General anesthesia means to render the entire patient to a state of unconsciousness without sensations or movement. This is accomplished by administering a drug which is carried to the brain by the blood stream, where it suppresses certain sensory and movement capacities. The drug, or anesthetic agent, may be administered by having the patient inhale it, by injecting it directly into the blood stream, or by placing it in the rectum.
When the anesthetic is given by inhalation methods, it is absorbed from the lungs into the blood stream. Likewise, in rectal administration (which is not commonly used) the agent is absorbed from the rectum into the blood stream. When the anesthetic drug is in the blood, it is carried to all parts of the body. The drug has various effects on many tissues, but on most there is no significant effect. Anesthesia produced by the agent depends on the specific depressing action on various parts of the brain. Loss of all sensations occurs due to the suppression of the sensory centers of the brain to a state where there are no registrations of the impulses which may be transmitted to the area. Similarly, there is produced a suppression of the motor centers of the brain so that this area is incapable of initiating the impulses that normally travel down the nerve fibers to cause muscles to contract. The vital centers of the brain which control heart action and breathing are affected only when extremely large amounts of an anesthetic drug reach these centers. Thus, in general anesthesia the patient is rendered to a state where there are no sensations and no voluntary movements but where circulation and respiration continue.
There are many different general anesthetic agents, and each has its distinct properties. It is not the author’s intent in this book to delve into a study of the detailed specific actions of each anesthetic, for volumes have been written about each one. Each has its definite effects on various body structures, and all have certain advantages and disadvantages in certain conditions; each has its indications and contraindications. The anesthesiologist and the surgeon are familiar with the physical properties, potency, duration of action, safety ratio, effects on various organs, and all other pertinent features of each anesthetic agent.
The anesthetic drugs are eliminated from the body by various means. Some are rendered inactive (detoxified); others are excreted through the urine; still others are exhaled from the lungs. Most of those which are absorbed by inhalation are eliminated by exhalation, at least in part. Some agents are eliminated by more than one means. As the amount of effective anesthetic in the body decreases, the subject gradually returns to consciousness and all functions return.
General anesthesia is controlled to the desired depth of unconsciousness by many specific signs the patient exhibits. The anesthetist follows very closely the patient’s blood pressure, pulse, and variations in respirations; also the eye movements, size of the eye pupil, tension of the muscles, and certain involuntary movements are indicative signs. Certain reflexes of the eyes, throat, and other muscles are continually tested. All these signs are utilized to induce and maintain the patient in the desired level of anesthesia.
General anesthesia is described as having four stages, each with a rather definite group of the anesthetic signs. Stage I is the beginning (induction) stage and takes the patient to unconsciousness. Stage II is light anesthesia, while Stage III is deeper and Stage IV the deepest. The anesthetist administers the anesthetic with close observation of the signs, so that the desired level is obtained and maintained. A few short procedures may be done in Stage I or II, but most operations require Stage III, for it provides the muscular relaxation so often needed.
The anesthetist keeps a record of the entire procedure, noting the time of each step in the operation and plotting a graph of the patient’s blood pressure, pulse, respirations, and other anesthesia signs. This becomes a part of the patient’s hospital chart for ready future reference.
All removable dentures should be left in the patient’s room. They have to be removed before anesthesia as they may loosen during the course of the anesthetic and obstruct. They are much safer in the patient’s own bedside stand, as they may get broken or misplaced if worn to the operating room.
The patient is taken to the operating room corridor by hospital cart. In the operating room most often the patient is placed in the desired position before anesthesia is begun. But frequently the patient is anesthetized in one position and then changed to the position of operation.
Before the general anesthetic is begun, the anesthetist may place drops in the patient’s eyes. This is an oily medication to prevent irritation to the surface of the eyeballs. When a person is conscious and the eyes are open, he blinks his eyelids to keep the eyes lubricated and protected with a thin film of solution from the tear glands. But under anesthesia the blinking reflex ceases even though the eyes are not completely closed. The exposed surfaces may dry and become irritated. This is especially true when ether fumes fill the air. The oily solution protects against irritation from such vapors and provides the essential lubricant, so that there is no discomfort later.
The induction of anesthesia may be rather quick or quite prolonged, depending on the agents used and the rate of administration. As the patient receives the anesthetic, a feeling of warmth steals over the body, and he experiences dizziness. He seems to be detached from reality, floating through space, but still conscious. The entire process is very pleasant, and a feeling of extreme happiness is experienced. There may be a ringing or buzzing in the ears, and minor sounds may seem very loud, yet very distant. Soon the individual becomes aware of an inability to move the limbs as everything seems to fade farther away from reality and the individual continues with the feeling of buoyancy in space. Finally consciousness is lost. The induction of general anesthesia is a pleasant experience, and most patients who have previously had an anesthetic and are about to have another anticipate with delight these few moments of euphoria.
