Shunji Kobayashi

Amsorb Plus and Drägersorb Free, two new-generation carbon dioxide absorbents that produce a low compound A concentration while providing sufficient CO2 absorption capacity in simulated sevoflurane anesthesia

PurposeThe properties of two new-generation CO2 absorbents, Amsorb Plus (Armstrong Medical, Coleraine, UK) and Drägersorb Free (Dräger, Lübeck, Germany), were compared with those of Amsorb (Armstrong Medical) and Sodasorb II (W.R. Grace, Lexington, MA, USA).MethodsThe concentration of compound A produced by each absorbent was determined in a low-flow circuit containing sevoflurane, and the CO2 absorption capacity of the absorbent was measured. The circuit contained 1000 g of each absorbent and had a fresh gas (O2) flow rate of 1 l·min−1 containing 2% sevoflurane. CO2 was delivered to the circuit at a flow rate of 200 ml·min−1.ResultsThe maximum concentrations of compound A were 2.2 ± 0.0, 2.3 ± 0.3, 2.2 ± 0.2, and 23.5 ± 1.5 ppm (mean ± SD) for Amsorb Plus, Drägersorb Free, Amsorb, and Sodasorb II, respectively. The maximum concentration of compound A for Sodasorb II was significantly higher than those for the other absorbents (P < 0.01). The CO2 absorption capacities (time taken to reach an inspiratory CO2 level of 2 mmHg) were 1023 ± 48, 1074 ± 36, 767 ± 41, and 1084 ± 54 min, respectively, and the capacity of Amsorb was significantly lower than that of the other absorbents (P < 0.01).ConclusionThe new-generation carbon dioxide absorbents, Amsorb Plus and Drägersorb Free, produce a low concentration of compound A in the circuit while showing sufficient CO2 absorption capacity.

Effect of humidity in the circuit on the CO2 absorption capacity of Amsorb and Sodasorb II.

acted as an artificial lung, and the CO2 was delivered at a flow rate of 200ml·min 1 into the distal portion of the bag. The artificial lung was ventilated at a rate of 10 ·min 1 with a measured expired tidal volume of 500 ml. The inspiratory–expiratory ratio was set at 1 : 2. The anesthesia system was flushed for 30min with 100% oxygen at a flow rate of 6 l·min 1 in the absence of the CO2 absorbent. After this preparation period, 500g of fresh absorbent was placed into the upper canister, and glass balls were placed in the lower canister as filler. The oxygen flow rate was reduced to 1 l·min 1, and the tidal volume setting was readjusted to maintain a volume of 500 ml. In the moisturized group, a heated respiratory humidifier (MR418 Humidification System, Fisher and Paykel, Auckland, New Zealand) was placed into the inspiratory limb, and the temperature of the humidifier was maintained at 37°C. Gas samples were obtained from the inspiratory limb just beyond the inspiratory valve. The CO2 analysis was performed with a Capnomac (Datex, Helsinki, Finland). Each experiment was repeated three times for each group, and the studies were conducted in random order. The measured values are expressed as means SD. The total time of use (minutes), the time until each absorbent reached exhaustion, as defined by the occurrence of CO2 rebreathing (1–5 mmHg), was compared between the groups by the Mann-Whitney U-test. A P value less than 0.05 was considered to indicate statistical significance. The total time of use of the CO2 absorbents is shown in Fig. 1. Humidification reduced the total time of use of Sodasorb II, but not that of Amsorb. Under normal conditions, the CO2 absorption capacity of Amsorb was 55.7%, 73.5%, 75.5%, 78.1%, and 78.9% that of Sodasorb II at 1, 2, 3, 4, and 5 mmHg, respectively. Under moisturized conditions, the CO2 absorption capacity of Amsorb was 66.6%, 80.6%, 84.8%, 87.3%, and 88.5% that of Sodasorb II at 1, 2, 3, 4, and 5mmHg, respectively.