Renal lactate extraction as an indicator of tissue hypoxia in haemorrhagic hypotension.

The interrelation between the renal cortical pO2 and renal fractional extraction of arterial lactate was investigated in dogs subjected to gradual haemorrhage up to 45-50% of their blood volume. The cortical pO2, measured by means of an implanted Silastic tube, responded immediately to graded haemorrhage. The renal lactate extraction increased parallel with the arterial lactate concentration when the cortical pO2 declined from the mean initial value of 36 mmHg to 15 mmHg. A further decline of the cortical pO2 was followed by a sharp fall in the renal lactate extraction. A decrease in lactate extraction correlated closely with the cortical pO2 below 15 mmHg during severe hypoperfusion. These results suggest that the changes in the renal lactate utilization are independent of the tissue oxygen tension until the cortical pO2 decreases to the level at which the renal metabolism becomes limited by the availability of oxygen. Below this cortical pO2 the renal lactate extraction decreases in proportion to the developing tissue hypoxia.