经颅多普勒超声在重型颅脑损伤病人中的应用

经颅多普勒超声在重型颅脑损伤病人中的应用 颅脑损伤病人受伤后早期是一个关键时期，因为此时期损伤脑组织的继发性缺血改变会使危险性增加。脑灌注压的监测在这个时期是非常重要的。一般来说，这需要进行有创的颅内压监测。而经颅多普勒超声(TCD)是一种无创、有效的监测脑血流变化的方法，对于重型颅脑损伤病人是推荐使用的。 【,,,】有文献报道，重型颅脑损伤后急性期继发性缺血损伤的发生率非常高。 【,】而且出现继发性缺血损伤的病人往往预后较差。因此，能建立足够的脑血流 【,，,,,,】灌注对于颅脑损伤病人是一个最重要的方面。这通常是通过脑灌注压监 【,，,,，,,】测来进行的，脑灌注压要维持在70mmHg以上。因为颅内压监测一般是有创的，因此容易产生感染和出血等并发症。并且，病人到达医院时，因为止血困难和时间不足而使得颅内压装置的放置被延误。 【,,】相对来说，TCD简便、无创，并且在急救情况下可以很快进行应用。但是，TCD监测的并不是脑血流量，而是通过脑基底动脉监测血流速率。Shigemori【,,】等人研究表明大脑中动脉的血流速率变化和大脑半球的脑血流量是紧密相关的。两者之间的关系取决于脑基底动脉的直径大小。例如，脑血管痉挛时由于血管收缩血流速率增加，同时实际血流量减少。 有些因素会影响血流速率的测定，例如接受超声波的角度，TCD搏动指数 【,,，,,】(PI)被认为对这些因素是不敏感的。PI可以反映脑血管的抵抗性。 【,,】Spyridon G等人研究表明脑灌注压小于70mmHg的病人比脑灌注压?70mmHg的病人有更高的搏动指数，并且PI对于较低的脑灌注压有很高的预测价值。颅内压升高或平均动脉压降低时脑灌注压会下降，而此时舒张期血流下降比收缩期 【,,，,,】更快。这就导致PI从正常值(?1)增加到2、3或者更多。一些研究将 【,,，,,，,,，,,，,,】PI和脑灌注压进行比较，发现二者密切相关。并且，在神经外 【,,，,,，,,】【,科病人中已经发现PI和颅内压之间呈线性或指数关系。有文献报道,，,,，,,】PI能帮助决定较低的自动调整的临界点。当脑灌注压到达可自动调整的低限时，PI开始迅速增加，而血管的抵抗性也达到低限。Chan和Lewis SB ,,,，,,,等人对重型颅脑损伤病人进行研究发现脑灌注压在可自动调整范围内(大于50mmHg)减少时，PI增加并不多。而脑灌注压在较低水平下降时，PI明显增 加。 【,,,,,】对于颅脑损伤病人，脑灌注压的最低界限为70mmHg。有文献报道脑 灌注压维持在70mmHg以上可以降低死亡率和改善生存质量。TCD波形显著受到 【,,】增高的颅内压或降低的脑灌注压影响。TCD由于其床旁的简便性，即使病人 在急诊室中，也可以马上应用并作出诊断。对于重型颅脑损伤病人需要早期而准 确的脑灌注压监测。通过TCD建立充足的脑灌注可以帮助决定用药时间。并且它 还可以帮助我们通过安全、无创的方法来预测病人的病情发展趋势。这些对于病 人的预后都是至关重要的。 参考文献 1. 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