Resuscitation from hemorrhagic shock: recovery of oxygen carrying capacity or perfusion? Efficacy of new plasma expanders

SUMMARY Potential shortages and perceived issues with the biosafety of blood have strengthened interest in the search for alternatives to blood. Currently available plasma expanders are effective in recovering pressure by volume expansion but are not safely deployed beyond the transfusion trigger. Conventional reasoning indicates that this limitation relates to oxygen carrying capacity reaching the threshold where it no longer can satisfy the metabolic demand of the organism; however, recent findings show that this limitation is also determined by other physical factors such as their viscosity and colloidal osmotic pressure. These fluid transport properties have a strong influence on the maintenance of microvascular perfusion and function in conditions of extreme hemodilution that obtain when resuscitation is continued beyond the transfusion trigger with plasma expanders. This realization leads to the possibility of developing new plasma expanders whose physical properties enhance microvascular function compensating for the decreased intrinsic oxygen carrying capacity in extreme hemodilution via enhanced microvascular perfusion. This review presents experimental, systemic and microvascular findings obtained using polyethylene glycol conjugated albumin solutions in extreme hemodilution and shock resuscitation in the hamster window chamber model, concluding that plasma expanders of this type can be effectively used beyond the transfusion trigger.