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　　Epidural anesthesia

　　Author's note: Next weeks we'll be discussing the epidural technique.

　　1.  How common is the formation of an epidural abscess following an epidural catheterization?
　　2.  How well does skin decontamination work?

　　最近我们将讨论硬膜外麻醉：

　　1、硬膜外穿刺置管术后发生硬膜外脓肿的几率？
　　2、怎样进行皮肤消毒最有效？

　　参考答案：

　　1、硬膜外穿刺置管术后发生硬膜外脓肿的几率？

　　Wang等[1]对硬膜外穿刺置管术后脊髓/硬膜外脓肿形成的文章进行了综述，而不管是否同时伴有脑膜感染。作者认为硬膜外穿刺置管术后脊髓/硬膜外脓肿形成的几率约为1：5000，对于免疫抑制或导管留置时间延长的患者发生硬膜外脓肿的几率更高。值得注意的是，35-82%的病例为医源性感染植入病原体S. aureus所致。诊断依靠临床表现、实验室检查、MRI或CT以及脊髓造影术。死亡率约为5-10%，治疗包括拔除导管、明确致病菌、外科解除脊髓压迫、延长抗生素治疗时间。作者因此建议，植入硬膜外导管时应严格执行无菌操作，使用一次性注射器及药物，每次注射必须使用硬膜外过滤器。此外，作者建议应每天更换穿刺部位敷料，并评价患者及穿刺部位情况。

　　2、怎样进行皮肤消毒最有效？

　　与硬膜外阻滞相关的硬膜外感染的机制尚不清楚，但是硬膜外脓肿部位的菌群与皮肤常驻菌群相同。对消毒的方法进行研究和比较，Sato等[2]对60名接受背部手术的患者进行研究，使用10%聚维酮碘（10%PI）或含0.5%洗必泰的80%酒精（0.5%CHE）消毒后发生皮肤感染，其对感染部位进行切皮取样69对样本。样本之一样本放入10ml的脑-心脏浸剂肉汤培养基中，放于37度空气中96h，另一份样本被切成3微米，用于革兰氏染色行显微镜检查。结果培养分离出13种革兰氏染色阳性的葡萄球菌属（表皮葡萄球菌69.2%；S. hyicus 15.4%；S. capitis 15.4%），其中使用10% PI消毒的34例中11例培养出葡萄球菌属（32.4%），而使用0.5% CHE消毒的35例中2例培养出葡萄球菌属（5.7%），差异有统计学意义（P < 0.01）。此外，使用10% PI和0.5% CHE消毒的34例和35例中分别有4例（11.8%）和5例（14.3%）显微镜下可见大量革兰氏阳性球菌。球菌在皮肤小囊和角质层形成致密菌落。对17，584个汗腺进行检查未发现有机体。作者得出结论，需要对消毒后切除部位皮肤的生物体进行隔离，尤其是使用10% PI消毒时。同时作者认为，硬膜外穿刺部位皮肤菌群的感染可能是硬膜外阻滞相关的硬膜外感染的潜在机制之一。

　　How common is the formation of an epidural abscess following an epidural catheterization?

　　Wang et al. (1) provides a good review of the literature relevant to the formation of spinal/epidural abscess with or without concurrent meningeal infection following epidural catheterization. The authors report that the incidence of spinal/epidural abscess is approximately 1:5000 catheterizations, with immunocompromised patients and those with prolonged catheter placements being considered more prone to developing an epidural abscesses. Of note, S. aureus, a pathogen that can be transmitted iatrogenically, is isolated in 35-82% of the cases. The diagnosis based upon clinical findings, laboratory studies and MRI or CT plus myelography. With a mortality of 5-10%, prompt treatment including removal of the catheter, microbiological studies, surgical decompression of the spinal cord, and prolonged antibiotic treatment is in order. The authors suggested that insertion of epidural catheters be performed under strict aseptic conditions, that disposable syringes and unbroken vials are used for each injection, and that epidural filters should be utilized for every administration. Moreover, the authors suggested that any dressing should be changed daily, in part to evaluate the patient and the insertion site.

　　How well does skin decontamination work?

　　The mechanism of epidural infection associated with epidural block is not clearly understood, however, the flora found in epidural abscesses have been identified as those resident on the native skin flora. Methods of disinfection have been developed and compared. Sato et al (2) excised 69 paired skin specimens after skin disinfection with 10% povidone-iodine (10% PI) or 0.5% chlorhexidine in 80% ethanol (0.5% CHE) from 60 patients having back surgery. One of the specimen pairs was placed in 10 ml brain-heart infusion broth and incubated in air at 37 degrees C for 96 h. The other specimen was sectioned at 3 microns and prepared with Gram's stain for microscopic examination. The authors isolated 13 gram-positive staphylococcal species (Staphylococcus epidermidis, 69.2%; S. hyicus, 15.4%; and S. capitis, 15.4%) from the cultures, especially from skin specimens disinfected with 10% PI versus 0.5% CHE (11 of 34 cultures [32.4%] vs. 2 of 35 cultures [5.7%]; P < 0.01). In addition, a number of gram-positive cocci were observed with the microscope in 4 (11.8%) and 5 (14.3%) of 34 and 35 skin specimens disinfected with 10% PI and 0.5% CHE, respectively. The cocci formed a dense colony in each follicle and in the stratum corneum. No organism was present in any of 17,584 sweat glands examined. The authors concluded that isolation of viable organisms from excised skin specimens after disinfection, especially with 10% PI, suggests that contamination of the epidural space by the skin flora may be a potential mechanism of epidural infection associated with epidural block. 

　　References:

　　1.  Wang LP, Schmidt JF. [Severe infections after epidural catheterization]. Ugeskr Laeger 1998;160(22):3202-6.
　　2.  Sato S, Sakuragi T, Dan K. Human skin flora as a potential source of epidural abscess. Anesthesiology 1996;85(6):1276-82.