Anesthesia waste gas exposure carries risks to health care providers. When we administer anesthesia, we pay a great deal of attention to the concentration of Nitrous Oxide and halogenated agents such as Sevoflurane or Desflurane that our patient receives. We know that too much or too little of these gases can harm our patients. We are often less compulsive about avoiding exposure to ourselves, or even our operating room colleagues to waste anesthetic gases. As we near the start of a new academic year, let’s review some of the hazards to promote good lifelong practices.
A few years ago I worked with the Kaiser Permanente education department to create a training video on anesthesia waste gases, which can be found at the link.
What Are Waste Anesthetic Gases?
Anesthetic waste gases consist of:
- gases and vapors that leak into the surrounding treatment room from the patient’s anesthetic breathing circuit during medical procedures
- gases expelled from the building as part of the scavenger system
- gases exhaled by the patient in the recovery room period
These gases are so potent that trace gas exposure is typically measured in parts per million.
1% of an anesthetic gas equals 10,000 parts per million. Our goal is to minimize exposure to these waste anesthetic gases to less than 2 parts per million of the halogenated agents and less than 25 parts per million of nitrous oxide.
Don’t rely on your sense of smell to protect you. Anesthetic gases cannot be detected by smell until concentrations are very high. For example, Halothane cannot be smelled by 50% of the general population until the concentration is 125 times the NIOSH recommended exposure limit of 2 ppm.
Why Worry About Exposure?
Why should we worry about waste anesthetic gas exposure to ourselves and our perioperative staff? First of all, there are health effects. Exposure to high concentrations of waste anesthetic gases – even for a short time – may cause difficulties in judgment, loss of coordination, impaired manual dexterity, drowsiness, headache, irritability, fatigue, and nausea.
There is evidence that long-term exposure can reduce fertility, and cause neurological, renal and hepatic disease.
In addition, anesthetic gases are potent greenhouse gases. Almost all anesthetic gases introduced into the circuit or exhaled by patients’ end up in the atmosphere where they contribute to global warming. Nitrous oxide can also deplete the ozone layer.
Additional Health Risks of Nitrous Oxide
Nitrous oxide has other health effects. It irreversibly binds methionine synthetase, the enzyme that regenerates the active form of vitamin B12. Vitamin B12 (cobalamin) is necessary for DNA synthesis and methylation reactions. Its deficiency is associated with anemia, neurologic, psychiatric, hematologic, cardiovascular, and gastrointestinal manifestations. [1]
Ninety minute exposure to 50% nitrous is enough to halve the function of the B12/folate pathway, raising homocysteine levels. Exposure/duration is important. Inhibition of methionine synthetase by nitrous is irreversible. New enzyme must be produced which can take 2-7 days.
Nitrous should be avoided when possible in patients with malnutrition, pernicious anemia, B12/folate deficiencies, and bone marrow suppression, among others. It’s use in serial anesthetics over a short period (less than time frame for regeneration of methionine synthetase) or in really long cases is also questionable.
Minimize Exposure
It’s impossible to completely prevent exposure to waste anesthetic gases. However, there are a few things that we can do to minimize exposure such as maintaining a good mask seal, maintaining the scavenging system and refilling the vaporizer container appropriately.
Good Seal
Exposure to waste anesthetic gases occurs more commonly whenever we provide anesthesia for surgery around the airway and when caring for patients when obtaining a mask seal is difficult. Good examples include pediatric mask inductions, patients with beards, and tonsillectomies. Too small an uncuffed endotracheal tube can also release significant amounts of waste gas onto your surgical team.
Check the Scavenging System
Ensure the scavenging system on the anesthesia machine is working. The scavenging system evacuates anesthetic waste gases from our anesthesia machine through a vacuum source and expels it into the atmosphere. To function properly, the vacuum must be properly adjusted. Make sure all the connections are tight. The circuit must be as closed as possible, including having a proper mask fit. Failure to properly use the scavenging system can easily produce exposures of 60 parts per million of a halogenated agent and 3,000 parts per million of nitrous oxide.
Carefully Fill the Vaporizer
When possible, fill the vaporizer before the patient and Operating Room crew are in the room. If it is necessary to refill the vaporizer during a case, make sure that proper adapters are used and avoid spills.
