Central venous oxygen saturation (ScvO2)

Reviewed and revised 15th November 2013

USES

• surrogate for SvO2 thus provides a surrogate measure of oxygen flux, reflecting the balance between oxygen delivery (DO2) and consumption (VO2).
• (controversially) advocated by the Surviving Sepsis Guidelines as part of early goal directed therapy for septic shock (target ScvO2 >70%)
• may have a role in the management of postoperative patients

DESCRIPTION

• can be measured intermittently (venous gas) or continuously via a spectrophotometer
• continuous systems typically have either: — a standard CVC with specialised fiberoptics on the tip (e.g. PreSep CVC, attaches to a Vigileo monitor), or — a fiberoptic line that can be fed down a lumen of a pre-existing CVC (e.g. CeVox, attaches to a PiCCO monitor)

METHOD OF INSERTION AND/OR USE

Insertion and use

• as per central line insertion
• SvO2 monitor is either built in to the CVC or can be fed down a lumen in an already sited CVC
• perform calibration

O2 flux = oxygen delivery (DO2) – oxygen consumption (VO2) O2 flux = (cardiac output x (Haemoglobin concentration x SpO2 x 1.34) + (PaO2 x 0.003)) – VO2

Interpretation of scvO2

• Normal oxygen extraction is 25–30% corresponding to a ScvO2 >65%
• < 65% = Impaired tissue oxygenation
• >80% = High PaO2; or suspect: — Cytotoxic dysoxia (e.g. cyanide poisoning, mitochrondial disease, severe sepsis) — Microcirculatory shunting (e.g. severe sepsis, liver failure, hyperthyroidism) — Left to right shunts

OTHER INFORMATION

Utility

• rarely used in Australasia (except as part of the ARISE trial)
• response to therapy can be quickly observed when connected to a continuous spectrophotometer
• studies show that ScVO2 is consistently higher than SvO2 by approximately 5% (when averaged over multiple measurements) but parallels changes in response to volume loading
• ScvO2 > 70% forms part of the strategy adopted in early goal directed therapy which showed a significant mortality reduction in sepsis (16%)
• these patients often already have a CVL in situ (venous access, CVP monitoring)

Problems

• recent data showing that lactate clearance in sepsis is non-inferior to continuous ScVO2 monitoring (Jones, JAMA, 2010)
• titration of end of resuscitation to ScvO2 may not be required (ICU Monitor, 2010 – summary of Jones, JAMA, 2010)
• ScvO2 does not reflect myocardial perfusion (upstream from the opening of the coronary venous sinus)

Difference between ScvO2 and SvO2

• ScvO2 is normally < SvO2 because it contains predominantly SVC blood from the upper body — blood from the upper body has a higher oxygen extraction ratio, and thus a lower SO2 than IVC blood — of major organs at rest, the brain has high oxygen extraction ratio and the kidneys have the lowest
• situations where ScvO2 > SvO2: -> anaesthesia – because of increase in CBF and depression of metabolism -> TBI where cerebral metabolism depressed -> shock – because of diversion of blood from splanchnic circulation + increased oxygen extraction and therefore IVC saturation decreases.

COMPLICATIONS

• same as those associated with central line insertion
• equipment failure
• CeVox can block a CVC lumen completely and is prone to drift
• Potential misinterpretation of the measured values if devices are incorrectly calibrated or malpositioned

References and Links

LITFL

• CCC — Lactate Clearance vs ScvO2 Monitoring in Severe Sepsis
• CCC — SvO2 versus ScvO2
• CCC — Mixed venous oxygen saturation (SvO2) monitoring

Journal articles

• Jones AE, Shapiro NI, Trzeciak S, Arnold RC, Claremont HA, Kline JA; Emergency Medicine Shock Research Network (EMShockNet) Investigators. Lactate clearance vs central venous oxygen saturation as goals of early sepsis therapy: a randomized clinical trial. JAMA. 2010 Feb 24;303(8):739-46. doi: 10.1001/jama.2010.158. PubMed PMID: 20179283; PubMed Central PMCID: PMC2918907.
• Nebout S, Pirracchio R. Should We Monitor ScVO2 in Critically Ill Patients? Cardiol Res Pract. 2012;2012:370697. doi: 10.1155/2012/370697. Epub 2011 Sep 21. PubMed PMID: 21941671; PubMed Central PMCID: PMC3177360.
• van Beest P, Wietasch G, Scheeren T, Spronk P, Kuiper M. Clinical review: use of venous oxygen saturations as a goal – a yet unfinished puzzle. Crit Care. 2011;15(5):232. doi: 10.1186/cc10351. Epub 2011 Oct 24. Review. PubMed PMID: 22047813; PubMed Central PMCID: PMC3334733.
• Walley KR. Use of central venous oxygen saturation to guide therapy. Am J Respir Crit Care Med. 2011 Sep 1;184(5):514-20. doi: 10.1164/rccm.201010-1584CI. Review. PubMed PMID: 21177882. [Free Fulltext]