In vitro performance of prefilled CO₂ absorbers with the Aisys^®

Abstract

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 (F_ICO₂) 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 F_ICO₂ threshold because the exhaustion rate (the rate of rise once F_ICO₂ 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 F_ICO₂ 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 F_ICO₂ 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.