[Soda lime--service life, consumption and costs in relation to fresh gas flow].
ABSTRACT 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)
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ABSTRACT: Several cases of unexpected high carboxyhemoglobin (COHb) levels in patients undergoing general anesthesia were observed. To avoid carbon monoxide (CO) intoxication, the use of high fresh gas flows and frequent changes of the absorbent were recommended. However, due to economic and ecologic considerations, low-flow anesthetic techniques have advantages. Thus, the subject urgently needed to be reexamined. In 1001 patients undergoing enflurane or isoflurane anesthesia, blood samples were taken 30 min after fresh gas flow reduction to 0.5 L/min and analyzed for COHb. The absorbent canisters, containing soda lime, were used for several days. The statistical mean and SD of COHb was 1.17% +/- 0.97% in the range of 0%-7.6%. There was no statistical difference between the COHb values when broken down by the duration of use of the absorbent canisters. In no case were dangerously high COHb levels observed. As recently revealed, only dry absorbents produce CO if exposed to volatile anesthetics containing a CHF2-moiety. Thus, all measures must be avoided that dry out the absorbent. Low-flow anesthesia preserves the moisture content of the absorbent and, thus, seems to be a factor protecting from CO generation.Anesthesia & Analgesia 08/1995; 81(1):144-6. · 3.30 Impact Factor