Anesthesiology as a special field of endeavor has made clear the many physiologic changes occurring in the patient during anesthesia. The pharmacologic effects of anesthetic agents and techniques on the central nervous system and the cardiovascular and respiratory systems are now better understood. New drugs have been introduced for inhalation, intravenous, spinal, and regional anesthesia. In addition, drugs, such as muscle relaxants and hypotensive or hypertensive agents, are used for their specific pharmacologic effect. Older anesthetic techniques, such as spinal and caudal anesthesia, have been improved by the refinement of the continuous technique and more accurate methods of controlling the distribution of the administered drug. Marked advances in anesthesia have taken place in pulmonary, cardiac, pediatric, and geriatric surgery. Improved management of airway and pulmonary ventilation is reflected in the techniques and equipment available to prevent the deleterious effects of hypoxia and hypercarbia. An increased understanding of the altered hemodynamics produced by anesthesia in the ill patient has resulted in better fluid, electrolyte, and blood replacement preoperatively in patients with a decreased blood volume and electrolyte imbalance, thus allowing many patients once thought to be too ill for surgery, the opportunity for safe operative care.

Although the number of anesthesiologists has increased within recent years, it still is not enough to meet the increased surgical load. Surgeons, therefore, may find that they will be assigned certified registered nurse anesthetists (CRNAs) to administer anesthesia. Although CRNAs have excellent training they must be supervised by a physician. Hence the surgeon must bear in mind that in the absence of a trained anesthesiologist, it is the surgeon who is legally accountable should catastrophe from any cause, compromise the outcome of the surgical procedure. Under these circumstances, the surgeon should be knowledgeable about the choice of anesthetic agents and techniques, and their indications and complications. Further, he or she should be familiar with the condition of the patient under anesthesia by observing the color of blood or viscera, the rapidity and strength of the arterial pulsation, and the effort and rhythm of the chest wall or diaphragmatic respirations. Knowing the character of these conditions under a well-conducted anesthesia, the surgeon will be able readily to detect a patient who is doing poorly.

It is this point of view that has caused us to present in this practical volume the following short outline of modern anesthetic principles. This outline makes no pretense of covering fully the physiologic, pharmacologic, and technical details of anesthesiology, but it offers to the surgeon some basic important information.

The intraoperative role of the anesthesiologist as a member of the surgical team is severalfold, including the assurance of adequate pulmonary ventilation, maintenance of a near-normal cardiovascular system, and conduction of the anesthetic procedure itself. One cannot be isolated from the other.

Preventing the subtle effects of hypoxia is of prime importance to the anesthesiologist. It is well known that severe hypoxia may cause sudden disaster, and that hypoxia of a moderate degree may result in slower but equally disastrous consequences. Hypoxia during anesthesia is related directly to some interference with the patient’s ability to exchange oxygen. This commonly is caused by allowing the patient’s tongue partially or completely to obstruct the upper airway. Foreign bodies, emesis, profuse secretions, or laryngeal spasm may also cause obstruction of the upper airway. Of these, aspiration of emesis, although rare, represents the greatest hazard to the patient. General anesthesia should not be administered in those patients likely to have a full stomach unless adequate protection of the airway is assured. A common guideline in adults with normal gastrointestinal motility is a 6- to 8-hour interval between the ingestion of solid food and induction of anesthesia. In addition, members of the surgical team should be capable of performing endotracheal intubation. This will reduce the possibility of the patient’s asphyxiating, as the endotracheal tube is not always a guarantee of a perfect airway. Other conditions known to produce a severe state of hypoxia are congestive heart failure, pulmonary edema, asthma, or masses in the neck and mediastinum compressing the trachea. As these conditions may not be directly under the anesthesiologist’s control, preoperative evaluation should be made by the surgeon, the anesthesiologist, and appropriate consultants. In complex airway cases, the patient may be intubated using topical anesthetics and a flexible fiberoptic bronchoscope that serves as an internal guide for the overlying endotracheal tube.

Before any general anesthetic technique is commenced, facilities must be available to perform positive-pressure oxygen breathing, and suction must be available to remove secretions and vomitus from the airway before, during, and after the surgical procedure. Every effort should be expended to perform an adequate tracheobronchial and oropharyngeal cleansing after the surgical procedure, and the airway should be kept free of secretions and vomitus until the protective reflexes return. With the patient properly positioned and observed, all these procedures will help to reduce the incidence of postoperative pulmonary complications.

Fluid therapy during the operative procedure is a joint responsibility of the surgeon and the anesthesiologist. Except in unusual circumstances, anemia, hemorrhage, and shock should be treated preoperatively. During the operation transfusions should be used with caution as there can be significant risks associated with transfusions. Most patients can withstand up to 500 mL of blood loss without difficulty. However, in operative procedures known to require several units of blood, the blood should be replaced as lost as estimated from the quantity of blood within the operative field, the operative drapes, and the measured sponges and suction bottles. The intravascular volume can be expanded by cross-matched packed red blood cells, specifically indicated for their oxygen-carrying capacity, when the hematocrit (Hct) is ≤23% to 25% or the hemoglobin (Hb) is ≤7 g/dL. In emergency situations when blood is not available, synthetic colloids (dextran or hydroxyethyl starch solutions), albumin, or plasma may be administered to maintain an adequate expansion of blood volume. All blood products are used with caution because of the possibility of transmitting homologous viral diseases. Infusions of Ringer’s lactate (a balanced electrolyte solution), via a secure and accessible intravenous catheter, should be used during all operative procedures, including those in pediatrics. Such an arrangement allows the anesthesiologist to have ready access to the cardiovascular system, and thereby a means of administering drugs or treating hypotension promptly. In addition, large, centrally placed catheters may be used to monitor central venous pressure or even cardiac performance if a pulmonary artery catheter is placed into the pulmonary vasculature. As many modern anesthetic agents may produce vasodilation or depression of myocardial contractility, anesthesiologists may volume load patients with crystalloid solutions. This maintains normal hemodynamic parameters and a good urine output. However, this fluid loading may have serious after effects in some patients; thus the anesthesiologist must monitor the type and volume of fluids given to the patient during the operation and communicate this to the surgeon.