P_v-aCO₂ and P_v-aCO₂/C_a-vO₂ as surrogates for cardiac output and oxygen metabolism in septic shock patients

The study investigates the link between the venous-to-arterial carbon dioxide gap (P_v-aCO₂) and cardiac output (CO), as well as the venous-to-arterial carbon dioxide gap to arterial-venous oxygen content difference (P_v-aCO₂/C_a-vO₂) ratio and the oxygen delivery to oxygen consumption (DO₂/VO₂) ratio in septic shock patients, with myocardial dysfunction as a secondary subgroup analysis. A retrospective observational study was conducted in intensive care units (ICUs) from July 1, 2018, to March 31, 2024, focusing on patients with septic shock. Participants were divided into two groups for subgroup analysis: those with myocardial dysfunction and those without, based on ejection fraction (EF). The study collected fundamental data, baseline clinical variables, and prognostic indicators to compare the two groups. The study also examined the correlations between P_v-aCO₂ and CO, P_v-aCO₂/C_a-vO₂ and DO₂/VO₂ in the overall cohort and subgroups. The study involved 597 septic shock patients. In the overall cohort, a negative correlation was found between P_v-aCO₂ and CO (r = − 0.63, P < 0.01) and between P_v-aCO₂/C_a-vO₂ and DO₂/VO₂ (r = − 0.71, P < 0.01). In subgroup analysis, 127 patients had myocardial dysfunction, and 470 did not. No significant differences were noted in basic data, lactate, and other indicators (P > 0.05). However, significant differences were observed in intubation rate, CO, EF, vasoactive inotropic score (VIS), C-reactive protein (CRP), DO₂, P_v-aCO₂/C_a-vO₂, sequential organ failure assessment (SOFA) score, acute physiology and chronic health evaluation (APACHE-II) score, and 28-day mortality rate (P < 0.05) between groups. In myocardial dysfunction subgroup, P_v-aCO₂ negatively correlated with CO (r = − 0.57, P < 0.01), and P_v-aCO₂/C_a-vO₂ negatively correlated with DO₂/VO₂ (r = − 0.80, P < 0.01). Similarly, in non-myocardial dysfunction subgroup, P_v-aCO₂ negatively correlated with CO (r = − 0.62, P < 0.01), and P_v-aCO₂/C_a-vO₂ negatively correlated with DO₂/VO₂ (r = − 0.68, P < 0.01). The correlation of P_v-aCO₂/C_a-vO₂ with DO₂/VO₂ was significantly stronger in myocardial dysfunction subgroup (P = 0.008), while the P_v-aCO₂-CO correlation was similar between subgroups (P = 0.44). In septic shock patients, P_v-aCO₂ and P_v-aCO₂/C_a-vO₂ correlate well with CO and DO₂/VO₂, indicating they could be surrogate markers for these parameters. As a secondary finding, the correlation of P_v-aCO₂ and P_v-aCO₂/C_a-vO₂ is stronger in patients with myocardial dysfunction.