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

Introduction: 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.

Materials and methods: 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.

Result: 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).

Conclusions: 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.