The limit of anemia tolerance during hyperoxic ventilation with pure oxygen in anesthetized domestic pigs.

Background: During acellular replacement of an acute blood loss, hyperoxic ventilation (HV) increases the amount of O-2 physically dissolved in the plasma and thereby improves O-2 supply to the tissues. While this effect could be demonstrated for HV with inspiratory O-2 fraction (FiO(2)) 0.6, it was unclear whether HV with pure oxygen (FiO(2) 1.0) would have an additional effect on the physiological limit of acute normovolemic anemia. Methods: Seven anesthetized domestic pigs were ventilated with FiO(2) 1.0 and subjected to an isovolemic hemodilution protocol. Blood was drawn and replaced by a 6% hydroxyethyl starch (HES) solution (130/0.4) until a sudden decrease of total body O-2 consumption (VO2) indicated the onset of O-2 supply dependency (primary endpoint). The corresponding hemoglobin (Hb) concentration was defined as ` critical Hb' (Hb crit). Secondary endpoints were parameters of myocardial function, central hemodynamics, O-2 transport and tissue oxygenation. Results: HV with FiO(2) 1.0 enabled a large blood-for-HES exchange (156 +/- 28% of the circulating blood volume) until Hb crit was met at 1.3 +/- 0.3 g/dl. After termination of the hemodilution protocol, the contribution of O 2 physically dissolved in the plasma to O-2 delivery and VO2 had significantly increased from 11.7 +/- 2 to 44.2 +/- 9.7% and from 29.1 +/- 4.2 to 66.2 +/- 11.7%, respectively. However, at Hb crit, cardiovascular performance was found to have severely deteriorated. Conclusion: HV with FiO(2) 1.0 maintains O-2 supply to tissues during extensive blood-for-HES exchange. In acute situations, where profound anemia must be tolerated (e.g. bridging an acute blood loss until red blood cells become available for transfusion), O-2 physically dissolved in the plasma becomes an essential source of oxygen. However, compromised cardiovascular performance might require additional treatment. (C) 2013 S. Karger AG, Basel