Topical anesthetics in gel form
- Application of local anesthesia to the mucosa in the mouth, trachea, and esophagus
Furthermore, about 20% of people who develop LAST use an anesthetic that blocks nerves in an extremity (such as an arm or leg). However, there are some factors that could increase your risk even more. Check some of them below:
- Metabolic acidosis (build-up of acids in the body)
- Existing health disease (especially ischemia, arrhythmia, conduction abnormalities, or low ejection fraction)
- Age – People over 65 years old are more likely to develop LAST.
- Kidney or liver disease
- Pregnancy
- Mitochondrial diseases
- Hypoxia (reduced oxygen levels in the blood)
However, some anesthetic medicines may also increase your risk of LAST. One of them is Bupivacaine. Physicians have also identified that specific techniques for giving local anesthesia may also increase the risk of LAST. These include:
- Infiltration techniques (injecting the anesthetic subcutaneously)
- Central neuraxial blocks (epidural and caudal blocks)
- Continuous infusion of local anesthesia
In addition, the risk of developing LAST significantly increases when an anesthetic injection is administered in body parts that have a lot of blood vessels.
Is There a Way To Prevent Local Anesthetic Systemic Toxicity?
Unfortunately, it is not always possible to prevent LAST. However, doctors may recommend some tips to reduce the risk. For instance, some doctors may give you the lowest effective dose of an anesthetic or use ultrasound imaging to guide a local anesthetic injection, which reduces the risk of injecting into a blood vessel.
Diagnosis
Physicians usually diagnose LAST based on the symptoms. They usually diagnose it quickly because it is a medical emergency and they cannot delay it. Sometimes, healthcare professionals will perform an electrocardiogram (ECG or EKG) to diagnose LAST. This is a painless and quick test used to measure the electrical activity of the heart. It may also help diagnose irregular heart rhythms (arrhythmias).
Treatment
Usually, physicians recommend the following treatment options for people who develop LAST. Examples include:
- Airway management – During this option, doctors will provide ventilation and oxygen therapy to manage your breathing.
- Seizure prevention or treatment – This involves medicines (such as benzodiazepines) to prevent or treat seizures.
- IV infusion or lipid emulsion – Healthcare providers will inject this medicine into a vein to reverse LAST. It absorbs local anesthetic from the blood and other body tissues.
- CPR – Physicians usually recommend this treatment option to restore heart function.
After treatment, you should stay in the hospital for about 5-6 hours to make sure the treatment is effective and you do not develop other complications.
Frequently Asked Questions
How quickly does local anesthetic systemic toxicity (LAST) develop?
LAST usually develops within a few minutes after a local anesthetic is injected. However, in some cases, symptoms may appear 30 minutes or longer after the procedure, especially with continuous infusions or slow absorption from tissues.
Which local anesthetics are most commonly associated with LAST?
Any local anesthetic can potentially cause LAST if it enters the bloodstream in excessive amounts. However, Bupivacaine has historically been associated with a higher risk of severe cardiovascular toxicity. Other local anesthetics, such as Lidocaine, Ropivacaine, and Mepivacaine, can also cause LAST under certain circumstances.
Is local anesthetic systemic toxicity common?
No. LAST is considered a rare complication of local anesthesia. Thanks to careful dosing, ultrasound-guided injections, and improved monitoring techniques, it occurs infrequently. Nevertheless, healthcare providers are trained to recognize and treat it immediately because it can become life-threatening.
Can LAST occur after dental procedures?
Yes. Although uncommon, LAST can occur after dental procedures that require local anesthetics, particularly if the medication is accidentally injected into a blood vessel or if excessive doses are used. Dentists are trained to reduce this risk by using proper injection techniques and monitoring patients.
Can children develop local anesthetic systemic toxicity?
Yes. Children can develop LAST, although it is rare. The risk may increase if the anesthetic dose is too high for the child’s weight. Healthcare providers carefully calculate doses based on body weight to minimize this risk.
What should I do if I experience symptoms of LAST after receiving a local anesthetic?
Seek emergency medical attention immediately. Early symptoms, such as ringing in the ears, numbness around the mouth, dizziness, confusion, or a metallic taste, should never be ignored because they may rapidly progress to seizures or serious heart problems.
Can LAST cause permanent damage?
If treated promptly, most people recover completely without long-term complications. However, delayed diagnosis or treatment may lead to brain injury, heart damage, or other serious complications caused by prolonged seizures or cardiac arrest.
Who is at the highest risk of developing LAST?
People with liver disease, kidney disease, heart disease, pregnancy, metabolic disorders, advanced age, or reduced oxygen levels may have a higher risk. Individuals receiving large doses of local anesthetics or injections into highly vascular areas are also at increased risk.
How do healthcare providers reduce the risk of LAST during procedures?
Healthcare professionals lower the risk by calculating the correct dose, injecting the medication slowly, frequently aspirating before injection to check for blood vessel placement, using ultrasound guidance when appropriate, and closely monitoring the patient throughout the procedure.
Can I receive local anesthesia again after experiencing LAST?
Yes, in many cases, but only after discussing your medical history with your healthcare provider. If you have previously experienced LAST, your medical team may choose a different anesthetic, use a lower dose, or take additional precautions to reduce the risk of recurrence. If you have any other questions, ask your healthcare provider.
