Chapter 14. Anesthesia—Local and Regional

When the equipment and the experienced personnel to give deep sedation or general anesthesia are not available, local and regional anesthetic techniques should be used. As one experienced anesthesiologist wrote, "We must assume that supplies of compressed gases will soon run out and replacements will be unobtainable. This leaves us with local techniques, spinal and epidural analgesia, all of which can be given by the surgeon in the absence of a trained anesthetist."1

Pharmacology

Topical anesthetics are slowly absorbed through normal skin. However, they are rapidly absorbed through the mucosa as well as through abraded, burned, and denuded skin. When using topical anesthetics in these areas—especially if used in the tracheobronchial tree—the maximum dose should be considerably less than that used for infiltration.2,3 Tetracaine, for example, produces higher blood levels at 5 minutes with mucosal application than with subcutaneous infiltration.4 When used in dentistry, topical anesthetics generally anesthetize only the outer 1 to 3 mm of mucosa.5

Common Anesthetics

Good topical anesthetics include lidocaine (lignocaine), cocaine, and tetracaine. Some anesthetics, such as procaine and mepivacaine, are not effective topically due to poor mucous membrane penetration.3

Lidocaine/lignocaine (amide) (2% to 10%) has a peak anesthetic effect in from 2 to 5 minutes. Its maximum safe total dose in a healthy 70-kg adult is ~250 mg and it is 3 mg/kg in children. Anesthetic effect lasts 30 to 45 minutes.2,3 Lidocaine gel 4% can be made by adding 2 mL of 2% lidocaine without epinephrine to 1 mL of a water-soluble jelly (e.g., K-Y). This gel works well, if placed under an occlusive dressing, to ease the pain of herpes zoster and other skin lesions.

Bupivacaine (amide) (0.25% to 0.5%) has a peak anesthetic effect in 2 to 5 minutes. Its maximum safe total dose in a healthy 70-kg adult is 400 mg/24 hours; it is 2 mg/kg in children, although it is not officially recommended for use in children <12 years old. Similarly, it is not recommended as a spinal anesthetic in those <12 years old. Anesthetic effect lasts 4 to 8 hours.

Cocaine (ester) (4% = usual dose) has a unique vasoconstricting effect. It reaches peak anesthetic effect in 2 to 5 minutes. However, it is addictive. The maximum safe total dose in a healthy 70-kg adult is 200 mg (2 to 3 mg/kg) and it is 2 mg/kg in children. The anesthetic effect lasts from 30 to 45 minutes.2,3 Staying within the maximum adult dose is easy if the standard package of 4 mL of the 4% solution is used. While making your own topical solution with cocaine obtained from noncommercial vendors may seem logical in an emergency, the problem is that neither the strength nor the purity of the ingredient is known.

Tetracaine (ester) (0.5% = ...