Russell C. Brockwell, M.D.
Committee on Equipment and Facilities

he anesthesia machine, or as it has come to be referred to in recent years, the “Anesthesia Workstation,” has gone through a remarkable process of evolution over the past 25 years. These changes have led us from the simple pneumatic appliance that was the early anesthesia machine to the fully integrated, multifunctional computer-controlled workstation we know today. Today’s systems may now incorporate everything from gas/vapor mixing to generating an electronic anesthesia record while simultaneously retrieving and displaying high-definition imaging results from your hospital’s computer system.

Anesthesia Workstation Self Tests
The importance of using an appropriate pre-use workstation check list has been taught to anesthesia care providers (ACPs) for many years. In fact, even today, the somewhat outdated 1993 Food and Drug Administration (FDA) Anesthesia Apparatus Checkout Recommendations continue to be taught and used by many clinicians. Unfortunately, despite the availability of such check lists, some ACPs do not always perform a complete and appropriate daily pre-use workstation checkout procedure. As a result, patient mishaps continue to occur and appear with some frequency in our literature. In an effort to improve user compliance with pre-use checkout procedures for the anesthesia workstation, manufacturers are increasingly including self tests on their newer systems. These tests are usually semiautomatic and require some limited user intervention at various times during the testing.

Workstations equipped with such self-testing systems typically have an electronic display that shows which workstation subsystems are being tested. The self-test systems instruct the user what to do when a user intervention is required to complete a component of the self tests (e.g., occluding the y-connector, adjusting the APL setting, etc.). If all the workstation’s components pass these self tests, a notice is displayed, the workstation’s internal log is updated, and the system is ready for use. Complications arise when the self-diagnostics detect a problem and the ACP does not heed the warnings generated by them; or worse yet, the self tests are “bypassed” or skipped entirely. In the case of the latter, no safety advantage is gained by having these systems available.

It is vitally important for ACPs using workstations that have self-test features to be aware of exactly what their system’s self tests do and do not evaluate. Users should not assume that the self tests alone are entirely adequate for pre-use workstation preparation. For example, with some self-tested systems that have add-on vaporizers, the automatic leak tests may not routinely test for internal vaporizer leaks (which can result in awareness during anesthesia). As a result, these leaks can go undetected if the automated self tests are run with the vaporizer’s dial set to the “OFF” position. On such systems, the “leak test” portion of the machine self test should be repeated with each vaporizer individually, while the vaporizer control dial is set to the “ON” position.

The ASA Committee on Equipment and Facilities (in conjunction with the FDA, representatives from the American Association of Nurse Anesthetists [AANA] and anesthesia workstation manufacturers) is in the final stages of developing a revised set of guidelines to replace the 1993 check list. Because of the recent divergence in anesthesia workstation designs, the revised guidelines will focus primarily on what the minimum standard should be for what is checked during your pre-use workstation assessment, not on exactly how each check is to be performed. This was a necessary change from the 1993 recommendations since many newer anesthesia workstations possess unique designs that mandate make/model-specific tests. Unfortunately the days of having a “one-checklist-fits-all” type of approach for educating ACPs will no longer work. The new apparatus pre-use check list guidelines will provide a framework for individual institutions to develop their own specific pre-use protocols that may or may not incorporate the use of self-testing features. The new pre-use check list guidelines are expected to be adopted within a year or so.

Integrating ICU-Style Ventilation Features
Over the past two to three years, anesthesia workstation manufacturers have placed a great deal of emphasis on improving the design of anesthesia ventilators, making them capable of delivering advanced ventilation techniques such as synchronized intermittent mandatory ventilation (SIMV), pressure-controlled ventilation (PCV) and pressure support (PS) ventilation. These features have been available in our intensive care units (ICUs) for many years, but due to limitations of previous ventilator designs, they have heretofore not been readily available to the anesthesiologist using a traditional workstation. The flexibility that these ventilation modes offer the clinical anesthesiologist is significant. PCV may allow more effective, less traumatic ventilation strategies for our sickest patients, potentially helping us to avoid or prevent worsening of ventilator-associated lung injury. Ventilation features such as PS and SIMV + PS also may be helpful with our everyday cases.

Take, for example, a patient who needs a little respiratory assistance when spontaneously breathing through an endotracheal tube (ETT) or a supraglottic airway (such as a laryngeal mask airway) to prevent atelectasis and to achieve adequate minute ventilation. The use of SIMV with or without PS can provide the patient with assisted breaths in synchrony with their respiratory efforts. The synchronization of the mechanical breath with the patient’s own respiratory efforts may reduce the need for skeletal muscle relaxants and deep anesthesia to prevent “bucking.” The addition of PS by itself can help to overcome added resistance experienced when the patient breathes spontaneously through the anesthesia circuit and the airway device (either an ETT or supraglottic airway). Since adding PS functionally reduces this resistance, it allows the patient to breathe larger tidal volumes with less effort and could possibly reduce development of perioperative atelectasis.

Monitoring Carbon Dioxide Absorber Temperatures
With much recent attention regarding reports of fires in the breathing system related to inhaled anesthetic interactions with CO₂ absorbent materials, devices that allow ACPs to monitor absorber canister temperatures are sure to be seen on upcoming anesthesia workstations. The topic of breathing system fires related to absorbent/anesthetic interactions sparked a consensus conference that was held by the Anesthesia Patient Safety Foundation in April 2005. The conference highlighted the hazards of inhaled anesthetic interactions with desiccated “strong base” absorbent materials and the risks they pose for our patients. The early detection of excessive heat production in the absorber assembly was identified as one key to preventing serious patient injury. The use of sensors that can monitor temperatures within the absorber assembly may help to provide early warning of potential problems. One thing is for sure, these sensors likely will be one of the hottest new machine safety devices to appear.

As we know, the only thing that is certain in life, and indeed in the future of our specialty, is change. As our anesthesia workstations continue to change with advances in technology, we must each do our individual best to take advantage of these new developments so that we can continue to give the highest quality care to our patients.

Russell C. Brockwell, M.D., is Associate Professor, University of Alabama-Birmingham Department of Anesthesiology and Chief of Anesthesiology, Birmingham VA Medical Center, Birmingham, Alabama.