Ultrasound-Guided Peripheral Nerve Block in the Anesthetic Considerations for Vascular Surgery – An Alternative Choice for Neuroaxial Anesthesia Techniques

Abdominal aortic aneurysm, with its incidence approaching approximately 8% in the population, accounts for more than 8,000 deaths annually in the United States. It is a multifactorial disease associated with atherosclerosis. Age, male gender, smoking, and the family history of abdominal aortic aneurysm are thought to be the risk factors for the disease (Ashton et al., 2002, Fleming et al., 2005). The natural history of abdominal aortic aneurysm is characterized by the progressive enlargement of the aneurysm, which ultimately leads to the rupture and the subsequent death of the patient. The aorta wall consists of a thin intima, a thick tunica media, and an adventitia, composed of endothelium for a thin intima, smooth muscle layers for a thick tunica media, and a connective tissue including the vasa vasorum and nervi vascularis for the adventitia, respectively. The wall of aorta is particularly vulnerable to an injury owing to the continuous exposure to high pulsate blood pressure and shear stress. Once degenerated which most commonly occurs by atherosclerosis, cystic medial necrosis, a condition in which the collagen and elastic fibers in the tunica media of the aorta are degenerated and replaced by the mucoid connective tissues, will immediately take place. It will subsequently result in the circumferential weakness, dilatation, and as a consequence, the development of aneurysm. The other etiological conditions that lead to the development of aneurysm include some hereditary basis such as Marfan’s and Ehlers-Dnlos syndromes, the infection including syphilis and tuberculosis, and vasculitis associated with autoimmune diseases such as Takayasu’s arteritis and rheumatoid arthritis (White et al., 1993, Shah et al., 1997). The prognosis of abdominal aortic aneurysm is strongly correlated with the size of aneurysm, and the risk of rupture is 1-2% for 5 years for an aneurysm less than 5cm in diameter, whereas it is more than 20-40% for those more than 5cm in diameter. Hence, an elective operation is indicated if the diameter of aneurysm is >5.5cm (Sakalihasan et al., 2005).

Shortly after the introduction of EVAR in the treatment of abdominal aortic aneurysm, general anesthesia was preferentially used for the anesthetic management of EVAR because of the following reasons; 1.The first generation device had required the induced hypotension technique during the deployment of the graft.2. The procedure times were often long.3. The considerable number of patients had required conversion to open repair during the EVAR procedure.However, as the second-generation fully stented modular stent graft had come to be widely used, which, through the refinement of the first-generation brand, do not require the induced hypotension technique during the deployment of the graft, and as the physicians had gained the experiences with newer generation devices, which subsequently resulted in the shorter procedure times, a variety of regional anesthesia techniques has come to be used.These techniques include paravertebral peripheral nerve block, spinal anesthesia, continuous spinal anesthesia, epidural and combined spinal anesthesia, and regional anesthesia.Owing to the serious comorbidities of the patients who are undergoing EVAR procedure, the use of less invasive anesthetic techniques for the anesthetic management of EVAR, such as regional anesthesia techniques, has been shown to result in the lower perioperative mortality, reduced ICU admission and stay, reduced hospital length of stay, and the reduced rate of early complications (Asakura et al. 2009b, Asakura, 2010a, Ruppert et al, 2006, Verhoeven et al., 2005).The use of neuroaxial anesthesia including epidural and spinal anesthesia may have potentially beneficial effects on patients such as the suppression of the surgical stress, positive effect on post-operative nitrogen balance, and reduced blood loss, these advantages are often counterbalanced by the increased risk of developing subdural and epidural hematoma in patients undergoing EVAR who are frequently medicated with anticoagulants pre-operatively and with the use of heparin during the surgical procedure (Asakura et al. 2008a, Asakura, et al. 2009b, Asakura, 2010a, Park et al., 2001).The incidence of development of hematoma associated with the use of neuroaxial anesthesia is relatively low and is estimated to be approximately 1:150,000-1:200,000 in normal individuals (Horlocker et al., 2000).Although it is difficult to precisely ascertain the relative risk of the incidence of subsequent development of epidural/subdural hematoma in the population who is undergoing anticoagulant therapy, the consensus statement regarding the use of neuroaxial anesthesia and the concomitant use of anticoagulant drugs has been recently provided from the American Society of Regional Anesthesia, given the considerable number of case reports published thus far reporting the development of epidural hematoma in whom an anticoagulation therapy was administered (Horlocker et al., 2010).Bleeding in the neuroaxial space which most commonly occurs in an epidural space due to the presence of prominent venous plexus, is a potentially catastrophic complication of neuroaxial anesthesia, and the only minor proportion of patients fully recovered neurologically after the prompt diagnosis and the immediate decompression laminectomy.Among 61 cases of spinal hematoma that had been previously reported in the review of literature, 25 of those had received intravenous or subcutaneous injection of heparin.Furthermore, 5 additional cases had undergone vascular surgery, which means that they were treated with heparin intra-operatively (Vandermeulen et al. 1994).Hence, nearly a half of reported cases were associated with the use of heparin.Although the use of neuroaxial anesthesia in patients who are going to receive heparin is not totally contraindicated, the consensus statement suggests that the careful cautions must be paid in patients receiving neuroaxial anesthesia who are treated with anticoagulant medications (Horlocker et al. 2010).

