Prognostic value of Pv-aCO₂ and LCR in patients with septic shock

Objective To investigate the prognostic value of central venous-to-arterial carbon dioxide difference (Pv-aCO₂) and lactate clearance rate (LCR) in patients with septic shock. Methods One hundred and fifty-six patients with septic shock admitted to our hospital from January 2014 to March 2017 were enrolled in our study. According to the 6 h Pv-aCO₂ and the 6 h LCR level, patients were divided into the low Pv-aCO₂ group (Pv-aCO₂< 6 mmHg) versus high Pv-aCO₂ group (Pv-aCO₂ ≥ 6 mmHg), and low LCR group (LCR≤10%) versus high LCR group (LCR> 10%). Pv-aCO₂, LCR, APACHEⅡ, SOFA score and mortality in patients of two groups were compared. The receiver operating characteristic (ROC) curve was used to analyze the prognostic value of Pv-aCO₂ and LCR at different time points in patients with septic shock. Pearson correlation analysis was used to analyze the correlation between Pv-aCO₂ and LCR. Results The APACHEⅡ, SOFA score and mortality in the high Pv-aCO₂ group were significantly higher than those in the low Pv-aCO₂ group(24.16±7.50) vs (19.38±6.72), (8.96±3.18) vs (6.92±2.70), 62.2% vs 17.6%, all P< 0.05, while the 6-hour LCR and success rate of achieving 6-hour early goal-directed therapy (EGDT) in high Pv-aCO₂ group were significantly lower than those in the low Pv-aCO₂ group (17.28%±6.92%) vs (26.53%±10.26%), 52.4% vs 85.1%, all P< 0.05. APACHEⅡ, SOFA score, 6-hour Pv-aCO₂ and mortality of low LCR group were significantly higher than those in high LCR group (23.72±7.41) vs (19.75±6.63), (9.05±3.16) vs (6.83±2.74), (7.48±3.70) mmHg vs (4.92±2.25) mmHg, 66.1% vs 24.5%, all P< 0.05, while the success rate of achieving 6-hour EGDT of low LCR group was significantly lower than those in high LCR group (48.4% vs 80.9%, P< 0.05). The ROC curve showed that the optimal cut-off values of 12-hour Pv-aCO₂ and LCR for evaluating prognosis of septic shock patients were 7.25 mmHg and 12.45%, and the sensitivity and specificity were 80.6% and 90.4%for Pv-aCO₂, 85.2% and 92.7% for LCR. Correlation analysis showed that Pv-aCO₂ was negatively correlated with LCR at 6, 12 and 24 hour in patients with septic shock (r=-0.648, P< 0.01; r=-0.706, P< 0.01; r=-0.591, P< 0.01). Conclusion Changes in PvaCO₂ and LCR are associated with the severity and prognosis of patients with septic shock, and patients with 12 h Pv-aCO₂> 7.25 mmHg and 12 h LCR< 12.45% are more likely to have poor prognosis.