As most patients are anxious in the preoperative period, premedication with an anxiolytic agent is often given in the preoperative holding area. Once upon the operating table, the patient is preoxygenated before being induced rapidly and smoothly with an intravenous hypnotic and narcotic.
Induction of a full general anesthesia requires airway control with either a laryngeal mask airway (LMA) or an endotracheal tube, whose placement may require transient muscle paralysis.
Muscle relaxants such as succinylcholine or nondepolarizing neuromuscular blocking agents should be used for those operations requiring muscular looseness if it is not provided by the anesthetic agent. By the use of these drugs, adequate muscular relaxation can be obtained in a lighter plane of anesthesia, thereby reducing the myocardial and peripheral circulatory depression observed in the deeper planes of anesthesia. In addition, the protective reflexes, such as coughing, return more quickly if light planes of anesthesia are maintained. Finally, however, it is important to note that the mycin-derivative antibiotics may interact with curare-like drugs so as to prolong their effect with inadequate spontaneous respiration in the recovery area and may lead to extended respiratory support.
When the maximum safe dosages of local anesthetic agents are exceeded, the incidence of toxic reactions increases. These reactions, which are related to the concentration of the local anesthetic agent in the blood, may be classified as either central nervous system stimulation (i.e., nervousness, sweating, and convulsions) or central nervous system depression (i.e., drowsiness and coma). Either type of reaction may lead to circulatory collapse and respiratory failure. Resuscitative equipment consisting of positive-pressure oxygen, intravenous fluids, vasopressors, and an intravenous barbiturate should be readily available during all major operative procedures using large quantities of local anesthesia. The intensity of anesthesia produced by the local anesthetic agents depends on the concentration of the agent and on the size of the nerve. As the size of the nerve to be anesthetized increases, a higher concentration of anesthetic agent is utilized. Since the maximum safe dose of lidocaine (Xylocaine) is 300 mg, it is wise to use 0.5% lidocaine when large volumes are needed.
The duration of anesthesia can be prolonged by the addition of epinephrine to the local anesthetic solution. Although this prolongs the anesthetic effect and reduces the incidence of toxic reactions, the use of epinephrine is not without danger. Its concentration should not exceed 1:100,000; that is, 1 mL of 1:1,000 solution in 100 mL of local anesthetic agent. After the operative procedure has been completed and the vasoconstrictive effect of the epinephrine has worn off, bleeding may occur in the wound if meticulous attention to hemostasis has not been given. If the anesthetic is to be injected into the digits, epinephrine should not be added because of the possibility of producing gangrene by occlusive spasm of these end arteries, which do not have collaterals. Epinephrine is also contraindicated if the patient has hypertension, arteriosclerosis, and coronary or myocardial disease.
In any surgical practice, occasions arise when the anesthesiologist should refuse or postpone the administration of anesthesia. Serious thought should be given before anesthesia is commenced in cases of severe pulmonary insufficiency; with elective surgery in the patient with myocardial infarction less than 6 months prior; severe unexplained anemia; with inadequately treated shock; in patients who recently have been or are still on certain drugs such as monoamine oxidase (MAO) inhibitors and certain tricyclic antidepressants that may compromise safe anesthesia; and, finally, in any case in which the anesthesiologist feels he or she will be unable to manage the patient’s airway, such as Ludwig’s angina, or when there are large masses in the throat, neck, or mediastinum that compress the trachea.