Peripheral nerve block; an alternative for neuroaxial anesthesia in the anesthetic management of EVAR
An alternative regional anesthesia technique that can be used is peripheral nerve blockade (PNB), which has been shown to provide an effective unilateral analgesia with a fewer serious neurological complications even with the use of heparin (Asakura, et al, 2008a, Gray, 2006).Historically, the technique of peripheral nerve block appeared in the early 20 th century, but the needle advancement was guided by mostly the knowledge of anatomy.Hence, the rate of success was limited, and it was somewhat like an art of the skilled hands.However, as a result of the advance of ultrasound machine technology (Asakura, et al., 2008b), the anesthesiologists come to perform peripheral nerve block with more than 90% rate of success virtually without any complications.As such, ultrasound-guided peripheral nerve block has come to gain popularity recently worldwide (Marhofer et al. 2007).

Lumbar plexus block for the anesthetic management of EVAR
During the surgical procedure of EVAR, skin incisions are made in the groin areas to gain the access to the common iliac arteries.The nerve to the lower extremity and groin areas are supplied from the lumbar and sacral plexus (Fig. 1).The plexus runs between the psoas major muscle and the quadrates lumborum muscle which is termed as the psoas compartment.The lumbar plexus is formed from ventral rami with L1-4 in addition to the various types of additional contribution from T12 and L5.The branches of lumbar plexus form iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral, and obturator nerves.The first lumbar ventral ramus supplies iliohypogastric and ilioinguinal nerves.The genitofemoral and the lateral femoral cutaneous nerves originate from the second ramus.The femoral nerve is formed from the united ventral rami of L2-4.From the anterior division of L2-4, the obturator nerve is formed.The psoas compartment block is usually performed by advancing the needle into the space between the psoas major and the quadrates lumborum muscles, and the once the plexus is approached, a large volume of local anesthetics is injected which subsequently anesthetize the hip and anterolateral thigh.For the standard lumbar plexus block, the patient is usually placed in the lateral decubitus position, with the hip fixated and the operative side uppermost.The block is conducted by the standard nerve stimulation method (Asakura, et al., 2008a).A 21-gauge 100-mm-long needle is advanced perpendicular to the skin until it contacts to the transverse process of the 5 th lumbar spine.A nerve stimulator is set to deliver 0.5-1.0mAcurrent impulse at 2Hz.By further advancing the needle, the localization of the lumbar plexus is confirmed by identifying the contraction of the quadriceps femoris (Asakura, et al., 2008a, Capdevila, et al., 2002).Following the confirmation of the negative aspiration of blood and the cerebrospinal fluids, a large volume of local anesthetics are usually injected.The procedure has been traditionally carried out by the nerve stimulation method under the confirmation of the landmarks of the body.After confirming the top of the iliac crest, a line is drawn to the spinous process of the 4 th lumbar spine.Classically, a textbook describes to advance the needle 5cm lateral to the midline of the spine on this line.However, a considerable number of serious complications associated with the use of lumbar plexus block, such as intrathecal injection, epidural injection, inadvertent vascular puncture, and retroperitoneal bleeding (Aida et al., 1996, Aveline et al., 2004, Ludot, et al., 2008, Weller, et al., 2003) have been reported.These complications have, at least in part, resulted from the depth of the plexus inside the body, which also makes it difficult to perform ultrasound-guided lumbar plexus block partly owing to the presence of bony structures.In particular, the use of heparin during the surgical procedures of EVAR makes the retroperitoneal bleeding as the serious complication with the use of lumbar plexus block, although the complication is often self-limiting in contrast to the bleeding in neuroaxial space, which often results in the inreversible neurological damage.Hence, we analyzed the computed tomography of the consecutive patients in our facility that had undergone any elective surgery and characterized the precise localization of the lumbar plexus at the fourth lumbar spine level in the Japanese population.
In the study, axial transverse sections of computed tomography of the fourth lumbar spine level were used to measure the following distances; a distance from the skin to the transverse process, a distance from the skin to the lumbar plexus nervous trunks, a distance from the median sagital plane to the lumbar nerve trunks, and a distance from the skin to the lateral border of psoas major muscle (Fig. 2).On the basis of cadaver study, the lumbar plexus was identified to run between the fleshy slip of the main part of psoas major and the accessory part of the psoas that constitutes the posterior part of the psoas major muscle (Kirchmair et al., 2001).These two parts of the muscle fuses to form the psoas major.The femoral nerve and the lateral femoral cutaneous nerve run inside a thin fascia at the level of the junction of the posterior third and the anterior two-thirds of the muscle.In the measurements made from the computed tomography, the junction of the posterior third and anterior two-third of the psoas major was used as the plane of the femoral nerve (Fig. 3).Fig. 2. The following variables were measured; 1)The distance from the skin to the transverse process, 2) The distance from the skin to the femoral nerve, 3) The distance from the median sagital line to the femoral nerve, 4) The distance from the median sagital line to the lateral border of the psoas major muscle.

