TRIMETHAPHAN VERSUS SODIUM-NITROPRUSSIDE FOR THE CONTROL OF PROXIMAL HYPERTENSION DURING THORACIC AORTIC CROSS-CLAMPING - THE EFFECTS ON SPINAL-CORD ISCHEMIA

Sodium nitroprusside (SNP) has been used to control the proximal hyper tension associated with thoracic aortic cross-clamping (TACC) during t horacic aortic surgery. It worsens neurologic outcome, presumably by f urther decreasing distal arterial pressure and increasing cerebrospina l fluid (CSF) pressure, thereby worsening the spinal cord perfusion pr essure (SCPP). Trimethaphan does not increase CSF pressure. Therefore, the present study investigates the effect of trimethaphan versus SNP to control proximal hypertension during TACC on neurologic outcome. Tw o groups, each with eight mongrel dogs, were studied. All animals unde rwent descending TACC for 45 min. The mean proximal aortic blood press ure was maintained at 95-100 mm Hg by the use of SNP or trimethaphan. Distal aortic pressure was allowed to vary. The dogs were neurological ly evaluated 24 and 48 h later by a blinded observer. During cross-cla mping, there was no difference in mean proximal aortic pressure betwee n groups. After 10 min of cross-clamping, distal aortic pressure was h igher (P < 0.01), CSF pressure was lower (P < 0.01), and SCPP was high er (P < 0.005) in the trimethaphan group as compared with the SNP grou p (group effect). Neurologic outcome as assessed by Tarlov's score was better at 24 and 48 h in the trimethaphan group (P < 0.05). Histopath ologic injury trended with worsened neurologic outcome. We conclude th at 1) trimethaphan produced higher SCPP than SNP, and 2) neurologic ou tcome was better in the trimethaphan group.