●Examination of spinal, epidural and neurostimulation needles used in the performance of different anesthetic techniques is relevant to the evaluation of the quality of such needles, as well as of the safety of the techniques and their complications [ 1 – 7 ].
● Needles can have imperfections in their tips. The presence of such imperfections may increase the degree of damage to tissues. Examining needles of this type at higher magnifications has the advantage of accurate identification of minute needle-tip defects, which include fissures seen along the surface of the needle tips. These fissures are generated during the production phase of spinal needles, more specifically in the polishing process. The resulting defect causes the needle tip to become more fragile. Examination of needle tips under scanning electron microscopy may be used to improve quality control of the needles used in regional anesthesia, and may help in setting standards to minimize or avoid the presence of imperfections in spinal needles.
●There are presently various types of neurostimulation needles. Few of these needles have noninsulated tips, but for some, only a minimal portion of the tip is noninsulated.
● Scanning electron microscopy may be a useful tool in the evaluation of quality controls and the establishment of standards for different products used in regional anesthesia. These techniques may help to reduce the presence of imperfections in these products, thus improving the safety and effi cacy of regional anesthesia techniques (Figs. 1.1 , 1.2 , 1.3 , 1.4 , 1.5 , 1.6 , 1.7 , 1.8 , 1.9 , 1.10 , 1.11 , 1.12 , 1.13 , 1.14 , 1.15 , 1.16 , 1.17 , 1.18 , 1.19 , 1.20 , 1.21 , and 1.22 ) [ 3 – 8 ].
1. Reina MA. Contribute of electron microscopy in regional anesthesia. Reg Anesth Pain Med Suppl. 2011;36:E81–5.
2. Reina MA, Lopez A, Badorrey V , De Andres JA, Martín S. Dura- arachnoid lesions produced by 22G Quincke spinal needles during a lumbar puncture. J Neurol Neurosurg Psychiatry. 2004;75:893–7.
3. Reina MA, De León Casasola OA, López A, De Andrés JA, Martín S, Mora M. An in vitro study of dural lesions produced by 25 gauge Quincke and Whitacre needles evaluated by scanning electron microscopy. Reg Anesth Pain Med. 2000;25:393–402.
4. Reina MA, López A, Machés F, De Leon Casasola O, De Andrés JA. Electron microscopy and the expansion of regional anesthesia knowledge. Tech Reg Anesth Pain Management. 2002;6:165–71.
5. Reina MA, Castedo J, López A. Cefalea pospunción dural. Ultraestructura de las lesiones durales y agujas espinales usadas en las punciones lumbares. Rev Arg Anestesiol. 2008;66:6–26.
6. Reina MA, De Andrés JA, López A. Subarachnoid and epidural anesthesia. In: Raj P , editor. Textbook of regional anesthesia. Philadelphia: Churchill Livingstone; 2002. p. 37–24.
7. López A, Reina MA, Machés F, De Leon Casasola O, De Andrés JA, García Trapero J. Electron microscopy in quality control of equipment used in regional anesthesia. Tech Reg Anesth Pain Management. 2002;6:172–9.
8. Reina MA, López A, De Andrés JA, Machés F. Possibility of nerve lesions related to peripheral nerve blocks. A study of the human sciatic nerve using different needles. Rev Esp Anestesiol Reanim. 2003;50:274–83.
●Anesthesiologists use different types of catheters in the performance of continuous regional anesthetic techniques such as epidural, subarachnoid, and paravertebral blocks, as well as peripheral nerve blocks.
●Epidural catheters may have a single distal orifi ce located at the tip of the catheter (open-end catheters) or three lateral orifi ces located lateral to the tip, which is closed and may be oriented in various positions. The use of subarachnoid catheters specifi cally designed for continuous regional anesthesia or analgesia is less frequent. In the past, the same type of epidural catheter was placed inside both the epidural and subarachnoid spaces. In the 1980s, special types of microcatheters were manufactured for continuous subarachnoid anesthetic techniques, but production of these types of catheters was discontinued in 1991, after cases of cauda equina syndrome had been reported following the use of this technique. At present, various types of subarachnoid catheters are manufactured. A few of these catheters are indicated for short-term placement (about 2 or 3 days) in surgical interventions and postoperative management of pain. Other catheters are designed with materials suitable for long-term placement lasting several months, such as in the management of chronic pain.
