title: Dehydration of Baralyme increases compound A resulting from sevoflurane degradation in a standard anesthetic circuit used to anesthetize swine.
abstract: In 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.
  
  
  CONCLUSIONS
  The 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.
authors.affiliation: Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California-Davis, USA.
authors.forename: E P
authors.initials: EP
authors.lastname: Steffey
authors.forename: M J
authors.initials: MJ
authors.lastname: Laster
authors.forename: P
authors.initials: P
authors.lastname: Ionescu
authors.forename: E I
authors.initials: EI
authors.lastname: Eger
authors.forename: D
authors.initials: D
authors.lastname: Gong
authors.forename: R B
authors.initials: RB
authors.lastname: Weiskopf
mesh_terms: D000764:Anesthesia, Closed-Circuit; D018685:Anesthetics, Inhalation / Q000737:chemistry* / Q000633:toxicity; D000818:Animals; D017609:Barium Compounds; D002126:Calcium Hydroxide; D003681:Dehydration; D004987:Ethers / Q000737:chemistry* / Q000633:toxicity; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry* / Q000633:toxicity; D008738:Methyl Ethers; D017680:Potassium Compounds; D000077149:Sevoflurane; D013552:Swine; D013696:Temperature
chemical_list: D018685:Anesthetics, Inhalation; D017609:Barium Compounds; D004987:Ethers; D006845:Hydrocarbons, Fluorinated; D008738:Methyl Ethers; D017680:Potassium Compounds; D000077149:Sevoflurane; C068927:Baralyme; C078742:fluoromethyl 2,2-difluoro-1-(trifluoromethyl)vinyl ether; D002126:Calcium Hydroxide