Volume 9, No. 4 • Winter 1994

CO Researcher Notes, Compares CO Production From Different Absorbents – Not to be Basis for Choice

Edmond I. Eger, II, M.D.

To the Editor

Data presented in our recent publication’ concerning the production of carbon monoxide (CO) from the degradation of volatile anesthetics by carbon dioxide absorbents was not intended to be used as the sole basis for choosing a particular absorbent or anesthetic.’ The data show a greater production of CO from a given anesthetic exposed to Baralyme brand absorbent at comparable levels of absorbent dryness. Dryness is important because drying of the absorbent to below-normal levels of water content increases production of CO, particularly as complete dryness is approached. If fresh, dry gas flows over, and dries the soda lime and Baralyme equally, CO production might be particularly increased with Baralyme. However, this presumes equal drying of the absorbents. Reports assert, without publication of supporting comparative data, that the hydrate of barium hydroxide in Baralyme’ resists drying more than the mixture of water and absorbent found in soda lime.’,’ If true, this would modify the presumption of equal drying, and thus may balance or change the relative likelihood of CO production associated with the use of one absorbent as opposed to the other. Further studies will be needed to assess these and other factors as determinants of absorbent and anesthetic choice.

Edmond I. Eger, II, M.D.,

Professor and Vice Chairman for Research University of California, San Francisco, CA


  1. Fang Z, Eger El II. Factors causing the production of carbon monoxide from the action of carbon dioxide absorbents on volatile anesthetics. APSF Newsletter 1994; 9: 25-28.
  2. Andrews J. Inhaled anesthetic delivery systems. ed: R Miller, Anesthesia, 4th edition. New York: Churchill Livingston, 1994: p. 207.
  3. Adriani J, Batten D. The efficiency of mixtures of barium and calcium hydroxides in the absorption of carbon dioxide in rebreathing appliances. Anesthesiology 1942; 3: 1-10.