To the Editor:—

In a recent study 1(supported by Abbott—the supplier of Amsorb®) comparing degradation of volatile anesthetics and formation of carbon monoxide (CO), COHB, and compound A in the presence of different carbon dioxide absorbants, Kharasch et al.  report that for desflurane the order of CO formation was Baralyme®> “classic” sodalime > “new” sodalime > Amsorb®. The foundation for this statement seems to be lacking. Use of the symbol “>” usually implies statistical significance. However, in this case, the only statistically significant differences are those between Baralyme®and the other three absorbants. In other words, Amsorb®, although causing less CO formation than does Baralyme®, causes no less CO formation than that caused by either “new” or “classic” sodalime.

In addition, the statistical methodology used in this complicated study design is inadequately described. A simple statement that analysis of variance was used is not informative. Which type of analysis of variance was used and which multiple comparison procedures did the authors utilize to support their statements?

Although the flaws described above might seem to be of minor importance, a major objection is that the final statements “in comparison with sodalime and Baralyme®, Amsorb®caused minimal if any CO formation, …” and “These findings seem relevant to patient safety” can now be used by the study sponsor as evidence of product superiority when in fact for the most relevant volatile anesthetic in terms of CO production (desflurane) no difference between Amsorb®and sodalime has been demonstrated.

Kharasch ED, Powers KM, Artru AA: Comparison of Amsorb®, sodalime, and Baralyme®degradation of volatile anesthetics and formation of carbon monoxide and compound A in swine in vivo . A nesthesiology 2002; 96: 173–82