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In anesthetized patients, cardiovascular instability is commonly the first recognized symptom of Local Anesthetic Systemic Toxicity (LAST) because the typical early neurological warning signs—such as circumoral numbness, facial tingling, metallic taste, tinnitus, and restlessness—are masked by general anesthesia. 1, 2
Why Cardiovascular Manifestations Appear First in Anesthetized Patients
- Under general anesthesia, patients cannot report the prodromal central nervous system (CNS) symptoms that typically herald LAST, including perioral tingling, pressured speech, auditory changes, and restlessness 1, 3
- Approximately one-fifth of reported LAST cases present with isolated cardiovascular disturbance without preceding neurological symptoms, and this proportion is higher in anesthetized patients who cannot communicate subjective symptoms 2
- The cardiovascular system manifestations—including bradycardia, hypotension, arrhythmias, and cardiovascular collapse—become the first objectively detectable signs when CNS warning symptoms are obscured by anesthesia 1, 2
Clinical Presentation Sequence in Awake vs. Anesthetized Patients
- In awake patients, LAST typically progresses through a predictable sequence: CNS excitation (tingling, tinnitus, metallic taste) → seizures or CNS depression → cardiovascular toxicity → cardiac arrest 1, 3
- In anesthetized patients, this protective early warning system is eliminated, and practitioners may first observe unexplained tachycardia, hypertension, or sudden cardiovascular collapse without preceding recognizable signs 1, 2
- Bupivacaine is particularly notorious for causing sudden profound bradycardia and asystole, which may occur with minimal warning even in the absence of prior CNS symptoms 3, 2
Critical Monitoring Implications
- ECG monitoring should be continuous during regional anesthesia in anesthetized patients, though cardiovascular signs and ECG changes represent late manifestations of toxicity 4
- Unexplained cardiovascular instability during or immediately after local anesthetic administration in an anesthetized patient should trigger immediate consideration of LAST, even without seizure activity 1, 2
- Bupivacaine-induced cardiovascular toxicity is particularly severe and may manifest as sudden ventricular arrhythmias including fibrillation at doses below those causing convulsions 3, 5
Common Pitfall to Avoid
- Do not attribute unexplained cardiovascular instability in anesthetized patients to other causes (hypovolemia, surgical stimulation, anesthetic depth) without first considering LAST, especially if local anesthetic was recently administered 1, 2
- Cardiovascular collapse from LAST can occur suddenly and may be refractory to standard resuscitation, requiring immediate lipid emulsion therapy (1.5 mL/kg of 20% solution over 1 minute, followed by infusion of 0.25 mL/kg per minute) 4, 6