Regional venous-arterial CO2 to arterial-venous O2 content difference ratio in experimental circulatory shock and hypoxia

Background: Venous-arterial carbon dioxide (CO2) to arterial-venous oxygen (O-2) content difference ratio (Cv-aCO(2)/Ca-vO(2)) > 1 is supposed to be both sensitive and specific for anaerobic metabolism. What regional hemodynamic and metabolic parameters determine the ratio has not been clarified. Objectives: To address determinants of systemic and renal, spleen, gut and liver Cv-aCO(2)/Ca-vO(2). Methods: Post hoc analysis of original data from published experimental studies aimed to address effects of different fluid resuscitation strategies on oxygen transport, lactate metabolism and organ dysfunction in fecal peritonitis and endotoxin infusion, and from animals in cardiac tamponade or hypoxic hypoxia. Systemic and regional hemodynamics, blood flow, lactate uptake, carbon dioxide and oxygen-derived variables were determined. Generalized estimating equations (GEE) were fit to assess contributors to systemic and regional Cv-aCO(2)/Ca-vO(2). Results: Median (range) of pooled systemic Cv-aCO(2)/Ca-vO(2) in 64 pigs was 1.02 (0.02 to 3.84). While parameters reflecting regional lactate exchange were variably associated with the respective regional Cv-aCO(2)/Ca-vO(2) ratios, only regional ratios were independently correlated with systemic ratio: renal Cv-aCO(2) /Ca-vO(2) (beta = 0.148, 95% CI 0.062 to 0.234; p = 0.001), spleen Cv-aCO(2)/Ca-vO(2) (beta = 0.065, 95% CI 0.002 to 0.127; p = 0.042), gut Cv-aCO(2)/Ca-vO(2) (beta = 0.117, 95% CI 0.025 to 0.209; p = 0.013), liver Cv-aCO(2)/Ca-vO(2) (beta = - 0.159, 95% CI - 0.297 to - 0.022; p = 0.023), hepatosplanchnic Cv-aCO(2)/Ca-vO(2) (beta = 0.495, 95% CI 0.205 to 0.786; p = 0.001). Conclusion: In a mixed set of animals in different shock forms or during hypoxic injury, hepatosplanchnic Cv-aCO(2)/Ca-vO(2) ratio had the strongest independent association with systemic Cv-aCO(2)/Ca-vO(2), while no independent association was demonstrated for lactate or hemodynamic variables.