EFFECT OF SODIUM-NITROPRUSSIDE ON PARAPLEGIA DURING CROSS-CLAMPING OFTHE THORACIC AORTA

Sodium nitroprusside (SNP) is usually used to control excessive proxim al pressure after aortic cross-clamping. To assess the effect of SNP o n circulatory dynamics, somatosensory evoked potentials, and neurologi c out-come, 10 adult mongrel dogs that underwent 45 minutes of cross-c lamping of the thoracic aorta were randomly assigned to receive either 50 mg/kg of SNP or no treatment for excessive proximal hypertension. There was a statistically significant difference noted between the SNP -treated animals and the control animals in terms of the proximal mean arterial pressures (112 +/- 13 versus 142.2 +/- 15 mm Hg, respectivel y; p < 0.05) and the mean distal arterial pressures (15 +/- 3 mm Hg ve rsus 23 +/- 1 mm Hg; p = 0.04). However, the electrical activity of th e spinal cord, as indicated by the somatose somatosensory evoked poten tials, returned significantly faster in the nontreated group than in t he SNP-treated group (15 +/- 9 versus 44 +/- 13 minutes; p < 0.05). Co ntrol animals exhibited a significantly better neurologic outcome and no paraplegia 24 hours postoperatively. We conclude that the use of SN P to treat excessive proximal hypertension may be detrimental to the s pinal cord during cross-clamping of the thoracic aorta, resulting in a decline in the ischemic tolerance.