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Lactate (LCT) is used to identify critically ill patients at risk of death. Low central venous oxygen saturation (SvO2) is also associated with increased mortality. It is physiologically plausible that patients with low SvO2 and high LCT do worse versus those with only one of SvO2 or LCT abnormal, or with both normal. However, the prognostic value of combining LCT and SvO2 is unknown. We studied the association between ICU mortality and combinations of SvO2 and LCT abnormality.
We used a retrospective single-centre cohort methodology using data obtained from the comprehensive electronic clinical information system (CareVue™). All patients who underwent LCT and SvO2 measurement (from internal jugular or subclavian vein) during the first 24 hours after ICU admission (2004 to 2009) were included. Baseline (demographic, physiological), daily follow-up (physiological, SOFA) and 30-day mortality data were recorded. Worst admission values were used to combine SvO2/LCT into four groups (SL groups: 0 to 3) dichotomised by mean (SvO2) and median (LCT): 0 - N/N; 1 - L/N; 2 - N/H; 3 - L/H. Descriptive analysis used standard statistical techniques. Variables individually associated (P < 0.20) with SvO2 and/or LCT, and mortality were included in a multivariate logistic regression model (with mortality as the dependent variable) using forward stepwise inclusion. Variables with adjusted P < 0.05 remained in the final model.
A total of 1,544 patients were included. Mean (SD) SvO2 was 63.6 (11.3) and median (IQR) LCT 3.85 (4.3). Overall mortality was 20.2%. Univariate analysis showed a statistically significant association between SL group and mortality (P < 0.001). This association did not remain significant in multivariate analysis: only LCT (not SvO2) was associated with mortality when adjusted for other variables.
In this population LCT but not SvO2 predicts 30-day ICU mortality. These data does not support the hypothesis that patients with low SvO2 and high LCT do worse compared with when only one of SvO2 or LCT is abnormal, or if both are normal.