Use Lowest Safe Flow
No matter which anesthetic agent you choose, strict attention to lowering fresh gas flows is the primary method to reduce waste gas exposure and release. The lowest flow will depend on choice of agent as well as type of breathing circuit. For example, a Bain Circuit will require a much higher base flow to provide safe anesthesia than a CO2 absorber based system.
Consider TIVA
Total intravenous anesthesia, or TIVA, can minimize or totally avoid anesthetic waste gas. However, TIVA is not always appropriate to the patient or the surgery and requires special administration pumps.
Common Errors Increasing Anesthesia Waste Gas Exposure:
Be Selective in Choice of Anesthetic Gas
- Allowing high flow gas to flow into the room
- Loose application of the mask, especially with pediatric inductions
- Too small an uncuffed ETT
- Flushing the circuit into the room to speed dissipation of the gas
- The room is contaminated whenever the anesthesia provider disconnects the breathing circuit without closing the circuit, turning off the vaporizer, or decreasing gas flow
- Leaving the flows on high during the entire case
- Spills
- Not cleaning spills appropriately
- Removing mask from patient’s face while still “outgassing”
Good Practice to Minimize Anesthesia Waste Gas
- Ensure your scavenging system is working and machine connections are tight
- Make sure the filler cap is tight when filling the vaporizer, Stop filling before the line and then wait a few seconds before removing the filler cap and agent bottle from the cassette.
- Avoid spilling liquid anesthetic – clean any spills promptly and properly.
- Close the breathing circuit before you prefill it.
- When anesthetizing an adult, wait until the mask is applied to the face before turning on the vaporizer for either a child or an adult.
- With any anesthetic, pediatric or adult, minimize circuit disconnections while anesthetic is flowing. Either turn off the vaporizer, decrease flows, or plug the circuit.
- For maintenance, use the lowest flows appropriate. The minimal recommended flow may vary depending on the agent used.
- Decreasing total amount of anesthetic vaporized not only helps protect you and your staff, it decreases global warming.
- Toward the end of the case, use high flow oxygen to wash anesthetic into the scavenger system.
- If you disconnect to flush the circuit, close the end of the hose to prevent gas escape. Flush the bag into the circuit, not the room.
- Once the endotracheal tube or LMA is removed, replace the mask on the patient’s face for several minutes. this let’s you verify optimal ventilation as well as allows the scavenger system to remove the majority of remaining exhaled anesthetic
Minimizing Anesthesia Waste Gas Exposure in Pediatric Anesthesia
Anesthetizing young children is challenging because they frequently panic when in stressful situations, such as an operating room surrounded by strangers and unfamiliar equipment. It’s common practice to avoid frightening the child by blowing anesthetic gas across their face instead of applying a tight mask fit. However, this method increases exposure of everyone else in the room.
If you keep the child cooperative they are unlikely to fight the mask. Explain to the child in terms they can understand what will happen and what they will feel. Play the “blow up the balloon game”- which requires a good mask seal to work. Kids love to play pretend. Tell them stories during induction which incorporate the sensations of floating, different smells, or sounds being distorted. For younger children sing songs. Have the child lie down when possible since they may startle awake if they lean backwards as they start to fall asleep.
If the child does struggle, hold the mask firmly but gently to speed induction.
Locations Without Scavenger Systems
I have practiced in many developing world operating rooms that lacked scavenger systems. Waste gas was actively vented into the operating room. By the end of the day, all of us tended to be a bit “buzzed”. I have made errors which arguably could have been avoided if I had not been breathing halothane fumes for 12 hours.
My teams would frequently improvise simple, passive scavenging by attaching long sections of ventilation tubing to the machine scavenger port and placing the end out a window, or at least as far away from the operating table as possible. We also tried to use low flows — although this was not always possible if using a Bain circuit.
When working in unscavenged locations, consider frequent breaks to clearer air.
Global Warming
Anesthesia waste gases are potent greenhouse gases. Reducing occupational exposure to waste anesthetic gases can also minimize the contribution of these waste anesthetic agents to global warming. Because Desflurane and Nitrous Oxide have the highest climate impact, I personally stopped using them unless they had significant advantages to the patient’s morbidity and mortality over alternative drugs.
For further discussion of anesthesia waste gas and global warming see:
Anesthetic Waste Gases: Protecting Patients and the Planet?
With a little attention to detail, you can minimize exposure to waste anesthesia gases for you and your colleagues. Always protect yourself and your team, in addition to your patient.
