A system to vent away anesthesia gases in pediatric operating rooms run by KidsOR or others
After reading the introduction below, you may want to read our Proposed Research Plan.
Author: Lawrence Kincheloe
Target Organization: Public Invention (in collaboration with Robert Read & Dave Tipping)
Status: Draft Concept Proposal
License: Creative Commons Attribution 4.0 International (CC-BY-4.0) / MIT (Open Source)
In clinical, veterinary, or research environments, waste anesthetic gases (WAGs)—primarily halogenated ethers like isoflurane, sevoflurane, and desflurane—must be captured and neutralized to prevent environmental release and occupational health hazards. The current standard practice utilized by Dave Tipping and others involves passing waste air streams through a chemical absorber bed, typically loaded with Sodium Hydroxide ( / pure lye). While is cheap, universally accessible, and chemically effective, it acts as a consumable reactant rather than a catalyst. As it binds to the fluorine/chlorine atoms to form mineral salts, it becomes saturated.
There is no automatic indicator or notification when the bed is saturated (spent), leading to gas breakthrough.
There are no active, low-cost sensors in the workspace to alert personnel if anesthetic gas leaks or escapes into the room.
Transitioning to a heated or UV-activated solid-state catalytic system (such as or Zeolites) eliminates the need for raw , but still generates corrosive hydrogen fluoride () gas, requiring its own sacrificial lime or water-scrubbing consumables.
Instead of simply replacing one complex consumable system with another, this project proposes a dual-track approach focusing on smart monitoring (highly accessible IoT sensors) and optimized, smart chemical absorption.
Rather than redesigning the chemical scrubbing process entirely, we can significantly increase safety by designing a low-cost, open-source ambient gas detector.
The Concept: A wall-mounted or desktop sensor unit that continuously measures volatile organic compounds (VOCs) and isolates the specific parts-per-million (ppm) threshold of anesthetic gases.
Hardware Integration: The unit can leverage existing open-source IoT sensor architectures, such as the Krake platform, using a microcontroller (e.g., ESP32) paired with sensitive metal-oxide semiconductor (MOS) gas sensors or photoionization detectors (PID).
Alert Mechanism: If room levels of the gas exceed safe occupational exposure limits, the device triggers visual/audio alarms and sends remote alerts via IoT protocols (Wi-Fi, MQTT).
To keep the system highly accessible and low-cost, we can continue using widely available lye () but solve the "exhaustion blind spot" by inventing an inline exhaustion sensor.
pH-Based Optical Sensing: As neutralizes during halogen capture, its pH drops from highly basic () toward neutral. By integrating a simple colorimetric pH indicator (e.g., phenolphthalein embedded in a transparent viewing window) or an inline electronic pH/conductivity probe, the system can automatically flag when the chemical bed is depleted.
Byproduct Trap Alert: Integrating a simple, cheap color-change warning directly on the canister ensures operators know exactly when to swap or recharge the lye bed without relying on guesswork.
Alert Mechanism: A simple white led and color sensor along with a pH sensor could alert when the the solution is sufficiently saturated to warrant replacement. The device triggers visual/audio alarms and sends remote alerts via IoT protocols (Wi-Fi, MQTT).
For field or low-resource settings, design an optimized, modular blueprint for a 3D-printable or DIY-constructible scrubbing canister that utilizes locally sourced materials (like grocery-store lye/wood ash) and features the aforementioned smart-sensing integrations. This could be added in addition to the existing system as a second stage open source emergency backup, while also acting as a modular extension without replacing existing hardware solutions.
To successfully transition this from a one-pager to an active Public Invention repository, we require support in the following domains:
An expert to verify the cross-sensitivity of off-the-shelf VOC sensors (such as the BME680 or specialized electrochemical sensors) to halogenated ethers like isoflurane and sevoflurane, establishing calibration parameters.
To help write the microcontroller logic for reading the sensor output, mapping it to PPM equivalents, and triggering the notification stack. Mechanical/Industrial Design: To model a 3D-printable chamber housing the medium alongside a transparent viewing port for colorimetric pH indicators or electronic sensor insertion.
Conduct a literature search or simple test bench setup to determine which low-cost electronic sensors reliably react to trace anesthetic gases.
It seems that halogenated ethers are generally detectable by VOC sensors, if the UV lamp has sufficient energy to ionize them https://pmc.ncbi.nlm.nih.gov/articles/PMC12115474/.
This is absolutely still a problem we need to solve.. and we've been struggling for the last 10 years or so. Courtney has access to all the information regarding the anesthetic machines, vaporizers and types of agents.. I've got a better handle on the construction of the facilities and what we might need to do to either exhaust externally or to coexist with the general ventilation of some of our spaces.. or where we might need to capture to dispose / recycle.
The one clarification would be the spherasorb / capture in the anaesthetic machines is purely for carbon dioxide in the patient's breath.. this then gets remixed with the oxygen and left-over anesthetic agent(s) and fed back to the patient.. the machine has an exhaust port that in the US / Europe is connected to an 'AGSS" (Anesthetic Gas Scavenging System) that is a pressurized system that is expensive to install and maintain. In the 140 operating theatres we have installed there have possibly been 10 with AGSS systems. Where there isn't an AGSS system there can be quite a bit of waste gas exhaust out of the machines into the room! On modern machines this is kept to a minimum by optimization software which is primarily there to stop wasting money on the agents... but serves as a useful reducer of waste gases into the room. The vast majority of OR's we have installed and that existing in low- or middle-income countries don't have such systems, and we know anesthetic gases do exhaust into the operating rooms.
We have reports of surgical teams getting drowsy as the day goes on. Even without such a drastic effect, it is a serious problem having volatile gas discharged into an OR. We do provide a long length of tubing referred to as a passive scavenging tube.. it comes in 30m lengths and allows us to at least get the gases out of the OR.. and ideally to a vent on an external wall. But it's cumbersome and can be tripped over and get trapped in doorways etc. If this gets blocked thankfully the machine has a safety blow off valve.. but then we are back to square one.