• E C van Woerkens, A Trouwborst, and R Tenbrinck.
• Department of Anesthesiology, Erasmus University, Rotterdam, The Netherlands.
• Crit. Care Med. 1991 Aug 1; 19 (8): 1025-9.

ObjectiveTo determine the accuracy of in vivo mixed venous hemoglobin saturation (Svo2) measurements with a fiber optic thermodilution catheter during acute changes in hematocrit.DesignComparison of fiberoptic in vivo Svo2 values with in vitro Svo2 values obtained with a multiwavelength spectrophotometer.SettingOperating room in a university hospital.PatientsSix consecutive patients who are Jehovah's Witnesses.Measurements And Main ResultsBefore and after each step of hypervolemic hemodilution and after every 500 mL of blood loss, blood gases were analyzed and hemodynamic, hemoglobin, hematocrit, and in vitro and in vivo Svo2 measurements were made. Hematocrit values were measured in the range of 40% to 18%. Plotting all in vivo Svo2 values (n = 74) against the in vitro Svo2 measurements obtained during the entire study period gives r2 = .86. The accuracy of in vivo Svo2 measurements was not affected by changes in hematocrit or cardiac output. The Svo2 catheter value at the beginning of the study differed from the in vitro Svo2 value by -0.86 +/- 2.56% and at the end of the study period of 8 to 10 hrs by 0.71 +/- 3.04%.ConclusionsThe accuracy of the studied fiberoptic continuous measuring Svo2 system was not affected by changes in hematocrit or cardiac output. No significant drift in the in vitro Svo2 measurements was observed.

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