An anesthetic is used to produce a state of insensibility in order to perform surgical or diagnostic procedures. The term encompasses many substances, each with a different spectrum of activity.
What are anesthetics?
The term anesthetic is very general and is applied to many agents that induce local or whole-body insensibility. The term anesthetic is very general and is applied to many agents that induce local or whole-body insensibility. A local anesthetic is used for local anesthesia. It is used almost exclusively to eliminate pain during surgery or pain therapy. It contains analgesics as the only group of active ingredients. A general anesthetic, on the other hand, is used for general anesthesia (anesthesia). In addition to painkillers, general anesthetics also contain substances that deactivate consciousness, dampen motor activity and inhibit autonomic reactions. Accordingly, they consist of a mixture of hypnotics (sleeping pills), analgesics (painkillers) and relaxants (for muscle relaxation). Anesthetics can be inhaled or injected intravenously. Because of the large number of substances they contain, there is no single mechanism of action. Although the anesthetics in use today can be described according to the Meyer-Overton correlation, its underlying assumptions about the mechanism of action are outdated.
Function, effect, and targets
Basically, two groups of anesthetics are distinguished. These are, first, drugs that act locally and, second, drugs that affect the entire body. Local anesthetics must be applied in such a way that they cannot disperse in the body but remain in place. Therefore, they must not enter the bloodstream when injected. In addition to an injection, it can also be applied in the form of gels, ointments, sprays or patches. All local anesthetics contain aminoamides or amino esters as active ingredients. These substances exert their effect by blocking the sodium channels on the membranes of nerve cells. In this way, they stop the transmission of stimuli and anesthetize this area. In contrast to local anesthetics, the use of narcotics poses greater challenges. Narcotics always consist of a mixture of several substances that have very different effects. Thus, soporifics, analgesics and muscle relaxants must be effectively combined. The combination of active ingredients must be selected in such a way that there are no undesirable cross-reactions between the individual substances. Before the narcotic is used, a preoperative assessment of the individual risk must first be made by the anesthesiologist using the so-called ASA risk classification. According to the ASA risk classification, the perioperative risk is divided into six severity levels. The composition of the narcotic is then based on this assessment. Furthermore, the anesthesiologist must also decide how to induce anesthesia. There are two methods for this. Induction of anesthesia can be by inhalation or by injection. This also depends on various factors. Different agents are used for both forms of anesthetic induction. For inhalation, gaseous anesthetics such as isoflurane or sevoflurane are used. In addition, relaxants must also be used for muscle relaxation during intubation. Induction of anesthesia via intravenous injection requires soluble substances such as ketamine. According to current knowledge, the mode of action of the various substances is based on their complex interaction with receptors and ion channels. The GABA, NMDA and opioid receptors play a prominent role. How the anesthetics act on the receptors is currently still the subject of research. In the past, the Meyer-Oberton hypothesis suggested that inhalational anesthetics act nonspecifically on the lipid components of the central nervous system. Although the effect of the anesthetics can still be well described according to the so-called Meyer-Oberton correlation, this hypothesis can no longer be upheld without reservation. However, it is not ruled out.
Risks, side effects, and hazards
Side effects and complications can occur with the use of both local anesthetics and anesthetics.If large quantities of local anesthetics enter the bloodstream as a result of an unnoticed intravenous injection, intoxication of the body occurs, which can lead to fatal circulatory collapse. In addition, ester-type local anesthetics in particular can sometimes cause allergies. This should be clarified before their use. However, performing anesthesia poses greater challenges for the physician. Therefore, it may only be performed in the presence of a specially trained anesthesiologist. First of all, it is important to inform the patient comprehensively about the anesthesia and its possible effects. For risk assessment, the general surgical risks, problems with the anesthesia procedure and previous illnesses of the patient are included in the evaluation. The ASA status (ASA risk classification) should be determined. Advanced age and possible further illnesses of the patient are of particular importance in the risk assessment. However, mortality induced specifically by anesthetic procedures plays only a minor role overall. Today, it is between 0.001 and 0.014 percent. Main attention must be paid to respiratory monitoring during anesthesia. The main causes of anesthesia-related mortality are problems in securing breathing, incorrect handling of cardiovascular problems, inadequate anesthesia care, or incorrect administration of medication. The most important challenge, however, is airway management. If oxygenation of the patient is not successful despite all measures taken, the airway must be opened as a last resort. Problems can arise from foreign bodies entering the airway, acute bronchoconstriction, or spasm of the laryngeal muscles. Other anesthesia-related complications may include cardiovascular disturbances, intraoperative wakefulness, allergic reactions, or malignant hyperthermia. Even after surgery, nausea, vomiting, postoperative tremors, or disturbances in cognitive brain function are still possible due to the use of anesthetics.
