Hitchon P W, Lobosky J M, Yamada T, Johnson G, Girton R A
Department of Surgery, Veterans Administration Medical Center, Iowa City, Iowa.
Neurosurgery. 1987 Dec;21(6):849-57. doi: 10.1227/00006123-198712000-00011.
Although somatosensory evoked potentials are being used in the evaluation of spinal cord injury and the monitoring of cord function during surgical procedures, their limitations in the face of fluctuations in blood pressure await further clarification. To study the effect of hypotension upon spinal cord blood flow (SCBF) and spinal evoked potentials (SEPs), we subjected five anesthetized lambs to graded hypotension to a mean arterial pressure (MAP) of 80, 60, 40, and less than or equal to 30 mm Hg. Five animals served as controls. Maximal hypotension was associated with a significant decrease in renal and sciatic nerve blood flow of 83% and 77%, respectively. SCBF, on the other hand, showed no decrease with hypotension down to a MAP of 40 mm Hg. As hypotension progressed, a gradual but significant slowing in nerve conduction velocity was noted without alteration in the cord conduction velocity from L7 to L1. Control animals demonstrated a decline in sciatic nerve blood flow of 48%, without any change in latency or amplitude of nerve action potentials. These findings suggest that, in hypotension, the peripheral nerve (lacking autoregulation) becomes ischemic, resulting in slowing of nerve conduction velocity with an increase in latency and decrease in amplitude of SEPs. Cord conduction velocity, on the other hand, remains unchanged. Caution is advised in relying upon SEPs generated by peripheral nerve stimulation to monitor cord function in situations where profound hypotension is anticipated. Variations in SEPs may reflect alterations in the peripheral nerve and not the spinal cord.
尽管体感诱发电位正被用于脊髓损伤的评估以及手术过程中脊髓功能的监测，但其在面对血压波动时的局限性仍有待进一步阐明。为了研究低血压对脊髓血流（SCBF）和脊髓诱发电位（SEPs）的影响，我们对五只麻醉的羔羊进行了分级低血压处理，使其平均动脉压（MAP）分别降至80、60、40和小于或等于30 mmHg。五只动物作为对照。最大程度的低血压与肾血流和坐骨神经血流分别显著减少83%和77%相关。另一方面，在MAP降至40 mmHg的低血压过程中，SCBF并未减少。随着低血压的进展，观察到神经传导速度逐渐但显著减慢，而从L7到L1的脊髓传导速度没有改变。对照动物的坐骨神经血流减少了48%，神经动作电位的潜伏期或波幅没有任何变化。这些发现表明，在低血压状态下，外周神经（缺乏自身调节）会发生缺血，导致神经传导速度减慢，SEPs的潜伏期延长和波幅降低。另一方面，脊髓传导速度保持不变。在预期会出现严重低血压的情况下，依靠外周神经刺激产生的SEPs来监测脊髓功能时应谨慎。SEPs的变化可能反映的是外周神经的改变而非脊髓的改变。
