The dangers of veterinary anesthesia gas: isoflurane and anesthetic gases

Gaseous general anesthesia in human or animal medicine uses various anesthetic gases that can present a potential danger to practitioners and participants in the operating room. Among these substances, isoflurane (integrated into the equimolar mixture of oxygen and nitrous oxide), a particularly volatile halogenated gas.

Rather unknown to the general population, isoflurane is an anesthetic agent of the halogenated ethers family used mainly in animal medicine by inhalation. It is a very volatile anesthetic gas to be handled with care and it can be dangerous for the health of practitioners and workers in veterinary clinics.

Veterinary anesthesia is carried out in three stages: first the anesthesia induction phase (gaseous or intravenous), then the anesthesia maintenance phase via a veterinary medical gas system, and finally the recovery phase (reducing then stopping the gas injection coupled with analgesics administration to treat pain).

Isoflurane, and more specifically the anaesthetic mixture (equimolar mixture of oxygen and nitrous oxide) incorporating isoflurane, is administered via a gas anesthesia machine. This medical equipment delivers the anesthetic mixture throughout the operation. It is during the first two phases of the veterinary anesthesia that the mixture is likely to cause ambient air contamination. Indeed, administered anesthetic gases are not metabolized; they are generally exhaled unchanged (95%) by the anesthetized animal. The gaseous anesthesia machine therefore has an air discharge circuit loaded with isoflurane or anesthetic gas. The subject’s exhaled air is recovered generally by a mask placed on the animal’s respiratory tract. This air passes through an activated carbon filter blocking the harmful gases before being released into the ambient air of the operating room or outside via a ventilation circuit.

Exposure to residual anesthetic gases (or waste anaesthetic gases) from the exhaust system represents a real potential danger. However, before and after anesthesia procedures, other exposures to volatile anesthetic agents are possible: used isoflurane and anesthetic gas mixtures are handled and stored by the workers, increasing accident risks.

Isoflurane, C3H2ClF5O, (CAS number 26675-46-7) is a colorless, highly volatile, halogenated anesthetic gas with a slightly pungent acrid odor. It is an anesthetic gas commonly used in veterinary practice. It may be used for induction of anesthesia, but it is most often used for anesthesia maintenance in combination with nitrous oxide and / or oxygen.

Because it is a particularly volatile gas, exposure to isoflurane occurs primarily through the respiratory tract. Being a numbing gas, exposure to isoflurane high concentrations will have a narcotic effect and may lead to unconsciousness. In its liquid form, isoflurane is irritating and corrosive when in contact with the skin and mucous membranes. In an occupational situation, repeated exposure to isoflurane can induce various health effects in veterinary surgeons and vet workers: fatigue, reduced reaction time, headaches and hypotension. This halogenated substance crosses the placenta. And some studies also point to a few cases of toxic hepatitis due to isoflurane exposure in the workplace.

There are no regulatory exposure limits in France for isoflurane, however the NIOSH (National Institute for Occupational Safety & Health, an American federal agency dedicated to workers safety and health) recommends a value lower than 2 ppm (or 15 mg / m3) in the ambient air to guarantee workers safety in presence of anesthetic gas and volatile substances. Finland, Germany, Switzerland and Sweden set the 8-hour occupational exposure limit (OEL) at 10 ppm for isoflurane.

Besides isoflurane, the different anesthetic gases used by veterinarians are nitrous oxide (laughing gas N2O), halothane, enflurane, methoxyflurane, sevoflurane, desflurane and xenon.

Like isoflurane, anesthetic gases used by vets as well as in conventional surgical medical settings, can cause various health effects. Exposure to these residual waste anesthetic gases can, in the same way as isoflurane, cause adverse health effects to personnel in the operating room or when handling the product.

Some studies have observed a correlation between chronic occupational exposure to anesthetic gases and the appearance of health effects. Beyond anesthetic symptoms (drowsiness, dizziness, loss of consciousness) caused by a leak from the gas anesthesia machine or by a gas spillage in liquid form, these anaesthetic gas chemicals can cause other hazards. Indeed personnel exposed to these gases for a long period of time or chronically, depending on the concentration in the air, may be subject to various physiological impacts: headaches, dizziness, fatigue, psychomotor performance decrease, renal and hepatic disorders, chronic, or even damage to the reproductive system.

The presence of isoflurane and anesthetic gas concentrations in ambient air during veterinary anesthesia, or in a room where equipment is stored, constitutes a danger which requires protective measures.

The primary protective measure against anesthetic gas exposure lie first and foremost in proper use and proper maintenance of the gas anesthesia system and the gas evacuation circuit in order to avoid any accident leading to a leak.

Ventilation of the operating room is also an important factor for workers protection. In France, the national health department requires the presence of ventilation devices in the operating room to keep ambient air quality below 2 ppm of halogenated anesthetic gases and less than 25 ppm for nitrous oxide.

At the same time, the storage of used gases must be done in compliance with the safety instructions and manufacturers’ recommendations. Implementation and proper monitoring of protocols integrating the dangerousness of anesthetics makes it possible to minimize risks associated with waste anesthetic gases.

Operating rooms can also be equipped with anesthetic gas detectors, an infrared photoacoustic monitor dedicated to the measurement of these gases and volatile substances.

Contamination of ambient air by gaseous and volatile anesthetic agents represents a danger that is difficult to assess depending on the exposure configuration, the exposure time, the available ventilation and the gas concentration.

Various recommendations can be applied concerning the use of a respiratory protection mask against residual anesthetic gas and in particular isoflurane concentrations present in veterinary operating rooms. In Canada, for example, the CNESST (Commission for Standards, Equity, Health and Safety at Work) recommends wearing a self-contained breathing apparatus (SCBA) or the use of a much more practical supplied air respirator system. The SAR system provides air via a breathing air circuit completely independent of the environment in which it is located.

Some manufacturers of medical and respiratory protection equipment such as our partner Dräger recommend the use of a gas mask fitted with class AX-P3 filters. Wearing a gas mask is a solution much less restrictive than supplied air systems and is the most popular one. Nevertheless it presents an intoxication risk in the presence of anesthetic gas at very high concentrations.