General Anesthesia and General Anesthetic Drugs

General anesthesia is a state of drug-induced reversible inhibition of central nervous function, during which surgical procedures can be carried out in the absence of consciousness, responsiveness to pain, defensive or involuntary movements, and significant autonomic reflex responses (A).

The required level of anesthesia depends on the intensity of the pain-producing stimuli, i.e., the degree of nociceptive stimulation. The skilful anesthetist, therefore, dynamically adapts the plane of anesthesia to the demands of the surgical situation. Originally, anesthetization was achieved with a single anesthetic agent (e.g., diethylether— first successfully demonstrated in 1846 by W. T. G. Morton, Boston). To suppress defensive reflexes, such a "mono-anesthesia" necessitates a dosage in excess of that needed to cause unconsciousness, thereby increasing the risk of paralyzing vital functions, such as cardiovascular homeostasis (B). Modern anesthesia employs a combination of different drugs to achieve the goals of surgical anesthesia (balanced anesthesia). This approach reduces the hazards of anesthesia. In C are listed examples of drugs that are used concurrently or sequentially as anesthesia adjuncts. In the case of the inhalational anesthetics, the choice of adjuncts relates to the specific property to be exploited (see below). Muscle relaxants, opioid analgesics such as fentanyl, and the parasympatholytic atropine are discussed elsewhere in more detail.

Neuroleptanalgesia can be considered a special form of combination anesthesia, in which the short-acting opi-oid analgesics fentanyl, alfentanil, remi-fentanil is combined with the strongly sedating and affect-blunting neurolep-tic droperidol. This procedure is used in high-risk patients (e.g., advanced age, liver damage).

Neuroleptanesthesia refers to the combined use of a short-acting analgeLullmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.

sic, an injectable anesthetic, a short-acting muscle relaxant, and a low dose of a neuroleptic.

In regional anesthesia (spinal anesthesia) with a local anesthetic (p. 204), nociception is eliminated, while consciousness is preserved. This procedure, therefore, does not fall under the definition of general anesthesia.

According to their mode of application, general anesthetics in the restricted sense are divided into inhalational (gaseous, volatile) and injectable agents.

Inhalational anesthetics are administered in and, for the most part, eliminated via respired air. They serve to maintain anesthesia. Pertinent substances are considered on p. 218.

Injectable anesthetics (p. 220) are frequently employed for induction. Intravenous injection and rapid onset of action are clearly more agreeable to the patient than is breathing a stupefying gas. The effect of most injectable anesthetics is limited to a few minutes. This allows brief procedures to be carried out or to prepare the patient for inhalation-al anesthesia (intubation). Administration of the volatile anesthetic must then be titrated in such a manner as to counterbalance the waning effect of the injectable agent.

Increasing use is now being made of injectable, instead of inhalational, anesthetics during prolonged combined anesthesia (total intravenous anesthe-sia—TIVA).

"TIVA" has become feasible thanks to the introduction of agents with a suitably short duration of action, including the injectable anesthetics propofol and etomidate, the analgesics alfentanil und remifentanil, and the muscle relaxant mivacurium. These drugs are eliminated within minutes after being adminster-ed, irrespective of the duration of anesthesia.

Combined Thymectomy
B. Traditional monoanesthesia vs. modern balanced anesthesia
Propofol Duration Action
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