Use of Central Venous Oxygen Saturation to Guide Therapy

The use of pulmonary artery catheters has diminished, so that other technologies are emerging. Central venous oxygen saturation measurement (Scv(O2)) as a surrogate for mixed venous oxygen saturation measurement (S (v) over bar (O2)) is simple and clinically accessible. To maximize the clinical utility of Scv(O2) (or Sc (v) over bar (O2)) measurement, it is useful to review what the measurement means in a physiologic context, how the measurement is made, important limitations, and how this measurement may be helpful in common clinical scenarios. Compared with cardiac output measurement, S (v) over bar (O2) is more directly related to tissue oxygenation. Furthermore, when tissue oxygenation is a clinical concern, S (v) over bar (O2) 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(O2) 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 S (v) over bar (O2), or its properly measured Scv(O2) 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).