Reducing Greenhouse Gas Emissions: Modifying Nitrous Oxide Delivery at Stanford (Preprint)

Abstract

Reducing greenhouse gas emissions is a priority that must be addressed to prevent the negative impacts of climate change. Inhalational anesthetic agents are a major source of potent greenhouse gases, and reducing their emissions is a goal that can be readily addressed. Nitrous oxide (N2O) has a prolonged environmental half-life combined with a low clinical potency, leading to relatively large amounts of N2O being stored in cryogenic tanks and H cylinders for use, thus increasing the chance of pollution through leaks. Building on the results of previous studies, Stanford Health Care (SHC) N2O emissions were analyzed at two campuses and targeted for waste reduction as a precursor to system wide reductions.

To determine the extent of N2O pollution at SHC. Subsequently, to determine if using E-cylinders for storage and delivery of N2O at the point of care in its ambulatory surgery centers could reduce emissions within SHC’s system.

Phase 1: Total Palo Alto, CA SHC N2O purchase data for CY2022 was collected and compared (volume and cost) to total Palo Alto clinical delivery data using Epic electronic health record. Phase 2: A pilot study was conducted in the 8 operating rooms of SHC campus A (Redwood City). The central N2O pipelines were disconnected, and E-cylinders were used in each operating room. E-cylinders were weighed before and after use on a weekly basis for comparison to Epic N2O delivery data over a 5-week period. Phase 3: After successful implementation, the same methodology was applied to Campus B, one of three facilities in Palo Alto.

Phase 1: Total N2O purchased in 2022 was 8,217,449 liters (33,201.8 lbs.), at a total cost of $63,298. Of this, only 780,882.2 liters (9.5%) of N2O was delivered to patients, with 7,436,566.8 liters (90.5%) or $57,285 worth lost or wasted. Phase 2: Total weight of N2O use from E-cylinders was 7.4 lbs (1lb N2O = 247.5L) or 1,831.5 liters at campus A. Epic data showed total N2O volume delivered was 1,839.3 liters (7.4 lbs). Phase 3: Total weight of N2O use from E-cylinders was 10.4 lbs or 2,574 Liters at campus B (confirming reliability within error propagation margins). Epic data showed total N2O volume delivered was 2840.3 liters (11.5 lbs). Over Phase 2 and 3, total use for campuses A and B was less than the volume of 3 E-cylinders (1 E-cylinder = 1590 liters).

Converting N2O delivery from centralized storage to point-of-care E-cylinders dramatically reduced waste and expense with no detriment to patient care. The results of this study provide strong evidence for analyzing N2O storage in healthcare systems that rely on centralized storage as well as consideration of E-cylinder implementation to reduce emissions. The reduction in N2O waste will help meet SHC’s goal of Scope 1 and 2 emissions reduction by 50% before 2030.