图 2.8 用于外周麻醉阻滞的导管。(a) 带有各自导管的针头 (a)；硬膜外导管 (b) 与沿导管 a 引入的外周导管 (c) 进行比较；外周导管 c 的探针 (d)。(b) 导管 a 放大倍数的细节。(c, d) 更高倍率的探针 d 的细节。扫描电子显微镜。放大倍数：a，×15；b , ×35; c , ×100; d , ×50
1. López A, Reina MA, Machés F, De Leon Casasola O, De Andrés JA, García Trapero J. Electron microscopy in quality control of equipment used in regional anesthesia. Tech Reg Anesth Pain Management. 2002;6:172–9.
●Lumbar punctures often are associated with unintentional paresthesias. The tip of the needle in contact with the spinal nerve root initiates depolarization of the axons, which the patient describes as electric shocks in the dermatomes innervated. The paresthesia is triggered by a mechanical stimulus along the axon [ 1 – 3 ].
●Most paresthesias are caused by puncturing of the cauda equina nerves rather than by inadvertent injection within the conus medullaris [ 4 ].
大多数感觉异常是由刺穿马尾神经引起的，而不是由无意中注射到脊髓圆锥内引起的 [4]。
●Paresthesias due to a traumatic lesion of the nerve have different consequences depending on the size of needle, the type of needle tip, and the depth of the lesion in the nerve root. The damage probably is greater when the roots are exposed to stretching or if the needle is introduced with excessive force. Because direct vision of structures within the spinal canal is not feasible, precise evaluation of the degree of damage to the nerves presently relies solely on clinical evaluation. In theory and based on “in vitro” studies, nerve penetration is possible with 25-gauge or even smaller needles [ 1 , 2 ].
●Nerve roots are located around the posterior area less frequently [ 5 , 6 ]. This anatomic consideration might be of interest during lumbar puncture procedures, because the spinal needle may advance a few millimeters inside the dural sac without increasing the risk of nerve root damage and paresthesias.
●During lumbar puncture, the needle enters the dural sac and progresses a few millimeters before reaching the surface of the nerve roots. As the needle advances, it may contact the nerves located toward the posterior aspect of the dural sac, which would correspond to centrally located nerves if the needle followed a sagittal plane. Otherwise, as the needle is diverted from the sagittal plane, it might pierce nerves lateral to the spinal cord. In patients without spine pathology, paresthesias may be caused by inadequate positioning of the patient during lumbar puncture, which often is associated with inadvertent rotation of the spinal column.
●After nerve root damage, it is diffi cult to determine the number of axons affected as well as the mechanisms of injury, namely compression or sectioning of the nerves, the latter of which is less frequent. Because there are vessels (small capillaries, arteries, or veins) inside as well as on the surface of nerve roots, the likelihood of intraneural hematomas should be considered. The process of reabsorption, infl ammatory cascade, and repair of nerve lesions may lead to local fi brosis and, therefore, chronic alteration of conduction in some axons.
1. Reina MA, De Andres J, Hernández JM, Navarro RA, Pastor J, Prats-Galino A. Looking for the development of paresthesias in the subarachnoid and epidural anaesthesia. A clinical and anatomical analysis. Reg Anesth Pain Med. 2011;36(Suppl):E17–22.
2. Reina MA, Lopez A, Villanueva MC, De Andrés JA. Possibility of cauda equina nerve root damage from lumbar punctures performed with 25-gauge Quincke and Whitacre needles. Rev Esp Anestesiol Reanim. 2005;52:267–75.
3. Palacio F, Reina MA, Fornet I, López A. Parestesias con diferentes técnicas de bloqueo subaracnoideo con una aguja 27-G. Rev Esp Anestesiol Reanim. 2007;54:529–36.
4. Reynolds F. Damage to the conus medullaris following spinal anaesthesia. Anaesthesia. 2001;56:238–47.
6. Cohen MS, Wall EJ, Kerber CW, Abitbol JJ, Garfi n SR. The anatomy of the cauda equina on CT scans and MRI. J Bone Joint Surg Br. 1991;73:381–4.
7. Reina MA, Machés F, López A, De Andrés JA. The ultrastructure of the spinal arachnoid in humans and its impact on spinal anesthesia, cauda equina syndrome and transient neurological syndrome. Tech Reg Anesth Pain Manag. 2008;12:153–60.
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