• E P Steffey, M J Laster, P Ionescu, E I Eger, D Gong, and R B Weiskopf.
• Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, USA.
• Anesth. Analg. 1997 Dec 1; 85 (6): 1382-6.

UnlabelledIn a model anesthetic circuit, dehydration of Baralyme brand carbon dioxide absorbent increases degradation of sevoflurane to CF2=C(CF3)OCH2F, a nephrotoxic vinyl ether called Compound A. In the present study, we quantified this increase using "conditioned" Baralyme in a circle absorbent system to deliver sevoflurane anesthesia to swine. Mimicking continuing oxygen delivery for 2 days after completion of an anesthetic, we directed a conditioning fresh gas flow of 5 L/min retrograde through fresh absorbent in situ in a standard absorbent system for 40 h. The conditioned absorbent was subsequently used (without mixing of the granules) in a standard anesthetic circuit to deliver sevoflurane to swine weighing 78 +/- 2 kg. The initial inflow rate of fresh gas flow was set at 10 L/min with the vaporizer at 8% to achieve the target end-tidal concentration of 3.0%-3.2% sevoflurane in approximately 20 min. The flow was later decreased to 2 L/min, and the vaporizer concentration was decreased to sustain the 3.0%-3.2% value for a total of 2 h (three pigs) or 4 h (eight pigs). Inspired Compound A increased over the first 30 +/- 60 min to a peak concentration of 357 +/- 49 ppm (mean +/- SD), slowly decreasing thereafter to 74 +/- 6 ppm at 4 h. The average concentration over 2 h was 208 +/- 25 ppm, and the average concentration over 4 h was 153 +/- 19 ppm. Pigs were killed 1 or 4 days after anesthesia. The kidneys from pigs anesthetized for both 2 h and 4 h showed mild inflammation but little or no tubular necrosis. These results suggest that dehydration of Baralyme may produce concentrations of Compound A that would have nephrotoxic effects in humans in a shorter time than would be the case with normally hydrated Baralyme.ImplicationsThe vapor known as Compound A can injure the kidney. Dehydration of Baralyme, a standard absorbent of carbon dioxide in inhaled anesthetic delivery systems, can cause a 5- to 10-fold increase in Compound A concentrations produced from the inhaled anesthetic, sevoflurane, given at anesthetizing concentrations in a conventional anesthetic system.

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