As introduction, one is reminded that in convergent evolution, the basic concept is: animals of different species, if placed in the same environment, would tend to develop similar traits, be it in the way they look or in the way they handle environmental factors.
The Spring 1992 issue of the Anesthesia Patient Safety Foundation Newsletter contained an article’ which presented and discussed the concept of an .anesthesia workstation.” The major focus of the article rested in stressing standardization of equipment among European, American, and other manufacturers as well as issues of safety. However, of equal if not greater importance was the description of what this ‘workstation’ is all about. One finds that it is a unit capable of delivering anesthetic gas mixtures and monitoring physiological variables (to include inspired/expired C02 among others). Also encountered is the concept that alarms should be prioritized and the recommendation that anesthetic mixtures should be sampled and monitored downstream from the vaporizers. Major emphasis is placed on the issue that ‘MONITORS MUST COME ON AUTOMATICALLY WITH THE ANESTHESIA MACHINE’ (emphasis in the original).
This is a tall order, and one might look at it as if it were a bold step forward. On the other hand, it is reasonable to note that about 20 years ago there appeared a monograph’ in which this author introduced the concept of a single unit capable of delivering all gases and monitoring and recording in a continuous fashion the patients vital signs. Such a unit was called an ‘anesthesia module” ( advance the concept that one should think more in terms of a unit that incorporates monitoring, recording and decision implementation subunits into a single compact and mobile tool. For such a unit … we prefer the words ‘ANESTHESIA MODULE’).’ The use of continuous monitoring of ventilatory functions was proposed and an example of one such module incorporating a capnometer coupled to a continuous recorder was also shown. The concept that alarms and signals to be displayed should be prioritized was discussed (‘In this context, one should … establish a certain order or priorities so that all messages may be organized in a certain order on the basis of their content,…’). Equally interesting, the concept that monitoring of all delivered gas mixtures should be carried out downstream from the vaporizer was also espoused.
As for the value of, and need for, high quality monitoring, it was stated as ‘…the acquisition of information is the cornerstone of anesthesia. Without it anesthesia is not possible, and its quality and quantity determine the quality of anesthesia itself.’
Today, one could be tempted to say that we are looking at a case of convergent evolution in the development of anesthesia equipment.
However, on second look, one observes that even though the environment remains the same (i.e., the operating room) the pressures leading to the development of the “anesthesia module’ and the ‘anesthesia workstation’ were quite different.
In the current situation today, the major emphasis was placed on issues of standardization and safety with limited consideration being given to underlying systematic issues. Conversely, the case 20 years ago for the ‘anesthesia module” was based on a systematic analysis of the administration of anesthesia viewed as a process (a series of sequential and interdependent decisions). The proposed module was advanced as a means of delivering to the anesthetist accurate information upon which to make a decision. A plea was made to the effect that in many instances, a glut of information clutters and hinders the decision-making process, hence again the need to prioritize messages. Finally, it was pointed out that the structure and the format of the message are critical and that in fact in many instances the content and format of the incoming message control the decision itself. Ultimately, the need for continuous recording was stressed.
Data Need Leads to Module
Historically then, this “module’ was developed and tested because a systematic analysis of the anesthetic process pointed to the primacy of the decision-making sequence and because valid decisions can be made only on the basis of immediate access to reliable information.
If the hypothesis that this is a case of convergent evolution is correct, then the proposed current workstation is equivalent to the old module only if it came about under the pressure of analogous systematic analysis of its functions. A brief list of such criteria follows.
One should give serious consideration, and for obvious reasons, to issues that are part of the anesthetists behavior at his workstation without being necessarily part of the ‘anesthetic process.”
First, one would need access to extensive and detailed studies of time and motion during administration of an anesthetic. These would be of great value in determining where to put controls and message displays (in rows? in vertical stacks? in clusters?). Unfortunately, very little has been done beyond observation in this area’,’ and certainly hardly enough to lead to the design of an experimentally tested workstation.
Second, one should recognize that all monitoring can be reduced to the transmission of a signal from one point (the patient) to another point (the record). Within this context the signal to be transmitted must be clearly defined in terms of its frequency and amplitude in order to insure errorless transmission.
In regard to blood pressure, it has been shown that while the blood pressure is measured or sampled, the actual signal being transmitted is “blood pressure changes over time’ and the collected data indicate that this latter signal has a much smaller amplitude than the blood pressure itself and that it is nonperiodic. This lack of periodicity precludes the selection of a sampling frequency which is wholly dependent on the frequency of the signal itself. Hence, the unreliability of the sphygmomanometer and the need for continuous and independent recording of the blood pressure is demonstrated.’ Later studies have confirmed this.’ Unfortunately, similar studies for the pulse rate and the end-expiratory pCO2, just to name two valuable pieces of information, simply do not exist.
A third issue in the construction of any such piece of equipment has to do with human performance, and this subject should be divided into two separate subsections. The first is the recognition that managing an anesthetic is for the most part a .surveillance Wk,” often quite monotonous. While work has been done on the subject of improving performance during monotonous surveillance tasks (both experimentally and in the industry) none has appeared that specifically addresses anesthesia. Finally the issue of actual human performance in terms of body mechanics should be addressed. For instance, placing flowmeter controls seven feet above the floor obviously will not do (ditto for push buttons that are 3.0 mm in size and closely clustered or stacked). The basic information pertaining to this issue is readily available,’ but so far one would have to guess that it has not been thoroughly evaluated and incorporated by the manufacturers of anesthesia equipment (my personal experience with industry representatives is that they are not aware of the existence of such information).
In summary, it would be my opinion that because of the perception that much “good” will be generated by the standardization and consequent supposed safety of anesthesia workstations, there will occur a prompt widespread adoption of such recommendations. Unfortunately, the adoption of standards that are not based on a sound and systematic analysis of the issues could result in hampering rather than enhancing any understanding and managing of the anesthesia process for a long time to come.
Dr. Boba is a member of the Department of Anesthesia, Northern Dutchess Hospital, Rhinebeck, NY, and the Department of Medicine (Intensive Care), Saint Francis Hospital, Poughkeepsie, NY. He has long been interested in the theoretical aspects of the anesthetic process and of medicine in general.
1. Weitzner S. European “workstation” rules will influence U.S. Anesthesia machines. Anesthesia Patient Safety Foundation Newsletter 1992,7.1-6.
2. Boba A. Essays on future trends in anesthesia. Springer Verlag, Berlin Heidelberg. New York, 1972.
3. Boba A. ibid., P. 22 (by permission).
4. Drui AB, Behm RJ, and Martin WE. Predesign investigation of the anesthesia operational environment. Anesthesia and Analgesia … Current Researches 1973:52:584-591.
5. McDonald JS and Dzwonczyk R. An activity analysis of the anesthesiologist’s Interoperative time period. Anesthesiology 1984; 61:A466.
6. Boba A. Blood pressure changes over time during anesthesia (general considerations and observational data about the amplitude and the frequency of the signal). Anesthesiology [email protected]
7. Logas WC, McCrathy RJ, Narbone RF, and Ivankivich AD. Analysis of the accuracy of the anesthetic record. Anesthesiology 1987;66:SI07.
8. Damon A, Stoudt HW, and McFarland RA. The human body in equipment design. Cambridge: Harvard University Press, 1966.