每周一问(NO.92)：硬膜外麻醉(二)
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Epidural anesthesia
1. What patient factors make performing an epidural technique difficult?
2. What technical factors make performing an epidural technique difficult?
3. What makes the epidural technique difficult to learn and perform?
硬膜外麻醉：
1、硬膜外麻醉困难的患者因素有哪些？
2、硬膜外麻醉困难的技术因素有哪些？
3、为什么硬膜外麻醉技术很难学习和掌握？
参考答案：
1、 硬膜外麻醉困难的患者因素有哪些？
Sprung等[1]通过对595名实施椎管内麻醉的患者进行研究，试图发现患者个体特点在预测椎管内麻醉的困难程度中的作用。操作前，作者收集患者基本数据：体质（正常型、偏瘦型、肌肉型、肥胖型）、脊柱标志（佳=棘突容易触及、劣=棘突不易触及、差=棘突不能触及）、脊柱解剖（通过检查和体检分为正常或畸形）。操作的难易程度通过操作是否顺利来判断，即首次穿刺点成功、更换穿刺点成功、穿刺成功总的穿刺间隙数。
作者发现，穿刺部位间隙标志的清晰程度与操作的难易度最相关，而异常的脊柱解剖和体质也与之相关。因此，作者得出结论，患者背部操作间隙的清晰程度和明显的解剖异常较之体质能更好的预测椎管内麻醉的难易程度。
2、 硬膜外麻醉困难的技术因素有哪些？
硬膜外麻醉操作成功因缺乏明确的指证（不像蛛网膜下腔麻醉可以观察到明确的脑脊液流出），因此造成操作上的困难。此外，阻力消失试验的异体反应也使得硬膜外技术很难学习和掌握。Hiemenz等[2]建立模型模拟进入硬膜外前、后力的变化，分析硬膜外穿刺针进入过程中阻力的变化，结果发现，个体内和个体间阻力的顺应性变化存在差异，以至于不能获取正常的顺应性。
虽然其它的一些因素如穿刺针的类型、穿刺入路等，也可能对穿刺造成影响，但是Sprung等[1]发现穿刺困难与下列因素无关：脊髓或硬膜外、入路、穿刺针类型或规格。令人惊讶的是，胸段硬膜外麻醉比腰段更容易。
3、 为什么硬膜外麻醉技术很难学习和掌握？
对局部麻醉技术的学习不同个体存在较大差异[3]。Konrad等[3]通过与臂丛阻滞、气管插管或动脉穿刺的比较发现，对第一年的麻醉科住院医生而言，硬膜外麻醉技术最难掌握。一些人将其归于该方法教学上本身就很难理解[3]，而另一部分人则认为硬膜外麻醉阻滞后效果的多变性是其原因[4]。Kopacz等[4]试图确定以前从未进行过类似操作的住院医生必须至少进行多少次操作训练后方能达到熟练掌握，他对所有开始CA-1的麻醉科住院医生（n=7）在其最初6个月实施的局部麻醉技术进行记录。作者通过客观的标准判断硬膜外、蛛网膜下腔麻醉操作及气管插管的成功率，如蛛网膜下腔麻醉操作获得脑脊液、硬膜外麻醉后出现随后的麻醉平面、气管插管后呼吸末CO2检测。作者发现，每一种技术得学习曲线类似。在20例蛛网膜下腔麻醉和25例硬膜外麻醉操作后曲线明显升高，然而，直到45例蛛网膜下腔麻醉和60例硬膜外麻醉操作后，方达到90%的成功率。近期对44所美国住院医生培训机构的调查表明，大多数毕业的住院医生达到了该标准，硬膜外麻醉的平均例数为150例[5]。
What patient factors make performing an epidural technique difficult?
