Risk reduction is the concern of every anesthesiologist. To prevent adverse outcomes, we should first understand how they occur. This leads to the development, implementation, and, ideally, confirmation of preventative strategies. In this issue of Anesthesiology, Caplan et al.  present an analysis of adverse anesthesia outcomes originating from gas delivery equipment (GDE) using data collected in the American Society of Anesthesiologists (ASA) Closed Claims Project database of 3,791 claims for occurrences between 1962 and 1991. GDE accounted for 34 of 1,542 (2.2%) of claims before 1985 but only 18 of 1,495 (1.2%) of claims since 1985.  Adverse outcomes from GDE are rare and appear to be decreasing,* but when they occur, the injuries usually are severe; therefore we cannot afford to be complacent.
Although the study has a number of stated limitations, including small number of claims, long period of data acquisition, and missing information of potential interest, such as equipment age, model, and design, certain messages are clear:(1) claims involving equipment misuse (human fault or error) were three times more common than “pure” equipment failure, and 70% of these were deemed the direct result of actions of the primary anesthesia provider; and (2) the use or better use of monitoring could have prevented injury in 78% of claims. In this study, 86% of claims resulted from occurrences in the operating room and therefore involved anesthesia gas delivery systems.
The evolution of contemporary anesthesia delivery systems (machine, vaporizer, breathing system, scavenging system, and ventilator) demonstrates the application of the principles of risk reduction to create systems that should be safer. However, because of the many other changes that have taken place in the practice of anesthesia during the 30-yr period represented by Caplan et al.'s data, including the introduction in 1986 of the ASA Standards for Basic Anesthetic Monitoring, it is not possible to determine the precise contribution of changes in the anesthesia delivery system to the decrease in GDE-related claims.
Modern anesthesia delivery systems comprise pneumatic, mechanical, and electronic components that are extremely reliable. Unexpected “pure” equipment failure is rare in a system that has been well maintained and properly checked. Recognition of the possibility of human error and the limitations of human vigilance has led to a three-level approach to anesthesia gas delivery system design:(1) Where possible, design is such that human error cannot occur (e.g., use of keyed connections, fail-safe systems);(2) If human error cannot be prevented, the system is designed to prevent such errors from causing injury (e.g., gas flow proportioning systems for N2O/O2; ventilator high pressure limits); and (3) If neither of the previous safety approaches is possible, the system should be equipped with monitors and alarms to alert the user to an operator error or adverse condition that may be caused by an equipment failure or change in the patient's condition. 
Two voluntary consensus standards, the ANSI Z79.8 published in 1979  and superseded in 1988 by ASTM F1161–88,  defined standard specifications for minimum performance and safety requirements for anesthesia gas machines. The currently applicable ASTM standard requires a preoperational checkout, concentration-calibrated vaporizers, an oxygen analyzer, alarms enabled by a master switch, prioritized alarms, breathing system pressure monitoring, and volume monitoring or capnometry.  Contemporary machines exceed the ASTM standard, and additional safety features are being incorporated into new models.
The anesthesia breathing system, the single largest source of GDE-related claims,  also has undergone design changes to promote safety. By limiting the opportunities for the user to configure the circuit, opportunities for human error are reduced. Consider how the bag/ventilator circuit selector switch decreases the need for user-made disconnections and reconnections or how a positive end-expiratory pressure (PEEP) valve that is designed as part of the circuit or built into the ventilator avoids the potential problems associated with freestanding PEEP valves. However, even with contemporary breathing systems, the user remains responsible for making a limited number of connections. The correctness and integrity of such connections is the user's responsibility, and it is appropriate that any resulting misconnection or subsequent disconnection be considered user error. Circuit anti-disconnect devices have been suggested, but to date none have been adopted.  With the data from Caplan et al.'s study, maybe it is time to reconsider them. Retaining devices to prevent disconnection at the machine common gas outlet now are standard. 
