Abstract: Objective To understand the changes of the blood gas and the tissue hypoxia in rabbits during graded progressive hemorrhage.Methods The values of arteriovenous pH and PCO₂ gradients(AVpH and AVPCO₂) were compared with that of blood lactate in their relationship to changes in tissue oxygen delivery(DO₂) in 10 rabbits during graded progressive hemorrhage.Results AVpH,AVH⁺ and AVPCO₂ increased progressively as cardiac output(Qt) decreased,at the same time the blood lactate concentration increased.The relationship between cumulative blood loss,AVpH,AVH⁺,AVPCO₂ and blood lactate concentration was biphasic;In the early stage of hemorrhage,AVpH,AVH+,AVPCO₂ gradients and blood lactate concentration changed gradually and later these variables changed more rapidly.The inflection points in all cases were similar.The inflection point corresponds to the critical DO₂(DO₂-crit).Conclusion Rapidly expanding AVpH and AVPCO₂ indicates the onset of tissue hypoxia,which may serve as a repress reliable parameters of tissue hypoxia during hypoperfusion.

Key words: arteriovenous pH gradient, arteriovenous PCO₂ gradient, tissue hypoxia, hypoperfusion