In Reply:—

Dr. Gage raises the important problem of the possible impact of intraoperative monitoring on the behavior of surgical teams. He suggests that transcranial doppler monitoring may have led to improved surgical technique and thus may explain the less than anticipated neuropsychologic deterioration after coronary artery bypass surgery in our trial. 1He references a study in carotid endarterectomy in which the surgeons were able to listen to the transcranial doppler recordings of microembolic signals. 2In our pilot work we, too, used to make the records audible to the surgeon, but we found that this caused alarm and was distracting. Only a research fellow with headphones was aware of the transcranial Doppler signals in theatre in the reported study.

However, there is the more general possibility that any form of monitoring may motivate the surgeon in a less specific way. Cardiac surgeons, aware of the evidence of a deleterious role for cerebral microemboli during coronary artery bypass grafting, have had their attention drawn to those surgical manipulations most closely related to the release of embolic material. Knowing a patient will be monitored may lead to even greater care being taken at these times.

It is important to recall early research on the importance of the impact of observation on behavior. Studies first published in the 1930s of the Hawthorne plant of Western Electric manipulated various conditions (e.g. , light levels, rest breaks), and each change resulted in an increase in productivity. 3Productivity also increased on return to the original conditions. The effect has been interpreted as the impact of the feeling of being studied and is typically referred to as “the Hawthorne effect.” The impact of observation and study in surgery and its impact on surgical behavior in general, raise important issues in the design of studies and the generalization of research findings.

Kong F, Butterworth J, Aveling W, Stump D, Harrison MJG, Hammon J, Stygall J, Rorie KD, Newman SP: Clinical trial of the neuroprotectant Clomethiazole in coronary artery bypass graft surgery: A randomized controlled trial. A nesthesiology 2002; 97: 585–91
Ackerstaff RG, Jansen C, Moll FL, Vermeulen FE, Hamerlijnck RP, Mauser HW: The significance of microemboli detection by means of transcranial Doppler ultrasonography monitoring in carotid endarterectomy. J Vascular Surgery 1995; 21: 963–9
Mayo E: The human problems of an industrial civilization, 2nd edition. New York, MacMillan, 1946, pp 55–76