What Happens if Lidocaine Gets in the Bloodstream?: Understanding Systemic Toxicity (LAST)

While generally safe when used as directed, systemic toxicity from local anesthetics like lidocaine is a rare but serious complication, occurring in as many as 1 in 2,000 peripheral nerve blocks. It's critical to understand what happens if lidocaine gets in the bloodstream, leading to adverse effects on the central nervous and cardiovascular systems.

Quick Summary

An unintended surge of lidocaine in the bloodstream can trigger systemic toxicity (LAST), a medical emergency affecting the nervous and cardiovascular systems. The severity depends on the concentration, potentially causing symptoms from dizziness and tremors to seizures, heart arrhythmias, and cardiac arrest.

Key Points

• Local Anesthetic Systemic Toxicity (LAST): Lidocaine toxicity occurs when the drug's plasma concentration exceeds safe levels.

• Biphasic Effects on the Central Nervous System (CNS): Symptoms can range from initial excitatory signs like dizziness and tinnitus to later CNS depression, seizures, and respiratory arrest.

• Cardiovascular Risks: High lidocaine levels can cause severe heart problems, including slow heart rate, low blood pressure, arrhythmias, and cardiac arrest.

• Causes of Overexposure: Toxicity can result from accidental injection into a blood vessel, overdose, or rapid absorption from certain areas, including misuse of topical products.

• Emergency Intervention: If LAST is suspected, stop lidocaine, manage the airway, and administer rescue medications like lipid emulsion.

• Lipid Emulsion: This intravenous therapy helps reverse severe cardiotoxicity by absorbing lidocaine from the blood.

Lidocaine is a local anesthetic that blocks sodium channels in nerve cells to prevent pain signals. When used properly in local or regional anesthesia, minimal amounts enter the bloodstream. However, situations like accidental injection into a blood vessel, using too much, or rapid absorption from certain tissues can cause lidocaine levels in the blood to become toxic. This condition is called Local Anesthetic Systemic Toxicity (LAST) and can quickly become serious, affecting the brain and heart.

Symptoms of Local Anesthetic Systemic Toxicity (LAST)

LAST symptoms usually start in the nervous system before affecting the heart and blood vessels. Symptoms can appear quickly, sometimes within minutes.

Central Nervous System (CNS) Effects

Initial symptoms often show increased activity in the CNS, which can later become depressed.

• Mild/Early Symptoms:
  • Feeling lightheaded or dizzy
  • Numbness or tingling around the mouth
  • A metallic taste
  • Ringing in the ears (tinnitus)
  • Blurred or double vision
  • Feeling restless, agitated, or unusually happy (euphoria)
• Severe Symptoms:
  • Muscle twitching and shaking
  • Difficulty speaking clearly
  • Seizures
  • In severe cases, the CNS can slow down too much, leading to difficulty breathing, losing consciousness, and coma.

Cardiovascular System (CVS) Effects

Heart and blood vessel problems usually happen at higher lidocaine levels but can sometimes occur without prior CNS symptoms.

• Initial Symptoms:
  • Faster heart rate and higher blood pressure
• Late/Severe Symptoms:
  • Slow heart rate or irregular heart rhythms
  • Very low blood pressure
  • Problems with the heart's electrical signals
  • Dangerous heart rhythms like ventricular tachycardia or fibrillation
  • The heart stopping and the circulatory system failing.

Mechanisms of Systemic Absorption

Several factors can cause dangerous amounts of lidocaine to enter the bloodstream:

• Injection into a Blood Vessel: Accidentally injecting lidocaine directly into a blood vessel is the most immediate and serious cause, with symptoms potentially appearing within minutes.
• Using Too Much: Giving a dose higher than recommended for the patient's size can lead to toxic levels.
• Misusing Topical Products: Applying topical lidocaine over a large area, on damaged skin (like cuts or burns), or covering the application area can significantly increase how much lidocaine gets absorbed into the body.
• Speed of Absorption: How quickly lidocaine enters the bloodstream depends on the area it's applied or injected into. Areas with lots of blood vessels, like during an intercostal nerve block, can lead to much higher blood levels than injections under the skin.
• Liver or Kidney Problems: People with liver or kidney issues may not be able to process and remove lidocaine from their body effectively, leading to a buildup of the drug and toxicity.

