Local Anesthetic Systemic Toxicity Last

Overview

Local anesthetic systemic toxicity — doctors often call it LAST — is a rare but serious reaction that can happen when numbing medicine (called a local anesthetic) gets into the bloodstream in larger amounts than the body can safely handle. Local anesthetics are the medicines used to numb a part of your body so you don't feel pain. They are used every day in dentistry, minor surgery, stitches, childbirth and many other procedures. Normally they stay where they are put. But if too much of the medicine reaches the blood, it can affect two things in particular: the brain and the heart. This is what LAST means. It is a medical emergency, but it is rare, and healthcare teams are trained to spot it and treat it straight away.

No, it is uncommon. Rates vary depending on the type of procedure and the amount of numbing medicine used, but most estimates put it at a handful of cases per 10,000 injections or fewer. In routine dental work and small skin procedures it is very rare indeed.

Anyone who receives a local anesthetic can, in theory, be affected — from a child having a tooth filled to an adult having a nerve block for surgery. Some people have a higher chance of it, including people with a low body weight, very young children and frail older adults, people with heart, liver or kidney problems, pregnant women, and people having large amounts of numbing medicine or certain types of nerve blocks. Your healthcare team weighs these factors when planning your care.

Symptoms

Common symptoms

• A metallic taste in the mouth
• Tingling or numbness around the mouth, lips or tongue
• Ringing, buzzing or other noises in the ears
• Feeling dizzy, light-headed or 'floaty'
• Blurred or odd vision
• A strange feeling that something is not right — many people describe it as 'feeling weird'
• Feeling restless, agitated or suddenly very sleepy
• Slurred speech or trouble finding words
• Muscle twitching or shaking, especially in the face or hands
• Feeling sick or vomiting
• Later signs, if the reaction is not treated: a seizure, an irregular heartbeat, collapse or difficulty breathing

Symptoms in children

• Young children may not be able to describe early signs, so watch for behaviour changes
• Sudden unusual sleepiness or being hard to wake
• Confusion, staring or not responding normally
• Twitching, jerking or shaking movements
• Vomiting or complaining of feeling unwell
• Crying in a way that seems different from usual, or sudden stillness
• Breathing changes or going floppy

Symptoms in older adults

• New or sudden confusion, which can be mistaken for other conditions
• Agitation or restlessness that is out of character
• Dizziness or unsteadiness, which may lead to a fall
• Unusual drowsiness
• Irregular heartbeat, palpitations or chest discomfort
• Slurred speech or weakness, which can be confused with a stroke
• Older adults with heart, liver or kidney disease are at higher risk and may show signs at lower doses

Causes

Main causes

• Receiving a larger amount of numbing medicine than your body can clear quickly
• The medicine accidentally going into a blood vessel instead of the surrounding tissue
• Injecting into an area that is inflamed or infected, where the medicine spreads differently
• Giving the injection quickly rather than slowly
• Using certain types of numbing medicine that stay in the body longer
• Applying large amounts of numbing cream or gel to broken skin or to a large area
• Combining more than one kind of numbing medicine, or mixing numbing medicine with other substances
• Repeated doses given close together

Risk factors

• Low body weight or small body size
• Being very young or being frail and older
• Heart, liver or kidney problems
• Pregnancy
• Taking certain medicines that affect the heart rhythm or blood pressure
• Having a large volume of numbing medicine or a specialised nerve block
• Having a procedure in an area with a lot of blood vessels, such as the neck or certain nerve sites
• Not having eaten, or being very tired or anxious — these do not cause LAST, but they can make early signs harder to notice

When to see a doctor

See a doctor urgently if:

• If you feel unwell in any way during or soon after a numbing injection, tell the clinician immediately — even if it seems minor
• If you have had a mild reaction in the past (such as a metallic taste or dizziness), tell your dentist, GP or surgeon before any future procedure
• If you have heart, liver or kidney problems and are due to have a procedure with numbing medicine, mention it when you are booked in
• If you are taking medicines for your heart or blood pressure, tell the team planning your procedure

Book a routine appointment if:

• You feel anxious about a past numbing injection or about an upcoming procedure
• You want to know whether a previous reaction was related to numbing medicine
• You are planning dental work, surgery or a procedure and want to discuss your history beforehand
• You have questions about which type of numbing medicine is safest for you

Diagnosis

LAST is diagnosed from the story and the timing rather than from a single test. A clinician recognises it when someone develops the typical warning signs — such as a metallic taste, tingling around the mouth, dizziness, confusion or twitching — shortly after receiving numbing medicine. Treatment usually starts straight away based on these signs, without waiting for test results.

