Anesthesia Student Survival Guide.pdf - Index of

72 ● AnesthesiA student survivAl Guide
the low pH and metabisulfite preservative in the solutions used. Plain,
preservative-free 2-chloroprocaine in appropriate intrathecal doses
appears to be no more neurotoxic than other commonly used spinal
anesthetic solutions, and it may carry a reduced risk of TNS (see below).
Transient neurologic symptoms (TNS): Patients receiving spinal anesthesia
may have transient hypesthesias, paresthesias, and motor weakness in
the legs or buttocks. TNS is significantly more common with lidocaine
than with bupivacaine or tetracaine (and likely 2-chloroprocaine). TNS
symptoms typically resolve within 3 days, but occasionally may persist
for as long as 6 months.
● Methemoglobinemia: Larger doses of prilocaine and benzocaine (a common
ingredient in local anesthetic sprays) can convert hemoglobin to methemoglobin.
Infusion of 1–2 mg/kg of methylene blue reverses this reaction.
● Hypersensitivity/Allergy: While an adverse reaction to a local anesthetic
is not uncommon, a true allergy is exceedingly rare. Allergic reactions are
most often associated with esters because of sensitivity to their metabolite,
para-aminobenzoic acid (PABA). Should this occur, consider switching to
an amide anesthetic.
Treatment of Local Anesthetic Toxicity
Infusion of 20% lipid emulsion solution (such as Intralipid) has been reported to
be effective in reversing the symptoms of local anesthetic toxicity. The presumed
mechanism of action is that the lipid-soluble fraction of the local anesthetic
is sequestered in the lipid emulsion and effectively removed from the plasma.
Although this treatment is still being investigated, the following treatment
protocol has been proposed (see www.lipidrescue.org):
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Bolus 1.5 mL/kg of 20% lipid emulsion, then run 0.25 mL/kg/min for
30–60 min.
Repeat the bolus dose for persistent asystole.
Increase the infusion rate for hypotension.
Case Study
A 70 kg otherwise healthy male patient is undergoing bilateral inguinal
herniorrhaphy under local anesthesia administered by the surgeon and intravenous
sedation you are giving. The surgeon is planning to infiltrate the skin
with lidocaine prior to skin incision.