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Case Reports  |   October 2004
Intraneural Injection during Anterior Approach for Sciatic Nerve Block
Author Affiliations & Notes
  • Xavier Sala-Blanch, M.D.
    *
  • Jaume Pomés, M.D.
  • Purificación Matute, M.D.
    *
  • Josep Valls-Solé, M.D.
  • Anna Carrera, M.D.
    §
  • Xavier Tomás, M.D.
  • Anna I. García-Diez, M.D.
  • * Staff Anesthesiologist, Especialista Senior, Department of Anesthesiology, Hospital Clínic, † Staff Radiologist, Especialista Senior, Unitat de Radiología osteomuscular, CDI, Hospital Clínic, ‡ Staff Neurologist, Consultor Senior, Unitat d’ Electromiografia, Hospital Clínic, § Associate Professor, Department of Anatomy and Human Embriology, University of Barcelona, Barcelona, Spain.
Article Information
Case Reports
Case Reports   |   October 2004
Intraneural Injection during Anterior Approach for Sciatic Nerve Block
Anesthesiology 10 2004, Vol.101, 1027-1030. doi:
Anesthesiology 10 2004, Vol.101, 1027-1030. doi:
DESPITE the technological advances in nerve approach and neurostimulation techniques, the percentage of nerve block procedure associated neuropathies has not decreased significantly. It is still between 1.7% and 1.9%.1,2 Use of nerve stimulation techniques do not guarantee avoidance of nerve puncture.3,4 Bearing these questions in mind, we devised a research protocol, which was approved by the Ethical Committee of our Hospital, in which we included a computerized tomographic (CT) scan examination with the aim of having better chances of avoiding vulnerable structures in the path of the needle from the skin to the nerve when using the anterior approach for sciatic nerve block. We describe two cases in which, after localizing the nerve with nerve stimulation, CT scanning revealed that the needle has been placed intraepineurally.
Case Report
A 75-yr-old woman, 75 kg, 158 cm, American Society of Anesthesiologists physical status III having a history of noninsulin-dependent diabetes mellitus treated with oral hypoglycemic agents was scheduled for transmetatarsal amputation of the right foot because of a severe vasculopathy. The patient gave her written informed consent to perform a continuous sciatic nerve block using the anterior approach.5 A CT image confirmed possible access to the sciatic nerve along an anatomical path that avoided contact with other significant structures (fig. 1). After setting up a peripheral blood access line, administering oxygen at a rate of 4 l/m, sedating the patient with 1 mg of midazolam, and anesthetizing the injection site with 3 ml of 1% mepivacaine we inserted the 100 mm stimulation needle (Plexolong®; Pajunk GmbH, Geisingen, Germany). Final position of the needle tip was determined by nerve stimulation. Nerve stimulation (Stimuplex® HNS 11; B Braun Melsungen AG, Melsungen, Germany) performed at a frequency of 2 Hz and pulse duration of 300 μs. The initial stimulation current intensity was set at 1.5 mA, and the needle was advanced until we observed a plantar flexion at a depth of 9 cm. Further advancement of the needle allowed a decrease in intensity to 0.3 mA, an intensity commonly used for administration of anesthetic near the nerve. After needle stabilization, we first administered 2 ml of 1.5% mepivacaine, which induced no pain or discomfort, followed by another 18 ml of mepivacaine to which we had added 1 ml of nonionic, iso-osmolar iodine contrast medium (Iohexol-Omnipaque® 300; Nycomed Ireland, LTD., Cork, Ireland) without resistance or pain. CT images showed contrast medium around the nerve and between nerve fascicles with a small bubble of entrapped air intraepineurally (fig. 2). Contrast medium showed along the entire 9.5-cm length of nerve explored (fig. 3). Normal flat nerve morphology before needle puncture changed to circular morphology after the injection (fig. 2). A catheter was inserted through the needle to a depth of 3 cm. A further dose of 10 ml of 1.5% mepivacaine mixed with 0.5 ml of iodine contrast medium was administered. Further scan sequences showed the catheter inside the epineurium (fig. 4). The catheter was left in place for 3 days after the surgical procedure to administer a continuous infusion of 0.2% ropivacaine at a rate of 5 ml/h. Motor and sensory functions of the foot recovered when the infusion was discontinued.
