[Charcoal and isoflurane alveolar washout in low-flow circuit]

The inclusion of charcoal filters in anaesthetic low-flow systems contributes to the acceleration of the kinetics of isoflurane (Forane). In twenty subjects, scheduled for extra- and intracranial surgery, ventilated with a low-flow system (Ohmeda Excel OAV7750 with rebreathing cassette) with a mean total flow of 0.7 l/min, awakening was complete within 5 minutes from stopping isoflurane and including charcoal in the circuit. At the awakening, the expiratory concentration of isoflurane was 0.23% (95% confidence intervals: 0.19-0.27%): these values are similar to those of MACawake of isoflurane after fast alveolar washout. The use of charcoal during low-flow anaesthesia makes low-flow systems more flexible in their use; the anaesthetic level is more easily controllable and accidental overdosing of volatile anaesthetics can be immediately removed.