Distribution of renal cortical and Medullary tissue oxygenation in hemorrhagic shock

Renal cortical and medullary tissue oxygen tension, systemic oxygen supply as well as central and renal hemodynamics were investigated in dogs during graded hemorrhage and subsequent reinfusion of shed blood. The measurements of tissue gas tension were carried out by means of implanted Silastic tubes. The baseline renal cortical PO2 was 35 mmHg and the corresponding medullary PO2 25 mmHg. The lowest mean cortical and medullary oxygen tensions--8 and 12 mmHg, respectively--were recorded during the severest hypotension at 40% blood loss. After reinfusions of shed blood the cortical PO2 underwent a transient increase to the original preshock level decreasing slowly thereafter. Concomitantly, the medullary PO2 reached the prehemorrhage value remaining then stationary until the end of the experiment. Arterial blood PO2 was normal throughout the study. Renal venous PO2 fell during the deepest shock but consistently exceeded the corresponding tissue PO2 levels. It is concluded that hemorrhagic hypotension impaired tissue oxygenation of both cortex and medulla, the effect being greatest in the cortex.