Lumbar and thoracic spinal cord oxygen tension during aortic cross-clamping

In order to investigate the changes in tissue oxygen and the efficiency of the collateral circulation in the different regions of the spinal cord (SC) during aortic occlusion, surface PO2 (sPO2) was measured on the exposed SC in the pig in the lumbar (L3-5) as well as in the thoracic (Th6-8) parts before, during and after a 45 minute occlusion. The pigs were divided into two groups: group IA: cross-clamping of the aorta immediately below the left subclavian artery; group II: occlusion of the aorta immediately above the arteria radicularis magna anterior (ARMA). In response to occlusion, the sPO2 distal to the occlusion always decreased significantly (group IA: mean lumbar sPO2 from 42.3 mm Hg to 3.2 mm Hg, mean thoracic sPO2 from 34.9 mm Hg to 3.9 mm Hg; group II: mean lumbar sPO2 from 28.0 mm Hg to 7.9 mm Hg). Mean thoracic sPO2 in group II remained constant. No statistically significant differences between the distal regions could be established. The collateral circulation in the thoracic as well as in the lumbar region was insufficient at least during occlusion.