Effect of sodium nitroprusside on paraplegia during cross-clamping of the thoracic aorta.

Sodium nitroprusside (SNP) is usually used to control excessive proximal pressure after aortic cross-clamping. To assess the effect of SNP on circulatory dynamics, somatosensory evoked potentials, and neurologic outcome, 10 adult mongrel dogs that underwent 45 minutes of cross-clamping 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, respectively; p < 0.05) and the mean distal arterial pressures (15 +/- 3 mm Hg versus 23 +/- 1 mm Hg; p = 0.04). However, the electrical activity of the spinal cord, as indicated by the somatosensory evoked potentials, returned significantly faster in the nontreated group than in the SNP-treated group (15 +/- 9 versus 44 +/- 13 minutes; p < 0.05). Control animals exhibited a significantly better neurologic outcome and no paraplegia 24 hours postoperatively. We conclude that the use of SNP to treat excessive proximal hypertension may be detrimental to the spinal cord during cross-clamping of the thoracic aorta, resulting in a decline in the ischemic tolerance.