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. Graphic Jump Location
Classification of drug subgroups and selected prototype
agents used in general anesthesia.
++ Table Graphic Jump Location Table 15–1. Classification
of Commonly Used General Anesthetics ||Download (.pdf)
Table 15–1. Classification
of Commonly Used General Anesthetics
|General Anesthetic||Subclass||Prototype||Other Significant Agents|
|Inhaled anesthetics||Volatile liquids||Halothane||Enflurane, desflurane, isoflurane, sevoflurane|
|Intravenous anesthetics||Barbiturates||Thiopental||Thiamylal, methohexital|
|Opioids||Morphine||Fentanyl, alfentanil, remifentanil|
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 ...