numero rivista e pagine: HSR Proceedings in Intensive Care and Cardiovascular Anesthesia 2010; 2(3): 209-211
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Erroneously low continuous ScvO2 reading due to red blood cells transfusion

Authors: P. Grassi*1, D. Leone1, C. Vassallo1

Department of Anesthesia and Intensive Care, Azienda Ospedaliero Universitaria, Ospedale di Cattinara, Trieste, Italy

Corresponding author: * Corresponding author:
Paolo Grassi, MD
Department of Anesthesia and Intensive Care
Azienda Ospedaliero Universitaria, Ospedale di Cattinara
Strada di Fiume, 447 - 34149 Trieste, Italy

E-mail: paolo.grassi@aots.sanita.fvg.it


Hemoglobin oxygen saturation in superior vena cava (ScvO2) is used as a parameter to guide hemodynamic management in shock patients and it can be continuously read through a central venous catheter equipped with a fiberoptic spectrophotometric probe (Edwards PreSep catheter) connected to a specific monitor (Edwards Vigileo).
We report of an episode of erroneous ScvO2 reading by this technology in a patient with septic shock who was receiving an erythrocytes transfusion through the PreSep catheter main lumen. We think this artifact should be known by intensivists since it can lead to ScvO2 misinterpretation and subsequent erroneous therapeutic decisions.


Keywords: hemoglobin, oxygen saturation, desaturation, transfusion


Hemoglobin oxygen saturation in superior vena cava (ScvO2) is a commonly used parameter for hemodynamic monitoring in intensive care units (ICU) and operating rooms [1,2]. Even if ScvO2 cannot be considered a completely reliable surrogate for SvO2, it is nevertheless a useful tool for the evaluation of the balance between oxygen delivery and consumption in major surgery and critical illness [3].
A modified central venous catheter with a built-in infrared spectrophotometric probe for real-time hemoglobin oxygen saturation measurement is currently available from the market (PreSep central venous oxymetry catheter, Edwards Lifesciences, Irvine, CA, USA). This device, when coupled with either an Edwards Vigileo or an Edwards Vigilance monitor (both Edwards Lifesciences, Irvine, CA, USA) gives continuous ScvO2 reading after an initial calibration. We report here on a patient equipped with a PreSep catheter who apparently developed profound ScvO2 desaturation during an erythrocytes transfusion through the catheter’s main lumen.


Case report

A 57-years-old otherwise healthy male patient was admitted to the ICU with a diagnosis of septic shock. He underwent intestinal resection one year before for rectal cancer and was reoperated one month before current admission because of intestinal occlusion due to visceral adherences. He subsequently developed fever, abdominal pain and hypotension and explorative laparotomy revealed gut perforation and peritonitis.
In the ICU he was treated with broad spectrum antibiotics, intravenous immunoglobulin and noradrenaline infusion because of persistent hypotension despite massive fluids administration.
For hemodynamic monitoring the patient was equipped with a Flow-Track sensor (Edwards Lifesciences, Irvine, CA, USA) on a radial arterial line and with a PreSep central venous catheter inserted in his left internal jugular vein, the tip of which was confirmed to be correctly positioned in superior vena cava by chest radiography. Both devices were connected to a Vigileo monitor revealing a cardiac index of 2,4 L/min/m2 and an ScvO2 of 78%.
One hour later, because of plasma volume expansion with cristalloid and colloid solutions, hemoglobin concentration dropped below 7 g/dl and the physician in charge ordered a 2 units red blood cells transfusion. After the transfusion was started through the main lumen (14 gauge) of the PreSep catheter, and without any other evident modification in physiologic conditions or therapeutic intervention, an ScvO2 value of 35% was displayed on the Vigileo monitor.
Since no other overt hemodynamic changes potentially responsible for this phenomenon was detectable, a causal association between the starting of the red cells transfusion and the ScvO2 drop was hypothesized by the attending nurse.
The transfusion was then stopped by clamping the infusion line and immediately ScvO2 raised and reached the stable value of 78%.
Transfusion was then started again and ScvO2 dropped immediately and reached 35% after 20-30 seconds (Figure 1). 



Figure 1

Left: Vigileo monitor trend lines showing rapid increase in ScvO2 after clamping red cells transfusion line without any perturbation in cardiac index. Right: ScvO2 drops to 35% immediately after restarting transfusion, with a 2 points signal quality index.


Of note, displayed signal quality index (SQI) at this point was 2, indicating an acceptably good signal.
This procedure was repeated twice and was regularly followed by exactly the same phenomenon. We ascribed therefore the ScvO2 drop to the passage close to the catheter’s spectrophotometric probe of highly concentrated stored red cells rich in desaturated hemoglobin.



We believe physicians caring for critically ill and surgical patients should be aware of this possible artifact since ScvO2 misinterpretation could potentially lead to inappropriate therapeutic decisions unfavourably affecting patients’outcome.



  1. Rivers EP, Ander DS, Powell D. Central venous oxygen saturation monitoring in the critically ill patient Curr Opin Crit Care 2001; 7: 204-2011.
  2. Marx G, Reinhart K. Venous oximetry Curr Opin Crit Care 2006; 12: 263-268.
  3. Silva JM jr, Toledo DO, Magalhães DD, et alii. Influence of tissue perfusion on the outcome of surgical patients who need blood transfusion J Crit Care 2009; 24: 426-434.

Conflict of interest: No conflict of interest acknowledged by the authors.