When the patient is asleep it is important for the anesthetist to maintain an open airway to the lungs, so that breathing will continue. Life depends on an uninterrupted supply of oxygen inhaled into the lungs and the liberation of the waste gas carbon dioxide by exhalation. There is no provision in the body for the storage of oxygen, so it is imperative that the patient be provided with an open passageway to the lungs at all times. Under anesthesia the muscles relax, and the tongue has a tendency to fall back in the throat. The throat muscles may also become flaccid, and secretions may collect in the throat and not be swallowed. These tend to narrow the normal air route, so, to make certain of an adequate air passageway to the lungs, the anesthetist often uses an anesthetic airway. These are simple tube devices which are placed into the upper respiratory tract after the induction of anesthesia. With the airway tubes in place the breathing rate will continue according to the body’s demand for oxygen and the amount of carbon dioxide that has accumulated in the body, just as it normally does.
The commonest anesthetic airway is the oropharyngeal (mouth-throat) tube. This extends from the lips to the back of the throat to assure an unobstructed passageway to the upper end of the trachea (“windpipe”). An anesthesia mask may be held over this to give the anesthetic or oxygen. Often an endotracheal (inside-trachea) tube is used. This is placed within the trachea via the mouth (orotracheal tube) or via the nose (nasotracheal tube). This tube may be connected to the anesthesia and oxygen supply. It is commonly used in chest, head, and neck operations. To be sure, the placing of the tube would be uncomfortable in an unmedicated person, but they are not installed until after the induction of anesthesia and the patient is unconscious. Most patients do not realize that such a tube was employed during their anesthesia.
With most general anesthetics the anesthetist will administer oxygen by mask throughout the procedure. Air is approximately 20 per cent oxygen, and when this is increased to a greater percentage respirations become more efficient. When inhalation type general anesthesia is employed, the anesthetic is most often mixed with oxygen in a definite ratio to obtain the desired effects and yet assure adequate oxygen supply. Often a device is placed in the anesthetic system which readily absorbs the carbon dioxide gas as soon as it is exhaled, to eliminate rebreathing this waste product. Everything is directed at maintaining efficient respirations throughout a general anesthetic.
It must be mentioned that today surgeons do not often depend on one anesthetic agent to produce the desired general anesthesia for an operation. Rather, a mixture of various agents and routes of administration are employed. Induction of anesthesia may begin by one agent and throughout the course of the procedure others added. By this plan the advantages of each specific agent may be utilized. Also lesser amounts of each of them are required, so the quantities used are far from the dangerous doses. For example, it is a common combination of anesthetics to begin by an injectable agent in the vein and then use inhalation agents during the course of the operation. General anesthetics may also be used in combination with spinal or other local anesthesia.
In the course of an anesthetic many other drugs may be given at any time for their specific actions. These may be to facilitate the operation or the anesthesia. Frequently drugs are employed to give better muscle relaxation at the operative site. Others may be given to reduce throat secretions, stimulate respirations, raise the blood pressure, alter the heart rate, or any other desired effect. The various combinations of anesthetics and other drugs seem innumerable.
Inhalation Anesthesia. This is the commonest type of general anesthesia. In this method the anesthetic drug is inhaled by the patient and absorbed from the lungs into the blood stream, by which it is transported to the brain to produce its narcotizing effects.
The drugs used to produce anesthesia by inhalation are volatile or gaseous.
Volatile Agents. These are in liquid form but readily evaporate on exposure to become a vapor which can be inhaled. The common ones are:
- Ether (ethyl ether)
- Vinethene (divinyl ether)
These are supplied m spouted cans which facilitate their use in delivering one drop at a time or in pouring the contents into an anesthetic machine.
Gaseous Agents. The gaseous anesthetic agents are in the form of a gas under natural conditions. The common agents of this type are:
- Nitrous oxide (N2O)
They are supplied in large metal cylinders, or tanks, which contain the gas under pressure. Under such pressure the gas may become liquid but immediately reverts back to a gaseous state as the pressure is released with its use.
