To the Editor:-We read with interest the article by Weinger et al. In particular, the discussion of transesophageal echocardiography (TEE) use in relation to vigilance and workload caught our attention. Vigilance is, for most anesthesia providers, a main component of clinical quality. Vigilance is the Holy Grail of our profession. The suggestion that use of a device, technique, or method of anesthesia leads to decreased vigilance provokes strong reactions because vigilance is so widely recognized as a central theme in practice.
According to the authors, this study of residents coping with TEE and automated records indicates that TEE use increases workload and decreases vigilance. Readers who use TEE doubtless will be disturbed by this interpretation. These readers recognize that the use of TEE requires effort but regard these efforts as amply rewarded by the knowledge gained. Rather than decreasing their vigilance, they consider that the broader and more precise view of cardiac and pulmonary function provided by TEE increases their vigilance by increasing their ability to detect and classify clinically relevant events. They are mindful of evidence that TEE use improves outcomes in cardiac surgery [3–5]and in postoperative settings, facts inconsistent with the idea that vigilance is impaired by its use.
Weinger et al. use the term vigilance in a technical way. In the psychology laboratory, vigilance refers to sustained attention or a state of readiness to detect and respond to certain small changes occurring at random time intervals in a given environment. Accordingly, this psychological sense of vigilance is probably applicable during low tempo, low-signal rate periods.
Cardiac anesthesia typically involves high tempo periods that require divided attention, i.e., the smooth, rapid, coordinated switching of attention between different tasks. The processes of divided attention and attention switching during multi-task situations are fundamentally different from sustained attention during low-signal rate periods. Such periods include, but are not limited to, induction, preparation to go on bypass, surgical manipulations like the release of an aortic occlusive clamp, and the period of separation from bypass. How human experts manage the demands of such high tempo periods (and how information technology modulates human expertise and changes these demands) is the subject of intense study in a variety of domains, including anesthesia. 
One role of technology is to make the cognitive tasks of anesthesia easier by reducing the uncertainty associated with inferences based on indirect or ambiguous data. This is the purpose of TEE. Intraoperative TEE provides valuable information about cardiovascular anatomy and physiology not otherwise obtainable by inspection or analysis of hemodynamic data. Assembling, testing, and maintaining a view of current and likely future patient state is, we think, what most of our colleagues in anesthesia would regard as vigilance, although many researchers on human cognition in complex domains would use the term situation awareness to describe this behavior. [8,9]
In this study, the impact of TEE was assessed by residents with variable exposure to cardiac anesthesia, who were at the early stages of developing expertise in cardiac anesthesia and in TEE. The large variability shown in Figure 2for the TEE task may well reflect their learning about TEE more than any other factor. This causes us to ask whether the experience of the TEE user determined performance on this task. There are also other factors that may have led to long periods of user focus of attention on TEE. To be used optimally, TEE assessment should be continuously integrated with overall clinical status, surgical manipulations, drug administration, and data from other monitors. The practice of removing the ultrasound machine makes it more likely that the residents would be inclined to devote substantial time and attention to the TEE examination in the period just after induction of anesthesia.
In light of these observations, what are readers to make of Weinger et al.'s study? We take this as yet another example of the ways in which human-technology interactions are as complex as the inherent complexity of the domain in which they take place. Direct attempts to disentangle technology from human expertise are unlikely to yield compelling, extensible results in domains where the exercise of clinical skill is so tightly tied to the details of informational tools. The use of TEE (just like any monitor), requires judgment with its application; knowing when to use it is as important as knowing when to stop using it and re-direct attention on a task with a higher priority. In the balance, it is expertise and experience that should be measured with the use of any information technology.
In summary, the vigilance of clinical practice is the construction and maintenance of a view of the patient and procedure that contains the relevant clinical details. TEE use during cardiac anesthesia assists in this cognitively demanding work and, in the right hands, improves vigilance and decreases workload. 
Solomon Aronson, M.D., F.A.C.C.
Department of Anesthesia and Critical Care; The University of Chicago Medical Center; 5841 South Maryland Avenue; Chicago, Illinois 60637
Richard Cook, M.D.
Assistant Professor; Department of Anesthesia and Critical Care; The University of Chicago Medical Center; Director; Cognitive Technologies Laboratory
(Accepted for publication December 2, 1997.)