Patterns of central venous oxygen saturation, lactate and veno-arterial CO2 difference in patients with septic shock

Tissue hypoperfusion is reflected by metabolic parameters such as lactate, central venous oxygen saturation (ScvO2) and the veno-arterial CO2 (vaCO2) difference. We studied the relation of these parameters over time and with outcome in patients with severe septic shock.

In this single-center, prospective observational cohort study, adult patients (≥18 years) with circulatory shock were included. Echocardiography and simultaneous arterial and venous blood gases were done on enrolment (0 h) and at 24, 48 and 72 h. The partial pressure of CO2, lactate and ScvO2 were recorded from the central venous blood samples. The vaCO2 was calculated as the difference in CO2 between paired venous and arterial blood gas samples.

Of the 104 patients with circulatory shock, 79 patients (44 males) with septic shock aged 49.8 (standard deviation ± 14.6) years and with sequential organ failure assessment (SOFA) score of 11.0 ± 3.4 were included. 71 patients (89.9%) were ventilated (11.4 ± 12.3 ventilator-free days). The duration of hospitalization was 16.6 ± 12.8 days and hospital mortality 50.6%. Lactate significantly decreased over time with a greater decrement in survivors than nonsurvivors (-0.35 vs. -0.10, P < 0.001). For every l/min increase in cardiac output, vaCO2 decreased by 0.34 mmHg (P = 0.006). There was no association between ScvO2 and mortality (P = 0.930). 0 h SOFA and vaCO2 ≤6 mmHg were strongly associated (P = 0.005, P = 0.018, respectively) with higher odds of mortality. However, this association was evident only in those with ScvO2 >70% and not in ScvO2 ≤70%.

In septic shock, vaCO2 ≤6 mmHg is independently associated with mortality, particularly in those with normalized ScvO2 consistent with metabolic microcirculatory abnormalities in these patients.