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General anesthesia is a state characterized by analgesia, unconsciousness, amnesia, skeletal muscle relaxation, and inhibition of sensory and autonomic reflexes. The extent to which any individual anesthetic drug can exert these effects varies with the drug, the dosage, and the clinical situation.

Drugs used as general anesthetics are central nervous system (CNS) depressants with actions that can be induced and terminated more rapidly than those of conventional sedative-hypnotics (Chapter 13). An ideal anesthetic drug would induce anesthesia smoothly and rapidly while allowing for prompt recovery after its administration is discontinued. The drug would also possess a wide margin of safety and be devoid of adverse effects. No single anesthetic agent is capable of achieving all of these desirable effects without some disadvantages when used alone. The modern practice of anesthesiology commonly involves the use of combinations of intravenous and inhaled drugs, taking advantage of their individual favorable properties while attempting to minimize adverse reactions. This common practice is known as balanced anesthesia.Classification of drug subgroups and specific drugs used for balanced anesthesia are listed in Figure 15–1 and Table 15–1.

Figure 15–1.

Classification of drug subgroups and selected prototype agents used in general anesthesia.

Table 15–1. Classification of Commonly Used General Anesthetics

The anesthetic technique will vary depending on the proposed type of diagnostic, therapeutic, or surgical intervention. For minor procedures, so-called monitored anesthesia care or conscious sedation is used, employing oral or parenteral sedatives, often in conjunction with local anesthetics (Chapter 16). These techniques provide profound analgesia, but with retention of the patient’s ability to maintain a patent airway and to respond to verbal commands. For more extensive surgical procedures, anesthesia frequently includes the use of preoperative benzodiazepines, induction of anesthesia with intravenous thiopental or propofol, and maintenance of anesthesia with a combination of inhaled and intravenous anesthetic drugs. Such protocols also often include the use of neuromuscular-blocking drugs (Chapter 5). Monitoring of vital signs is the standard method of assessing the depth of anesthesia during surgery.

Although physical therapists are not usually involved in working directly with patients while under general anesthesia, a basic understanding of the mechanism of action and subsequent residual effects of these medications and how they may influence rehabilitation outcomes for several days after their use is important.

Modern anesthetics act very rapidly and achieve deep anesthesia quickly. With older and more slowly-acting anesthetics, the progressively greater depth of central depression associated with increasing dose or time ...

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