Abstract
Memsorb (TM) (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 (TM) performance was tested during target-controlled closed-circuit anesthesia (TCCCA) with desflurane in O-2/air using a Zeus IE (R) anesthesia workstation (Drager, Lubeck, 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 O-2 concentration (FIO2) and 5.0% end-expired desflurane concentration (F(ET)des). Minute ventilation (MV) was adjusted to maintain 4.5-6.0% FETCO2. The O-2/air (40% O-2) sweep flow into the Memsorb (TM) was manually adjusted in an attempt to keep inspired CO2 concentration (FICO2) <= 0.8%. The following data were collected: FIO2, F(ET)des, FICO2, FETCO2, MV, fresh gas flow (FGF, O-2 and air), sweep flow, and cumulative desflurane usage (Vdes). Vdes of the Zeus IE (R)-Memsorb (TM) combination was compared with historical Vdes observed in a previous study when soda lime (DragerSorb 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 FICO2 <= 0.8% and FETCO2 <= 6.0%, except in one patient in whom the target Zeus IE (R) FGF had to be increased to 0.7 L/min for 6 min. FIO2 and F(ET)des were maintained close to their targets. Zeus IE (R) FGF after 5 min was 0 [0,0] mL/min. Average Vdes after 50 min was higher with Memsorb (TM) (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 (TM) maintained FICO2 <= 0.8% and FETCO2 <= 6.0%, and FIO2 remained close to target. Modest amounts of desflurane were lost with the use of the Memsorb (TM). The need for adjustments of sweep flow, minute ventilation, and occasionally Zeus IE (R) FGF indicates that the Memsorb (TM) system should preferentially be integrated into an automated closed-loop system.