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Low -Flow Anesthesia
Elizabeth E Hansen and Lynn D Martin
As many of you know, I love low-flow and closed-circuit anesthesia. It kept me focused and in the moment. In my own hands, this meant just enough oxygen to cover oxygen consumption (around 200-300 mL/min/m2 or 3-5 mL/kg/minute) and just enough vapor to maintain end-tidal sevoflurane (or in days of yore, halothane) at MAC. A couple of months back, we published a “Remembering the classics: the art of low flow anesthesia” in the PAAD based on the original article by Jeff Feldman, entitled, “Managing fresh gas flow to reduce environmental contamination” (Anesth Analg. 2012 May;114(5):1093-101. PMID: 2241553). In reading the latest issue of the Anesthesia Patient Safety Foundation’s newsletter I found this article by Jeffrey M. Feldman, MD, MSE and Samsun Lampotang, PhD, FSSH, FAIMBE on low flow anesthesia. I asked Elizabeth Hansen and Lynn Martin to review it for us using their quality improvement and implementation science lens in their discussion.
I accidentally posted this on June 8th which many of you may have missed…I am reposting it today. Myron Yaster MD
Feldman JM and Lampotang S, “Patient Safety and Low-Flow Anesthesia” APSF Newsletter Volume 37, No. 2, June 2022 https://www.apsf.org/article/patient-safety-and-low-flow-anesthesia
Drs Feldman and Lampotang recently wrote about patient safety and low-flow anesthesia, a practice which reduces the carbon footprint of inhaled anesthetics (potent greenhouse gasses), decreases cost, and reduces heat and humidity loss.1 Their concise definition of low-flow anesthesia is “Reducing fresh gas flow below minute ventilation to the lowest level consistent with equipment capabilities and provider comfort while ensuring safe and effective care for the patient.”
The article highlights the artform and physics of low flow anesthesia. This includes vigilance in ensuring adequate oxygen and anesthetic agent delivery as patient consumption becomes more significant at lower flows. The authors caution that low-flow is associated with a slow rate of change of both volatile agent and oxygen concentration. The authors provide recommendations to set alarms for FiO2, carefully follow the uptake of anesthetic agent as it decreases over time, which can be countered by increasing the concentration on the vaporizer.
Some are reluctant to provide low-flow anesthesia due to outdated concerns of compound A or liability considerations. However, as the authors point out, modern carbon dioxide absorbents do not contain a strong base and thus do not create compound A. Despite FDA labeling requiring higher flows with sevoflurane, “off label” use of low-flow sevoflurane anesthesia is safe and meets the standard of care.2
The authors provide a clear and compelling case for the safety of low-flow anesthesia. This APSF newsletter article will be invaluable for those who may be new to low-flow anesthesia and would like a primer on the finer points of its art and science.
At Seattle Children’s Hospital, we have a hospital-wide goal of delivering carbon neutral care by 2025, which includes reducing our emissions from anesthetic gasses, our 3rd largest source of emissions. To achieve this goal, we have taken several steps, including utilization of low-flow anesthesia (lower default FGF on quick start of the anesthesia machine, clinical decision best practice reminders if flows are higher than 1L/min). We also eliminated the use of desflurane, one of the more potent greenhouse gasses. Its global warming potential is about 2,500 times higher than carbon dioxide.
We have calculated the carbon dioxide equivalents of the inhaled anesthetics for each case for the last 4 years, using data from the EMR, and pulled that into AdaptX™ OR Advisor software (AdaptX™, Seattle, WA) so we could see which cases had the highest emissions. We can parse the data by surgery type, length of surgery, type of airway, and anesthesia provider - attending, CRNA, fellow or resident.
Once the data was available, we could really identify where we needed to focus our attention. We could see which anesthesia providers had the lowest emissions and seek out tips from them, which included avoiding nitrous oxide (another potent greenhouse gas, one that warms about 300 times more effectively than CO2 and also depletes the ozone layer). The low emitters used more IV anesthetics and kept their fresh gas flows as low as possible.
The large environmental impact of nitrous oxide and higher flows for induction drove up our case average emissions, even if later in the case we turned our flows down or used TIVA. To address this, we started using even lower flows for induction, and we stopped routine use of nitrous oxide. This created a spirited conversation within the group, as many had been using the same techniques for years and worried the children would not tolerate this change. But, we tried it and found it worked very well, with similar patient experiences, and no change in time to anesthesia ready, pain or nausea rates, or PACU length of stay while decreasing our CO2 emissions another 3-fold.
Looking at our actual use of anesthesia gasses in the ORs with AdaptX™ charts also led to an unexpected but very important discovery. While our measured emissions came down dramatically, our purchasing of nitrous oxide remained very steady. By 2020, nitrous oxide accounted for 98% of our emissions from anesthesia gasses based on procurement data. Other institutions have found significant leaks in their central supply of nitrous oxide tanks (Brian Chesebro, personal communication; Seglenieks 2022). With transition to portable cylinders and decommissioning of central supply sources, we estimate our pollution from nitrous oxide can be reduced by over 90%.
Feldman JM and Lampotang S, “Patient Safety and Low-Flow Anesthesia” APSF Newsletter Volume 37, No. 2, June 2022 https://www.apsf.org/article/patient-safety-and-low-flow-anesthesia accessed June 7, 2022
Thomas B, “Off-Label Low-Flow Sevoflurane: Regulatory Red Herring or Liability Landmine?” APSF Newsletter Volume 37, No. 2, June 2022
Seglenieks R, Wong A, Pearson F, McGain F. Discrepancy between procurement and clinical use of nitrous oxide: waste not, want not. Br J Anaesth. 2022 Jan;128(1):e32-e34. doi: 10.1016/j.bja.2021.10.021. Epub 2021 Nov 19. PMID: 34802695.