Only carbon dioxide absorbents free of both NaOH and KOH do not generate compound A during in vitro closed-system sevoflurane - Evaluation of five absorbents

Background insufficient data exist on the production of compound A during c losed-system sevoflurane administration with newer carbon dioxide absorbent s. Methods: A modified PhysioFlex apparatus (Drager, Lubeck, Germany) was conn ected to an artificial test lung (Inflow at the top of the bellow congruent to 160 ml/min CO2; outflow at the Y piece of the lung model congruent to 2 00 ml/min, simulating oxygen consumption). Ventilation was set to obtain an end-tidal carbon dioxide partial pressure of approximately 40 mmHg. Variou s fresh carbon dioxide absorbents were used: Sodasorb (n = 6), Sofnolime (n = 6), and potassium hydroxide (KOH)-free Sodasorb (n = 7), Amsorb (n = 7), and lithium hydroxide (n = 7). After baseline analysis, liquid sevoflurane was Injected into the circuit by syringe pump to obtain 2.1% end-tidal con centration for 240 min. At baseline and at regular intervals thereafter, en d-tidal carbon dioxide partial pressure, end-tidal sevoflurane concentratio n, and canister inflow (T degrees (in)) and canister outflow (T degrees (ou t)) temperatures were measured. To measure compound A(insp) concentration i n the inspired gas of the breathing circuit, 2-ml gas samples were taken an d analyzed by capillary gas chromatography plus mass spectrometry. Results: The median (minimum-maximum) highest compound A(insp) concentratio ns over the entire period were, in decreasing order: 38.3 (28.4-44.2)* (Sof nolime), 30.1 (23.9-43.7) (KOH-free Sodasorb), 23.3 (20.0-29.2) (Sodasorb), 1.6 (1.3-2.1)* (lithium hydroxide), and 1.3 (1.1-1.8)* (Arnsorb) parts per million (*P < 0.01 vs. Sodasorb). After reaching their peak concentration, a decrease for Sofnolime, KOH-free Sodasorb, and Sodasorb until 240 min wa s found. The median (minimum-maximum) highest values for T degrees (out), w ere 39 (38-40), 40 (39-42), 41 (40-42), 46 (44-48)*, and 39 (38-41) IC (*P < 0.01 vs. Sodasorb), respectively. Conclusions: With KOH-free (but sodium hydroxide [NaOH]containing) soda lim es even higher compound A concentrations are recorded than with standard So dasorb. Only by eliminating KOH as well as NaoH from the absorbent (Amsorb and lithium hydroxide) is no compound A produced.