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]
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.