Memsorb™, a novel CO₂ removal device part II: in vivo performance with the Zeus IE^®

Memsorb™ (DMF Medical, Halifax, Canada) is a novel device based upon membrane oxygenator technology designed to eliminate CO₂ from exhaled gas when using a circle anesthesia circuit. Exhaled gases pass through semipermeable hollow fibers and sweep gas flowing through these fibers creates a diffusion gradient for CO₂ removal. In vivo Memsorb™ performance was tested during target-controlled closed-circuit anesthesia (TCCCA) with desflurane in O₂/air using a Zeus IE® anesthesia workstation (Dräger, Lübeck, Germany). Clinical care protocols for using this novel device were guided by in vitro performance results from a prior study (submitted simultaneously). After IRB approval, written informed consent was obtained from 10 ASA PS I-III patients undergoing robot-assisted radical prostatectomy. TCCCA targets were 39% inspired O₂ concentration (F_IO₂) and 5.0% end-expired desflurane concentration (F_ETdes). Minute ventilation (MV) was adjusted to maintain 4.5-6.0% F_ETCO₂. The O₂/air (40% O₂) sweep flow into the Memsorb™ was manually adjusted in an attempt to keep inspired CO₂ concentration (F_ICO₂) ≤ 0.8%. The following data were collected: F_IO₂, F_ETdes, F_ICO₂, F_ETCO₂, MV, fresh gas flow (FGF, O₂ and air), sweep flow, and cumulative desflurane usage (Vdes). Vdes of the Zeus IE®-Memsorb™ combination was compared with historical Vdes observed in a previous study when soda lime (DrägerSorb 800 +) was used. Results are reported as median and inter-quartiles. A combination of manually adjusting sweep flow (26 [21,27] L/min) and MV sufficed to maintain F_ICO₂ ≤ 0.8% and F_ETCO₂ ≤ 6.0%, except in one patient in whom the target Zeus IE® FGF had to be increased to 0.7 L/min for 6 min. F_IO₂ and F_ETdes were maintained close to their targets. Zeus IE® FGF after 5 min was 0 [0,0] mL/min. Average Vdes after 50 min was higher with Memsorb™ (20.3 mL) compared to historical soda lime canister data (12.3 mL). During target-controlled closed-circuit anesthesia in patients undergoing robot-assisted radical prostatectomy, the Memsorb™ maintained F_ICO₂ ≤ 0.8% and F_ETCO₂ ≤ 6.0%, and F_IO₂ remained close to target. Modest amounts of desflurane were lost with the use of the Memsorb™. The need for adjustments of sweep flow, minute ventilation, and occasionally Zeus IE® FGF indicates that the Memsorb™ system should preferentially be integrated into an automated closed-loop system.