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High lactate (LCT) identifies critically ill patients, predicts risk of mortality and guides resuscitation. Low central venous oxygen saturation (SvO2) is associated with mortality and is used as a resuscitation target. A change in LCT, but not in SvO2, has been shown to relate to outcome. It is physiologically plausible that those with low SvO2 and high LCT do worse versus those with only one of SvO2 or LCT abnormal, or with both normal. Early changes in these combinations may also determine subsequent changes in organ performance. We hypothesised that changes in combinations in SvO2 and LCT from day 1 to day 2 predicted changes in total SOFA between day 2 and day 4.
We used a retrospective cohort methodology using data obtained from the electronic clinical information system. All included patients underwent LCT and SvO2 measurement (from internal jugular or subclavian vein) in the first 24 hours after ICU admission. 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. Variables individually associated (P < 0.20) with a change in total SOFA between day 2 and day 4 were included in a multivariate linear regression model (with change in total SOFA 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. Complete data on all change variables were available for 675 patients. Mean (SD) SvO2 was 63.6 (11.3) and median (IQR) LCT 3.85 (4.3). Mean (SD) APACHE II and age were 22.4 (6.2) and 64.9 (15.9), respectively, and 61.9% were male. The mean fall (SD) in total SOFA from day 2 to day 4 was 1.05 (2.78). APACHE II (adj. P < 0.001), day 1 SL group (adj. P = 0.019) and SOFA (adj. P < 0.001), and C-reactive protein >209 mg/l (adj. P = 0.006) were independently associated with Δ-SOFA. Changes in SL group were not associated with improvements in organ function (adj. P = 0.12).
APACHE II, SL group and total SOFA (both on day 1) and C-reactive protein >209 mg/l were associated with worsening organ function between day 2 and day 4. Improvement in combinations of SvO2 and LCT were not associated with changes in organ performance.