INTRATHECAL MAGNESIUM-SULFATE PROTECTS THE SPINAL-CORD FROM ISCHEMIC-INJURY DURING THORACIC AORTIC CROSS-CLAMPING

Background: Paraplegia is a known complication after surgery on the de scending thoracic aorta. Thoracic aortic crossclamping causes an incre ase in proximal aortic and cerebrospinal fluid pressures. Sodium nitro prusside, though effectively decreasing proximal aortic pressure, has been implicated in worsening the incidence of paraplegia by further in creasing cerebrospinal fluid pressure and decreasing distal blood pres sure, thereby reducing spinal cord perfusion pressure. Intravenous adm inistration of magnesium sulfate has been shown to offer some spinal c ord protection when used with mild hypothermia. This study investigate d the effect of intrathecal magnesium on the prevention of paraplegia when sodium nitroprusside is used to control proximal hypertension dur ing thoracic aortic cross-clamping in a dog model of spinal cord ische mia. Methods: Two groups of eight dogs underwent thoracic aortic cross -clamping via a small thoracotomy incision for 45 min. Proximal, dista l, and central venous pressures and cerebrospinal fluid pressures were monitored. Temperature was maintained at 36 degrees C. Sodium nitropr usside was used to control proximal hypertension. The control group re ceived no magnesium sulfate, and a second group received 3 mg/kg intra thecal magnesium sulfate before thoracic aortic crossclamping. The dog s were neurologically evaluated 24 h later by an observer blinded to t he dogs' group. Spinal cord segments were obtained for histologic exam ination. Results: Proximal mean arterial pressure, cerebrospinal fluid pressure, spinal cord perfusion pressure, and central venous pressure were not statistically different between the two groups. Neurologic o utcome, however, was statistically different between the groups. None of the eight dogs in the magnesium group had any measurable neurologic injury, in contrast to the control group, in which seven of the eight dogs had severe neurologic injury (P < 0.005). Post mortem histologic data supported these findings. Conclusions: Intrathecal magnesium can prevent spinal cord injury despite markedly negative spinal cord perf usion pressure during thoracic aortic cross-clamping in a canine model of spinal cord ischemia.