Anaesthetic circuits

Abstract

An anaesthetic circuit or system can be defined as that part of anaesthetic apparatus which is used to connect the patient to the anaesthetic machine deployed to deliver predetermined volumes and concentration of oxygen, anaesthetic gases and volatile agents. This can easily be achieved by using a length of tubing, supplying the anaesthetic mixture from the machine to the patient. But it is highly desirable to have a proper circuit or system between the patient and the anaesthetic machine due to the following reasons: (a) The patient is to be provided with a desired, balanced and congenial breathing atmosphere. Some anaesthetic circuits may tend to modify the concentration of gases and vapours which are actually delivered to the patient. (b) The re-breathing of exhaled anaesthetic mixture requires to be prevented or minimised. Accumulation of CO2 due to re-breathing also reduces the inspired concentration of O2 and anaesthetic mixture in use. (c) The mixing of inspired gases with room air as well as the pollution of theatre atmosphere from expired gases has to be prevented. (d) The resistance to expiration needs to be minimised.