In a model anesthetic circuit, dehydration of Baralyme(R) 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(R) 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(R) 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(R). Implications: The vapor known as Compound A can injure the kidney. Dehydration of Baralyme(R), 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.
ASJC Scopus subject areas
- Anesthesiology and Pain Medicine