The effects of the concentration and function of hemoglobin on the survival of rats after hemorrhage.

Hemodilutional techniques of resuscitation, which are becoming popular, add anemia to the acute increase in the affinity of hemoglobin for oxygen that occurs in massively transfused patients when old liquid stored blood is used. A model simulating these conditions was established in rats, using blood stored in citrate for different durations ("fresh" for 1 day, P50 of 34.5 torr, and "old" for 14 to 20 days, P50 of 23.5 torr). Animals were exchange transfused of 90% of the original red cell mass with fresh or old blood at one of three different hematocrits, then hemorrhaged and treated with the same blood used for exchange. There was little difference in survival throughout the range of hematocrits when fresh blood was used (10 of 17, 11 of 16, and 10 of 16 rats). Survival was significantly less in recipients of old blood at low hematocrits (five of 21), but not at higher hematocrits (nine of 19, eight of 14). Ability to salvage the most vulnerable subgroup was tested in rats exchange transfused with old blood at low hematocrits, hemorrhaged, and treated with fresh or old blood, each at low or high hematocrits. Again survival was comparable with fresh blood at low or high hematocrits and old blood at high hematocrits (15 of 20, 19 of 21, 18 of 25) but was lower with old blood at low hematocrits (12 of 24). These results indicate that the oxygen-delivering capacity of blood can become a limiting factor in promoting survival after hemorrhage in otherwise normal animals when it is reduced below half of normal by a combination of anemia and impaired function of hemoglobin. Above that level, fresh blood was more efficacious than old blood in this model.