Central station data displays: an experimental evaluation of observer performance. Part 2: Factors affecting performance, and a comparison of analogue and digital data.

16 experienced ICU nurses monitored simulated central station VDU displays for the occurrence of ectopic beats and for signs of deterioration in general cardiovascular status. Each period of monitoring lasted for 1 h, and on separate occasions each nurse monitored 1, 2, 4 or 6 displays simultaneously. For primary clinical tasks, the data showed that the nurses' performance improved with each test. The identification of ventricular ectopic beats (VEBs) improved within the 1 h of each test except when 6 screens were being viewed simultaneously, with a similar result for the identification of deterioration of cardiovascular status. The nurses showed a marked preference for analogue signals over digits for the identification of VEBs. The highest priority clinical task was the identification of deteriorating cardiovascular status. When this task was performed efficiently less attention was given to minor tasks, and the nurse rated herself as very tired.