There is a high incidence of
paraplegia associated with thoracic aortic cross-clamping, even when
cardiopulmonary bypass or shunts are used. In 56 adult baboons, spinal cord blood flow (SCBF), vascular anatomy, and
paraplegia rates were evaluated. Tissue blood flow was measured by radioactive
microspheres. Various procedures were used to increase SCBF and to prevent
ischemia-reperfusion injury. It was found that the rate of
paraplegia was inversely correlated with neural tissue
ischemia (SCBF) and directly correlated with reperfusion
hyperemia. Two methods completely prevented
paraplegia. These two methods were a thoracic shunt with occlusion of the infrarenal aorta or
cerebrospinal fluid drainage plus intrathecal
papaverine injection, both of which were associated with an increased SCBF. Furthermore,
papaverine dilated the anterior spinal artery (ASA) (p = 0.007) and increased the blood flow through the lower ASA. Whereas procedures utilizing a
calcium channel blocker (
flunarizine),
allopurinol,
superoxide dismutase (SOD),
laminectomy alone, and a thoracoabdominal shunt not perfusing the arteria radicularis magna (ARM) all failed to prevent
paraplegia,
allopurinol (p = 0.026) and SOD (p = 0.004) did prevent gastric stress lesions, indicating that their failure to prevent
paraplegia was not due to a lack of activity. Of great clinical interest is that, if a shunt is used and the ARM is perfused, infrarenal aortic cross-clamping increases SCBF, thus preventing
paraplegia. Intrathecal application of
papaverine proved to be even more effective in increasing SCBF and also completely prevented
paraplegia. As this is a safer procedure than the insertion of shunts, this is the method of choice for the prevention of
paraplegia associated with thoracic aortic cross-clamping. The preliminary trial using intrathecal
papaverine in human beings has thus far shown no adverse side effects from the
drug, and no
paraplegia has occurred.