Comparison of Mild vs. Severe LAST Symptoms

Feature	Mild/Early Systemic Toxicity	Severe/Late Systemic Toxicity
Onset	Often starts within minutes, but can be delayed with slower absorption.	Can develop rapidly following early signs or appear without warning.
CNS Manifestations	Lightheadedness, dizziness, circumoral numbness, tinnitus, metallic taste, visual changes, restlessness, agitation.	Seizures, unconsciousness, coma, respiratory depression.
Cardiovascular Manifestations	Initial hypertension and tachycardia.	Hypotension, bradycardia, other arrhythmias, cardiac arrest.
Typical Progression	Excitatory CNS symptoms first, followed by CNS depression and CVS effects.	Rapid progression, often bypassing milder signs and leading directly to CNS depression or cardiac collapse.
Risk Factors	Incorrect injection technique, dose error, rapid absorption, increased patient sensitivity.	High-dose or repeated exposure, underlying heart disease, liver/kidney disease, infancy/elderly.

Emergency Management and Treatment

If LAST is suspected, immediate medical help is needed. The main goals are to make sure the person can breathe, has good circulation, and to give specific treatments.

1. Stop Lidocaine: Immediately stop giving or applying the lidocaine.
2. Get Help: Call for emergency services and experienced medical staff.
3. Support Breathing: Make sure the person is getting plenty of oxygen and help them breathe if needed. Fixing low oxygen and acidity in the blood is important as it can worsen toxicity.
4. Control Seizures: Give medication like midazolam or diazepam to stop seizures. Propofol can be used, but it should be considered carefully because it can affect the heart.
5. Treat Heart Problems: If blood pressure drops or heart rhythm is abnormal, follow standard protocols but use smaller doses of epinephrine. Avoid certain medications like vasopressin, calcium channel blockers, and beta-blockers. Sodium bicarbonate can be given for severe rhythm problems.
6. Use Lipid Emulsion: For severe heart problems caused by LAST, giving a 20% lipid emulsion through a vein is recommended. This treatment helps remove lidocaine from the blood and tissues, reducing its harmful effects on the heart and brain.

Conclusion

Lidocaine is a valuable medication, but if it gets into the bloodstream at high levels, it can cause serious toxicity. Recognizing the symptoms, from initial nervous system signs like dizziness and ringing in the ears to severe heart problems, is vital for quick and effective care. Preventing toxicity by using the correct dose and administration technique is key. If an overdose or accidental injection occurs, immediate medical attention, including breathing support, seizure control, and lipid emulsion therapy, is crucial for a positive outcome. For more detailed information on managing LAST, refer to guidelines from sources like {Link: NCBI Bookshelf https://www.ncbi.nlm.nih.gov/books/NBK499964/}.

Frequently Asked Questions

What are the first signs that lidocaine has entered the bloodstream excessively?

The first signs often involve the central nervous system and can include lightheadedness, dizziness, a metallic taste in the mouth, numbness around the mouth, and ringing in the ears (tinnitus).

How can lidocaine enter the bloodstream at toxic levels?

Toxic levels can be reached through accidental injection into a blood vessel, overdosage during a procedure, or rapid absorption from highly vascularized tissues, which can occur when applying high doses of topical products to damaged or large areas of the skin.

Are there any long-term consequences of local anesthetic systemic toxicity (LAST)?

Most patients recover from LAST without long-term issues, especially with rapid intervention. However, severe complications like prolonged seizures, respiratory arrest, or cardiac arrest can lead to long-term neurological or cardiac damage in rare cases.

What is lipid emulsion therapy, and how does it help with lidocaine toxicity?

Lipid emulsion therapy is an intravenous treatment for severe LAST. The lipid emulsion acts like a 'sink,' absorbing the lipid-soluble lidocaine from the bloodstream and tissues, which reduces the drug's concentration in the brain and heart.

Does lidocaine toxicity present differently in children?

Children, especially infants under 6 months, are at an increased risk of a serious blood problem called methemoglobinemia from lidocaine exposure. Symptoms can include pale, gray, or blue-colored skin.

What should be done immediately if someone shows signs of lidocaine toxicity?

Immediate steps include stopping lidocaine administration, calling for emergency medical assistance, ensuring the person's airway is clear, and providing oxygen.

Can topical lidocaine products cause systemic toxicity?

Yes, although systemic absorption from patches and gels is typically low, overuse, covering large areas of the body, or applying to compromised skin can lead to toxic blood levels and systemic toxicity.