Tissue oxygenation in septic respiratory failure

The relationships between tissue oxygenation and the different haemodynamic and respiratory parameters were studied in 20 patients with ARDS of septic origin. Good regressions were found between O2 delivery and cardiac index (r = 0.8507), O2 delivery and systemic vascular resistance (r = -0.7051), O2 extraction ratio and mixed venous O2 saturation (r = 0.8978), O2 consumption and cardiac index (r = 0.6593), O2 consumption and systemic vascular resistance (r = -0.6548), and O2 consumption and mixed venous O2 saturation (r = -0.7068). The correlation among the parameters of tissue oxygenation was more expressed between O2 extraction ratio and O2 consumption (r = 0.7285), than between O2 delivery and O2 consumption (r = 0.6095). A better result was achieved by multiple regression analysis, where the multiple r was 0.9748 between O2 consumption and O2 delivery + O2 extraction ratio, whereas the other variables did not increase the multiple r significantly. These regressions also proved the relationship following from the Fick equation, that is O2 consumption is the result of O2 delivery multiplied with the O2 extraction ratio.