* Professor, ‡ Associate Professor, Department of Anesthesiology and Perioperative Care, † Clinical Neurophysiologist, Division of Operating Room Services, University of California, San Francisco, San Francisco, California.
Anesthesiology. 2013 Nov;119(5):1109-19. doi: 10.1097/ALN.0b013e31829d4a92.
Transcranial motor-evoked potentials (TcMEPs) monitor spinal cord motor tract integrity. Using a swine model, the authors studied the effects of vasodilatory hypotension, hemorrhage, and various resuscitation efforts on TcMEP responses.
Twelve pigs were anesthetized with constant infusions of propofol, ketamine, and fentanyl. Animals were incrementally hemorrhaged, until bilateral tibialis anterior TcMEP amplitude decreased to less than 40% of baseline or until 50% of the blood volume was removed. Mean arterial pressure (MAP), cardiac output (CO), and oxygen delivery (DO2) were examined. Resuscitation with phenylephrine, epinephrine, and colloid were evaluated. In seven animals, vasodilatory hypotension was examined. Paired comparisons and multivariate analysis were performed.
Hemorrhage significantly reduced (as a percentage of baseline, mean±SD) TcMEPs (left, 33±29%; right, 26±21%), MAP (60±17%), CO (49±12%), and DO2 (43±13%), P value less than 0.001 for all. Vasodilation reduced MAP comparably, but TcMEPs, CO, and DO2, were not significantly lowered. After hemorrhage, restoration of MAP with phenylephrine did not improve TcMEPs, CO, or DO2, but similar restoration of MAP with epinephrine restored (to percentage of baseline) TcMEPs (59±40%), and significantly increased CO (81±17%) and DO2 (72±19%) compared with both hemorrhage and phenylephrine, P value less than 0.05 for all. Resuscitation with colloid did not improve TcMEPs. Multivariate analysis revealed that changes in TcMEPs were more closely associated with changes in CO and DO2 as compared with MAP.
Hypotension from hemorrhage, but not vasodilation, is associated with a decrease in TcMEP amplitude. After hemorrhage, restoration of TcMEPs with epinephrine but not phenylephrine indicates that CO and DO2 affect TcMEPs more than MAP. Monitoring CO may be beneficial in major spine surgery when using TcMEP monitoring.
经颅运动诱发电位（TcMEP）可监测脊髓运动束的完整性。作者使用猪模型研究了血管扩张性低血压、出血以及各种复苏措施对 TcMEP 反应的影响。
12 头猪在异丙酚、氯胺酮和芬太尼的持续输注下麻醉。动物逐渐出血，直到双侧胫骨前肌 TcMEP 幅度降低至基线的 40%以下，或直到 50%的血液量被抽出。检查平均动脉压（MAP）、心输出量（CO）和氧输送（DO2）。评估使用苯肾上腺素、肾上腺素和胶体进行的复苏。在 7 只动物中检查了血管扩张性低血压。进行了配对比较和多变量分析。
出血显著降低（相对于基线的百分比，均值±标准差）TcMEP（左侧，33±29%；右侧，26±21%）、MAP（60±17%）、CO（49±12%）和 DO2（43±13%），所有 P 值均小于 0.001。血管扩张同样降低了 MAP，但 TcMEP、CO 和 DO2 没有显著降低。出血后，用苯肾上腺素恢复 MAP 并不能改善 TcMEP、CO 或 DO2，但用肾上腺素恢复相同的 MAP 则恢复了 TcMEP（59±40%），并显著增加了 CO（81±17%）和 DO2（72±19%），与出血和苯肾上腺素相比，所有 P 值均小于 0.05。用胶体复苏并不能改善 TcMEP。多变量分析显示，与 MAP 相比，TcMEP 的变化与 CO 和 DO2 的变化更为密切相关。
出血引起的低血压，但不是血管扩张，与 TcMEP 幅度降低有关。出血后，用肾上腺素而不是苯肾上腺素恢复 TcMEP 表明，CO 和 DO2 对 TcMEP 的影响大于 MAP。在使用 TcMEP 监测时，在大型脊柱手术中监测 CO 可能是有益的。
