[Charcoal and isoflurane alveolar washout in low-flow circuit]. / Carboni attivi e washout alveolare dell'isofluorano in circuito a basso flusso.

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.

Effects of a heat and moisture exchanger on carbon dioxide equilibrium during mechanical ventilation with the Bain circuit.

The introduction of a heat and moisture exchanger (HME) into the anaesthetic circuit may cause a rise in carbon dioxide (CO2) tension through an increase in dead space. We studied the effects of the Ultipor Pall BB50 filter included 'in series' in the Bain circuit on CO2 equilibrium. Arterial carbon dioxide tension (PaCO2) was measured in 81 patients scheduled for elective surgery before and after the insertion of the filter. Results showed that: females were always more hyperventilated than males when fresh gas flow was set at 70 ml kg-1 ideal body weight; the inclusion of the filter increased the PaCO2 in the group as a whole (the difference was statistically, but not clinically, significant); PaCO2 increased after the application of the filter only in females; the effects of the filter were completely independent of the patient's age. It is concluded that the use of the Ultipor Pall BB50 filter is a safe procedure during mechanical ventilation with the Bain breathing system and there is no need to modify ventilation.