Sprung et al. (1) in a study of 595 neuraxial blocks, attempted to determine whether any patient characteristics would be useful in predicting a difficult neuraxial block. Prior to the procedures, the authors collected demographic data, body habitus (normal, thin, muscular, obese), spinal landmarks (good = easily palpable spinous processes, poor = difficult to palpate spinous processes, none = unable to positively identify spinous processes), and spinal anatomy (assessed by inspection and examination as normal or deformed). Ease or difficulty of the placement was measured by whether the procedure was completed at the first (first-level success) or second spinal level and the total number of new skin punctures (attempts) necessary to complete the procedure.
The authors found that the quality of landmarks best correlated with technical difficulty as measured by both first-level success and number of attempts. Abnormal spinal anatomy and body habitus also correlated with difficulty, as measured by number of attempts. The authors concluded that an examination of the patient's back for the quality of landmarks and obvious anatomical deformity better predicts the ease or difficulty of neuraxial block than does body habitus.
What technical factors make performing an epidural technique difficult?
The lack of a definitive confirmatory sign (like CSF with a spinal technique) upon reaching the epidural space can contribute to difficulty in performing an epidural technique. In addition, the nonhomogenous response to loss of resistance techniques makes the epidural technique even more difficult to learn and perform. In an attempt to model the forces prior to and within the epidural space, Hiemenz et al.(2) analyzed the force resistance patterns obtained during the placement of an epidural needle. The authors discovered that the variance in compliance within and between individuals was so diverse, that a compliance normogram could not be derived.
Although other technical factors, like the type of epidural needle and the approach to the epidural space, have been suggested as making placements easier or more difficult, Sprung et al.(1) found no association between measures of placement difficulty and any of the following: spinal versus epidural, approach, needle type, or needle gauge. Perhaps surprisingly, thoracic epidurals were found to be less difficult than lumbar epidurals.
What makes the epidural technique difficult to learn and perform?
The learning of regional anesthetic techniques is a multidimensional function with wide intra- and interindividual scattering (3). When compared to placing a brachial plexus block, an endotracheal tube or an arterial line, Konrad et al. (3) noted that the epidural technique was the most difficult procedure for first year anesthesia residents to learn. While some have suggested that this was due to difficulties in teaching the block (3), others site the variability in exposure to the block (4). Kopacz et al. (4), in attempting to determine the minimum number of blocks a previously inexperienced resident must perform to reach consistency during training, recorded every regional anesthetic technique attempted by all beginning CA-1 anesthesiology residents (n = 7) during their first 6 months of training on a daily basis. Comparing epidural and spinal techniques and endotracheal intubation, the authors used the objective measures of success as obtaining cerebrospinal fluid during attempted spinal anesthesia, subsequent anesthetic block during epidural placement, and detection of end-tidal carbon dioxide for endotracheal intubation. The authors noted that learning curves for each technique were of similar shape, and significant improvement over baseline was noted after 20 spinal and 25 epidural anesthetics. However, a 90% success rate was not reached and maintained until 45 spinal and 60 epidural anesthetics are performed. Most graduating residents reach this number; a recent survey of 44 US residency programs noted that the cumulative experience of graduating residents was a median of 150 epidural anesthetics (5).
References:
1. Sprung J, Bourke DL, Grass J, et al. Predicting the difficult neuraxial block: a prospective study. Anesth Analg 1999;89(2):384-9.
2. Hiemenz L, Stredney D, Schmalbrock P.Development of the force-feedback model for an epidural needle insertion simulator. Stud Health Technol Inform 1998;50:272-7.
3. Konrad C, Schupfer G, Wietlisbach M, Gerber H. Learning manual skills in anesthesiology: Is there a recommended number of cases for anesthetic procedures? Anesth Analg 1998;86(3):635-9.
4. Kopacz DJ, Neal JM, Pollock JE. The regional anesthesia "learning curve". What is the minimum number of epidural and spinal blocks to reach consistency? Reg Anesth 1996;21(3):182-90.
5. Smith MP, Sprung J, Zura A, Mascha E, Tetzlaff JE. A survey of exposure to regional anesthesia techniques in American anesthesia residency training programs. Reg Anesth Pain Med 1999;24(1):11-6.
作者: 西门吹血
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