General anesthesia

General anesthesia implies the use of an agent which not only produces analgesia, i.e., loss of pain sensation but also loss of consciousness. In addition to this loss of conscious­ness anesthetic agents possess the power of eliminating motor nerve impulses which result in more or less complete muscular relaxation. This property is possessed by the agents in varying degrees, and determines in part the choice of anesthetic depending, of course, on the degree of muscular relaxation required by the particular operation.

Preanesthetic medication. Legitimately regarded as part of the anesthetic procedure is the administration of preparatory drugs. A sedative drug, such as morphine, will allay ap­prehension, reduce the amount of anesthetic agent required, and make the anesthesia smoother. Atropine will minimize pharyngeal secretions reducing the tendency to obstruc­tion and aspiration. The dosage of these drugs should be carefully individualized. The aged can tolerate much less sedation than the young adults. Factors, which alter the meta­bolic rate, will correspondingly increase or decrease the dosage required. Fever, pain, ex­citement will all increase the amount of premedication required. The anesthetic agent to be used and the degree of relaxation to be achieved must also modify the dosage.

Stages and signs of general anesthesia. General anesthesia is divided into four stages. The first is the stage of analgesia in which there is a progressive loss of sensation but not of consciousness. The second is the stage of excitement during which the patient, though already unconscious, tends to exhibit a hyperactivity which occasionally requires forcible restraint. The third is the stage of surgical anesthesia during which operations may be car­ried out. There may be certain reflex responses to stimuli but these diminish and relaxation increases as anesthesia deepens. This stage is divided into four planes. Entry into the first plane is indicated by loss of the eyelid reflex; into the second plane by cessation of eyeball movement; into the third plane by beginning intercostal paralysis; and into the fourth plane by complete intercostal paralysis; breathing being entirely diaphragmatic. The fourth, ago­nal stage is that of complete respiratory paralysis; this should be regarded as very danger­ous and usually constitutes a respiratory emergency.

Respiration may be irregular in the second stage but becomes full and regular in the first plane of the third stage. The pupil may be dilated during excitement but contracts in the first plane of the third stage. As anesthesia deepens the pupil tends to dilate, that is the sign of inadequate respiratory exchange. Deep anesthesia in one patient may be produced by a low concentration of the drug, while it may require an unusually high concentration in an­other. The anesthetist must therefore think of the patient’s response rather than of percentages.

The immediate postoperative period is of great importance, as several hours may elapse before complete consciousness is regained. During this time the upper air passages must be kept open. Constant attendance by a nurse is essential.

The air passages. Of primary importance in giving any anesthetic is the patency (Patency - the state of being freely open) of the air passages. After relaxation occurs, the tongue tends to drop back and, aided by the accumulation of mucus, a partial obstruction of the pharynx may thus occur. This is avoided to a large extent by elevation of the pa­tient’s chin and by holding the head back, the fingers of the anesthetist grasping the under surface of the mandible for this purpose.