Local Anesthetic Systemic Toxicity - Symptoms, Treatment and Risk Factors

Introduction

Local anesthetics (LAs) are commonly used by healthcare providers like anesthesiologists, surgeons, dentists, etc. Many people mistakenly believe these LAs are completely safe without side effects. However, there is a potential risk of local anesthetic systemic toxicity (LAST), which can affect the central nervous and cardiovascular systems. In severe cases, it can be fatal. LAST can happen with any local anesthetic, regardless of its use.

What Is Meant by Local Anesthetic Systemic Toxicity?

Local anesthetic systemic toxicity (LAST) is a severe and potentially life-threatening reaction when a local anesthetic for pain relief enters the bloodstream and spreads throughout the body. This reaction is very rare and usually happens soon after the local anesthetic injection.

What Are the Symptoms of LAST?

Local anesthetic systemic toxicity (LAST) symptoms are related to the amount of local anesthetic in the bloodstream.

For instance, with Lidocaine, the symptoms may start with:

• Tongue numbness.

• Feeling lightheaded.

• Experiencing visuals.

• Hearing disturbances.

The symptoms then progress to:

• Muscle twitches.

• Unconsciousness.

• Seizures.

The symptoms have severe outcomes like:

• Coma.

• Breathing disturbances (respiratory arrest).

• Heart-stopping (cardiac arrest).

What Are the Treatment Followed for LAST?

Immediate action is essential if a patient shows signs of local anesthetic systemic toxicity (LAST).

• Stop the injection immediately if any signs of the local anesthetic getting into the blood vessels are noticed.

• Call for qualified help and get the LAST kit and checklist ready.

• Prepare to transfer the patient to the nearest medical facility for further treatment, as cardiopulmonary bypass (CPB) may be needed if standard life-saving measures fail.

• Manage the patient's airway by giving them 100 % oxygen, using a mask or tube to control their breathing, and preventing low oxygen levels and acidity in the blood, as these can worsen LAST.

• If the patient experiences seizures, use medications like benzodiazepines to control them and prevent further complications. Other drugs like Propofol or Thiopental can also be used with caution. A medication called Succinylcholine can help stop muscle movements during seizures.

• Address any heart rhythm problems and provide support for the cardiovascular system. In some cases, CPR may be required for an extended period.

• Amiodarone is the primary medication to treat abnormal heart rhythms, avoiding drugs like Lidocaine and other sodium channel blockers.

• Limit the dose of epinephrine (a medication used in emergencies) to prevent harmful effects on the heart.

• Vasopressin and calcium channel blockers should also be avoided as they may worsen low blood pressure.

• Administer lipid rescue by giving a 20 % lipid emulsion and standard life-saving measures or when neurotoxicity is suspected. The specific amounts and rates of the lipid emulsion are not crucial, but they should be given carefully according to the guidelines.

• Keep the patient under close monitoring and transfer them to a medical facility with appropriate monitoring capabilities for further care.

What Are the Risk Factors Associated With LAST?

Factors that increase the risk of local anesthetic systemic toxicity (LAST) can be divided into three categories: the drug, the patient's characteristics, and the technique used during administration.

1. The Drug Itself:

   1. The ratio of the drug dose needed to cause severe cardiovascular collapse compared to the dose that triggers seizures is called the CC/CNS ratio.

   2. A lower CC/CNS ratio means the drug is more likely to harm the heart, while a higher ratio indicates a safer drug.

   3. Using drugs with higher CC/CNS ratios, like Ropivacaine and Levobupivacaine, can be safer when long-acting local anesthesia is needed.

   4. All local anesthetics, however, have the potential to induce LAST.

   5. Local anesthetics may have different effects on blood vessels. Some may cause blood vessels to constrict, slowing down the absorption of the drug, while others may dilate blood vessels, leading to faster absorption.

   6. The correct dose of local anesthetic should be used to achieve the desired pain relief or anesthesia.

   7. People may respond differently to the same dose depending on factors like how the drug is given, the patient's characteristics, and individual differences.

2. The Patient Characteristics:

1. The ratio of the drug dose needed to cause severe cardiovascular collapse compared to the dose that triggers seizures is called the CC/CNS ratio.

2. A lower CC/CNS ratio means the drug is more likely to harm the heart, while a higher ratio indicates a safer drug.

3. Using drugs with higher CC/CNS ratios, like Ropivacaine and Levobupivacaine, can be safer when long-acting local anesthesia is needed.

4. All local anesthetics, however, have the potential to induce LAST.

5. Local anesthetics may have different effects on blood vessels. Some may cause blood vessels to constrict, slowing down the absorption of the drug, while others may dilate blood vessels, leading to faster absorption.

6. The correct dose of local anesthetic should be used to achieve the desired pain relief or anesthesia.

7. People may respond differently to the same dose depending on factors like how the drug is given, the patient's characteristics, and individual differences.

3. The Technique Used During Administration:

1. Different regional anesthesia techniques carry varying risks of local anesthetic systemic toxicity (LAST).

2. Infiltration techniques (injecting local anesthetics into tissues) have the highest association with LAST, followed by spinal injections and continuous infusions of local anesthetics.

3. Factors like the dose of the local anesthetic and the blood flow at the injection site can influence the risk of LAST.

4. Specific techniques like fascial plane blocks, continuous catheter techniques, and local anesthesia during joint replacement surgeries have their risks for LAST.

5. Some types of local anesthetics, like liposomal Bupivacaine, may have a lower risk of LAST, but caution is still necessary.

6. Tumescent anesthesia used in liposuction and topical anesthesia in the airway can also pose risks.

7. Intravenous injections of local anesthetics, such as Bier blocks, and other less common situations can also lead to LAST.

8. Awareness of these risks and taking proper precautions to prevent and manage LAST is crucial, particularly in non-hospital settings and when administered by non-anesthesiology specialists.

Conclusion

Local anesthetic systemic toxicity (LAST) is a severe and life-threatening problem that can occur when using local anesthetics. Healthcare providers must know the causes, risk factors, and ways to prevent and treat them to keep patients safe. Prevention is the most critical aspect of managing LAST. Healthcare providers should know the correct dosage and maximum allowed dose of local anesthetics. Before injecting, they should check for any signs of complications and ask patients about any symptoms they might be experiencing.