Catheterization and Cardiovascular Diagnosis zyx 9:25-31 (1983) Estimation of Mixed Venous Oxygen Saturation William J. French, MD, Potter Chang, PhD, Sarah Forsythe, MS, and J. Michael Criley, MD Pulmonary artery oxygen saturation (PA) was measured directly and estimated from venal cavae samples in 175 adults without intracardiac shunts to ascertain which of four formulas (MV1, MV2, MV3, or MV4) best estimated mixed venous oxygen satu- ration. Because the formula MVl, which favored IVC samples, most closely approxi- mated pulmonary artery saturation, we recommend its use to estimate systemic flow in patients with left-to-right shunts. In addition, a difference between directly measured PA and calculated MV1 of 6% or greater Indicates the presence of a left-to-right shunt in 97% of cases. Key words: shunt, mlxed venous oxygen saturatlon INTRODUCTION zyxwvut Mixed venous or pulmonary artery blood is an admixture of heterogenous oxygen contents from the venae cavae and coronary sinus. To calculate blood flow by the direct Fick method, an accurate estimate of mixed venous oxygen content is necessary. This estimate requires that the vena caval samples be “mathematically mixed” in order to estimate the systemic venous oxygen content or saturation [ zyxw 1-61. Because of the uncertainty of whether a formula weighted toward superior or inferior venae caval blood samples best estimates mixed venous oxygen situation, the purpose of this study is to compare various formulas used to estimate mixed venous oxygen saturation in adult patients without shunts in order to ascertain which formula provides the best estimate of the observed pulmonary artery saturation. A second purpose is to define the difference between directly measured and estimated mixed venous oxygen saturations required for a firm diagnosis of a left-to-right shunt. From the Harbor-UCLA Medlcal Center, UCLA School of Medicine, Torrance, Callfornla and The UCLA School of Publlc Health, Los Angeles. Address reprint requests to William J. French, MD, Harbor-UCLA Medical Center, zyxw Box 4, lo00 West Carson Street, Torrance, CA 90509. Received May 14, 1982, revision accepted August 24, 1982. 0098-6569/83/0901-0025$02.50 zyxwvu 0 1983 Alan R. Liss, Inc.