Low flow anesthesia increases the use of CO2 absorbents, but independent data that compare canister life of the newest CO2 absorbents are scarce. Seven different pre-packed CO2 canisters were tested in vitro: Amsorb Plus, Spherasorb, LoFloSorb, Medisorb, Medisorb EF, LithoLyme, and SpiraLith. CO2 (160 mL min(-1)) flowed into the tip of a 2 L breathing bag that was ventilated with a tidal volume of 500 mL, a respiratory rate of 10/min, and an I:E ratio of 1:1 using the controlled mechanical ventilation mode of the Aisys (®) (GE, Madison, WI, USA). In part I, canister life of each brand (all of the same lot) was tested with 12 different fresh gas flows (FGF) ranging from 0.25 to 4 L min(-1). In part II, canister life of six canisters each of two different lots of each brand were tested with a 350 mL min(-1) FGF. Canister life is presented as "FCU", fractional canister usage, the fraction of a canister used per hour, and is defined for the inspired CO2 concentration (FICO2) that denotes exhaustion. In part III, canister life per 100 g fresh granule content was calculated. FCU decreased linearly with increasing FGF. The relative position of the FCU-FGF curves of the different brands depends on the FICO2 threshold because the exhaustion rate (the rate of rise once FICO2 starts to increase) differs among the brands. Intra-lot variability was 18 % or less. The different prepacks can be ranked according their efficiency (least to most efficient) as follows: Amsorb Plus = Medisorb EF < LoFloSorb < Medisorb = Spherasorb = LithoLyme < SpiraLith (all for an FICO2 threshold = 0.5 %). Canister life per 100 g fresh granule content is almost twice as long when LiOH is used as the primary absorbent. The most important factors that determine canister life of prepacks in a circle breathing system are the chemical composition of the canister, the absolute amount of absorbent present in the canister, and the FICO2 replacement threshold. The use of the fractional canister usage allows cost comparisons among different prepacks. Results should not be extrapolated to prepacks that fit onto other anesthesia machines.

We confirmed the existence of a SGE of N(2)O. Surprisingly, when using an Fa of 65% N(2)O, the magnitude of the SGE was the same with large or small VN(2)O. The classical model and the graphical representation of the SGE alone should not be used to explain the magnitude of the SGE. We speculate that changes in ventilation/perfusion inhomogeneity in the lungs during general anaesthesia result in a SGE at levels of VN(2)O previously considered by most to be too small to exert a SGE.

Low fresh gas flows (FGFs) decrease the use of anesthetic gases, but increase CO absorbent usage. CO absorbent usage remains poorly quantified. The goal of this study is to determine canister life of 8 commercially available CO absorbent prepacks with the Zeus. Pre-packed CO canisters of 8 different brands were tested in vitro: Amsorb Plus, Spherasorb, LoFloSorb, LithoLyme, SpiraLith, SpheraSorb, Drägersorb 800+, Drägersorb Free, and CO2ntrol. CO (160 mL min) flowed into the tip of a 2 L breathing bag that was ventilated with a tidal volume of 500 mL, a respiratory rate of 10/min, and an I:E ratio of 1:1 using the controlled mechanical ventilation mode of the Zeus (Dräger, Lubeck, Germany). In part I, canister life of 5 canisters each of 2 different lots of each brand was determined with a 350 mL min FGF. Canister life is the time it takes for the inspired CO concentration (FCO) to rise to 0.5%. In part II, canister life was measured accross a FGF range of 0.25 to 4 L min for Drägersorb 800+ (2 lots) and SpiraLith (1 lot). In part III, the calculated canister life per 100 g fresh granule content of the different brands was compared between the Zeus and (previously published data for) the Aisys. In vitro canister life of prefilled CO absorber canisters differed between brands, and depended on the amount of CO absorbent and chemical composition. Canister life expressed as FCU (the fraction of the canister used per hour) was proportional to FGF over 0.2-2 L min range only, but was non-linear with higher FGF: FCU was larger than expected with FGF > 2 L min, and even with FGF > minute ventilation FCU did not become zero, indicating some CO was being absorbed. Canister life on a per weight basis of the same brand is higher with the Zeus than the Aisys. Canister life of prefilled CO absorber canisters differs between brands. The FCU-FGF relationship is not linear across the entire FGF range. Canister life of prepacks of the same brand for the Zeus and Aisys differs, the exact etiology of which is probably multifactorial, and may include differences in the absolute amount of absorbent and different rebreathing characteristics of the machines.

No abstract

Background: The Zeus ® (Dräger, Lübeck, Germany), an automated closed-circuit anesthesia machine, uses high fresh gas flows (FGF) to wash-in the circuit and the lungs, and intermittently flushes the system to remove unwanted N 2 . We hypothesized this could increase desflurane consumption to such an extent that agent consumption might become higher than with a conventional anesthesia machine (Anesthesia Delivery Unit [ADU ® ], GE, Helsinki, Finland) used with a previously derived desflurane-O 2 -N 2 O administration schedule that allows early FGF reduction.