Effects of hemodilution on gastric and intestinal oxygenation

To determine the effects of hemodilution on gastric and intestinal oxygenation, isolated segments of canine stomach and small bowel were perfused by a pressurized reservoir with blood at hematocrits of 40 and 20%. Arteriovenous O2 difference, blood flow, and arterial and venous pressures were monitored continuously as perfusion pressure was reduced in 30-mmHg steps from 180 to 30 mmHg. O2 consumption was calculated as the product of the steady-state arteriovenous O2 difference and blood flow at each perfusion pressure. Gastric and intestinal O2 uptake were relatively well maintained over most of the pressure range when the hematocrit was set at 40%. After hemodilution, gastric O2 uptake decreased significantly only at 90 and 60 mmHg, but intestinal O2 uptake was significantly reduced except at 30 mmHg. When gastric and intestinal O2 uptake were plotted as a function of blood flow, the O2 uptake vs. blood flow relationship were shifted down and to the right by hemodilution. Hemodilution also linearized the O2 uptake vs. blood flow relationship in the intestine. However, when O2 uptake was plotted as function of O2 delivery, the gastric O2 uptake vs. delivery curves at the two hematocrits were superimposed on each other, but the O2 uptake vs. delivery curves for the intestine diverged except at low rates of O2 delivery. We conclude that by reducing the O2-carrying capacity of the blood, hemodilution adversely affects gastric and intestinal oxygenation. Our results also indicate that hemodilution lowers gastric O2 uptake by reducing O2 delivery; however, hemodilution lowers intestinal O2 uptake not only by reducing O2 delivery but also by impairing O2 extraction.