Venous-arterial CO2 to arterial-venous O2 content ratio in different shock types and correlation with hypoxia indicators

Shock is a generalized form of acute circulatory failure characterized by low tissue perfusion. If not recognized early, it highly increases patient morbidity and mortality. Central venous-arterial CO2 (Carbon dioxide) to arterial-central venous O2 (Oxygen) content ratio (Pcv-aCO2/Ca-cvO2) has been used for the early prediction of anaerobic metabolism in septic shock patients. However, knowledge about the usability of this ratio in cardiogenic shock is scarce.We retrospectively collected the data of patients admitted to our 18-bed intensive care unit (Haga Hospital, Department of Intensive Care, The Hague, The Netherlands) with a diagnosis of septic shock or cardiogenic shock in 2018. All patients who had undergone Swan-Ganz or Pulse index Continuous Cardiac Output device insertion were included in the study. The hemodynamic variables were recorded both at ICU admission and during catheterization.Forty-six (n= 46) patients with a mean age of 62 ± 13 years and 52% female gender were enrolled in the study. The Acute Physiology and Chronic Health Evaluation IV (APACHE IV) score was 96 ± 39. Twenty-four patients had septic shock, and twenty-two were diagnosed with cardiogenic shock. Although Pcv-aCO2 (Central venous-arterial CO2) and ScvO2 (Central venous oxygen) were not found different between the cardiogenic and septic shock groups, the Pcv-aCO2/Ca-cvO2 ratio was significantly lower in patients with cardiogenic shock (p= 0.035). The Pcv-aCO2/Ca-cvO2 ratio had a weak correlation with ScvO2 (r= 0.21, p= 0.040). Pcv-aCO2 and ScvO2 showed negative lower moderate correlation (r= -0.40, p= 0.030). Twenty patients [nine (19%) with cardiogenic shock, and eleven (23%) with septic shock] died during their ICU or hospital stay. Although Ca-cvO2, Pcv-aCO2, and ScvO2 were not associated with mortality, a higher Pcv-aCO2/Ca-cvO2 ratio was associated with increased mortality (p= 0.035).The Pcv-aCO2/Ca-cvO2 ratio is a valuable hypoxia indicator in states of shock. However, cutoff levels should be identified for different shock types.