Mixed and central venous oxygen saturation in patients with septic shock: is there a difference?
© BioMed Central Ltd 2005
Published: 9 June 2005
The mixed venous oxygen saturation (mSVO2) is an important marker of global perfusion in patients with septic shock. There is some evidence that central venous oxygen saturation (cSVO2) can replace mSVO2. However, little is known about where it should be located: the superior vena cava (ccSVO2) or the right atrium (acSVO2). This study aimed at evaluating the differences between mSVO2 and cSVO2 (either from the cava or from the atrium) and the impact of them in patient management.
We included patients admitted to a tertiary universitary ICU with septic shock that had a Swan–Ganz catheter and a central venous catheter in place. Each patient was submitted to three sets of hemodynamic and respiratory monitoring, with a minimal interval of 4 hours. Each set included a blood gas analysis of samples collected from the proximal (acSVO2) and distal port of the Swan–Ganz catheter (mSVO2) and also from the central line catheter (ccSVO2). Each of these samples was analyzed by a blinded critical care physician who decided the hypothetical management for the patient. Statistical analysis was done using a paired Student t test. Results were considered significant if P ≤ 0.005.
We studied 22 sets of measures in seven patients (five female and two male) with a mean age of 60.57 ± 23.25 years. The mean values were 76.47 ± 8.02, 75.54 ± 11.96 and 70.90 ± 8.53 for ccSVO2, acSVO2 and mSVO2, respectively. There was a significant difference between ccSVO2 and mSVO2 (P = 0.009) and acSVO2 and mSVO2 (P = 0.01), but not between ccSVO2 and acSVO2 (P = 0.60). The concordances in patient management were 63.2%, 68.2% and 78.9% between ccSVO2 and mSVO2, acSVO2 and mSVO2 and ccSVO2 and acSVO2. When only sets with a ccSVO2 below 70 were considered, the concordance between ccSVO2 and mSVO2 was 75%.
Our results suggest that blood samples derived from a central catheter, even if it is located in the right atrium, may be not accurate enough to be used as a measure of tissue oxygenation and may lead to improper management of the patient, mainly when the values are above 70%.