Anatomical localization of the lumbar plexus in the Japanese population
Although several literatures have described the anatomical localization of lumbar plexus thus far, no similar information in the Japanese population is totally lacking (Farny et al., 1994, Kirchmair et al., 2001).The present study was undertaken in order to precisely identify www.intechopen.comUltrasound-Guided Peripheral Nerve Block in the Anesthetic Considerations for Vascular Surgery -An Alternative Choice for Neuroaxial Anesthesia Techniques 143 the anatomical localization of the lumbar plexus in the Japanese population.The study included 100 Japanese adult patients (59 males and 41 females) who had undergone any elective surgical procedure in our facility.The measurements of the distance from the skin to the transverse process, the distance from the skin to the femoral nerve, the distance from the median sagital plane to the femoral nerve, and the distance from the median sagital plane to the lateral border of the psoas major muscle in the Japanese population are significantly smaller than those described previously in the Canadian population, which presumably had made the procedure to be complicated-prone one (Farny et al., 1994).In their report, the distance from the skin to the transverse process in the Canadian females was reported to be 70±13mm and the distance from the skin to the transverse process in the Canadian males was 75±22mm.By contrast, in our hands, the same distance that corresponds to the Japanese male was 49.32mm (median: 47, range: 30-72mm), and that corresponds to the Japanese female was 48.41mm (median: 47, range: 25-86mm) (Fig. 4).Similarly, the average distance from the skin to the femoral nerve in the Canadian males and females were reported to be 99±21mm and 90±14mm, respectively, whereas that corresponds to the Japanese males was 66.6mm (median: 64, range: 64-90mm), and that to the Japanese female was 65.9mm (median: 66, range: 50-80mm) (Fig. 5).The distance from the median sagital plane to the lateral border of the psoas muscle in the Canadian males and females were reported to be 72.7 ± 10mm and 60 ± 8mm, whereas those correspond to the Japanese males and females were 54.88mm (median: 55, range: 47-64), and 49.31mm (median: 50; range: 34-67mm) (Fig. 6).In addition, although there was no description regarding the distance from the median sagital plane to the femoral nerve in the Canadian population, we measured those variables in the Japanese males and females.The distance from the median sagital plane to the femoral nerve in the Japanese male was 34.47mm (median: 35, range: 27-42mm), and that corresponds to the Japanese female was 32.63mm (median: 32, range 27-45mm) (Fig. 7).Fig. 4. The distance from the skin to the transverse process in the Japanese males (n=59) and the Japanese females (n=41).Results are expressed by the box-and-whisker plots.
In the standard textbook in the field of anesthesiology, the needle is suggested to advance at the point 3cm caudal to the line connecting the both iliac crest and 5cm lateral to the median sagital line (Wedel et al., 2005).However, the average distance from the median sagital line to the lateral border of the psoas major muscle in the Japanese female is 49.31mm, and there is a substantial risk of peritoneal puncture in approximately a half of this population if the needle is advanced at the point described in the textbook.In addition, although the needle is suggested to advance until it contacts to the transverse process of the fifth lumbar spine, there is some possibility that the needle will not contact to the transverse process if it is advanced at the point where the textbook recommends.Moreover, the literature suggests that the nerve trunks are located approximately 90(female)-99(male) mm deep inside the body in the Canadian population (Farny et al., 1994).However, they are located far more superficial levels in the Japanese population (male; 66.6mm, female 65.9mm).Accordingly, there is a potential risk of peripheral nerve damage if the needle is advanced as suggested by the textbook.In the Japanese population, the nerve trunks are located approximately 30mm lateral from the median sagital line (male; 34.47mm, female; 32.63mm).Literature suggests that the development of inadvertent epidural spread occurs in approximately 9-16% of the patients, and this adverse event is attributable to the retrograde diffusion of the local anesthetics to the epidural space (Enneking, et al., 2005).Given the nearer distance from the median sagital line to the femoral nerve in the Japanese population than in the Caucasion population, it must be always kept in mind that the Japanese patients carry more risks of inadvertent epidural spread than those described in the textbook previously.

