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GENERAL ARTICLES

The Elimination of Sodium and Potassium Hydroxides from Desiccated Soda Lime Diminishes Degradation of Desflurane to Carbon Monoxide and Sevoflurane to Compound A but Does Not Compromise Carbon Dioxide Absorption

M. A. Neumann, MD^*, M. J. Laster, DVM^*, R. B. Weiskopf, MD^*, D. H. Gong, BS^*, R. Dudziak, MD, H. Förster, MD, and E. I Eger, II, MD^*

*Department of Anesthesia, University of California San Francisco, San Francisco, California; and Department of Anesthesiology, Johann Wolfgang Goethe University, Frankfurt, Germany

Address correspondence to Edmond I Eger II, MD, Box 0464, University of California San Francisco, San Francisco, CA 94143-0464.

Normal (hydrated) soda lime absorbent (approximately 95% calcium hydroxide [Ca(OH)₂], the remaining 5% consisting of a mixture of sodium hydroxide [NaOH] and potassium hydroxide [KOH]) degrades sevoflurane to the nephrotoxin Compound A, and desiccated soda lime degrades desflurane, enflurane, and isoflurane to carbon monoxide (CO). We examined whether the bases in soda lime differed in their capacities to contribute to the production of these toxic substances by degradation of the inhaled anesthetics. Our results indicate that NaOH and KOH are the primary determinants of degradation of desflurane to CO and modestly augment production of Compound A from sevoflurane. Elimination of these bases decreases CO production 10-fold and decreases average inspired Compound A by up to 41%. These salutary effects can be achieved with only slight decreases in the capacity of the remaining Ca(OH)₂ to absorb carbon dioxide.

Implications: The soda lime bases used to absorb carbon dioxide from anesthetic circuits can degrade inhaled anesthetics to compounds such as carbon monoxide and the nephrotoxin, Compound A. Elimination of the bases sodium hydroxide and potassium hydroxide decreases production of these noxious compounds without materially decreasing the capacity of the remaining base, Ca(OH)₂, to absorb carbon dioxide.

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