We hypothesized that support of arterial perfusion pressure with diaspirin cross-linked Hb (DCLHb) would prevent the sepsis-induced attenuation in the systemic O₂ delivery-O₂ uptake relationship. Awake septic rats were treated with a chronic infusion of DCLHb or a reference treatment [norepinephrine (NE)] to increase mean arterial pressure by 10-20% over 18 h. Septic and sham control groups received normal saline. Isovolemic hemodilution to create anemic hypoxia was then performed in a metabolic box during continuous measurement of systemic O₂ uptake. O₂ delivery was calculated from hemodynamic variables, and the critical point of O₂ delivery (O_2 crit) was determined using piecewise regression analysis of the O₂ delivery-O₂ uptake relationship. Sepsis increased O_2 crit from 4.99 ± 0.17 to 6.69 ± 0.42 ml · min¹ · 100 g¹ (P < 0.01), while O₂ extraction capacity was decreased (P < 0.05). DCLHb and NE infusion prevented the sepsis-induced increase in O_2 crit [4.56 ± 0.42 ml · min¹ · 100 g¹ (P < 0.01) and 5.04 ± 0.56 ml · min¹ · 100 g¹ (P < 0.05), respectively]. This was explained by a 59% increase in O₂ extraction capacity in the DCLHb group compared with septic controls (P < 0.05), whereas NE treatment decreased systemic O₂ uptake in anemic hypoxia (1.51 ± 0.08 vs. 1.87 ± 0.1 ml · min¹ · 100 g¹ in septic controls, P < 0.05). We conclude that DCLHb ameliorated O₂ extraction capacity in the septic microcirculation, whereas NE decreased the metabolic demands of the tissues.