Fig. 1. Computed tomographic image of the lesser trochanter region for injection planning; a metallic marker shows the access to the normal flat sciatic nerve (white arrows)  .
Fig. 1. Computed tomographic image of the lesser trochanter region for injection planning; a metallic marker shows the access to the normal flat sciatic nerve (white arrows) 
	.
Fig. 1. Computed tomographic image of the lesser trochanter region for injection planning; a metallic marker shows the access to the normal flat sciatic nerve (white arrows)  .
×
Fig. 2. Computed tomographic image of the lesser trochanter region after injection of the anesthetic plus contrast medium. The contrast medium can be seen in the perineurium (white arrow) and between the nerve fascicles. A small air bubble can be seen inside the nerve (black arrow). The anterior-posterior and transversal diameter of the nerve is increased compared to that before injection  .
Fig. 2. Computed tomographic image of the lesser trochanter region after injection of the anesthetic plus contrast medium. The contrast medium can be seen in the perineurium (white arrow) and between the nerve fascicles. A small air bubble can be seen inside the nerve (black arrow). The anterior-posterior and transversal diameter of the nerve is increased compared to that before injection 
	.
Fig. 2. Computed tomographic image of the lesser trochanter region after injection of the anesthetic plus contrast medium. The contrast medium can be seen in the perineurium (white arrow) and between the nerve fascicles. A small air bubble can be seen inside the nerve (black arrow). The anterior-posterior and transversal diameter of the nerve is increased compared to that before injection  .
×
Fig. 3. Sagittal reformation showing the needle path from the anterior of the muscle to the nerve; the tip of the needle is marked with an arrow. The diffusion of the anesthetic plus contrast medium is also shown  .
Fig. 3. Sagittal reformation showing the needle path from the anterior of the muscle to the nerve; the tip of the needle is marked with an arrow. The diffusion of the anesthetic plus contrast medium is also shown 
	.
Fig. 3. Sagittal reformation showing the needle path from the anterior of the muscle to the nerve; the tip of the needle is marked with an arrow. The diffusion of the anesthetic plus contrast medium is also shown  .
×
Fig. 4. Location of catheter (white arrows). Injection of anesthetic plus contrast medium confirms that the catheter is inside the epineurium (black arrow)  .
Fig. 4. Location of catheter (white arrows). Injection of anesthetic plus contrast medium confirms that the catheter is inside the epineurium (black arrow) 
	.
Fig. 4. Location of catheter (white arrows). Injection of anesthetic plus contrast medium confirms that the catheter is inside the epineurium (black arrow)  .
×
Similar observations were made in another noninsulin-dependent diabetic woman with distal diabetic polyneuropathy and vasculopathy. She was 69 yr old, 53 kg, 152 cm, and ASA physical status III. In this patient, the depth of the needle was 9.5 cm, and the minimal stimulation intensity was 0.56 mA at pulse duration of 300 μs. The local anesthetic and contrast medium were administered following the same protocol as in the previous patient. A CT scan confirmed the diffusion of the contrast medium inside the nerve and along the entire length of 10 cm of explored nerve. The final administration trough the catheter of 10 ml dose of 1.5% mepivacaine mixed with 0.5 cm of iodine contrast medium showed its intraneural diffusion (fig. 5). At the end of the surgical procedure, motor and sensory functions recovered fully.
Fig. 5. Catheter (white arrow), epineurium (black arrows), and air bubble inside the epineurium, shown after catheter placement  .
Fig. 5. Catheter (white arrow), epineurium (black arrows), and air bubble inside the epineurium, shown after catheter placement 
	.
Fig. 5. Catheter (white arrow), epineurium (black arrows), and air bubble inside the epineurium, shown after catheter placement  .
