Hyperoxic ventilation increases the tolerance of acute normovolemic anemia in anesthetized pigs.

OBJECTIVE

To investigate the impact of prophylactic hyperoxic ventilation with Fio2 0.6 on the physiologic limit of acute normovolemic anemia.

DESIGN

Prospective, controlled, randomized experimental study.

SETTING

Experimental animal laboratory of a university hospital.

SUBJECTS

Fourteen anesthetized domestic pigs.

INTERVENTIONS

Animals were randomly ventilated with either Fio2 0.21 (group 0.21, n = 7) or Fio2 0.6 (group 0.6, n = 7), and acute anemia was induced by isovolemic blood-for-hydroxy-ethylstarch (HES) exchange using a 6% HES solution (130/0.4).

MEASUREMENTS AND MAIN RESULTS

The blood-for-HES-exchange was continued until a sudden decrease of total body oxygen consumption indicated the onset of oxygen supply dependency (primary end point); the corresponding hemoglobin (Hb) concentration was defined as "critical" (Hb(crit)). Secondary end points were changes in myocardial function, central hemodynamics, oxygen transport, and tissue oxygenation. Compared with room air ventilation (Fio2 0.21), hyperoxic ventilation with Fio2 0.6 enabled a larger blood-for-HES-exchange (139%, 124/156) of circulating blood volume vs. 87% (68/94, p < .05), until Hb(crit) was reached (1.5 g/dL [1.4/2.1] vs. 2.4 g/dL [2.0/2.8], p < .05). At Hb 2.4 g/dL (i.e., Hb(crit) in group 0.21), animals of group 0.6 still presented with superior oxygen transport, tissue oxygenation, and hemodynamic stability. However, hemodynamic and oxygen transport variables were found deteriorated more severely at Hb 1.5 g/dL (i.e., Hb(crit) of group 0.6) compared with group 0.21 at Hb 2.4 g/dL.

CONCLUSION

During cell-free volume replacement, hyperoxic ventilation with Fio2 0.6 generates a readily usable plasmatic oxygen reserve and thereby increases the tolerance toward acute normovolemic anemia.