In vitro performance of prefilled CO₂ absorbers with the Zeus®

Low fresh gas flows (FGFs) decrease the use of anesthetic gases, but increase CO₂ absorbent usage. CO₂ absorbent usage remains poorly quantified. The goal of this study is to determine canister life of 8 commercially available CO₂ absorbent prepacks with the Zeus^®. Pre-packed CO₂ canisters of 8 different brands were tested in vitro: Amsorb Plus, Spherasorb, LoFloSorb, LithoLyme, SpiraLith, SpheraSorb, Drägersorb 800+, Drägersorb Free, and CO2ntrol. 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 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^{− 1} FGF. Canister life is the time it takes for the inspired CO₂ concentration (F_ICO₂) to rise to 0.5%. In part II, canister life was measured accross a FGF range of 0.25 to 4 L min^{− 1} 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 CO₂ absorber canisters differed between brands, and depended on the amount of CO₂ absorbent and chemical composition. Canister life expressed as FCU_0.5 (the fraction of the canister used per hour) was proportional to FGF over 0.2–2 L min⁻¹ range only, but was non-linear with higher FGF: FCU_0.5 was larger than expected with FGF > 2 L min⁻¹, and even with FGF > minute ventilation FCU_0.5 did not become zero, indicating some CO₂ 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 CO₂ absorber canisters differs between brands. The FCU_0.5–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.