×
Discussion
Several factors may contribute to postoperative nerve damage after performing peripheral nerve block anesthesia. Modern current nerve stimulators, such as those used in our case studies, allow for the more precise positioning of the needle electrodes and minimize the risk of errors resulting from a possible malfunction of the equipment during nerve stimulation. The electrical current applied to the nerve (electrical charge = nC) will depend on two settings controlled by the nerve stimulator: current intensity and duration of the stimulus (measured in mA and μs, respectively).1,6 In the above cases, stimulus duration of 300 μs was used and current intensity was varied. Minimal current intensities to produce motor responses in our patients were 0.3 mA (90 nC) and 0.56 mA (168 nC), which, according to the literature, are in the range of intensities used for infusion of the anesthetic near the nerve6 . Finally, a disappearance of muscular twitch with 2 ml of local anesthetic without inducing paresthesia or discomfort and the reappearance with increased voltage (negative Raj test7) indicates correct performance of the technique. However, several tests confirmed that the nerve was punctured and that the anesthetic was actually administered intraepineurally in both patients. CT images showed contrast medium inside the nerve. The contrast occupied the interfascicular space, and the catheter inserted through the stimulator needle was positioned inside the nerve.
The fact that these two patients were diabetic should be taken into account. However, diabetic polyneuropathy would affect the excitability of distal more than proximal parts of the nerve.8 Therefore, a proximal approach to the sciatic nerve in a diabetic patient might not be expected to theoretically significantly alter the response to stimulation.8 
Nerve stimulation can induce specific motor responses. Nevertheless, because of the random distribution of nerve fibers into fascicles, the specific muscle group activated may vary among patients. Induction of specific movements may also be the consequence of selective stimulation of nerve fascicles if the needle has been placed intraneurally through the epineurium.
The structure of the sciatic nerve is different from other nerves. It has a thick, well-formed epineurium that covers two main nerve branches, the tibial and the peroneal nerves.9 These two nerves are functionally and structurally separate but share a common epineurium. These structural characteristics may explain why, for this specific nerve, to achieve nerve stimulation at the usual clinical intensities, the needle may have to go through the epineurium. As Vloka et al.  9 suggest, injecting the anesthetic within the epineural adventitia causes the contrast medium to spread into the epineurium around the perineurium that surrounds the fascicles. This procedure is different from an “intrafascicular” injection, which could indeed induce nerve damage. Vloka et al.  9 performed their studies in embalmed cadavers, in which the neural fascia might have suffered structural changes. This intraepineural adventitial administration explains the diffusion of the contrast medium observed in our two patients. The study by Reina et al.  10 suggested that by inserting the needle into the epineurium of the sciatic nerve, nerve damage may occur because the fascicles can be “easily touched.” However, the strong sheath of the perineurium is different from the loose tissue framework of the interfascicular epineurium. After puncture of the epineural adventitia the needle probably enters the nerve but separates the fascicles rather than punctures them. CT images showed that the local anesthetic diffused within the intraneural space as well as outside the epineurum. This may be the result of a partial administration of the anesthetic inside and outside because of needle displacement or of the retrograde flow from intraneural space.
The two cases described here demonstrate that, when using a nerve stimulation guided approach, puncture of the sciatic nerve can occur and the local anesthetic can be injected intraneurally (inside the epineurium). Although such procedure did not induce any noticeable nerve damage in the reported patients, intraneural administration of local anesthetic should be avoided. More extensive studies on the sciatic nerve as well as other peripheral nerves are indicated to improve our understanding of this phenomenon.
References
De Andres J, Sala-Blanch X: Peripheral nerve stimulation in the practice of brachial plexus anesthesia: a review. Reg Anesth Pain Med 2001; 26:478–83De Andres, J Sala-Blanch, X
Fanelli G, Casati A, Garancini P, Torri G: Nerve stimulator and multiple injection technique for upper and lower limb blockade: Failure rate, patient acceptance, and neurologic complications. Study Group on Regional Anesthesia. Anesth Analg 1999; 88:847–52Fanelli, G Casati, A Garancini, P Torri, G