Examples that would develop serious complications following lumbar plexus block
Followings are the typical examples of the Japanese patients who would develop serious complications if the needle would have advanced as suggested by the textbook.Figure 8 shows the computed tomography at the 4 th lumbar supine level from the 70-year-old female.In this case, if the needle is advanced 5cm laterally from the median sagital line into the depth at 9cm level, the needle would puncture peritoneal cavity.Similarly, in cases which are shown in figure 9, 10, and 11, the inadvertent peritoneal puncture and possible colonic perforations would have developed if the needle had been advanced as suggested by the textbook.In figure 12 and 13, the left kidney has descended as low as to the 4 th lumbar supine level.In these cases, if the needle was advanced as suggested by the textbook, inadvertent renal puncture would have developed.
In figure 14 and 15, inferior vena cava is present 3cm laterally from the median sagital line at the depth of 9cm from the skin.Thus, if the needle would have advanced 3cm laterally from the median sagital line, there would be the risk of inadvertent inferior vena cava puncture, which may result in serious consequences such as retroperitoneal hematoma, and inadvertent vascular injection of local anesthetics.From our observations, we suggest that the needle should be advanced 32 (female)-35 (male) mm laterally from the median sagital line in the Japanese population.If the needle puncture point is more than 5cm laterally from the median sagital line, there is a risk of inadvertent peritoneal puncture.In addition, the nerve trunks of lumbar plexus present at the depth of 64-66mm inside the body from the skin.

