Table 1 Studies comparing mixed venous oxygen saturation and central venous oxygen saturation

Varpula and colleagues [14]

n = 16; septic shock; ICU; 72 paired samples

Mean SvO₂ below mean ScvO₂ at all time points; bias of difference 4.2%

95% limits of agreement -8.1 to 16.5%; difference correlated with CI and DO₂

Difference between ScvO₂ and SvO₂ varied highly; SvO₂ cannot be estimated on basis of ScvO₂

Martin and colleagues [16]

n = 7; 580 comparative measurements; critically ill patients; ICU; with and without interventions

Difference ≥5% in 49% during periods of stability and in 50% during periods with therapeutic interventions

ScvO₂ monitoring not reliable

Chawla and colleagues [17]

n = 32 postsurgical and n = 21 medical; ICU

SvO₂ consistently lower than ScvO₂ with mean (± SD) bias -5.2 ± 5.1%

SvO₂ and ScvO₂ not equivalent; substitution of ScvO₂ for SvO₂ in calculation of VO₂ resulted in unacceptably large errors

Kopterides and colleagues [18]

n = 37; septic shock

Mean SvO₂ below mean ScvO₂; mean bias -8.5%

95% limits of agreement -20.2 to 3.3%; this resulted in higher VO₂ values

ScvO₂ and SvO₂ not equivalent in ICU patients with septic shock; substitution of ScvO₂ for SvO₂ in calculation of VO₂ resulted in unacceptably large errors

Ho and colleagues [19]

n = 20; cardiogenic or septic shock

ScvO₂ overestimated SvO₂ with mean bias 6.9%; 95% limits of agreement -5.0 to 18.8%; changes of ScvO₂ and SvO₂ did not follow the line of perfect agreement

ScvO₂ and SvO₂ are not interchangeable numerically

van Beest and colleagues [20]

n = 53; 265 paired samples; sepsis; ICU; multicentre

Mean SvO₂ below mean ScvO₂ at all time points; bias of difference 1.7%

95% limits of agreement -12.1 to 15.5%; identical results for change in ScvO₂ and SvO₂

Distribution of (ScvO₂ - SvO₂) (<0 vs. ≥0) similar in survivors and nonsurvivors

ScvO₂ does not reliably predict SvO₂ in patients with sepsis

Trend of ScvO₂ not superior in this context

ScvO₂ - SvO₂ ≥0 not associated with improved outcome

Scheinmann and colleagues [21]

n = 24; critically ill cardiac patients; CCU

ScvO₂ levels in superior vena cava are greater than SvO₂ in shock (58 ± 13 vs. 47.5 ± 15; r = 0.55); changes in ScvO₂ reflect changes in SvO₂ (r = 0.90); ScvO₂ from right atrium is similar to SvO₂ (49.2 ± 19 vs. 49.2 ± 19; r = 0.96)

SvO₂ consistently lower than ScvO₂

Poor correlation in heart failure or shock

Changes in ScvO₂ reflect changes in SvO₂

Dueck and colleagues [25]

n = 70; 502 comparative sets; neurosurgery

95% limits of agreement ranged from 6.8% to 9.3% for single values

Correlations between changes of SvO₂ and ScvO₂: r = 0.755, P <0.001

Numerical ScvO₂ values not equivalent to SvO₂ in varying haemodynamic conditions; trend of ScvO₂ may be substituted for the trend of SvO₂

Reinhart and colleagues [26]

n = 32; critically ill patients; ICU; continuous parallel measurements

ScvO₂ closely paralleled SvO₂, in vitro r = 0.88 and in vivo r = 0.81

ScvO₂ averaged (± SD) 7 ± 4% higher than SvO₂

ScvO₂ changed in parallel in 90% when SvO₂ changed more than 5%

Continuous fibreoptic measurement of ScvO₂

Potentially reliable tool to rapidly warn of acute change in the oxygen supply/demand ratio

Ladakis and colleagues [28]

n = 31 surgical and n = 30 medical; critically ill patients; ICU

Significant difference between mean ScvO₂ and SvO₂ (69.4 ± 1.1 vs. 68.6 ± 1.2%); r = 0.945 for total population

ScvO₂ and SvO₂ are closely related and interchangeable for initial evaluation

Tahvanainen and colleagues [29]

n = 42; critically ill patients; ICU; ScvO₂ as representative of real changes in pulmonary shunt

Significant correlation between measured variables between PA blood samples and both superior vena cava and right atrial blood samples (P <0.001)

ScvO₂ can replace SvO₂; exact SvO₂ value can only be measured from the PA itself