In the risk reduction process, system monitors are intended to detect those situations that cannot be prevented or corrected by design features and that require human intervention. Perhaps the greatest advance in the design of modern anesthesia delivery systems is their incorporation of integrated monitoring and prioritized alarm systems, such that certain basic monitors and alarms are automatically enabled (e.g., low O2alarm; circuit low pressure alarm).  The Closed Claims Project database includes occurrences in which monitors or alarms were absent, broken, disabled, ignored, or led to an inadequate response.  Appropriate use of monitoring and alarms ("electronic surveillance") has been the subject of much research, but clearly there is room for improvement in design and in user education. [7–9] Ideally, electronic monitoring should be user-friendly, automatically enabled when needed, have alarm threshold limits easily bracketed to “normal” conditions, be intelligent ("Smart Alarms"), and the alarm signal emitted should be appropriate in terms of urgency, specificity, and loudness, depending on the error detected and on workplace conditions. [7–9] Prevention of harm to the patient depends on a timely and focused response to the alarm. Verbal alarm messages have not found favor in the operating room environment, but as in aviation, they may be useful in situations that are likely to progress rapidly to injury, e.g., high pressure in the breathing system. Because monitors may fail or be fooled under certain conditions, it has been recommended that critical areas be doubly or triply monitored,  preferably by independent devices. Almost all of the situations leading to GDE-related claims are detectable by monitoring the breathing system for pressures, volumes, gas flows, and gas composition (CO2, N2O, O2, anesthetic agent) at the circuit Y-piece, i.e., as close to the patient as possible so as to most accurately reflect conditions at the airway. A novel sensor whereby all of these parameters may be monitored has been described.  Although overdose and underdose of potent inhaled anesthetic are detectable by agent analysis, such monitoring is not demanded by current standards.
The implementation of strategies to prevent adverse outcomes is associated with financial costs and sometimes even injurious side effects. Ideally, the safety and efficacy of such strategies should be confirmed by validation studies before being implemented. Such a rigorous scientific approach is not possible when it comes to adding safety design features to the anesthesia gas delivery system, and decisions should be made based on reasonableness and common sense. Because of insufficient data, Caplan et al.  were not able to specifically address the question of whether older anesthesia machines are more likely to be associated with GDE-related claims. Anesthesia machine obsolescence is a controversial issue [2,12,13]** and may become more so in this age of cost-containment. It is estimated that there are 40,000 anesthesia machines in use in the United States, their average age being 7 yr.*** Machines are usually purchased with a planned 10- to 15-yr replacement cycle, but there may be economic pressures to extend this, which may lead to an increase in the number of machines lacking desirable safety design features.
In a similar way, economic pressures have encouraged the growth of office-based anesthesia practice, and the safety of gas machines used in this setting has become a matter of increasing concern. Moss**** quotes an industry source that anesthesia machines classified as obsolete in the 1989 New Jersey Hospital Anesthesia Regulation are now being sold to offices in New Jersey. These are the types of settings in which use of machines that lack modern safety features may be particularly hazardous. Schreiber  has reported that litigation statistics of anesthesia equipment manufacturers indicate that older equipment is more likely to be involved in product liability litigation than is newer equipment and that the Medical Device Reporting to the Food and Drug Administration (FDA) indicates the same trend. 
Adverse outcomes in relation to GDE usually are complex in origin and involve specific errors, failures, and sequences of events. Caplan et al.'s study gives us valuable information about general categorical aspects of GDE-related claims, but detailed descriptions of occurrences leading to adverse outcomes offer additional educational value. Eichhorn  reviewed 70 anesthesia cases reported to the Harvard malpractice insurance carrier (CRICO) for the period 1976–1988. There were 11 major intraoperative accidents, of which 5 were related to GDE and involved user error. His brief synopsis of each of these cases provides an understanding of how such events occur and how they may be prevented by safety monitoring. Studies such as those of Eichhorn  and the Closed Claims Project  remind us that the in-depth study of clinical case material offers an important opportunity to advance the quality of medical care.
The work of Cooper et al. [15,16] and of others [17–19] showed that equipment misuse caused by human error was the dominant factor in GDE-related critical incidents. Caplan et al.'s  paper confirms this distinction between equipment misuse and pure equipment failure in the context of adverse outcomes. Critical incidents involving gas delivery equipment continue to occur. To decrease the likelihood of an adverse outcome, anesthesiologists need to have a good understanding of their anesthesia gas delivery systems and safety monitors, appreciate and use the safety design features of contemporary systems, and consider continuing education directed to anesthesia machines and equipment. [15,19]
Those who do not learn from history are condemned to repeat it! Dr. Caplan and his collaborators in the ASA Closed Claims Project are to be commended for once again giving the profession additional insights into rare occurrences with adverse outcomes.
James B. Eisenkraft, M.D.
Professor of Anesthesiology; Mount Sinai School of Medicine; Attending Anesthesiologist
The Mount Sinai Medical Center; New York, New York, 10029–6574
Electronic mail: email@example.com
*Cheney FW: Anesthesia patient safety and professional liability continue to improve. ASA Newsletter 1997; 61:18–9.
**Gravenstein JS: To “obsolete” old equipment or not? APSF Newsletter 1996; 11:13–24.
***Raymond T. Riddle, P.E. Divisional Manager of Regulatory Affairs, Ohmeda Medical Systems Division, Madison, Wisconsin.
****Moss E: Practice options: Flying without a net: Office based anesthesia in the 90's. ASA Newsletter 1997; 61:26–8