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The topic of question of day has been performed for many issues , which is a characterized program in our anesthesiology and pain block, we will improve it and make it more perfect in the future
This week we will discuss the topic about the possible reasons for failure to obtain CSF when performing the needle through needle technique of combined spinal epidural anesthesia, which is a common phenomenon in our practice

NO.24-Discuss the possible reasons for failure to obtain CSF when performing the needle through needle technique of combined spinal epidural anesthesia.
使用联合针进行腰硬联合麻醉时，无脑脊液流出的可能原因有哪些？

参考答案

使用联合针（针中针）进行腰硬联合麻醉时(CSE)，一般首先通过传统方法（通常使用阻力消失法）确定硬膜外间隙，再用腰麻针通过硬膜外针穿透硬膜，注入药物进行腰麻，然后拔出腰麻针，如常规硬膜外麻醉一样置入硬膜外管，此种腰麻针比普通的腰麻针要长一些。使用CSE麻醉时，尽管随后的硬膜外麻醉效果很理想，但腰麻时，未见脑脊液流出的几率大约5%。如果包括硬膜外置管（成功与不成功）在内，未见脑脊液流出的比率很高，最高可达到14%，可能有如下可能原因：
最简单的解释是腰麻时硬膜外针未在硬膜外间隙。腰麻针较硬膜外针长10-12 mm,此距离一般长于椎旁组织，但此时可能腰麻针未触及硬膜。
第二个可能原因是腰麻针越过硬膜外针的长度不足，腰麻针未触及硬膜。硬膜外间隙的前后距离一般为4-6 mm，但如果要腰麻针穿破硬膜，要求突出的针距要大于此长度，尤其使用中等钝性pencil-point腰麻针时更是如此。一项研究发现，在阻力消失后，如需获取脑脊液硬膜外针需前进0.5-1.5 cm。
另一较复杂的因素是硬膜外针长度的变异，此种变异可影响到腰麻针突出硬膜外针的长度。
此外，如果硬膜外针偏离了脊柱中线，腰麻针可能被置入了硬膜外旁间隙。
在两项研究中表明，侧卧位与坐位比较，获取脑脊液的失败率更高一些，这可能由于硬膜外针偏离了中线，或者侧卧位时脑脊液压力较低的缘故，脑脊液压力较低时，腰麻针更易于顶住硬膜，如帐篷状，而不宜于穿透硬膜。
另外，理论上存在这样的可能性，硬膜外针顶在硬膜上，而不是穿透硬膜，使硬膜圆锥的前后膜更加接近，甚至贴在一起，这样腰麻针可能刺穿硬膜外圆锥，达到硬膜外间隙的前侧。
In the needle-through-the-needle technique of combined spinal-epidural anesthesia (CSE), the epidural space is first localized by conventional means (usually by loss-of-resistance techniques). Then a spinal needle, somewhat longer than usual, is inserted through the epidural needle to achieve dural puncture and allow injection of the spinal portion of the block. The spinal needle is then removed and the epidural catheter passed as in a conventional epidural block. Failure to obtain CSF on passage of the spinal needle occurs in approximately 5% of CSE attempts in which the subsequent epidural block is found to be successful (1). A somewhat higher percentage of cases of failure to obtain CSF is observed (up to 14%) if all epidural placements (successful and unsuccessful) are included. There are several possible explanations:
The simplest explanation is that the epidural needle is not actually in the epidural space at the time of attempted spinal puncture. Extension of the spinal needle 10-12 mm (the usual distance reachable with the long spinal needle) beyond an epidural needle which is situated in paraspinous tissues would not be expected to hit the dural sac.
A second possibility is that the tip of the spinal needle does not extend far enough beyond the tip of the epidural needle to reach the dura. The average anterior-posterior dimension of the epidural space is 4-6 mm, but the amount of needle required to puncture the dura may exceed this, especially if modern blunter pencil-point needles are used. One study found that epidural needles needed to be advanced 0.5-1.5 cm after a loss of resistance in order to obtain CSF (2). The explanation for both of these findings may be tenting of the dura without puncture by a blunt-tipped needle.
A further complicating factor is variability in the length of epidural needles, which can vary the amount of spinal needle protruding beyond the end of the epidural needle.
Alternatively, if the epidural needle is angled off of midline with respect to the vertebrae, the spinal needle can be positioned into the lateral compartment of the epidural space.
It has been noted in two studies that the lateral position is more likely to result in a failure to obtain CSF than the sitting position. This may be due to misdirection off the midline of the epidural needle, or to lower CSF pressure in the lateral position.
(1). Another theory suggests that the tip of the epidural needle presses the dura mater without puncturing, thus bringing the anterior and posterior aspects of the dura closer together resulting in the spinal needle passing through the intrathecal space and exiting into the anterior epidural space
References:
1.Norris MC, Grieco WM, Borkowski M, et al.Complications of labor analgesia: epidural versus combined spinal epidural techniques. Anesth Analg 1994; 79:529-37.
2.Hollway TE, Telford RJ. Observations on deliberate dural puncture with a Tuohy needle: depth measurements. Anaesthesia 1991; 46:722-24.
3.Wildsmith JAW. Problems with combined spinal and epidural anesthesia. Regional Anesthesia and Pain Medicine 1998;23:388-9.