Urmey WF, Stanton J: Inability to consistently elicit a motor response following sensory paresthesia during interscalene block administration. Anesthesiology 2002; 96:552–4Urmey, WF Stanton, J
Choyce A, Chan VWS, Middleton WJ, Knight PR, Peng P, McCartney CJL: What is the relationship between paresthesia and nerve stimulation for axillary brachial plexus block? Reg Anesth Pain Med 2001; 26:100–4Choyce, A Chan, VWS Middleton, WJ Knight, PR Peng, P McCartney, CJL
Beck GP: Anterior approach to sciatic nerve block. Anesthesiology 1963; 24:222–4Beck, GP
Koscielniak-Nielsen ZJ, Rassmussen H, Jepsen K: Effect of impulse duration on patient’s perception of electrical stimulation and block effectiveness during axillary block in unsedated ambulatory patients. Reg Anesth Pain Med 2001; 26:428–33Koscielniak-Nielsen, ZJ Rassmussen, H Jepsen, K
Raj P, Rosenblatt R, Montgomery SJ: Use of nerve stimulator for peripheral blocks. Reg Anesth 1980; 5:14–21Raj, P Rosenblatt, R Montgomery, SJ
Patel J, Tomlinson DR: Nerve conduction impairment in experimental diabetes-proximodistal gradient of severity. Muscle Nerve 1999; 22:1403–11Patel, J Tomlinson, DR
Vloka JD, Hadzic A, Lesser JB, Kitain E, Geatz H, April EW, Thys DM: A common epineural sheath for the nerves in the popliteal fossa and its possible implications for sciatic nerve block. Anesth Analg 1997; 84:387–90Vloka, JD Hadzic, A Lesser, JB Kitain, E Geatz, H April, EW Thys, DM
Reina MA, López A, De Andrés JA, Machés F: Posibilidad de lesiones nerviosas relacionadas con los bloqueos nerviosos periféricos. Un estudio en nervio ciático humano con diferentes agujas. Rev Esp Anestesiol Reanim 2003; 50:274–83Reina, MA López, A De Andrés, JA Machés, F
Fig. 1. Computed tomographic image of the lesser trochanter region for injection planning; a metallic marker shows the access to the normal flat sciatic nerve (white arrows)  .
Fig. 1. Computed tomographic image of the lesser trochanter region for injection planning; a metallic marker shows the access to the normal flat sciatic nerve (white arrows) 
	.
Fig. 1. Computed tomographic image of the lesser trochanter region for injection planning; a metallic marker shows the access to the normal flat sciatic nerve (white arrows)  .
×
Fig. 2. Computed tomographic image of the lesser trochanter region after injection of the anesthetic plus contrast medium. The contrast medium can be seen in the perineurium (white arrow) and between the nerve fascicles. A small air bubble can be seen inside the nerve (black arrow). The anterior-posterior and transversal diameter of the nerve is increased compared to that before injection  .
Fig. 2. Computed tomographic image of the lesser trochanter region after injection of the anesthetic plus contrast medium. The contrast medium can be seen in the perineurium (white arrow) and between the nerve fascicles. A small air bubble can be seen inside the nerve (black arrow). The anterior-posterior and transversal diameter of the nerve is increased compared to that before injection 
	.
Fig. 2. Computed tomographic image of the lesser trochanter region after injection of the anesthetic plus contrast medium. The contrast medium can be seen in the perineurium (white arrow) and between the nerve fascicles. A small air bubble can be seen inside the nerve (black arrow). The anterior-posterior and transversal diameter of the nerve is increased compared to that before injection  .
×
Fig. 3. Sagittal reformation showing the needle path from the anterior of the muscle to the nerve; the tip of the needle is marked with an arrow. The diffusion of the anesthetic plus contrast medium is also shown  .
Fig. 3. Sagittal reformation showing the needle path from the anterior of the muscle to the nerve; the tip of the needle is marked with an arrow. The diffusion of the anesthetic plus contrast medium is also shown 
	.
Fig. 3. Sagittal reformation showing the needle path from the anterior of the muscle to the nerve; the tip of the needle is marked with an arrow. The diffusion of the anesthetic plus contrast medium is also shown  .
×
Fig. 4. Location of catheter (white arrows). Injection of anesthetic plus contrast medium confirms that the catheter is inside the epineurium (black arrow)  .
Fig. 4. Location of catheter (white arrows). Injection of anesthetic plus contrast medium confirms that the catheter is inside the epineurium (black arrow) 
	.
Fig. 4. Location of catheter (white arrows). Injection of anesthetic plus contrast medium confirms that the catheter is inside the epineurium (black arrow)  .
×
Fig. 5. Catheter (white arrow), epineurium (black arrows), and air bubble inside the epineurium, shown after catheter placement  .
Fig. 5. Catheter (white arrow), epineurium (black arrows), and air bubble inside the epineurium, shown after catheter placement 
	.
Fig. 5. Catheter (white arrow), epineurium (black arrows), and air bubble inside the epineurium, shown after catheter placement  .
×