Evaluation of the Sevoflurane Consumption During General Anesthesia When Using the MemsorbTM Membrane and Low Gas Flow Versus the Classical Chemical Absorbents With 2L.Min-1 Gas Flow for CO2 Removal From the Anesthesia Circuit.

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).