ABSORBER

Although this term could be applied to an acoustic or liquid absorber it is most commonly used to refer to a carbon dioxide absorber of the type used in rebreathing anaesthetic circuits. It consists of a container filled with soda-lime through which the patient's expired gases are passed. It may take the form of a canister (e.g. Waters canister) mounted between the facepiece and breathing bag so that gas passes through in both directions, or it may be included in a circle closed circuit (see Circle absorber).

The soda-lime absorbs carbon dioxide from the expired gases so that the remainder can be fed back to the patient with a small supplement of fresh anaesthetic gases. This arrangement is economical with the gases used, reduces pollution of the room air, conserves heat and moisture, and does not normally require humidification. Disadvantages are that alkaline dust may pass to the patient, and the canister holding the granules may be a cause of leaks.

The soda-lime usually consists of a mixture of 90% calcium hydroxide, 5% sodium hydroxide, and 1% potassium hydroxide, with silicates to prevent powdering. It is essential for effective operation that moisture (14-19%) be incorporated within the granules. Durasorb is an improved soda-lime which is pink in colour which turns to white when it becomes inactive.

Content and Design Copyright 2000 Dr. Malcolm C Brown.  See Title Page for more details