Understanding Local Anesthetic Systemic Toxicity (LAST)
Local Anesthetic Systemic Toxicity (LAST) is a rare but critical adverse drug reaction caused by high levels of a local anesthetic in the bloodstream. This can occur due to accidental injection into a blood vessel, a high dose, or rapid absorption. Local anesthetics block voltage-gated sodium channels in nerve cells to prevent pain, but toxic concentrations can affect these channels in the central nervous system (CNS) and heart, leading to dysfunction. The clinical picture can be complex, and while prompt treatment with therapies like lipid emulsion is highly effective, delayed recognition can have severe consequences.
The Manifestations: What are the symptoms of the last syndrome?
The signs and symptoms of LAST primarily affect the central nervous system and the cardiovascular system, with presentations ranging from subtle to life-threatening. The clinical course is variable and influenced by the specific local anesthetic and patient factors.
Central Nervous System (CNS) Symptoms
Typically, CNS symptoms occur first, starting with excitation and progressing to depression.
Initial excitatory signs:
- Metallic taste
- Perioral paresthesia
- Tinnitus
- Dizziness
- Visual disturbances
- Agitation/Confusion
- Slurred speech
- Muscle twitching/tremors
Late depressive signs:
- Seizures
- Lethargy/Drowsiness
- Loss of consciousness/Coma
- Respiratory depression/arrest
Cardiovascular System (CVS) Symptoms
Cardiovascular effects are dangerous and can occur after CNS signs or, in atypical cases, without preceding neurological symptoms.
Cardiovascular signs:
- Heart rate changes (bradycardia, tachycardia)
- Hypotension
- Arrhythmias
- Decreased contractility/conduction abnormalities
- Cardiac arrest
Atypical Presentations
Atypical presentations occur in approximately 40% of cases, without the classic progression. Patients may present only with cardiovascular symptoms, and onset can be delayed by over an hour. Bupivacaine is more likely to cause significant isolated cardiac issues.
Factors Influencing LAST Severity
Factors like the local anesthetic used, dose, and patient characteristics influence risk and severity. High-potency agents like bupivacaine pose a higher cardiac toxicity risk. Patient factors include age extremes, pregnancy, and pre-existing heart, liver, or kidney disease.
Comparison of Mild vs. Severe LAST Symptoms
Severity guides medical response:
| Severity | Central Nervous System (CNS) Symptoms | Cardiovascular System (CVS) Symptoms |
|---|---|---|
| Mild | - Metallic taste - Numbness around mouth - Tinnitus - Dizziness - Agitation - Confusion |
- Mild hypertension - Mild tachycardia |
| Severe | - Seizures - Slurred speech - Visual disturbances - Loss of consciousness - Respiratory depression - Coma |
- Hypotension - Bradycardia - Arrhythmias - Conduction blocks - Cardiac arrest (asystole, VF) |
Emergency Management of LAST
Rapid response is essential. Key steps involve discontinuing the anesthetic, supportive care, and targeted treatment, including 20% lipid emulsion.
Immediate Actions include:
- Stop Injection: Immediately cease anesthetic administration.
- Call for Help: Activate emergency protocols.
- Airway Management: Ensure a patent airway, provide oxygen, and assist ventilation.
- Seizure Control: Use benzodiazepines (Propofol cautiously due to hypotension risk).
- Lipid Emulsion Therapy: Infuse 20% lipid emulsion (bolus then infusion).
- ACLS: Implement ACLS for cardiac arrest, with modifications like using small epinephrine doses.
Conclusion: Vigilance and Preparedness
LAST is rare but severe. Prevention (lowest effective dose, intermittent injection, ultrasound guidance) is vital. Due to atypical presentations, suspect LAST with unexpected neurological or cardiovascular changes. Prompt recognition of what are the symptoms of the last syndrome? and immediate treatment are critical. More information is available from the Anesthesia Patient Safety Foundation.
