[Soda lime--service life, consumption and costs in relation to fresh gas flow]

The utilisation time of carbon dioxide absorbers in anaesthesia textbooks is nearly identically specified to last about 5 hours. Therefore in most departments the soda lime of the absorbers is changed routinely on a daily schedule. As rebreathing volume increases considerably with fresh gas flow reduction, the question arises as to whether the soda lime should be changed at even shorter intervals--if low-flow anaesthesia is performed routinely--to to guarantee carbon dioxide absorption safely. In three anaesthesia machines with different technical properties the carbon dioxide absorbers were only changed when the inspiratory carbon dioxide concentration increased to 1 vol. %, indicating definite exhaustion of the soda lime. If a fresh gas flow of 4.4 l/min was used exclusively, utilisation times of 42.7 and 62.3 hours were measured using absorbers filled with 1 l of soda lime pellets, whereas a utilisation time of 98.7 hours was noted with a 1.5 l absorber, all values being surprisingly higher than the above-mentioned figure. If, however, minimal flow anaesthesia is performed routinely in clinical practice, the percentage of time in which the fresh gas flow can really be reduced to 0.5 l/min does not exceed 50 to 80%. Under these conditions the utilisation time of the absorbers decreases to between one half (1/2) and one quarter (1/4) of the utilisation time which can be gained if a flow of 4.4 l/min is used. Thus, the performance of minimal-flow anaesthesia increases the consumption of soda lime two- to fourfold.(ABSTRACT TRUNCATED AT 250 WORDS)