Inhalation anesthesia may be given by the open drop method or by the use of an anesthetic machine. In the former technique, a perforated mask is placed over the patient’s nose and mouth through which the patient easily breathes. Onto the mask is poured one of the liquid anesthetic agents, one drop at a time. The fluid readily evaporates as it is spread over the mask, and the vapor is inhaled by the patient. In this open drop method, then, the anesthetic is merely added to the air inhaled by the patient and is allowed to escape into the surrounding air with exhalation. Air and the vapor are breathed in, while carbon dioxide, air depleted of oxygen, and some of the vapor are breathed out. Control of the anesthesia depth is brought about simply by varying the amount of liquid dropped on the mask. Sometimes oxygen is added to the system through a tube, placing the outlet under the edge of the mask. (The anesthetic vapors may also be delivered in this fashion, the technique known as insufflation anesthesia, but this is just a variation of the open method. It is useful in operations about the mouth and throat where the mask may be in the way.)
With use of the anesthetic machine, or “gas machine,” the anesthesia becomes more complicated but more efficient. The apparatus appears very complex, but the principles are easily understood. Medical oxygen and the gaseous anesthetics are supplied in large metal tanks. The flow from the tanks is directed through tubing to the anesthesia mask placed over the patient’s nose and mouth. Valves at the outlet of the tanks are used to regulate the flow of the gases, which is measured by the flow meters in the system. When the liquid anesthetics are used, the oxygen stream is directed through a vaporizer containing the anesthetic; this volatilizes the anesthetic to a vapor form so that it may be inhaled. This flow is also controlled by adjusting valves in the unit. All combinations of gaseous and volatile anesthetics may be given simultaneously, or any one may be given separately.
A breathing bag is placed in the system as a common mixing chamber for the oxygen and other gases. This fluctuates in size with the patient’s respirations and provides a reservoir of changing volume, accommodating the amounts breathed in and out of the system.
During the anesthetic the patient continues to utilize the oxygen and expel carbon dioxide. The latter must be removed from the system, which may be done by one of two ways. A one-way escape valve may be placed at the base of the mask. As the patient inhales, the valve is closed, so the flow of gases is only from the machine. When the patient exhales, the change in pressure opens the valve, so all the carbon- dioxide-laden gas passes out of the system into the surrounding air. When the one-way valve is not used, the carbon dioxide may be removed from the exhaled gas by placing a chemical absorber in the system. The exhaled gas passes back into the closed anesthetic system for rebreathing. But, as it passes through the chemical absorber, the carbon dioxide is removed. Both methods of eliminating this waste product gas have their advantages. The oxygen consumed by the patient is replaced by slow flow from the cylinder.
We shall not discuss any specific properties of drugs, for application of just a little knowledge in the field of pharmacology could indeed be dangerous. But a few facts about the anesthetic drugs which may be of interest to surgical patients may be mentioned.
Ether (ethyl ether) is the oldest of all the modern forms of anesthesia; yet, it is still the most commonly used because of certain advantages it has over others in most cases. Ether generally is considered the best and safest of the general anesthetics. It is a clear, flammable liquid which vaporizes readily at room temperature. It has a characteristic sharp odor. There is a wide margin of safety between the dosage required for anesthesia and the toxic dose. The anesthetic state produced by ether is favorable to most operations, and the desired muscle relaxation is obtained. The induction time and the time for recovery are somewhat longer than with the other inhalation agents, but complications from ether anesthesia are rare. Ether is commonly given by both the open drop and the gas machine methods.
Vinethene (divinyl ether) is a clear, colorless liquid which vaporizes freely. It has a sweet, pleasant odor. The induction is rapid, and the patient recovers rapidly. Vinethene produces a not unpleasant anesthesia, and there is little or no nausea or vomiting. It is useful for a multitude of short procedures and for quick induction when other anesthetics are to be used. It is not used for prolonged periods. Complications from this drug are rare. It is usually given by the open drop method.
Chloroform is a colorless, sweet-smelling liquid which is a powerful anesthetic agent. Its anesthetic strength allows for a greater percentage of oxygen to be given in the mixture, but at the same time the administration takes greater skill and closer observation. It is given most commonly by the open drop method and produces rapid anesthesia. The greatest uses of chloroform are found in operations of short duration. The recovery is as rapid as the induction. There is little irritation of the respiratory system with chloroform, and consequently it can be used on patients with respiratory diseases when other anesthetics cannot. American surgeons do not use chloroform routinely because of its high potency, but rather reserve its use for those cases where there is a definite advantage in its use.
