What should be monitored? The past, present, and future of physiological monitoring

The status of conventional monitoring by vital signs and present concepts of invasive monitoring with the balloon-tipped pulmonary artery (Swan-Ganz) catheter are reviewed. Survivors of high-risk general surgery were observed to have cardiac index (CI) values averaging 4.5 L/min.m2, oxygen delivery (DO2) greater than 600 mL/min.m2, and oxygen consumption (VO2) greater than 170 mL/min.m2. By contrast, those who subsequently died during their hospitalization maintained relatively normal CI, DO2, and VO2 values. However, in the immediate postoperative period, values for other hemodynamic variables were not greatly different for survivors and nonsurvivors or different from the normal range. A predictive index based on these observations predicted outcome correctly in 94% of the subjects in a subsequent prospective study. The use of survivor values as appropriate therapeutic goals was tested in prospective randomized clinical trials and was found to reduce mortality and morbidity significantly. Simultaneous invasive and noninvasive hemodynamic and oxygen-transport monitoring systems were evaluated in high-risk postoperative patients to describe unanticipated adverse circulatory events. Before the monitored event, about three-fourths of the patients exhibited normal function. At the nadir, cardiac functions decreased in about two-thirds, perfusion decreased in more than one-half, and paO2 fell in only one-fourth. Two-thirds recovered with increased cardiac function, more than one-half had improved perfusion, and paO2 increased in fewer than one-fifth of monitored events. These data provide an information base for criteria needed to develop therapeutic decision rules for noninvasive monitoring systems. When noninvasive data are continuously displayed early in the course of critical illness and high-risk conditions, therapy may be instituted early, while physiological deficits are still minimal and easily reversible.