Lignocaine Associated Systemic Toxicity (LAST)

 Lidocaine Associated Systemic Toxicity (LAST)

Lidocaine Associated Systemic Toxicity (LAST) is a potentially life-threatening condition that occurs due to the excessive absorption of local anesthetics, particularly lidocaine, into the systemic circulation. LAST can result from inadvertent intravascular injection, overdose, or rapid absorption from highly vascularized areas.

 

Pathophysiology:

Lidocaine, like other local anesthetics, works by blocking sodium channels, inhibiting the initiation and propagation of nerve impulses. However, when systemic levels of lidocaine become excessively high, these sodium channels are blocked in vital organs such as the heart and brain, leading to serious complications.

Clinical Presentation:

LAST can manifest with a variety of symptoms that often progress through two stages:

1. Neurological Symptoms:
   • Early signs include circumoral numbness, metallic taste, tinnitus, and dizziness.
   • As toxicity increases, more severe symptoms such as seizures, altered mental status, and coma can occur.
2. Cardiovascular Symptoms:
   • Initial signs include hypertension and tachycardia due to sympathetic stimulation.
   • Severe toxicity can lead to life-threatening arrhythmias, profound hypotension, bradycardia, and even cardiac arrest.

Diagnosis:

The diagnosis of LAST is primarily clinical, based on the rapid onset of neurological and cardiovascular symptoms following the administration of a local anesthetic. A high index of suspicion is necessary, especially if symptoms develop soon after injection.

Management:

1. Immediate Actions:

   • Stop the administration of the local anesthetic.
   • Secure the airway, provide oxygen, and support ventilation.
   • Seizures should be managed with benzodiazepines. Avoid large doses of propofol or other agents that may worsen cardiovascular depression.

2. Lipid Emulsion Therapy:

   • Intravenous lipid emulsion (20%) is the cornerstone of treatment for LAST. It acts as a "lipid sink," sequestering the local anesthetic and reducing its free plasma concentration.
   • The standard initial dose is a bolus of 1.5 mL/kg over 1 minute, followed by an infusion at 0.25 mL/kg/min.

3. Cardiovascular Support:

• Use standard advanced cardiovascular life support (ACLS) protocols for managing arrhythmias and cardiac arrest.
• Avoid the use of vasopressin, calcium channel blockers, beta-blockers, or other drugs that may exacerbate toxicity.
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Prevention:

• Dose Calculation: Careful calculation of the maximum allowable dose of lidocaine is crucial.
• Aspiration Test: Always aspirate before injecting to avoid intravascular administration.
• Slow Injection: Administer the drug slowly and in incremental doses with frequent monitoring for early signs of toxicity.

Conclusion:

LAST is a rare but serious complication of local anesthetic administration that requires prompt recognition and treatment. Understanding the pathophysiology, clinical presentation, and management strategies is essential for anesthesiologists to mitigate risks and ensure patient safety.