Volume 7, No. 3 • Fall 1992

Soda Lime Needs Monitor

Richard D. Thomason, M.D.

To the Editor

Recently, I had an occasion to discuss with a representative of a major anesthesia machine manufacturer the need for a more appropriate soda lime monitor. I suggested to him that with the present technology in the machines there should be no problem analyzing the C02 absorber for failure of the soda lime.

I have now decided that this idea should not be available to only one machine manufacturer. Since it was originally my idea and something which to my knowledge is not yet on the market, I am sending the idea to you so that it can be published and made common knowledge. Therefore, one manufacturer could not patent the idea or technology.

I myself have repeatedly gone to the assigned OR to find that the soda lime is exhausted to the point that the indicator dye is no longer effective. When brought to the attention of others, I get the response that this must be the reason their last few patients had such rapid pulses. I don’t really know why the expired C02 level wasn’t elevated to a point that they should have been suspicious, but evidently it wasn’t.

In this proposed design for a more appropriate soda lime monitor, the soda lime canister is connected by three vents with tubing to a sampling valve with two outlets. Using a continuous C02 monitor, failure of the C02 absorbent in the canister could be detected without relying on the indicator color change within the canister.

In any event, the idea is simple and I encourage someone to develop it. If I wasn’t at retirement age and still worked in a teaching hospital, I feel that it could be functional within a month of starting with off the shelf components.

Richard D. Thomason, M.D. Elkhart, IN