Background and objective Minimal- and low-flow anaesthesia (fresh gas flow below 1 L min−1) provide many advantages, including reduced cost, conservation of body heat and airway humidity. An airtight seal is essential between the airway device and the airway of the patient. Therefore, we investigated whether the airtight seal created by a laryngeal mask airway allows controlled ventilation of the lungs when the fresh gas flow is reduced to 0.5 L min−1 and compared this with an endotracheal tube.

Methods In a prospective clinical study, 207 patients were managed using a laryngeal mask or an endotracheal tube. After intravenous induction of anaesthesia and 15 min of high fresh gas flow, the flow was reduced to 0.5 L min−1. The breathing system was monitored for airway leaks, and the patients were assessed for complications after airway removal and postoperative discomfort.

Results Both the laryngeal mask and endotracheal tube allowed fresh gas flow reduction to 0.5 L min−1 in 84.7% and 98.3% of cases respectively (small leaks: 12% laryngeal mask, 1.7% endotracheal tube). Three patients with the laryngeal mask (3.3%l) had airway leaks that were too large to permit any reduction in the fresh gas flow.

Conclusions The use of the laryngeal mask airway was more likely to be associated with a gas leak than use of an endotracheal tube; however, if modern anaesthesia machines and monitors are used, in 96.7% of the patients managed with a laryngeal mask a reduction in the fresh gas flow to 0.5 L min−1 was possible. The incidence of coughing and postoperative complaints (sore throat, swallowing problems) was higher after use of an endotracheal tube.

Background and aim Compound A generation and accumulation in sevoflurane anaesthesia is dependent on fresh gas flow. We investigated the extent of generation of compound A.

Methods After Institutional Review Board approval and informed consent, patients with normal renal function were randomized to receive either sevoflurane (n = 33) or isoflurane (n = 43) minimal flow anaesthesia (0.5 L min−1) for at least 2 h under standardized conditions. Compound A concentrations were quantified and blood and urine samples were taken to assess renal involvement. Both groups were comparable.

Results No significant differences concerning blood chemistry and urine measurements were found. The maximum mean compound A concentration was observed 90 min after flow reduction being 40±9p.p.m. at a corresponding mean sevoflurane concentration of 2.1 ±0.5 vol%. Mean inspiratory compound A exposure was 102±l33p.p.mh−1.

Conclusion Compound A concentrations using 0.5 L min−1 fresh gas flow and a heated absorber were higher than previously published values using an inflow of 1 Lmin−1. Compound A exposure was similar to other clinical studies which did not show changes in renal and hepatic function.

The concentrations of nitrous oxide, sevoflurane and oxygen in the circle system of a closed-circuit anaesthesia machine, the PhysioFlex™, were measured in seven patients. During anaesthesia, the settings for each gas were changed and their concentrations recorded. At the induction of anaesthesia, it took 80– 510s (median 190 s) for the end-tidal sevoflurane concentration to reach 2.0%, and 920–2640 s (median 1500 s) for the oxygen in the breathing circuit to reach 30%. At this time, the nitrous oxide concentration was 60±3% (mean±SD). During anaesthesia, it took 90–480 s (median 140 s) for the end-tidal sevoflurane concentration setting to decrease from 3.0 to 1.0%, and 90–400 s (median 110 s) to return from 1.0 to 3.0%. When the inspired oxygen was increased from 30 to 50%, circuit concentrations reached equilibrium in 40–60 s (median 40 s), and when decreased from 50% back to 30%, equilibrium took 310–470 s (median 450 s). During recovery from anaesthesia, inspiratory sevoflurane concentration took 40–70 s (median 50 s) to decrease to 0.2%. The PhysioFlex™ provided adequate control of sevoflurane and oxygen concentrations, but not of increasing nitrous oxide concentrations.