On the basis of anatomic considerations, regional anesthesia may
be divided into infiltration anesthesia, intravenous regional anesthesia, peripheral
nerve blockade (including plexus blockade), central neural blockade, and topical
anesthesia. An additional method of local anesthetic injection, tumescent anesthesia,
is included because it is widely used in office plastic surgery practice.
Infiltration Anesthesia
Any local anesthetic may be used for infiltration anesthesia.
The onset of action is almost immediate for all agents after intradermal or subcutaneous
administration; however, the duration of anesthesia varies ( Table
14-4
). Epinephrine will prolong the duration of infiltration anesthesia
by all local anesthetics, although this effect is most pronounced when epinephrine
is added to lidocaine. The choice of a specific drug for infiltration anesthesia
largely depends on the desired duration of action.
The dosage of local anesthetic required for adequate infiltration
anesthesia depends on the extent of the area to be anesthetized and the expected
duration of the surgical procedure. When large surface areas have to be anesthetized,
large volumes of dilute anesthetic solutions should be used. These considerations
are particularly important when performing infiltration anesthesia in infants and
smaller children. As an example, consider a 4-kg infant receiving infiltration anesthesia
with the maximum safe dose of lidocaine, 5 mg/kg. Dosing to 5 mg/kg ×
4 kg permits the administration of 20 mg, which is 1 mL of a 2% solution
or 4 mL of a 0.5% solution. Lidocaine is effective for infiltration anesthesia in
concentrations as dilute as 0.3% to 0.5%, so the more dilute solution can be used
to more safely anesthetize a larger area.
Patients frequently experience pain immediately after the subcutaneous
injection of local anesthetic solutions,[71]
in
part because of the acidic nature of these solutions.[72]
[73]
For example, neutralization of lidocaine solutions by the addition of sodium bicarbonate
reduces pain on skin infiltration and may improve the onset of action (see earlier).
