Continuous Svo2measurement using a triple-lumen flow-directed pulmonary artery catheter with fiberoptic filaments has been described. The purpose of this study was to identify whether the availability of Svo2as a continuously monitored signal could have altered patient management decisions made by the medical staff on the basis of clinical and laboratory data and signals currently used in Id's. Subjects for this study were 15 critically ill patients requiring arterial cannulation and insertion of a pulmonary artery catheter. The central processor of the device was placed in a specially constructed wooden box in such a way as to conceal the digital display of the signal. The folded paper used for a continuous 72-h recording of the signal was also not available to the personnel managing the patient. In detailed and repeated assessments of the patient's status, the medical team managing the patient entered on a special form all clinical and laboratory data as well as medical decisions made. At the end of each study the Svo2value recorded at each assessment was entered on the form. The investigators then determined whether knowledge of Svo2would have changed the clinical decision actually made. The Svo2signal was continuously recorded for a total of 1065 h and 173 individual assessments. The Svo2signal as measured by the Oximetrix device was compatible with decisions made on the basis of standard measurements used in the ICU in a majority of cases. We could not document any incident in which awareness of Svo2would have resulted in a different yet more appropriate line of management than that based on the currently available data.