The Prognostic Value of Central Venous-to-Arterial CO2 Difference/Arterial-Central Venous O2 Difference Ratio in Septic Shock Patients with Central Venous O2 Saturation ≥80.

BACKGROUND: It is a great challenge for physician to assess the relationship between O2 delivery and O2 consumption in septic shock patients with high ScvO2. Recently, the venous-to-arterial CO2 difference/arterial-central venous O2 difference ratio (P(v-a)CO2/C(a-v)O2) has shown potential for reflecting anaerobic metabolism. Therefore, we evaluated the value of using the P(v-a)CO2/C(a-v)O2 ratio to predict mortality and assess anaerobic metabolism in septic shock patients with high ScvO2 (≥ 80%).

METHODS: This was a clinical investigation of septic shock patients on the P(v-a)CO2/C(a-v)O2 ratio in the intensive care unit (ICU) department. The patients' arterial and central venous blood gas levels were measured simultaneously at enrollment (T0) and 24 h (T24) after resuscitation.

RESULTS: A total of 61 patients with high ScvO2 at T24 after resuscitation were selected for analysis. The ICU mortality rate in the septic shock patients was 20% (12/61). The nonsurvivors had a significantly higher P(v-a)CO2, P(v-a)CO2/C(a-v) O2 ratio, arterial lactate level and lower lactate clearance at T24 after resuscitation. The P(v-a)CO2/C(a-v)O2 ratio had the biggest the areas under the receiver operating characteristic (AUC) for predicting ICU mortality. For predicting ICU mortality, a threshold of P(v-a)CO2/C(a-v)O2 ratio ≥1.6 was associated with a sensitivity of 83% and a specificity of 63%. Multivariate analysis showed P(v-a)CO2/C(a-v)O2 ratio at both T0 (RR 5.597, P = 0.024) and T24 (RR 5.812, P = 0.031) was an independent predictor of ICU mortality. Including the ratio into the regression model showed a bigger AUC than without the ratio (0.886 vs. 0.833).

CONCLUSIONS: The P(v-a)CO2/C(a-v)O2 ratio is an independent predictor of ICU mortality in septic shock patients with high ScvO2 after resuscitation. It is worthy of consideration to recruit microcirculation to correct the high ratio in high ScvO2 case.