DEHYDRATION OF BARALYME(R) INCREASES COMPOUND-A RESULTING FROM SEVOFLURANE DEGRADATION IN A STANDARD ANESTHETIC CIRCUIT USED TO ANESTHETIZESWINE

In a model anesthetic circuit, dehydration of Baralyme(R) brand carbon dioxide absorbent increases degradation of sevoflurane to CF2=C(CF3)O CH2F, a nephrotoxic vinyl ether called Compound A. In the present stud y, we quantified this increase using ''conditioned'' Baralyme(R) in a circle absorbent system to deliver sevoflurane anesthesia to swine. Mi micking continuing oxygen delivery for 2 days after completion of an a nesthetic, we directed a conditioning fresh gas flow of 5 L/min retrog rade through fresh absorbent in situ in a standard absorbent system fo r 40 h. The conditioned absorbent was subsequently used (without mixin g of the granules) in a standard anesthetic circuit to deliver sevoflu rane to swine weighing 78 +/- 2 kg. The initial inflow rate of fresh g as flow was set at 10 L/min with the vaporizer at 8% to achieve the ta rget 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 co ncentration was decreased to sustain the 3.0%-3.2% value for a total o f 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 (me an +/- SD), slowly decreasing thereafter to 74 +/- 6 ppm at 4 h. The a verage concentration over 2 h was 208 +/- 25 ppm, and the average conc entration over 4 h was 153 +/- 19 ppm. Pigs were killed 1 or 4 days af ter anesthesia. The kidneys from pigs anesthetized for both 2 h and 4 h showed mild inflammation but little or no tubular necrosis, These re sults suggest that dehydration of Baralyme(R) may produce concentratio ns of Compound A that would have nephrotoxic effects in humans in a sh orter time than would be the case with normally hydrated Baralyme(R). Implications: The vapor known as Compound A can injure the kidney. Deh ydration of Baralyme(R) a standard absorbent of carbon dioxide in inha led anesthetic delivery systems, can cause a 5- to 10-fold increase in Compound A concentrations produced from the inhaled anesthetic, sevof lurane, given at anesthetizing concentrations in a conventional anesth etic system.