Mixed venous oxygen saturation monitoring revisited : thoughts for critical care nursing practice

Christensen, Martin (2012) Mixed venous oxygen saturation monitoring revisited : thoughts for critical care nursing practice. Australian Critical Care, 25(2), pp. 78-90.

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Less invasive methods of determining cardiac output are now readily available. Using indicator dilution technique, for example has made it easier to continuously measure cardiac output because it uses the existing intra-arterial line. Therefore gone is the need for a pulmonary artery floatation catheter and with it the ability to measure left atrial and left ventricular work indices as well the ability to monitor and measure a mixed venous saturation (SvO2).


The aim of this paper is to put forward the notion that SvO2 provides valuable information about oxygen consumption and venous reserve; important measures in the critically ill to ensure oxygen supply meets cellular demand. In an attempt to portray this, a simplified example of the septic patient is offered to highlight the changing pathophysiological sequelae of the inflammatory process and its importance for monitoring SvO2.

Relevance to clinical practice

SvO2 monitoring, it could be argued, provides the gold standard for assessing arterial and venous oxygen indices in the critically ill. For the bedside ICU nurse the plethora of information inherent in SvO2 monitoring could provide them with important data that will assist in averting potential problems with oxygen delivery and consumption. However, it has been suggested that central venous saturation (ScvO2) might be an attractive alternative to SvO2 because of its less invasiveness and ease of obtaining a sample for analysis. There are problems with this approach and these are to do with where the catheter tip is sited and the nature of the venous admixture at this site. Studies have shown that ScvO2 is less accurate than SvO2 and should not be used as a sole guiding variable for decision-making. These studies have demonstrated that there is an unacceptably wide range in variance between ScvO2 and SvO2 and this is dependent on the presenting disease, in some cases SvO2 will be significantly lower than ScvO2.


Whilst newer technologies have been developed to continuously measure cardiac output, SvO2 monitoring is still an important adjunct to clinical decision-making in the ICU. Given the information that it provides, seeking alternatives such as ScvO2 or blood samples obtained from femorally placed central venous lines, can unnecessarily lead to inappropriate treatment being given or withheld. Instead when using ScvO2, trending of this variable should provide clinical determinates that are useable for the bedside ICU nurse, remembering that in most conditions SvO2 will be approximately 16% lower.

Impact and interest:

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ID Code: 68972
Item Type: Journal Article
Refereed: Yes
Keywords: SvO2 monitoring, continuous cardiac output, mixed venous oxygen, central venous oxygen
DOI: 10.1016/j.aucc.2011.10.001
ISSN: 1036-7314
Subjects: Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > NURSING (111000) > Clinical Nursing - Secondary (Acute Care) (111003)
Divisions: Current > QUT Faculties and Divisions > Faculty of Health
Current > Schools > School of Nursing
Copyright Owner: Copyright 2012 Australian College of Critical Care Nurses Ltd.
Copyright Statement: This is the author’s version of a work that was accepted for publication in Australian Critical Care. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Australian Critical Care, [VOL 25, ISSUE 2, (2012)] DOI: 10.1016/j.aucc.2011.10.001
Deposited On: 21 Mar 2014 00:23
Last Modified: 10 Apr 2014 01:16

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