Nitrous oxide (N2O) is a colorless gas with a sweetish odor. It has been referred to as “laughing gas” and “sweet air.” It is administered from compression tanks through tubes connccting with an oxygen tank and a mask over the patient’s face. The mixture of nitrous oxide and oxygen may be easily varied to the needs of the patient by adjusting the flow valves. Nitrous oxide is commonly given in combination with ether, this combination being one of the best general anesthetics. Nitrous oxide produces rapid anesthesia from which the patient recovers quickly. It is useful for short as well as long procedures. Nausea and vomiting are not frequent after-effects. Little irritation of the respiratory system is produced, so it is useful when it is necessary to operate on a patient with associated respiratory disease.
Ethylene is a colorless gas whose sweetish odor has been described as resembling that of burnt matches. Its characteristics and uses are very similar to those of nitrous oxide. Ethylene is dispensed in compression tanks which are used with an inhalation apparatus. There is rapid induction and rapid recovery, with little irritation of the respiratory system. Ethylene produces the muscle relaxation so often needed at the operative site.
Cyclopropane is one of the newer anesthetic gases. It is a powerful agent affording pleasant and rapid induction. It is supplied in pressure tanks and administered by apparatus. Since cyclopropane is such a powerful agent, only a small percentage of the gas is required in the mixture. The remainder can consist of oxygen, so the patient has more than an adequate supply. By the same token, its potency allows easy overdosage, so that it can be given only by skilled hands. Of all anesthetic agents cyclopropane is the least irritating to the respiratory passages; it is of greatest value in chest surgery or in cases with concurrent respiratory disease.
All of the inhalation anesthetics except nitrous oxide and chloroform will explode under certain conditions, especially where the oxygen concentration is high, as it is in the operating room. Everything is directed at avoiding such a disaster. All electrical devices are grounded; woolen blankets and other materials which may form static electricity are avoided; smoking is not allowed in the operating corridors, and electrocautery is not used when an explosive mixture is employed as an anesthetic. Such explosion accidents are extremely rare, but the hazard is always possible. This serves as another point that everything in the operating room may not be apparent to you, but never question any step in the procedure of your preparation for operation.
Intravenous Anesthesia. This is the production of an anesthesia state by the injection of a substance into a vein. The drug is transported to the brain where its actions on the various centers produce anesthesia. This is a type of general anesthesia, as consciousness is lost. The most common drug used for intravenous anesthesia is sodium pentothal, but there are several others of the same family of drugs which act in a similar manner.
Anesthesia produced by this means is the most pleasant of all general anesthetic methods. The induction period is usually quite short with loss of consciousness within a few moments. This period is extremely pleasing, and this form of anesthesia is always the preference of patients who have experienced various methods. The sensations of buzzing in the ears and exaggerated sounds are minimal, while the feelings of buoyancy and euphoria prevail.
The duration of anesthesia is brief and more must be continually added to the blood stream to maintain the desired depth of anesthesia. When the drug is no longer given, recovery is quite rapid. There rarely is nausea when the intravenous drugs are used. Intravenous anesthesia is useful for many types of operations but finds its greatest usefulness in procedures of short duration. Because of its ideal beginning stage, intravenous drugs are often used for the induction of anesthesia, with the addition of or change to another general anesthesia agent as soon as unconsciousness is lost. Often several different agents are used for one anesthetic. Small amounts of the intravenous drugs are often given with spinal and other local anesthetics to allay apprehension and anxiety, but usually not to a state of unconsciousness. Oxygen is usually given while a patient is anesthetized with an intravenous drug, and an open airway must be maintained; airway tubes are often used.
Rectal Anesthesia. Rectal anesthesia is actually just “partial anesthesia.” It is often called basal anesthesia. The drug placed in the rectum is absorbed into the blood stream, which transports it to the brain, where the necessary centers are depressed to produce anesthesia. But in the human the dosage of drug is never calculated to produce complete anesthesia. Rather, it is supplemented by anesthesia of another route, most often inhalation or local. Dosage of the rectal anesthetic drug is calculated according to the patient’s weight and physical state. The drug is given in solution through a rectal tube. The reaction of the drug is quite slow. After several minutes the patient falls into an apparently natural sleep. He is not rendered incapable of perceiving pain, however, so before any operative procedure is begun the supplemental anesthetic is given. The duration of the rectal anesthesia is prolonged, and the patient usually sleeps for several hours. This form of anesthesia is not frequently employed. Its greatest advantage is that less of the additional anesthetic agent is required, allowing little chance of approaching the toxic dosages. Less preoperative and postoperative sedation is required with rectal anesthesia than with the other forms of anesthesia.