Evaluation of the Sevoflurane Consumption During General Anesthesia When Using the MemsorbTM Membrane

Assessing the impact of anesthesia practice on global warming and carbon footprint becomes part of the standard of care and is a growing concern within the anesthesia community. Global Warming Potential (GWP) is a measure of how much a given mass of greenhouse gas contributes to global warming over a specified time period. The time period used, 20 versus 100 years, might drastically change the way we see impact of anesthesia on climate changes and GWP20 of CO2 is, by definition set at "1". Inhaled anesthetics have various GWP20: 349 for sevoflurane and 3714 for desflurane. These numbers might slightly change from one to another report/study. However, GWP20 and CDE20 alone are not sufficient to evaluate the environmental impact of anesthetic gases.

Other parameters must be included in the analysis: fresh gas flow (FGF), carrier gas (air, O2, N2O) and potency of the anesthetic gas. Unfortunately, the majority of trials did not fully consider the FGF reduction and the fact that desflurane can be administered with new closed or very low-flow anesthesia circuits as opposed as the recommended 2L.min-1 that must be used for sevoflurane according to its monography when classical chemical absorbents are used by the anesthesia team. Most of the calculations were made on a purely theoretical approach that could be different from actual measurements based on a strictly monitored anesthesia practice.

For sevoflurane, the standard FGF must be set at 2L.min-1 as there is still controversy concerning impact on renal function at lower flows if classical CO2 absorbents are used. It is still not recommended to administer sevoflurane during anesthesia with a FGF lower than 2L.min-1 in Canada when classical chemical absorbents are used according to Baxter monography when classical absorbents are used on the anesthesia circuit (http://www.baxter.ca/fr_CA/assets/downloads/monographs/Sevoflurane_FR.pdf). When continuous and accurate gas monitoring and analysis is used as recommended nowadays by all GCP guidelines (see Canadian guidelines for anesthesia practice), the use of closed or semi-closed-circuit anesthesia with very low FGF might allow for a reduction of more than 80% of the anesthetic gas administration and its consequent pollution.

Moreover, there are few clinical trials looking at the sparing effect on the consumption of anesthetic gases when the depth of anesthesia is properly monitored, with the bispectral index for instance. Indeed, and because the lack of appropriate and precise technology at the time of completion of these trials, most of the studies used only end-tidal concentration in % of the anesthetic gases to argue that they had decreased the consumption of gas during surgery. This remains a very indirect assessing method based on extrapolations as opposed to direct measurements. Studying the effect of the combination of BIS/NOL indices (depth of hypnosis / depth of analgesia) monitoring and the use of our Drager ventilators with low-FGF on precise consumption in mL of each gas in a clinical environment allows to get high quality data never reported in the past. The fact this study also uses the NOL index to ensure that level of analgesia is controlled and equivalent in all groups will also reinforce the idea that what this study measures in terms of anesthetic gas consumption is based on the real need for hypnosis for each participant, and not an overconsumption of gas because of poor control of nociception and analgesia.

Recently a new device was developed to extract CO2 from the ventilation-anesthesia circuit: the new membrane technology-based product (Memsorb™, DMF Medical Inc., Halifax, NS, Canada). All details on the technology of this new membrane are given in the Appendix 1 attached to this proposal (see at the bottom of the present text).

For the last 5 years, clinical trials have been conducted in humans on the use of this new membrane technology-based product (Memsorb™, DMF Medical Inc., Halifax, NS, Canada) and compared this membrane to the classical Drägersorb 800+ CO2 absorbent (Dräger, Lübeck, Germany). After REB committee approval and investigational testing authorization (ITA) by Health Canada, Dr O. Hung (from Halifax, Canada) reported out of 200 patients (100 with MemsorbTM, 100 with DraegersorbTM; ClinicalTrials.gov Identifier: NCT03014336) comparable data regarding the end-tidal CO2 with a median of 5.1% for memsorb™ and 5.0% for control (DraegersorbTM), stable over 2h of anesthesia. Vapor consumption data did not differ significantly between the 2 groups. Anesthesiologist used fresh gas flows at their discretion (from 0.3L.min-1 to 2.7L.min-1). As a conclusion to their study, Memsorb™ was shown to remove CO2 out of an anesthesia circuit as safely and as efficiently than the classical CO2 absorbent (Draegersorb) BUT without the known limitations of chemical absorbents at very low gas flow (0.3L.min-1).

The study here aims at determining whether replacing the classical chemical absorber Dräegersorb 800+ on Dräeger Perseus A500 machines (Dräeger, Lübeck, Germany) by the new membrane technology-based product (Memsorb™, DMF Medical Inc., Halifax, NS, Canada) with the help of high-quality monitoring (BIS and NOL) and high-end ventilators (Dräeger Perseus A500 machines; Dräeger, Lübeck, Germany) that allow minimal fresh gas flow, will significantly decrease the use of sevoflurane and its related atmospheric pollution.

Indeed, MemsorbTM membrane allows to safely reduce the gas flow of the Dräger A500 ventilator as low as 0.2L.min-1 for the administration of sevoflurane (as there is no chemical reaction between the memsorb membrane and the sevoflurane, see ref 16) into the breathing circuit whereas the classical DräegersorbTM has to use a minimal gas flow of 2L.min-1 as recommended by the above cited monography (as below 2L.min-1, the Draegersorb might interact with sevoflurane and produce toxic compounds).

The impact of the present study will be that it will demonstrate sevoflurane administration at 0.2L.min-1 when using the MemsorbTM membrane (Memsorb™, DMF Medical Inc., Halifax, NS, Canada) reduces anesthesia related pollution to its minimum compared to the mandatory FGF at 2L.min-1 that MUST be used with the classical Draegersorb CO2 absorbent. As a consequence of this study, it is expected that anesthesiologists will drastically change towards the use of MemsorbTM in their clinical practice to significantly lessen the major impact they have on the environment.

The primary endpoint of this study is to show a significant decrease of at least 25% of the sevoflurane consumption when using MemsorbTM versus DrägersorbTM. This will be expressed in mL.kg-1.h-1 of surgery and the primary objective will focus on H1 of surgery, H1 starting at the time of incision (T0).