This study cannot be powered to test for a statistical effect on clinically evident paraplegia as its frequency in our institution is 5% thus at our current activity of 30 cases per year of TAA and ..??… cases of thoracic stents., the study would need to run over 5 years. The numbers are sufficient to demonstrate a significant change in the relatively common end-points noted below. This study therefore serves to prove the utility of acetazolamide in modifying factors we consider influential in the development of paraplegia. Should this study prove positive we aim to roll out to an international multicentre study to test for clinical effectiveness in reducing paraplegia.