Reviewed and revised 15th November 2013
- 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
- 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
- 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)
- 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.
- 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
- CCC — Lactate Clearance vs ScvO2 Monitoring in Severe Sepsis
- CCC — SvO2 versus ScvO2
- CCC — Mixed venous oxygen saturation (SvO2) monitoring
- 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]