Why Don't All Vaporizers Have an "Empty" Alarm?

Q Dear Q&A,

Since anesthesia awareness is now in the public forum, I was wondering why the non-desflurane vaporizers don't have an "empty" alarm. Seems like an easy fix to prevent the vaporizer from running out during a case that goes unnoticed. Perhaps it has already been done and we are waiting for the upgrades to occur, but thought I would pass it along.

The above would prevent empty vaporizers, but it would not prevent failure to turn the vaporizer on during a case. With electronic charting being a future reality, is the APSF going to require all electronic charting to flag end-tidal anesthetic gas concentrations that approach awareness MAC values? While the programs are being written it would be of great value if the APSF came out with a list of requirements for electronic charting to prevent mishaps rather than leaving the algorithms to the programmers who usually know nothing about anesthesia.

Terry W. Bejot, MD
Lincoln, NE

A Dear Dr. Bejot,

The consensus is that low agent alarms would be useful on all vaporizers. However, the suggestion of minimizing the risk of patient awareness through the use of a low agent alarm would not be as efficacious as properly measured exhaled agent concentration, which yields an estimate of Minimum Alveolar Concentration (MAC) of the agent. It has been suggested that an exhaled agent concentration greater than 0.8 MAC will minimize the risk of awareness.1

The low agent alarm would be a very useful adjunct to monitoring the exhaled agent concentration to indicate the need to refill the vaporizer before it's operation is compromised by having too little agent in the vaporizer. Concern was expressed about retrofitting current vaporizers with reliable low level alarms, because most of the currently available vaporizers are purely mechanical and the alarm system would add complexities of a sensor, potential leak of agent, electronic circuitry, and battery power and maintenance to name a few issues. Add to that the complexities of a sensor/alarm system that must be immune from extraneous radio frequencies (cautery, cell phones, and other devices), and must alarm when the battery is low and when the agent is low or when the device is not working properly.

Some non-desflurane electronic vaporizers already provide a low-level alarm, while some manufacturers have indicated they do plan for monitoring the amount of liquid in all vaporizers on future anesthesia machines. Most likely, the market place will drive all manufacturers in this direction. Meanwhile, the use of exhaled end-tidal agent concentration should be employed and properly monitored to minimize the likelihood of patient awareness.

With regard to electronic charting, the Committee on Technology is not a standards-setting committee and will not be promulgating standards or requirements for medical records of any kind including computerized anesthesia records. Thank you for bringing this important topic to us for discussion.

The Committee on Technology


  1. Hardman J G, Aitkenhead AR. Awareness during anesthesia. Continuing Education in Anaesthesia, Critical Care & Pain. 2005 5(6):183-186.

How Do I Handle an Isoflurane Spill?

Q Dear Q&A,

I have been asked to come up with an emergency response plan if someone should drop a bottle of isoflurane liquid for inhalation anesthesia. Are there any published guidelines that address how to handle this situation if it occurs? Would this be the same procedure for sevoflurane?

Amanda Wilsey, CVT
Abbott Park, IL

A Dear Ms. Wilsey,

The answer to your question can be found in the Occupational Safety and Health Administration's Anesthestic Gases: Guidelines for Workplace Exposures available at http://www.osha.gov/dts/osta/anestheticgases/index.html/anestheticgases/index.html#G. These guidelines, published in 1999 and revised in 2000, apply to all liquid inhalational anesthetic agents and are excerpted as follows:

Anesthetic Gases: Guidelines for Workplace Exposures

These guidelines are not a new standard or regulation, and they create no new legal obligations. The guidelines are advisory in nature, informational in content, and are intended to assist employers in providing a safe and healthful workplace through effective prevention programs adapted to the needs of each place of employment. These guidelines are not intended to address issues to patient care. . . .


Small volumes of liquid anesthetic agents such as halothane, enflurane, isoflurane, desflurane, and sevoflurane evaporate readily at normal room temperatures, and may dissipate before any attempts to clean up or collect the liquid are initiated. However, when large spills occur, such as when one or more bottles of a liquid agent break, specific cleaning and containment procedures are necessary and appropriate disposal is required (AANA 1992).1 The recommendations of the chemical manufacturer's material safety data sheet (MSDS) that identify exposure reduction techniques for spills and emergencies should be followed.

In addition, OSHA Standard for Hazardous Waste Operations and Emergency Response (29 CFR 1910.120) would apply if emergency response efforts are performed by employees. The employer must determine the potential for an emergency in a reasonably predictable worst-case scenario, and plan response procedures accordingly. Only adequately trained and equipped workers may respond to spills. When the situation is unclear or data are lacking on the exposure level, the response needs to be the same as for high levels of exposure. Responses to incidental releases of liquid anesthetic agents where the substance can be absorbed, neutralized, or otherwise controlled at the time of release by employees in the immediate release area, or by maintenance personnel do not fall within the scope of this standard.

Because of the volatility of liquid anesthetics, rapid removal by suctioning in the OR is the preferred method for cleaning up spills. Spills of large volumes in poorly ventilated areas or in storage areas should be absorbed using an absorbent material, sometimes called a sorbent, which is designed for clean-up of organic chemicals. "Spill pillows" commonly used in hospital laboratories, vermiculite, and carbon-based sorbents are some of the materials commercially available and regularly used for this purpose. Caution should be exercised if broken glass bottles pose a hazard.

Both enflurane and desflurane are considered hazardous wastes under the EPA regulations because these chemicals contain trace amounts of chloroform (a hazardous substance), a by-product of the manufacturing process. Consequently, sorbents that have been saturated with enflurane or desflurane should be managed as an EPA hazardous waste material due to the trace concentrations of chloroform present. Isoflurane and halothane do not contain trace amounts of chloroform or any other regulated substance and are therefore not considered hazardous wastes by EPA.

To minimize exposure to all liquid anesthetic agents during clean-up and to limit exposure during disposal procedures, the following general guidelines are recommended. The waste material should be placed in a container, tightly sealed, properly labeled, and disposed of with other chemical wastes sent to a facility's incinerator or removed by a chemical waste contractor. After a large spill has occurred and the appropriate response action taken, airborne monitoring should be conducted to determine if the spill was effectively contained and cleaned up.

Determination of appropriate disposal procedures for each facility is the sole responsibility of that facility. Empty anesthetic bottles are not considered regulated waste and may be discarded with ordinary trash or recycled. Furthermore, the facility as well as the waste handling contractor must comply with all applicable federal, state, and local regulations.

To minimize exposure to waste liquid anesthetic agents during clean-up and disposal, the following general guidelines are recommended by the manufacturers of liquid anesthetic agents:


  1. American Association of Nurse Anesthetists (AANA). Management of waste anesthetic gases. Park Ridge, IL: 1992. Pp. 16-17.

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.

The information provided is for safety-related educational purposes only, and does not constitute medical or 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