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The use of pulmonary artery catheters has diminished, so that other technologies are emerging. Central venous oxygen saturation measurement (Scv^sub O^sub 2^^) as a surrogate for mixed venous oxygen saturation measurement (Sv^sub O^sub 2^^) is simple and clinically accessible. To maximize the clinical utility of Scv^sub O^sub 2^^ (or Sv^sub O^sub 2^^) measurement, it is useful to reviewwhatthemeasurementmeansin a physiologic context,how the measurement is made, important limitations, andhowthis measurement may be helpful in common clinical scenarios. Compared with cardiac output measurement, Sv^sub O^sub 2^^ is more directly related to tissue oxygenation. Furthermore,whentissue oxygenation is a clinical concern, Sv^sub O^sub 2^^ is less prone to error compared with cardiac output, where small measurement errors may lead to larger errors in interpreting adequacy of oxygen delivery. Scv^sub O^sub 2^^ should be measured from the tip of a central venous catheter placed close to, or within, the right atrium to reduce measurement error. Correct clinical interpretation of Sv^sub O^sub 2^^, or its properly measured Scv^sub O^sub 2^^ surrogate, can be used to (1) estimate cardiac output using the Fick equation, (2) better understand whether a patient's oxygen delivery is adequate to meet their oxygen demands, (3) help guide clinical practice, particularly when resuscitating patients using validated early goal directed therapy treatment protocols, (4) understand and treat arterial hypoxemia, and (5) rapidly estimate shunt fraction (venous admixture).
Keywords: early goal directed therapy; cardiac output; Fick equation; shunt fraction; oxygen extraction ratio
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Several studies assessing pulmonary artery catheter use failed to demonstrate benefit (1-3). Consequently, the use of pulmonary artery catheters to monitor critically ill patients and to guide therapy has diminished substantially (4). Some have suggested that the problem was not so much with the pulmonary artery catheter as with inadequate knowledge and interpretation (5). To fulfill the perceived clinical need for similar measurements a number of new technologies have emerged, including echocardiography (6), ultrasonic cardiac output monitors (7), arterial pulse pressure analysis techniques (8, 9), impedance techniques (10, 11), alternative dye dilution techniques (12), and so on, to provide alternative/additional measurements. In the absence of clinical trials analogous to those for pulmonary artery catheters, we do not know if these alternative/additional measurements are beneficial (13). To avoid a repeat of the pulmonary...