Semi Closed Circuit Anaesthesia
This type of General Anaesthesia is used mainly for maintenance of anaesthesia following induction. It can be used for induction of anaesthesia, but this is a slower process.
It requires an absorber system containing a CO2 Absorbent to remove CO2 from the expired patient gases, and a high degree level of patient monitoring, especially respiratory gas monitoring to measure levels of inspired and expired CO2 and the volatile agent.
Semi Closed Anaesthesia Explained
Semi Closed Anaesthesia is where the expired gases from the patient pass through a canister in the breathing system which contains a CO2 absorbent. This absorbent by an exothermic chemical reaction removes the CO2, so the patients expired gases can be rebreathed. Because of this exothermic chemical reaction, some warmth and humidity is added to the inspired gases.
Because the patients expired gases are re circulated (where the ‘circle’ comes from), this means that we do not have to add so much fresh gas to the system like an open system. So the fresh gas flow rate can be reduced to low flow, i.e., 1 litre per minute. If the flows were as low as a few hundred cc’s of gas, equivalent to the patients metabolic uptake of gases, this would be closed
circuit anaesthesia, or metabolic (basal) flow, or minimal flow.
Circle systems were first used back in 1930 by Brian Sword in the USA