NADH-localized fluorometry was used as a noninvasive technique to monitor changes in the energy state of intact tissue (muscle and connective tissue), without
anesthesia, as a function of blood plasma O(2)-carrying capacity in the hamster window chamber model. Acute moderate isovolemic
hemodilution was induced by two isovolemic
hemodilution steps: in the first step, 6% 70-kDa
dextran (Dex70) was used to induce an acute anemic state (18% Hct); in the second step, exchange transfusion of
polyethylene glycol (PEG)
maleimide-conjugated Hb (4 g/dl,
PEG-Hb) or Dex70 (6 g/dl) was used to reduce erythrocytes to 75% of baseline (11% Hct).
PEG-Hb had six copies of PEG (5 kDa) conjugated to each human Hb (0.48 g PEG/g Hb) through extension arm-facilitated chemistry. Systemic parameters, microvascular perfusion, functional capillary density, intravascular and interstitial Po(2), and intracellular
NADH fluorescence were monitored. Mean arterial blood pressure after extreme
hemodilution was statistically significantly reduced for Dex70 compared with
PEG-Hb. The presence of
PEG-Hb in the circulation maintained positive acid-base balance. While microvascular blood flows were not different, functional capillary density was significantly higher for
PEG-Hb than Dex70. Arteriolar Po(2) was higher in the presence of
PEG-Hb than Dex70, but tissue and venular Po(2) were not different. Cellular energy metabolism (intracellular O(2)) in the tissues was improved with
PEG-Hb. Moderate
hemodilution to 18% Hct (6.4 g Hb/dl) brings tissue O(2) delivery to the verge of inadequacy. Extreme
hemodilution to 11% Hct (3.7 g Hb/dl) produces tissue
anoxia, and high-O(2)-affinity
PEG-Hb (Po(2) at which blood is 50% saturated with O(2) = 4 Torr, 1.1 g Hb/dl) only partially decreases anaerobic metabolism without increasing tissue Po(2).