Simpson J I, Eide T R, Schiff G A, Clagnaz J F, Hossain I, Tverskoy A, Koski G
Department of Anesthesiology, Long Island Jewish Medical Center, New Hyde Park, New York 11402.
Anesthesiology. 1994 Dec;81(6):1493-9; discussion 26A-27A.
Paraplegia is a known complication after surgery on the descending thoracic aorta. Thoracic aortic cross-clamping causes an increase in proximal aortic and cerebrospinal fluid pressures. Sodium nitroprusside, though effectively decreasing proximal aortic pressure, has been implicated in worsening the incidence of paraplegia by further increasing cerebrospinal fluid pressure and decreasing distal blood pressure, thereby reducing spinal cord perfusion pressure. Intravenous administration of magnesium sulfate has been shown to offer some spinal cord protection when used with mild hypothermia. This study investigated the effect of intrathecal magnesium on the prevention of paraplegia when sodium nitroprusside is used to control proximal hypertension during thoracic aortic cross-clamping in a dog model of spinal cord ischemia.
Two groups of eight dogs underwent thoracic aortic cross-clamping via a small thoracotomy incision for 45 min. Proximal, distal, and central venous pressures and cerebrospinal fluid pressures were monitored. Temperature was maintained at 36 degrees C. Sodium nitroprusside was used to control proximal hypertension. The control group received no magnesium sulfate, and a second group received 3 mg/kg intrathecal magnesium sulfate before thoracic aortic cross-clamping. The dogs were neurologically evaluated 24 h later by an observer blinded to the dogs' group. Spinal cord segments were obtained for histologic examination.
Proximal mean arterial pressure, cerebrospinal fluid pressure, spinal cord perfusion pressure, and central venous pressure were not statistically different between the two groups. Neurologic outcome, 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.
Intrathecal magnesium can prevent spinal cord injury despite markedly negative spinal cord perfusion pressure during thoracic aortic cross-clamping in a canine model of spinal cord ischemia.
截瘫是降主动脉手术后已知的并发症。胸主动脉交叉钳夹会导致近端主动脉压和脑脊液压力升高。硝普钠虽然能有效降低近端主动脉压，但因进一步升高脑脊液压力和降低远端血压，从而降低脊髓灌注压，被认为会使截瘫发生率恶化。静脉注射硫酸镁与轻度低温联合使用时已显示出对脊髓有一定保护作用。本研究在脊髓缺血犬模型中，探讨了在胸主动脉交叉钳夹期间使用硝普钠控制近端高血压时，鞘内注射镁对预防截瘫的作用。
两组各8只犬经小切口开胸进行胸主动脉交叉钳夹45分钟。监测近端、远端和中心静脉压以及脑脊液压力。体温维持在36摄氏度。使用硝普钠控制近端高血压。对照组未接受硫酸镁，另一组在胸主动脉交叉钳夹前接受3mg/kg鞘内硫酸镁注射。24小时后由对犬分组不知情的观察者对犬进行神经学评估。获取脊髓节段进行组织学检查。
两组之间近端平均动脉压、脑脊液压力、脊髓灌注压和中心静脉压无统计学差异。然而，两组之间的神经学结果有统计学差异。镁组的8只犬均无任何可测量的神经损伤，而对照组的8只犬中有7只出现严重神经损伤（P<0.005）。死后组织学数据支持这些发现。
在脊髓缺血犬模型中，尽管胸主动脉交叉钳夹期间脊髓灌注压明显为负，鞘内注射镁仍可预防脊髓损伤。
