Storage of strain-specific rat blood limits cerebral tissue oxygen delivery during acute fluid resuscitation.

Abstract

The effect of blood storage on tissue oxygen delivery has not been clearly defined. Some studies demonstrate reduced microvascular oxygen delivery, whereas others do not. We hypothesize that storage of rat blood will limit its ability to deliver oxygen to cerebral tissue. Anaesthetized rats underwent haemorrhage (18 ml kg(-1)) and resuscitation with an equivalent amount of fresh or 7 day stored strain-specific whole blood. Arterial blood gases, co-oximetry, red cell counts and indices, and blood smears were performed. Hippocampal tissue oxygen tension (PBr(O2)), regional cerebral blood flow (rCBF), and mean arterial pressure (MAP) were measured before and for 60 min after resuscitation (n=6). Data [mean (SD)] were analysed by anova. After 7 days, there was a significant reduction in pH, Pa(O2), an increase in Pa(CO2), but no detectable plasma haemoglobin in stored rat blood. Stored red blood cell morphology demonstrated marked echinocytosis, but no haemolysis in vitro. MAP and PBr(O2) in both groups decreased after haemorrhage. Resuscitation with stored blood returned MAP [92 (SD 16) mm Hg] and PBr(O2) [3.2 (0.7) kPa] to baseline, whereas rCBF remained stable [1.2 (0.1)]. Resuscitation with fresh blood returned MAP to baseline [105 (16) mm Hg] whereas both PBr(O2) [5.6 (1.5) kPa] and rCBF [1.9 (0.4)] increased significantly (P<0.05 for both, relative to baseline and stored blood group). There was no evidence of haemolysis in vivo. Although resuscitation with stored blood restored cerebral oxygen delivery to baseline, fresh blood produced a greater increase in both PBr(O2) and rCBF. These data support the hypothesis that storage limits the ability of RBC to deliver oxygen to brain tissue.