Anaesthetic Apparatus
Anaesthesia means loss of feeling or sensation, so that no pain is felt. In surgery this result is obtained by using an anaesthetic. A distinction is to be made between general anaesthesia i.e. total unconsciousness and local anaesthesia i.e. only one area of the body is deprived sensation.
The beginnings of modern anesthetic equipment date back to Morton’s inhalation flagon in 1846. The numerous devices developed and introduced subsequently can be divided into four groups. Simple ether and chloroform masks for open inhalation anesthesia, from Simpson (1847) to Brown (1928). Vapour inhalators according to the draw over principle of Snow (1847) up to the Oxford vaporizer (1941). Closed or half-closed inhalation equipment for ether or chloroform with to and fro breathing, from Clover (1877) to Ombredanne (1908).
Equipment for anaesthesia with nitrous oxide. From 1868 onwards this led to the incorporation of gas bottles in anaesthetic equipment and between 1885 and 1890 to the construction of mixing-valves for nitrous oxide and oxygen. In addition, reducing valves, flow meters and vaporizers were developed. The first anaesthetic apparatus with circle system and CO2-absorber was constructed in 1925 by the Drager factory in Lubeck. Sudeck and Schmidt introduced this technique of anaesthesia in the university hospital of Hamburg-Eppendorf between 1920 and 1925.
General anaesthesia can be produced in separate ways, including intravenous injection with thiopental sodium or other agents. The older and still most widely used method, however is by inhalation of a gaseous or volatile anaesthetic. Early anaesthetics were either, nitrous oxide and chloroform.
At the present time a range of other agents are available. In modern surgery, especially for major operations, a combination of two or more anaesthetic agents may be employed, the gaseous or volatile anaesthetic being administered by means of a special apparatus, which enables the various agents to be accurately proportioned and controlled, so as to minimize the risk of overdosing.
A typical anaesthetic apparatus is shown in the accompanying illustration. The underlying principle is that the patient’s breath is circulated through the apparatus, in a closed circuit, the gas flow rate being controlled by means of valves and flow meters. The advantage of closed circuit is that loss of body heat and moisture is prevented. Besides, a considerable economy in the amount of anaesthetic used is effected.
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