If to address anesthesiology history, then it becomes clear that this specialty began with use of inhalation anesthesia — the well-known operation of U. Morton on which that showed a possibility of performing anesthesia by means of steam inhalation of ethyl ether. Further properties of other inhalation agents were studied — chloroform, and then and the halothane which opened itself an era of halogen containing inhalation anesthetics appeared. It is remarkable that all these drugs were forced out now by more modern and are practically not used.
Inhalation anesthesia represents a type of the general anesthesia at which achievement of a condition of an anesthesia is reached by inhalation of inhalation agents. Mechanisms of effect of inhalation anesthetics even are studied not completely today and are actively studied. A number of the effective and safe drugs allowing to carry out this type of anesthesia is developed.
The concept of IAC — the minimum alveolar concentration is the cornerstone of inhalation general anesthesia. The IAC is a measure of activity of inhalation anesthetic which is defined as its minimum alveolar concentration at a saturation stage which has enough for prevention of reaction of 50% of patients for a standard surgical incentive (a skin section). If graphically to represent logarithmic dependence of IAC on fat solubility of anesthetics, then the straight line will turn out. It means that force of inhalation anesthetic will depend directly on its fat solubility. In a condition of saturation the partial pressure of anesthetic in an alveolus (RA) is in an ekvilibriuma with partial pressure in blood (Ra) and, respectively, in a brain (Pb). Thus, RA can serve as an indirect indicator of its concentration in a brain. However, for many inhalation anesthetics in a real clinical situation process of achievement of saturation-ekvilibriuma can take several hours. Solubility coefficient "blood: gas" is very important indicator for each anesthetic as reflects the speed of alignment of all three partial pressures and, respectively, anesthesia approach. The less inhalation anesthetic is soluble in blood, the quicker there is an alignment of PA, Pa and Pb and, respectively, the quicker there comes the condition of anesthesia and an exit from it. However, the speed of approach of anesthesia is not the force of the most inhalation anesthetic yet that well shows an example with nitrous oxide – the speed of approach of anesthesia and an exit from it very fast, but as anesthetic nitrous oxide very weak (to its IAC it is equal to 105).
If to talk about concrete drugs, then the inhalation anesthetics which now are the most often applied are the halothane, isoflurane, sevoflyuran, desflyuran and nitrous oxide, at the same time the halothane is more and more forced out from daily practice owing to its gapatotoksichnost. Let's sort these substances in more detail.
Halothane — the classical galogensoderzhashchy agent. Strong anesthetic with very narrow therapeutic corridor (a difference between working and toxic concentration very small). Classical drug at induction in the general anesthesia of children with obstruction of respiratory tracts as allows to wake the child at increase of obstruction and decrease in minute ventilation, plus to everything, has rather pleasant smell and does not irritate respiratory tracts. The halothane is rather toxic — it concerns possible developing of postoperative dysfunction of a liver, especially against the background of other its pathology.
Isoflurane — isomer of enflurane which has the saturation pressure of vapors, close to a halothane. Possesses a pungent radio smell that does it unsuitable for inhalation induction. In view of not absolutely studied effects on a coronary blood stream ¸ it is not recommended to use for patients with an ischemic heart disease and also in a heart surgery though there are publications disproving the last statement. 2 IAC reduce the metabolic needs of a brain and for a dose and more it can be used for the purpose of a tserebroprotektion at neurosurgical interventions.
Sevoflyuran — rather new anesthetic which was less available in view of high price several flyings ago. Is suitable for inhalation induction as possesses rather pleasant smell and at the correct use causes almost instant switching off of consciousness and - for rather low solubility in blood. More kardiostabilen in comparison with a halothane and isoflurane. At deep anesthesia causes the muscle relaxation sufficient for a trachea intubation in children. At metabolism of a sevoflyuran the fluoride capable in certain conditions to show nephrotoxicity is formed.
Desflyuran — is similar on the structure to isoflurane, but has absolutely other physical properties. Already at the room temperature in the conditions of highlands it boils that demands use of the special evaporator. Has low solubility in blood (coefficient "blood: gas" even below, than at nitrous oxide) that causes fast approach of anesthesia and an exit from it. These properties do desflyuran preferable to use in bariatric surgery and at patients with disturbances of a lipometabolism.