Indicators
Ethyl violet, the pH indicator added to soda lime and Baralyme
to help assess the functional integrity of the absorbent, is a substituted triphenylmethane
dye with a critical pH of 10.3.[115]
Ethyl violet
changes in color from colorless to violet when the pH of the absorbent decreases
as a result of carbon dioxide absorption. The pH of fresh absorbent exceeds the
critical pH, and the dye exists in its colorless form ( Fig.
9-23A
). As absorbent becomes exhausted, however, the pH decreases below
10.3, and ethyl violet changes to its violet form (see Fig.
9-23B
) through alcohol dehydration. Ethyl violet is not always a reliable
indicator of the functional status of absorbent. Fluorescent lights can deactivate
the dye so
Figure 9-23
Ethyl violet changes from colorless to violet when the
pH of the absorbent decreases as a result of carbon dioxide absorption. A,
The pH of fresh absorbent exceeds the critical level, and the dye exists in its colorless
form. B, As absorbent becomes exhausted, the pH decreases
below 10.3, and ethyl violet changes to its violet form through alcohol dehydration.
(Adapted from Andrews JJ, Johnston RV Jr, Bee DE, Arens JF: Photodeactivation
of ethyl violet: A potential hazard of Sodasorb. Anesthesiology 72:59, 1990.)
that the absorbent appears white even though it is exhausted.[120]
