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.
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