Local Anesthestics

The concentration of local anesthetic (LA) is a crucial factor in determining the rate of diffusion into the nerve. In general, higher concentrations of LA will provide a more rapid onset. Bupivacaine is a longer-acting local anesthetic that may be preferred for procedures that require extended anesthesia or prolonged post-procedure pain control.

Epinephrine is often added to local anesthetic solutions to provide local vasoconstriction, which can prolong the duration of the block. There has been some concern about using epinephrine when performing procedures on digits. However, it is important to note that the risk of local anesthetic-associated gangrene is primarily associated with the acidity of the solution rather than the addition of epinephrine. Recent reviews have shown that epinephrine is safe to use in most situations.

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Local Anesthetic Systemic Toxicity (LAST)

LAST is a life-threatening condition which can occur when local anesthetic reaches high levels in the circulation. It can occur because of an inadvertent intravascular injection or overdose. While it is rare to overdose, it can be missed if multiple repairs or teams are performing procedures, as the doses are cumulative.

Symptoms include:

• Neurologic: Parethesia. Tinnitus, Visual Disturbances, AMS, Seizures, Coma

• Cardiac: Tachycardia, Transient Hypertension, Hypotension, Dysrhythmias, Cardiac Arrest

Early signs and symptoms are subtle and may not be readily apparent so a high index of suspicion is required.

Management

• Initial stabilization

  1. Stop the injection

  2. Manage ABCs

  3. Treat seizures with benzodiazepines

  4. Obtain EKG looking for treatable arrhythmias

• IV bolus of 20% lipid emulsion 1.5 ml/kg over 1 min followed by infusion at 15 ml/kg/h

  Early administration of lipid emulsion should be considered in suspected LAST to help reverse central nervous system symptoms and to interrupt the progression toward cardiovascular collapse. The lipid emulsion is thought to act as a "lipid sink," whereby lipid would bind the local anesthetic to remove it from target tissues. 

• After 5 min if patient is still unstable, give a maximum of two repeat boluses (1.5 ml/kg) and double the infusion rate (30 ml/kg/h)

  Infusion should continue for at least 10 minutes after cardiovascular stability has been achieved. Monitoring should continue because of possible persistent or recurrence of cardiovascular depression even after lipid emulsion treatment.

References

1. Lönnqvist PA. Toxicity of local anesthetic drugs: a pediatric   perspective. Paediatr Anaesth. 2012 Jan;22(1):39-43. doi:   10.1111/j.1460-9592.2011.03631.x. Epub 2011 Jun 14.

2. Wathen J, Neubrand T, Do H. Regional Anesthesia in the Pediatric   Emergency Department. Clinical Pediatric Emergency Medicine.18 (4).