Hemoglobin Oxygen Affinity Does Not Change in the Canine Model of Moderate Acute Normovolemic Hemodilution

As the amount of hemoglobin (Hb) decreases during moderate acute normovolemic hemodilution (ANH), it is unclear whether the Hb-oxygen affinity (HOA) changes accordingly. Thus, this study aimed to explore changes in HOA during moderate ANH.

A moderate ANH model of canine was established. Hemodynamic, blood gas, biochemical, oxygenation, and HOA-related parameters were measured. P ₅₀ was obtained using three methods. One was derived from the oxygen dissociation curve (ODC) by the Bloodox-2018 analyzer, and the other two were based on blood gas analyzers.

With decreased Hb and hematocrit (HCT) levels during ANH, the temperature (T) and base excess (BE) decreased, while Cl^- increased. Compared with baseline (BL), in hemodilution 1 (HCT decreased to 75% of the BL, H1) and hemodilution 2 (HCT decreased to 50% of the BL, H2), pH and HCO₃ ^- decreased. Methemoglobin (MetHb) levels in H2 were significantly higher than those in BL and H1. HOA-related parameters did not change significantly in moderate ANH. Factors that increase or decrease the P ₅₀ offset each other, leaving the P ₅₀ unchanged in moderate ANH. The P ₅₀ obtained based on the two blood gas analyzers was consistent, but neither was consistent with P ₅₀ derived from the ODC.