Since then, numerous clinical reports have described the use of CSF drainage in humans undergoing TAAA repair (reviewed by Ling, 2000 [Ling and Arellano, 2000]). Normal CSF pressure in humans has been documented to be approximately 13 to 15 mmHg (Drenger et al., 1997). Increased CSF pressures of 21 to 25 mm Hg have been demonstrated with aortic cross clamping (Drenger et al., 1997; WADA et al., 2001) . It has been advocated therefore to drain CSF in a controlled manner to maintain CSF pressure at approximately 10 mm Hg during TAAA repair (Carroccio et al., 2003). A prospective randomized controlled trial by Svensson et al. demonstrated a 12% (2 of 17) incidence of neurologic deficit in patients treated with CSF drainage compared to a 44% (7 of 16) incidence in the control group (p=0.0392) (Svensson et al., 1998). A more recent prospective randomized controlled trial of 145 patients by Coselli et al. demonstrated with an intent-to-treat analysis a significant reduction in paraplegia with CSF drainage to keep the CSF pressure around 10 mmHg (Coselli et al., 2002). Neurologic deficits occurred in 2 of 82 patients (2.7%) undergoing CSF drainage and 9 of 74 patients (12.2%) in the control group (p=0.026), representing an 80% reduction in relative risk. Both of these prospective randomized studies were terminated early at a planned interim analysis due to the significant benefit demonstrated by CSF drainage. Of note, complications related to the CSF drainage, such as headache, meningitis, or subdural hemorrhage were not observed in these studies.