Anesthetics

A anesthetic serves to create a state of numbness in order to be able to carry out surgical or diagnostic measures. The term includes many substances, each with a different spectrum of activity.

What are anesthetics?

The term anesthetic is very general and is used for many active ingredients that cause insensitivity locally or in the whole body. A local anesthetic is used for local anesthesia. It is used almost exclusively to eliminate pain during operations or pain therapy.

It contains analgesics as the only active ingredient group. A general anesthetic is used for general anesthesia (general anesthesia). General anesthetics contain substances that switch off pain, as well as substances that switch off consciousness, dampen motor skills and inhibit vegetative reactions. Accordingly, they consist of a mixture of hypnotics (sleeping pills), analgesics (pain relievers) and relaxants (for muscle relaxation).

Anesthetics can be inhaled or injected intravenously. Due to the large number of substances contained, there is no uniform mechanism of action. Although the anesthetics used today can be described according to the Meyer-Overton correlation, the underlying assumptions about the mechanism of action are outdated.

Function, effect & goals

There are basically two groups of anesthetics. On the one hand, these are drugs that act locally and, on the other hand, they affect the entire body. Local anesthetics must be applied in such a way that they cannot be distributed in the body, but rather remain in place. Therefore, they must not get into the bloodstream when injected.

In addition to an injection, it can also be used in the form of gels, ointments, sprays or plasters. All local anesthetics contain aminoamides or aminoesters as active ingredients. These substances develop their effect by blocking the sodium channels on the membranes of nerve cells. In doing so, they prevent the transmission of stimuli and numb this point. In contrast to local anesthetics, the use of narcotics is associated with greater challenges. Anesthetics always consist of a mixture of several substances that have very different effects.

Sleep pills, pain relievers and muscle relaxants must be effectively combined with one another. The combination of active ingredients should be chosen so that there are no undesirable cross-reactions between the individual substances. Before using the anesthetic, the anesthetist must first make a preoperative assessment of the individual risk using the so-called ASA risk classification. According to the ASA risk classification, the perioperative risk is divided into six degrees of severity. The composition of the narcotic is then based on this assessment. The anesthetist also has to decide how the anesthesia should be initiated.

There are two ways to do this. The induction of anesthesia can take place either by inhalation or by injection. That too depends on various factors. Different active ingredients are used for both forms of induction of anesthesia. Gaseous anesthetics such as isoflurane or sevoflurane are used for inhalation. In addition, relaxants for muscle relaxation must also be used 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 key role here. How the anesthetics act on the receptors is currently still the subject of research. In the past, the Meyer-Oberton hypothesis assumed that inhalation anesthetics had a non-specific effect on the lipid components of the central nervous system. Although the effect of anesthetics can still be described well today using the so-called Meyer-Overtone correlation, this hypothesis can no longer be unreservedly maintained. However, it is not excluded.

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Risks, side effects & dangers

Side effects and complications can occur with the use of local anesthetics as well as anesthetics. If large amounts of this substance get into the blood through an unnoticed intravenous injection of local anesthetics, the body becomes intoxicated, which can lead to fatal circulatory collapse. In addition, local anesthetics of the ester type in particular can sometimes cause allergies. This should be clarified before using them.

However, performing anesthesia presents the doctor with greater challenges. Therefore, it may only be performed in the presence of a specially trained anesthetist. First of all, it is important to fully inform the patient about the anesthesia and its possible effects. In order to assess the risk, the general operational risks, problems with performing anesthesia and previous illnesses of the patient are included in the assessment. The ASA status (ASA risk classification) should be determined. In the risk assessment, advanced age and possible further illnesses of the patient are particularly important.

However, the mortality specifically induced by anesthetic procedures plays only a subordinate role overall. Today it is between 0.001 and 0.014 percent. During anesthesia, the main focus must be on monitoring breathing. The main causes of anesthesia-related mortality are to be found in problems with breathing security, wrong actions in the case of cardiovascular problems, inadequate anesthesia care or incorrect medication administration. The main challenge, however, is airway management.

If, despite all the measures taken, the patient cannot be supplied with oxygen, the respiratory tract must be opened as the last resort. Problems can arise from the penetration of foreign bodies into the airways, acute narrowing of the bronchi or spasms of the larynx muscles. Cardiovascular disorders, intraoperative wakefulness, allergic reactions or malignant hyperthermia can also occur as further complications caused by anesthesia. Even after the operation, the use of anesthetics can still cause nausea, vomiting, postoperative tremors or disorders of the cognitive brain functions.