British Journal of Anaesthesia, Vol 82, Issue 2 193-198, Copyright © 1999 by The Board of Management and Trustees of the British Journal of Anaesthesia
W. Funk, M. Gruber, K. Wild and J. Hobbhahn
We have investigated gas composition during simulated inhalation induction
with sevoflurane to elucidate possible mechanisms of incidental prolonged
induction times and airway irritation. Using a circle system, 8%
sevoflurane in oxygen 6 litre min-1 was washed into an absorbing canister
filled with fresh soda lime containing 2.9% KOH (Draegersorb, 'D') or no
KOH (< 0.01%, Sofnolime, 'S'). The absorbent was dried by oxygen 20,000
litre before every second experiment. Maximum soda lime temperatures
attained after 4-6 min were 107 degrees C using dry D and 62 degrees C (61
degrees C) with dry S. Temperature did not increase with fresh soda lime.
With dry soda lime, sevoflurane was not detected at the T-piece for 3 min
and reached 6-7% within 6-10 min. After 1 min, we detected methanol and
compound A (CH2F-O-C(= CF2) (CF3)). Total amounts over 20 min were:
methanol 1125 mg (D dry), 334 mg (S dry) and < 5 mg (fresh soda lime);
compound A 148 mg (D dry), 13 mg (S dry) and 3-8 mg (fresh); and fluoride
8.5 mg (D dry), 3.3 mg (S dry) and 1 mg (fresh). Formaldehyde was detected
only with dry lime (D > 2.5 mg, S > 0.6 mg). In summary, the use of
moist soda lime is of crucial importance during inhalation induction. With
dry soda lime, the patient may inhale potentially toxic degradation
products in significant amounts. Sevoflurane degradation is aggravated by a
high KOH content of the lime. The observed airway irritation may be caused
by formic acid, which is generated in isomolar concentrations with methanol
(Cannizzaro reaction). The amount of compound A found with dry
KOH-containing lime is unlikely to be noxious.
CLINICAL INVESTIGATIONS
Dry soda lime markedly degrades sevoflurane during simulated inhalation induction
Department of Anaesthesiology, University of Regensburg, D-93042 Regensburg, Germany
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