Correlation of central venous-to-arterial carbon dioxide difference to arterial-central venous oxygen difference ratio to lactate clearance and prognosis in patients with septic shock: A prospective observational cohort study.

Background: To assess the relationship between the ratio of difference of venoarterial CO₂ tension (P (v-a) CO₂) and difference of arterio-venous oxygen content (C (a-cv) O₂), i.e., ΔPCO₂/ΔCaO₂ with lactate clearance (LC) at 8 and 24 h, to define a cutoff for the ratio to identify LC >10% and >20% at 8 and 24 h, respectively, and its association with prognosis in septic shock.

Methods: Adult patients with septic shock were included in this prospective, observational cohort study. Blood samples for arterial lactate, arterial, and central venous oxygen and carbon dioxide were drawn simultaneously at time zero (T0), 8 h (T8), and 24 h (T24). At T8, patients were divided into Group 8A (LC ≥10%) and Group 8B (LC <10%). At T24, patients were divided into Group 24A (LC ≥20%) and Group 24B (LC <20%).

Results: Ninty-eight patients were included. The area under the curve of ΔPCO₂/ΔCaO₂ at T8 (0.596) and T24 (0.823) was the highest when compared to P(v-a) CO₂ and C(a-v) O₂. The best cutoff of P(v-a) CO₂/C (a-v) O₂ as predictor of LC >10% was 1.31 (sensitivity 70.6% and specificity 53.3%) and for LC >20% was 1.37 (sensitivity 100% and specificity 50%). At both T8 and T24, P(v-a) CO₂/C (a-v) O₂ showed a significant negative correlation with LC. Groups 8A and 24A showed lower intensive care unit mortality than 8B and 24B, respectively. Values of P(v-a) CO₂/C (a-v) O₂ at T8 were comparable, but at T24, there was a significant difference between the survivors and nonsurvivors (P < 0.001).

Conclusion: ΔPCO₂/ΔCaO₂ predicts lactate clearance, and its 24 h value appears superior to the 8-h value in predicting LC and mortality in septic shock patients.