Cns Injury In Surgery Of The Descending Aorta

For some patients, up to 45 minutes of descending aortic occlusion is well tolerated, while in others paraplegia occurs after only 10 minutes. The discrepancy may be related to variability in the blood supply to the spinal cord. There are three major regions of blood supply: 1) cervical cord is supplied from the vertebral branch of the subclavian artery via the anterior spinal artery; 2) the mid-thoracic cord is supplied by spinal arteries rising from the level of about T7; 3) the lower cord is supplied from the large unpaired artery of Adamkiewitz arising in 90% of patients from T9 to L2 and in about 10% from T5 to T8. This contributes to the anterior spinal artery which can provide collateral circulation throughout the spinal cord. The anterior spinal artery can be continuous along the entire spinal cord or can be discontinuous. Anterior spinal occlusion causes paraplegia, incontinence, and loss of superficial sensation. Deep pin, vibration and position sensation, transmitted via the posterior columns, are preserved. If the anterior spinal artery is discontinuous, proximal occlusion can create ischemia and paraplegia. Intraoperative methods to determine spinal viability include so-matosensory evoked potentials and somatomotor evoked potentials. Some surgeons find them of limited use, however.

During cross-clamping of the descending aorta, extravascular conduits may be extremely helpful to protect the spinal cord. This includes left atrial-femoral arterial bypass, femoral-femoral bypass, or a passive shunt (Gott shunt from the proximal aorta to the distal aorta or to the femoral artery). In the case of aortic transection, however, none of these methods have been shown to definitively decrease the incidence of paraplegia.

Most often, however, if the cross-clamp time can be limited to less than 20 minutes, the "clamp and go" method is used without specific spinal protection methods other than speed of surgery. If the cross-clamp time exceeds 20-30 minutes, the incidence of paraplegia rises dramatically.

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