Numerous questions to the Committee on Technology are individually and quickly answered each quarter by knowledgeable committee members. Many of those responses would be of value to the general readership, but are not suitable for the Dear SIRS column. Therefore, we have created this simple column to address the needs of our readership.
How would you dispose of waste anesthesia agent? I am a biomedical technician working for a third party company. I was asked this question by an administrative officer in one of our client accounts.
Dear Mr. Shreve,
My answer would be to obtain advice from the engineering department of the hospital first, suggesting that you would like to use the hospital evacuation system to “suction” the liquid (vapor) from the waste container. I would make this suggestion based upon the current method of scavenging waste anesthetic gas, via suction and expulsion out the roof of the building, as I was told by our own engineers. Would suction of the liquid itself be feasible and allowable by engineering?
- In the past we had built an evaporator for this purpose that was connected to the hospital scavenging system. The evaporator was an Erlenmeyer flask into which the liquid agent was poured. The rubber stopper for the flask had 2 glass tubes, one short one that barely went through the rubber stopper that was connected to hospital suction (suction and scavenging were the same system in our hospital). The other glass tube was about 1/4 inch from the bottom of the flask and ran up through the rubber stopper and stuck up in the air, and sucked room air into the flask. This prevented liquid from entering the suction system and in the case of halothane left the thymol in the flask (very low vapor pressure) as the halothane evaporated (keeping thymol out of the suction system is important). We were also located at the end of the suction system so there was flow from many sources to dilute the anesthetic gas from our evaporator. The difficulty is that some anesthetic agents, although not considered flammable, will burn if mixed in correct proportions with oxygen or nitrous oxide – these are outside of the anesthetic concentrations of these agents. For example, sevoflurane is at the lower flammability level at 11 volumes-percent in oxygen and 10 volumes-percent in nitrous oxide,1 far outside of the anesthetic concentrations we use, but with a vapor pressure of approximately 200 mmHg at 25°C and an efficient evaporator we can achieve maximum concentrations of 26.3% at sea level. Typically these concentrations from the evaporator will be diluted in the vacuum piping system such that very, very low levels of sevoflurane would reach the vacuum pump. Smaller hospitals may have difficulty with limited suction flow dilution depending upon the time of day that the evaporation was occurring.
- The other issue that has been receiving much attention lately is the high oxygen concentrations reaching oil-lubricated suction pumps and causing flash fires and explosions that completely destroyed the pumps.2 The addition of combustible concentrations of anesthetic agents may represent serious hazards if attention is not paid to the physical characteristics of the suction system. Some hospitals use separate high flow low pressure scavenging systems that are not part of the suction system and may represent very little hazard. My advice is to learn about your scavenging system before you use a device like the evaporator described above. The evaporator has the advantage that it uses air rather than oxygen or nitrous oxide, but it will depend upon dilution with other gases downstream that may increase the oxygen concentration but additionally may further decrease the agent concentration. The evaporator can be used safely under almost all circumstances.
- Pharmacy hoods are usually not evacuated but are pressurized to prevent contamination. They are similar to the positive pressure orthopedic rooms. I would also suggest that not all suction is evacuated in a safe fashion outside the building with respect to inhalation agents. Some hospitals have special evacuation paths to present the anesthesia waste where no one can breathe it. Regular suction may, or may not, be expelled in a similar fashion. The NFPA has standards for the appropriate evacuation of waste anesthesia gases. Some appropriate waste gas systems may not be able to handle liquid agent; rather they can handle vapor. So that really leaves disposal of the agent by vaporizing into something that is evacuated according to the NFPA standards.
- Depending on where the waste agent resides I see a couple of possibilities.
- Quick and dirty method: put it in a negative pressure vent – if available in the hospital.
- Ask the manufacturer. In Germany and EU countries, they have to provide guidelines for disposal in the safety datasheets of the agents. Often it says there: Carry it to your next local collection point for harmful substances.
The Committee on Technology
- Wallin RF, Regan BM, Napoli MD, Stern IJ. Sevoflurane: a new inhalational anesthetic agent. Anesth Analg 1975;54:758-66.
- Allen M, Lees DE. Fires in medical vacuum pumps: do you need to be concerned? ASA Newsletter 2004;68(10). Available online at: http://www.asahq.org/Newsletters/2004/10_04/allen.html. Accessed June 19, 2006.
The information provided in this column is for safety-related educational purposes only, and does not constitute medical nor legal advice. Individual or group responses are only commentary, provided for purposes of education or discussion, and are neither statements of advice nor the opinions of APSF. It is not the intention of APSF to provide specific medical or legal advice or to endorse any specific views or recommendations in response to the inquiries posted. In no event shall APSF be responsible or liable, directly or indirectly, for any damage or loss caused or alleged to be caused by or in connection with the reliance on any such information.