Practical Application of Local Anesthetics

This involves considerable art, which must be learned in the clinic. It falls into two divisions (1) surface application to the mucous membranes, especially of the eye, nose, throat, and urethra and (2) injections about nerves, in different parts of their course and distribution, from their spinal roots to their ultimate fibrils. The advantages and disadvantages in comparison with general anesthesia and the selection of the local anesthetic agent also depend on clinical discrimination. Nervous, fearful, and excitable patients often suffer severely from apprehension, which also disposes toward accidents. They may be at least somewhat quieted by sedatives, morphine (0.015 g hypodermically) half an hour before the operation, or by barbiturates. The latter also tend to prevent convulsions. 

The onset of the action depends on the penetration into the nerve libers, and the duration on the sojourn of the drug. In general, the sensation becomes blunter in a few minutes but the anesthesia does not reach its maximum for 10 to 20 min and lasts 10 to 30 min, after a single application. The duration depends more on the concentration than on the total amount of the agent, so that it is more economical to use small quantities in high concentration, repeating if necessary. 

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