Chest
Volume 126, Issue 6, December 2004, Pages 1891-1896
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Clinical Investigations in Critical Care
Lack of Equivalence Between Central and Mixed Venous Oxygen Saturation

https://doi.org/10.1378/chest.126.6.1891Get rights and content

Study objective:

We compared paired samples of central venous O2 saturation (Scvo2) and mixed venous O2 saturation (Svo2) to test the hypothesis that Scvo2 is equivalent to Svo2. We also compared O2 consumption (Vo2) computed with Scvo2 (Vo2cv) to that computed with Svo2 (Vo2v).

Design:

Prospective, sequential, observational study.

Setting:

Combined medical-surgical ICU.

Patients:

Fifty-three individuals > 18 years of age of either sex who required a pulmonary artery catheter (PAC) to guide fluid therapy. Subjects were identified as postsurgical (32 patients) or medical (21 patients) according to their ICU admission diagnosis.

Interventions:

A PAC was inserted through the internal jugular or subclavian veins. Care was taken to place the PAC proximal port approximately 3 cm above the tricuspid valve. Blood samples were drawn from the proximal and distal ports in random order. An arterial blood sample also was drawn.

Measurements:

Cardiac output in triplicate, systemic pressure, and central pressure. We analyzed blood samples for hemoglobin concentration and O2 saturation (So2). Data were compared by correlation analysis and by the method of Bland and Altman.

Results:

Svo2 was consistently lower than Scvo2 (p < 0.0001), with a mean (≤SD) bias of −5.2 ≤ 5.1%. Similar differences in Scvo2 and Svo2 were present within each subgroup (p < 0.001). A lower Svo2 resulted in Vo2v values that were higher than the Vo2cv values for all patients in the study (mean Vo2v, 236.7 ≤ 103.4 mL/min; mean Vo2cv, 191.1 ≤ 84.0 mL/min; p < 0.001) as well as for patients within each subgroup (p < 0.001).

Conclusions:

Measurements of Scvo2 and Svo2 were not equivalent in this sample of critically ill patients. Moreover, substituting Scvo2 for Svo2 in the calculation of Vo2 produced unacceptably large errors. The decrease in So2 between Scvo2 to Svo2 may result from the mixing of atrial and coronary sinus blood. As such, this difference may be a marker of myocardial O2 consumption.

Section snippets

Materials and Methods

This was a prospective, sequential, observational study of patients who had been admitted to the George Washington University Hospital ICU over a period of 6 months. The study was approved by the institutional review board, and informed consent for participating in the study was obtained from the patient or from their next of kin.

We enrolled individuals of either sex who were > 18 years of age whose attending physicians determined that a PAC was required to guide fluid therapy. Enrollment in

Results

We enrolled 53 patients in the study, of whom 21 were women. Demographics and diagnoses for individuals are shown in Table 1. Thirty-two patients in the study were in the postoperative group, and 21 were in the medical group. All patients in the medical group were in shock, as defined by the use of vasopressor agents to maintain mean arterial pressure. Sepsis was the predominant diagnosis in the medical group (62%). Coronary artery bypass grafting and aortic or mitral valve replacement

Discussion

In the present study, we took blood from the right atrium to be representative of central venous blood. We exercised great care during the insertion of the PAC to position the proximal port approximately 3 cm above the tricuspid valve. Presumably, this position placed the Scvo2 sampling site anterior to the coronary sinus but sufficiently distal into the right atrium to allow for the mixing of superior and inferior vena cava blood. The location of this sampling site for measuring Scvo2 differs

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  • Cited by (155)

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    This study was financed in its entirety by The George Washington University Medical Center Department of Anesthesiology Research Fund.

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