Relationship Analysis of Central Venous-to-arterial Carbon Dioxide Difference and Cardiac Index for Septic Shock

To analyze the relationship of the central venous-to-arterial carbon dioxide difference (p(cv-a)CO₂) and cardiac index (CI) in patients with septic shock, an observational study was conducted in intensive care unit (ICU). 66 consecutive patients with septic shock and central venous oxygen saturation (ScvO₂) ≥ 70% were included after early fluid resuscitation. Measurements were taken at a 6 h interval (T0, T6, T12, T18, T24) during first 24 h after their admission into ICU, including heart rate (HR), mean arterial pressure (MAP), central venous pressure (CVP), p(cv-a)CO₂, cardiac index(CI, L/(min•m²)) and ScvO₂. Patients were divided into low p(cv-a)CO₂ group (n = 35) and high p(cv-a)CO₂ group (n = 31) according to a threshold of 6 mmHg for p(cv-a)CO₂ at T0. As a result, at T0, T6, T12, T18 and T24, there were respectively significant differences between low and high p(cv-a)CO₂ groups for CI (4.1 ± 1.4 vs 2.4 ± 0.6, 4.4 ± 0.9 vs 2.8 ± 0.7, 4.1 ± 1.3 vs 2.9 ± 0.6, 4.0 ± 1.3 vs 2.7 ± 0.8, 4.2 ± 1.4 vs 2.9 ± 0.8, p < 0.001 at each time point), 28-day mortality rate was 38.7%(12/31) for high p(cv-a)CO₂ group and 22.8% (8/35) for low p(cv-a)CO₂ group (p > 0.05), there were significant differences for p(cv-a)CO₂ (p < 0.05) between low and high p(cv-a)CO₂ groups, no differences for HR, MAP, CVP, ScvO₂ (p > 0.05). CI was inversely correlated with p(cv-a)CO₂ value (r = -0.804, p < 0.001), but not for ScvO₂(r = 0.08, p > 0.05). Receiver operating characteristic curve analysis confirmed the correlation of p(cv-a)CO₂ with CI (AUC: 0.782;p < 0.001; 95% confidence interval: 0.710-0.853). The cut-off value for the best predictive value of CI ≥ 2.2 L/(min·m²) was p(cv-a)CO₂ of 5.55 mmHg or lower with a sensitivity of 85.7% and specificity of 66.8%. Hence CI measured with USCOM is inversely correlated with p(cv-a)CO₂ values in guiding the resuscitation of patients with septic shock.