BARALYME(R) DEHYDRATION INCREASES AND SODA LIME DEHYDRATION DECREASESTHE CONCENTRATION OF COMPOUND-A RESULTING FROM SEVOFLURANE DEGRADATION IN A STANDARD ANESTHETIC CIRCUIT

Soda Lime and Baralyme(R) brand carbon dioxide absorbents degrade sevo flurane to CF2=C(CF3)OCH2F, a potentially nephrotoxic vinyl ether call ed Compound A. Dehydration of these absorbents increases both the degr adation of sevoflurane to Compound A and the degradation of Compound A . The balance between sevoflurane degradation and Compound A degradati on determines the concentration of Compound A issuing from the absorbe nt (the net production of Compound A). We studied the effect of dehydr ation on the net production of Compound A in a simulated anesthetic ci rcuit. Mimicking continuing oxygen delivery for 1, 2 or 3 days after c ompletion of an anesthetic, we directed a ''conditioning'' fresh gas f low of 5 L/min or 10 L/min retrograde through fresh absorbent in situ in a standard absorbent system for 16, 40, and/or 64 h. The conditione d absorbent was subsequently used (without mixing of the granules) in a standard anesthetic circuit in which a 3-L rebreathing bag substitut ed for the lung. Metabolism was mimicked by introducing 250 mL/min car bon dioxide into the ''lung,'' and the lung was ventilated with a minu te ventilation of 10 L/min. At the same time, we introduced sevofluran e in a fresh gas inflow of 2 L/min at a concentration sufficient to pr oduce an inspired concentration of 3.2%. Because of increased sevoflur ane destruction by the absorbent, progressively longer periods of cond itioning (dehydration) and/or higher inflow rates increased the delive red (vaporizer) concentration of sevoflurane required to sustain a 3.2 % concentration. Dehydration of Baralyme(R) increased the inspired con centration of Compound A by up to sevenfold, whereas dehydration of so da lime markedly decreased the inspired concentration of Compound A. I mplications: Economical delivery of modern inhaled anesthetics require s rebreathing of exhaled gases after removal of carbon dioxide. Howeve r, carbon dioxide absorbents (Baralyme(R)/soda lime) may degrade anest hetics to toxic substances. Baralyme(R) dehydration increases, and sod a lime dehydration decreases, degradation of the inhaled anesthetic se voflurane to the toxic substance, Compound A.