From the *Department of Anesthesiology, Hospital for Special Surgery, New York, New York; †Department of Anesthesiology, Universitá degli Studi di Firenze, Florence, Italy; ‡Department of Public Health, Weill Medical College of Cornell University, Hospital for Special Surgery, New York, New York; and §Department of Anesthesiology, University of California and Veterans Affairs Medical Center, San Diego, California.
Anesth Analg. 2016 Jan;122(1):226-33. doi: 10.1213/ANE.0000000000000985.
Hypotensive epidural anesthesia (HEA), as practiced at our institution, uses sympathetic blockade to achieve mean arterial blood pressure (MAP) of ≤50 mm Hg while administering epinephrine by infusion to support the circulation. HEA has not been associated with gross adverse effects on neurologic outcome or cognitive function in the postoperative period, suggesting adequate cerebral blood flow (CBF). However, the use of MAPs well below the commonly accepted lower limit of CBF autoregulation suggests that CBF should be significantly reduced below normal levels. To examine these conflicting hypotheses, we performed a prospective investigation of the effects of HEA on CBF velocity (CBFV), an accepted index of cerebral perfusion.
Fifty-two hip replacement patients were studied. HEA was induced by lumbar epidural injection of local anesthetic and infusion of epinephrine to achieve an MAP of ≤50 mm Hg. Propofol/midazolam sedation was administered. Baseline CBFV was recorded pre-HEA (after sedation and before local anesthetic injection) and continuously thereafter.
During HEA, MAP decreased by 40% and was stable throughout. The CBFVmean at baseline and at 3 HEA intervals during surgery was 46 ± 12 (SD), 45 ± 12, 47 ± 14, and 47 ± 14 cm·s, respectively. Although mean CBFVmean did not vary, there was considerable heterogeneity among patients. Twelve patients (23%) experienced reductions of CBFVmean of >20% during HEA intervals (99% lower confidence limit: 9%) and 6 (12%) reductions of >30% (99% lower confidence limit: 1%). There was no correlation between CBFVmean and MAP for MAPs between 100 and 40 mm Hg (R = 0.0015, P = 0.44). There were no instances of gross postoperative neurologic injury.
Both hypotheses proved partially correct. CBFV was sometimes well maintained during HEA, despite MAPs well below the commonly accepted lower limit of autoregulation. However, there was considerable interindividual heterogeneity with 23% of subjects having CBFV reductions >20% (99% lower confidence limit: 9%), with some reductions approaching the threshold for ischemic injury. The present data do not allow us to determine whether hypotension would be similarly tolerated in other circumstances.
我院采用的降压硬膜外麻醉（HEA）通过交感神经阻滞使平均动脉血压（MAP）降至≤50mmHg，并通过输注肾上腺素来维持循环。HEA 并未导致术后神经系统结局或认知功能出现明显的不良影响，这表明脑血流（CBF）充足。然而，MAP 明显低于公认的 CBF 自动调节下限，这表明 CBF 应明显低于正常水平。为了检验这些相互矛盾的假设，我们前瞻性地研究了 HEA 对 CBF 速度（CBFV）的影响，这是一种公认的脑灌注指标。
52 例髋关节置换患者参与了本研究。通过腰椎硬膜外注射局麻药和输注肾上腺素将 MAP 降至≤50mmHg 来诱导 HEA。给予异丙酚/咪达唑仑镇静。在 HEA 之前（镇静后和局部麻醉注射前）记录基线 CBFV，并在之后连续记录。
在 HEA 过程中，MAP 下降了 40%，且一直保持稳定。手术期间，基线时和 3 个 HEA 间隔的 CBFVmean 分别为 46±12（SD）、45±12、47±14 和 47±14cm·s。尽管平均 CBFVmean 没有变化，但患者之间存在相当大的异质性。12 名患者（23%）在 HEA 间隔期间经历了 CBFVmean 的下降超过 20%（99%置信下限：9%），6 名患者（12%）经历了下降超过 30%（99%置信下限：1%）。在 100-40mmHg 的 MAP 范围内，CBFVmean 与 MAP 之间没有相关性（R=0.0015，P=0.44）。没有出现明显的术后神经损伤。
两个假设都部分成立。尽管 MAP 明显低于公认的自动调节下限，但 CBFV 在 HEA 期间有时仍能得到很好的维持。然而，个体间存在很大的异质性，23%的患者 CBFV 下降超过 20%（99%置信下限：9%），有些下降接近缺血损伤的阈值。目前的数据还不能确定低血压在其他情况下是否也能得到类似的耐受。
