1. says

    Hi guys, noticed you assert in this article (and in that ScvO2 tracks lower than SvO2. I was wondering if you could give some references for that claim.

    Mixing patters are both unpredictable and critical to the result, and I agree that there is the potential for the lower % upper-body sat to weigh the ScvO2 down -- especially if the VBG is drawn from a short, fat resuscitation line in the neck (I highly discourage this…). Don’t forget, though, the mixing of the high-extraction-ratio blood from the coronary sinus that is reflected in the SvO2.

    To my knowledge (admittedly far from exhaustive), the majority of evidence on the topic suggests that in critically ill patients, any predictable relationship is out the window, regardless of the relationship in the normal/well state

    • says

      Thanks Megan

      In both webpages it is stated that there are situations where the classic SVO2- ScvO2 relationship is reversed:

      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.

      Obviously these excepts variably apply to most critically ill patients, hence is unsurprising that the ideal relationship does not bear out in real world studies in the crtically ill.


  2. says

    I remember reading somewhere Scv02 is lower than SvO2 as the lower body has a number of non-oxidative phosphorylation functions (e.g. liver, renal), and that is partly why the difference. This surely makes shock states with organ dysfunction impossible to correlate with the normal values…

    • says

      Yes Lewis, in the ‘normal’ state the relationship reflects different admixtures of venous return from different parts of the body with different oxygen extraction ratios
      In critically patients these admixtures and their OERs will vary, throwing the ‘normal’ relationship out

  3. Joe says

    Why are the goals in the latest Surviving Sepsis Campaign the inverse of the relationship?
    ScvO2 > 70% or SvO2 > 65% in which ScvO2 is greater than SvO2.

    • says

      In a normal healthy person ScvO2 (SVC only blood) is typically lower than Sv02 (SVC + IVC blood) because the brain has relatively higher O2 extraction and some visceral organs such as the kidney have low extraction ratios.
      As indicated in the table, In the shock state the relationship between ScvO2 and SvO2 can be reversed, due to overall higher oxygen extraction by tissues drained by the IVC: From the SSG: “Studies of patients with shock indicate that SvO2 runs 5% to 7% lower than ScvO2″
      I expect this explains the SSC guideline parameters.

  4. Kenneth Lo says

    Dear Editor , thanks for written the article
    As SvO2 is usually > SvcO2 , may I know the reason why the goal in surviving sepsis Guildlines :

    Central venous (superior vena cava) or mixed venous oxygen saturation 70% or 65% , respectively

    it is quite confusing.