Aspects of the spinal cord circulation as assessed by intrathecal oxygen tension monitoring during various arterial interruptions in the pig

Objective: We sought to study the effect of various modes of interruption o f the spinal cord blood supply on intrathecal oxygenation. Methods: In 24 pigs intrathecal PO2, PCO2, and pH were continuously monitor ed with a multiparameter catheter (Paratrend 7, Biomedical Sensors; Diametr ics Medical, Inc, St Paul, Minn) during and after aortic crossclamping or s elective interruption of segmental arteries and proximal collateral circula tion. Results: Proximal aortic clamping (n = 6) produced complete ischemia, where as a second clamp close to the celiac trunk (n = 4) partly protected agains t spinal cord ischemia. This is explained by prevention of the steal phenom enon in the excluded part of the aorta. Adding clamps to the subclavian art eries (n = 6) created complete spinal ischemia as the collateral circulatio n was interrupted. In another group (n = 4) all segmental arteries below T5 were occluded with no reaction in the intrathecal variables. Additional se lective clamping of supreme intercostal arteries (n = 4) showed the relativ e importance of the subclavian and vertebral collateral pathways. Conclusions: Continuous intrathecal PO2 was monitored during various modes of interruption of the spinal cord blood supply. This provided insight into the ischemia mechanisms and relative importance of the segmental contribut ion and proximal collateral pathways of the spinal cord circulation in pigs . A short literature review is given, and aspects of comparative anatomy ar e discussed.