The ever expanding AIDS epidemic has heightened the awareness of anesthesia personnel to the risk of contagious hazards in the workplace. When five years ago, it would have been rare to see a practitioner routinely using gloves when placing an intravenous or intraarterial line, it is now commonplace, not only in major urban hospitals, but also in suburban settings.
With this concern for contamination and infection in the operating room, hospitals are turning more and more to disposable equipment, such as breathing circuits, masks, laryngoscopes and airways. There has also been increased interest in completely disposable anesthesia circuits including the Y piece, breathing tubes, APL valve, unidirectional valves and carbon dioxide absorber. These units connect directly to the common gas outlet of the traditional anesthesia machine. While there is the obvious advantage of offering a totally disposable circuit with the familiar semiclosed circle architecture, there are also drawbacks.
In the late 1970’s, manufacturers’ representatives, anesthesia care providers and regulatory officials produced the first of several voluntary consensus standards affecting anesthesia equipment. The best known is probably the American National Standards Institute (ANSI) Z79 dealing with anesthesia gas machines. These standards and the anticipated 1988 F29.01.01 anesthesia machine standard from the American Society for Testing and Materials (ASTM), however, do not address the issue of anesthesia breathing systems distal to the common gas outlet.
As a result, and until such a standard is issued (work is presently underway on one ASTM draft F29.01.02), there are as many variations in the low pressure systems as there are manufacturers and assemblers of the components. When replacing the traditional portion of your low pressure system down stream from the common gas outlet with a totally disposable circle system, performance of the whole system may be radically altered.
Potential limitations with disposable circle systems may include incompetency of the one way or flutter valves or, conversely, the valves may present increased resistance during assisted or spontaneous ventilation. In addition, the APL valves may be coarse in their adjustability, making it difficult to avoid overinflation or a deflated reservoir bag. Absorber volume may be reduced which limits the efficiency of carbon dioxide removal and channelling of unprocessed gas through the absorbent is possible.
Another way, however, to provide a totally disposable anesthesia circuit for adults and children that does not require an absorber or the decontamination of nondisposable metal components at the end of a case is through the use of the Bain coaxial modification of the Mapleson D circuit. While the Bain is available with a machined metal head that provides a fixed position for the reservoir bag and an access port for a ventilator, it can be used by connecting the reservoir bag directly to the end of the Bain coaxial tube, obviating the need for the machined metal head. One additional step is required, however; the tail on the reservoir bag must be cut open and connected to the scavenger system. A simple C clamp may be applied to the tail to adjust airway pressure and prevent the bag from deflating, but at the same time allowing excess gas to escape. It is also possible to connect the Bain circuit to a ventilator without using the machined metal head.
Most anesthesia departments have familiarity with the Bain circuit. By modifying the Bain system as described, a totally disposable breathing system is produced that can save time and money by reducing both decontamination efforts in anesthetizing locations and the inventory of disposable supplies that must be kept on hand.
Topic prepared by David E. Lees, M.D. Professor and Chairman of Anesthesia, New York Medical College, member of the APSF Newsletter Editorial Board.
Dr. Lees addresses an important practical problem how to deal with the increasing pressures to decontaminate anesthesia apparatus. Disposables are a convenient and possibly cost-effective alternative His suggested modification to the Bain breathing system perhaps should be called a Bain modification to the Jackson-Rees system, since that is the configuration that arises. Certainly, this is not a fundamental change in design, but it still creates new ways for errors and failures for the unwary. Practical, effective safe waste-gas scavenging for such systems is not readily available Furthermore, the Bain system, as any breathing system, has its own unique and peculiar failure modes and presents numerous opportunities for misuse, especially by a new user. Suggestion: Don’t modify equipment or use it for a new application without giving careful thought and doing some in-vitro testing in search of its clinical effectiveness, characteristics, and hazards. There are just too many anecdotes about anesthetists who have gotten into trouble by improvising or using homemade modifications of equipment.
Jeffery B. Cooper, Ph. D. Massachusetts General Hospital