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The Basic Design Of Anaesthesia Machine

The anaesthesia machine is a continuous flow machine in which all the components are mounted on a table. Box shaped sections of welded steel or aluminium provide a rigid metal framework mounted on wheels with antistatic tyres (Castors) and brakes. Antistatic measures improve flow meter performance and where flammable vapours are used, reduce the risk of ignition.

The basic machine has provision for fixing two O2 cylinders and two N2O cylinders through the yoke assembly with PISS. There is also provision for connecting the pipeline gas source of O2 and N2O (from the wall outlet with quick couplers and yoke blocks at the machine end) instead of one of the cylinders at the yoke assembly. A pressure gauge is mounted on to the yoke assembly to read the pressure in the cylinder. Pressure regulators are located downstream of the yoke assembly, which reduce the high pressure in the cylinders to a low and constant pressure of 45-60 PSIG. From the pressure regulators, there are connections through high pressure tubings constructed of heavy duty materials to the flow meter assembly, which is secured to the back bar of the machine by one or more bolts. The back bar supports the flow meter assembly and the vapourisers. At the end of the back bar, there is the common gas outlet to which the breathing circuits are connected to provide the anaesthetic vapour containing O2 enriched gases to the patient.

The anaesthesia machine can be conveniently divided into three parts:  The high pressure system, which receives gases at cylinder pressure, reduces the pressure and makes it more constant,  the intermediate pressure system, which receives gases from the regulator or hospital pipeline and delivers them to the flow meters or O2 flush valve and  the low pressure system, which takes gases from the flow meters to the machine outlet and also contains the vapourisers.