British Journal of Anaesthesia, Vol 83, Issue 4 571-575, Copyright © 1999 by The Board of Management and Trustees of the British Journal of Anaesthesia
W. Funk, M. Gruber, W. Jakob and J. Hobbhahn
We have investigated inspiratory and end-tidal gas composition during
sevoflurane anaesthesia in a closed circle system with continuous gas flow
(70 litre min-1, Physioflex) to determine possible accumulation of
sevoflurane degradation products. During five abdominal operations in
adults lasting more than 2 h, anaesthesia was maintained with an end- tidal
concentration of 2% sevoflurane in 40% oxygen-air. The circle included an
absorbing canister filled with 1 litre of fresh soda lime. Samples were
obtained at the end of an expiration from the tracheal tube and from the
inspiratory limb before, and at selected times after, addition of
sevoflurane. The temperature of soda lime was 24.7 +/- 0.7 degrees C at the
beginning and reached a maximum of 31.2 +/- 1.0 degrees C after 20-30 min,
followed by a plateau. Inspiratory compound A (CH2F-O-C(= CF2)(CF3)) 3-8
ppm was detected after 10 min, but did not accumulate in the circle over 2
h without flushing. Expired concentrations were consistently lower with
1.5-3 ppm signalling absorption by patients. Calculated total amounts
absorbed over 2 h varied between 2.0 and 7.2 ppm h. Other degradation
products such as compound B or methanol were not detected. In summary, we
did not detect sevoflurane metabolites with soda lime in significant
amounts during closed circle anaesthesia with the Physioflex. The observed
concentrations of compound A were below the threshold of nephrotoxicity in
rats by a factor of more than 20.
CLINICAL INVESTIGATIONS
Compound A does not accumulate during closed circuit sevoflurane anaesthesia with the Physioflex
Department of Anaesthesiology, University of Regensburg, D-93042 Regensburg, Germany
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