Fig. 2. Oxy-hemoglobin dissociation curve illustrating the difference in gradient at Po²levels typical for arterial and venous blood. The greater affinity of deoxy-hemoglobin results in a greater step change in sulfur dioxide (So²) in venous blood than in arterial blood after an increase in fractional inspired oxygen concentration. This phenomenon has the potential to cause confusion in cases where venous saturation is employed as an endpoint for hemodynamic therapy.