Diaspirin cross-linked hemoglobin (DCLHb) ensures tissue oxygenation during hemodilution below the critical hematocrit

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Background

Normovolemic hemodilution (HD) is an effective blood sparing strategy in the perioperative setting. Despite physiologic compensation for reduced hematocrit (Hct) and O₂ content (CaO₂), tolerance to HD is limited. At a Hct called `critical' (Hct_crit), tissue hypoxia occurs.

Objective

To assess, whether HD can be extended below Hct_crit when using an hemoglobin-based O₂ carrier as diluent.

Methods

Twelve anesthetized, mechanically-ventilated pigs were hemodiluted by 1:1 exchange of blood with either 10% DCLHb (DCLHb, n=6) or 8% albumin (HSA, n=6) oncotically matched to DCLHb (diluents were provided by Baxter Healthcare Inc., Boulder, CO). In both groups, measurements were performed at baseline and after HD to (1) preset Hct-values of 15%, 8%, 4% 2%, 1% or (2) until the individual Hct_crit, defined by the onset of myocardial ischemia (ST-segment depression), was reached. Total body O₂-delivery and O₂-uptake (DO₂I, VO₂I), as well as local tissue O₂ partial pressure (tPO₂, MDO-Electrode,Eschweiler, Kiel, Germany) on the surface of liver and skeletal muscle were assessed during every measurement (Median ± [Q1-Q3]/2; rANOVA, MWU-test P<0.05).

Results

In the HSA-group, Hct_crit was 6.1±0.9%, at which all animals died. In the DCLHb-group, Hct_crit was not reached despite hemodilution to Hct 1.2%. At Hct 4%in the DCLHb-group, all parameters (CaO₂, DO₂I, tPO₂:P<0.05 vs HSA; VO₂I n.s.) were less altered than at Hct_critin the HSA-group.

Conclusion

During HD with DCLHb, O2-transport and tissue oxygenation were fully preserved at Hct 4%, while all HSA-animals had died at Hct 6.1%. The difference is due to the O₂ transporting capacity of DCLHb.