Reappraisal of the mechanism for cerebrospinal fluid hypertension during aortic surgery. Cerebrospinal fluid (CSF) hypertension during aortic surgery is a poorly understood, multifactorial event that may increase the risk of spinal cord injury. To assess the factors that may contribute to changes in CSF pressure during aortic surgery, measurements of ascending arterial and CSF pressures were made in 17 anesthetized mongrel dogs. Changes in CSF patterns were monitored under several conditions tested in random sequence. These included systemic hypertension produced by an infusion of phenylephrine, cross-clamping of the descending thoracic aorta, and manual, superior displacement of the transverse aortic arch (arch elevation), either alone or in conjunction with the cross-clamp. Hypertension, cross-clamping, and cross-clamping combined with arch elevation all produced significant increases in ascending mean arterial pressure (204 +/- 20, 170 +/- 8, and 158 +/- 11 mm Hg, respectively, vs. 117 +/- 8 mm Hg [control]; (p less than 0.01). Small, nonsignificant increases in CSF pressure were detected in the cross-clamp group, but none were detected with hypertension alone, despite significant increases in ascending arterial blood pressure in both groups. Thus, neither arterial hypertension nor cross-clamping alone could be demonstrated directly to cause significant CSF hypertension. However, when aortic elevation (displacement) was combined with cross-clamping, the rise in CSF pressure increased to significant levels, even though the ascending arterial hypertension was least severe in this group. In contrast, arch elevation alone did not produce any significant increase in ascending arterial pressure but did produce an approximately 114% increase in CSF pressure (15.2 +/- mm Hg vs. 7.7 +/- 1 mm Hg [control]; p less than 0.01. 