Tests that may be done

• Continuous monitoring of heart rate, blood pressure, breathing and oxygen levels
• An electrocardiogram (ECG) to check the heart's rhythm
• Blood tests to check oxygen, blood sugar, salt levels and how well your organs are working
• Blood tests to help rule out other causes of a seizure or confusion
• Tests to rule out other conditions, such as low blood sugar, a stroke or an allergic reaction

What to expect at your appointment

If LAST is suspected, you will be treated where you are, and an ambulance will usually be called. Staff will stop giving the numbing medicine, give you oxygen, check your breathing and heart, and start treatment straight away. You may be moved to an emergency department or a high-dependency unit for close watching. Most people are monitored for several hours, and you may be asked to stay overnight. You may feel shaken afterwards and want to talk it through — ask your team to explain what happened when you are ready.

Treatment

LAST is an emergency, but it is one that healthcare teams are trained and equipped to handle. Treatment focuses on supporting your breathing and circulation, stopping the effects of the numbing medicine, and protecting your brain and heart until the medicine has cleared from your body. The medicine naturally wears off over time, and the job of the medical team is to keep you safe while that happens.

Self-care at home

• During any procedure, speak up immediately if you notice a metallic taste, tingling lips, ringing ears, dizziness or a strange feeling
• Do not drive or travel home alone until the clinical team say you are ready
• After a reaction, ask for a written record of what happened and which medicine was involved, so future clinicians can plan safely
• Tell your dentist, GP and any surgeon about a previous reaction before future procedures
• Rest and drink fluids after the procedure, and avoid alcohol for the rest of the day
• Allow yourself time to recover emotionally — feeling anxious afterwards is common and understandable

Medical treatments

Treatment is given in a monitored setting. The team stops any further numbing medicine, gives oxygen and supports breathing, and monitors the heart continuously. They use medicines to calm the brain and stop seizures, and medicines to steady the heart rhythm and blood pressure. In more serious cases, hospital teams use a special rescue treatment that helps mop up the numbing medicine from the bloodstream and protect the heart. Fluids and close monitoring continue until you are stable. The exact plan is decided by the clinical team based on your symptoms and your overall health.

When is surgery considered?

Surgery is not used to treat LAST. In rare cases, if the heart rhythm becomes seriously unstable, specialised emergency heart support may be needed in an intensive care setting.

Living with this condition

Most people who have had LAST recover fully and go back to normal life within days. You may be advised to avoid driving, operating machinery or making important decisions for a short while after the event, especially if you were given sedating medicines. Follow whatever aftercare advice your team gives you, and keep a note of the numbing medicine involved in case you need a procedure in future.

Lifestyle tips

• Carry a note or card about your reaction if your clinician advises it
• Tell every healthcare professional you see — including your dentist — about the reaction before any procedure
• Keep a list of all your medicines and bring it to appointments
• Eat something light before procedures unless you have been told not to eat
• Avoid alcohol and recreational substances before medical or dental appointments
• Build a calm routine around appointments — a short walk, breathing exercises or taking a friend along can help with nerves

Diet and exercise

There is no special diet or exercise plan for LAST. Eating normally and staying hydrated is helpful around procedures. Gentle everyday activity is fine once you feel well. If you were told to fast before a procedure, follow that advice. If you have been unwell, build your activity back up gradually and rest when you need to.

Mental health and emotional wellbeing

Being part of a medical emergency can leave you feeling anxious, shaken or on edge — especially if you need numbing medicine again in the future. Some people have intrusive memories or trouble sleeping for a while. These feelings usually settle, but they deserve attention. Talk to your GP or clinical team if worry is affecting your sleep, mood or everyday life. Dental anxiety and procedure anxiety are very treatable, and there are techniques and support that can help. If you are struggling with your mental health or having thoughts of harming yourself, contact your local crisis line or emergency services straight away — you deserve immediate support.

Prevention

LAST cannot always be prevented, but the risk is kept very low by careful practice. Clinicians use the smallest amount of numbing medicine that will work, inject slowly, and check that they are not in a blood vessel before injecting. They keep emergency equipment and oxygen nearby and watch for early warning signs. Your part is just as important: tell the team about your health conditions, your medicines, any previous reaction, and speak up at once if you feel strange.

Screening programmes

There is no routine screening test for LAST. Instead, your clinician assesses your risk before a procedure by asking about your health, your medicines and any past reactions, and by choosing the safest type and amount of numbing medicine for you.

Complications

If left untreated

• Continued seizures
• Dangerous irregular heart rhythms
• Very low blood pressure
• Cardiac arrest (the heart stopping)
• Breathing problems
• In rare cases, lasting injury to the brain or heart if treatment is delayed

Long-term outlook

The outlook is good for most people. LAST is rare, is recognised quickly in modern practice, and has an effective emergency treatment. Many people feel back to normal within a day or two and have no lasting effects. If you ever need numbing medicine again, your team can plan around your history to make the procedure as safe as possible. Most people go on to have dental treatment, surgery and other procedures without any further problems.

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