Baralyme(R) dehydration increases and soda lime dehydration decreases the concentration of compound A resulting from sevoflurane degradation in a standard anesthetic circuit

Soda Lime and Baralyme(R) brand carbon dioxide absorbents degrade sevoflurane to CF2=C(CF3)OCH2F, a potentially nephrotoxic vinyl ether called Compound A. Dehydration of these absorbents increases both the degradation of sevoflurane to Compound A and the degradation of Compound A. The balance between sevoflurane degradation and Compound A degradation determines the concentration of Compound A issuing from the absorbent (the net production of Compound A). We studied the effect of dehydration on the net production of Compound A in a simulated anesthetic circuit. Mimicking continuing oxygen delivery for 1, 2 or 3 days after completion of an anesthetic, we directed a ''conditioning'' fresh gas flow 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 conditioned absorbent was subsequently used (without mixing of the granules) in a standard anesthetic circuit in which a 3-L rebreathing bag substituted for the lung. Metabolism was mimicked by introducing 250 mL/min carbon dioxide into the ''lung,'' and the lung was ventilated with a minute ventilation of 10 L/min. At the same time, we introduced sevoflurane in a fresh gas inflow of 2 L/min at a concentration sufficient to produce an inspired concentration of 3.2%. Because of increased sevoflurane destruction by the absorbent, progressively longer periods of conditioning (dehydration) and/or higher inflow rates increased the delivered (vaporizer) concentration of sevoflurane required to sustain a 3.2% concentration. Dehydration of Baralyme(R) increased the inspired concentration of Compound A by up to sevenfold, whereas dehydration of soda lime markedly decreased the inspired concentration of Compound A. Implications: Economical delivery of modern inhaled anesthetics requires rebreathing of exhaled gases after removal of carbon dioxide. However, carbon dioxide absorbents (Baralyme(R)/soda lime) may degrade anesthetics to toxic substances. Baralyme(R) dehydration increases, and soda lime dehydration decreases, degradation of the inhaled anesthetic sevoflurane to the toxic substance, Compound A.