flowmeters

2

The anaesthetic machine!

A - Flow meter; measures and controls the flow of oxygen (L/min) to the breathing circuit
B - Vaporizer; converts volatile anaesthetic liquid to a vapour/gaseous state and controls the amount allowed to diffuse into the circuit
C - Common or fresh gas outlet; where fresh oxygen, anaesthetic gas, and other gases enter the breathing circuit
D - Pressure gauge; reads the pressure of the breathing circuit, normally should read less than 30 mmH2O
E - Flush valve; allows high pressured O2 to bypass the flowmeter and vaporizer and is often used to pressure check the system or flush the circuit at the end of a procedure. Must NEVER be used if the patient is still connected (barotrauma!)
F - Pop-off valve; a safety feature where excess gas is vented into the scavenging system, with the pressure at which it pops being completely adjustable. It also allows Intermittent Positive Pressure Ventilation (IPPV) when closed
G - CO2 absorber canister; filled with either barium hydroxide or soda lime absorber, absorbs exhaled CO2
H - Scavenger system; ensures no contamination of the internal environment by the exhaled anaesthetic or any waste gases. Usually directed externally.
I - The connecting hose between the common gas outlet and inspiratory chamber of the CO2 canister in a rebreathing circuit (i.e. expired gases are circled through the CO2 absorber canister and back into the inspiratory limb combined with the fresh gas from the outlet)
J - Attachment for the rebreathing/reservoir bag; used as a volume reservoir that is 4-5 times the patients normal tidal volume.

I’ve added a second picture showing a correctly set up rebreathing circuit using a circle circuit which uses unidirectional valves and separate inspiratory and expiratory limbs. This particular system has the O2 gas running from an external cylinder via piping through the walls.