Ultrasound-guided lumbar plexus block
Lastly, the possibility of ultrasound-guidance for lumbar plexus block is going to be discussed.With the aid of ultrasound, it has come to be feasible to directly visualize the peripheral nerves, the needle, and the spread of local anesthetics.The ultrasoundguidance for peripheral nerve block has been shown to be efficacious in femoral nerve block, sciatic nerve block, brachial plexus block, and peripheral nerves of body trunks (Asakura, et al., 2010a, Asakura, et al., 2010b, Gray, 2006).However, bony structure has a high absorption coefficient of ultrasound, which makes the ultrasound-imaging of lumbar plexus limited in resolution, in addition to the location of nerve trunks deep inside the body.In general, the visualization of nerve structures by ultrasound requires the use of high frequency probes offering high-resolution images.However, the higher the frequency is, the smaller the penetration depth would be (Marhofer et al., 2007).In other words, for the blockade of nerves located deep inside the body, the ultrasound probes with lower frequency are required, which often are insufficient for offering highresolution images required for identifying nerve structures.In the standard textbook in the field of anesthesiology, there are subtitles dealing with ultrasound-guided supraclavicular and interscalene brachial plexus block, infraclavicular block, axillary block, ilioinguinal block, femoral nerve block, and sciatic nerve block, but no single description of ultrasound-guided lumbar plexus block (Gray, 2005).The first attempt to identify the structures of lumbar plexus by ultrasound using a curved array transducer with a frequency at 4 MHz appeared in 2001 using the healthy volunteers (Kirchmair et al., 2001).They reported the successful identification of psoas muscle, erector spinae, and quadratus lumborum muscle by ultrasonography but not the nerve structures of lumbar plexus.Shortly thereafter, an attempt of ultrasound-guided lumbar plexus block using cadavers appeared from the same group, which confirmed the feasibility and accuracy of ultrasound guidance in advancing the needle to the psoas major muscle, but again without identifying the nerve structures (Kirchmair et al., 2002).Hence, the knowledge of anatomical localization of the nerve structures of the lumbar plexus would appear to be the prerequisite for performing the "ultrasound-assisted" lumbar plexus block.In 2004, however, the successful identification of the nerve trunks of lumbar plexus in the pediatric cases has been reported (Kirchmair et al., 2004).The successful identification of the lumbar plexs in these pediatric cases had resulted from the superficial localization of the nerve trunks, which allowed the researchers to utilize the higher frequency (5-8MHz) transducer ultrasound equipments.So far, the direct visualization of the nerve trunks of lumbar plexus in adult cases appears to be unsuccessful.However, by combining the nerve stimulation in addition to the ultrasound assistance, the identification of lumbar plexus becomes feasible even in adult cases (Asakura et al., 2008a).More importantly, the direct visualization of the adjacent structures such as the kidneys by ultrasound may prevent an inadvertent renal puncture or peritoneal puncture and hence may reduce the incidence of the development of complications associated with the lumbar plexus block.

Conclusion
Endovascular aortic aneurysm repair has provided a substantial improvement in the perioperative patients' outcome including 30-day peri-operative mortality as compared with the traditional open surgical vascular reconstruction largely owing to its less invasive nature, especially in those whom serious comorbidities are present.In order to reduce the substantial risks associated with the anesthesia for EVAR in such seriously comorbid patients, various attempts have thus far been made.Particularly, the use of loco-regional anesthesia technique is a promising way to reduce the risks associated with the use of general anesthesia, such as the reduction in the incidence of development of respiratory complications.However, obstacles have also been met especially with the use of neuroaxial anesthesia because of the increased risks of developing subdural/epidural hematoma.Peripheral nerve block is the possible promising alternative for the use of neuroaxial anesthesia.During the surgical procedures of EVAR, skin incisions are made in the groin areas in order to gain the access to the femoral arteries.Anesthesia at the groin areas can be obtained by the posterior lumbar plexus block, which is traditionally approached by the nerve stimulation method.In comparison with the Caucasian population, the nerve trunks of lumbar plexus are located far more superficial and far more close to the median sagital plane in the Japanese and possibly in Asian populations.In order to prevent the potential risks of inadvertent renal and peritoneal puncture as well as inadvertent epidural spread, the lumbar plexus block should be carried out with the assistance of ultrasound-guidance.
Fig. 5.The distance from the skin to the femoral nerve in the Japanese males (n=59) and females (n=41).

Fig. 6 .
Fig. 6.The distance from the median sagital line to the lateral border of the psoas major muscle in the Japanese males (n=59) and females (n=41).

Fig. 7 .
Fig. 7.The distance from the median sagital line to the femoral nerve in the Japanese males (n=59) and females (n=41).

Fig. 8 .
Fig. 8.The computed tomography of a 70-year-old female at the 4 th lumbar spine level.Note that if the needle had advanced as suggested by the textbook, it would have punctured the peritoneal cavity.
Fig. 9. Computed tomography of the 4 th lumbar spine level from a 37-year-old female.

Fig. 10 .
Fig. 10.Computed tomography of the 4 th lumbar spine level from a 70-year-old female.Similarly, the needle would have penetrated the peritoneal cavity if the needle had been advanced as suggested by the textbook.

Fig. 11 .
Fig. 11.The computed tomography at the 4 th lumbar spine from a 74-year-old female.
Fig. 12. Computed tomography of the 4 th lumbar spine level from a 62-year-old female.

Fig. 13 .
Fig. 13.Computed tomography of the 4 th lumbar spine level from a 62-year-old female.In these two cases, if the needle had been advanced as suggested by the textbook, an inadvertent renal puncture would have developed.

Fig. 14 .
Fig. 14.The computed tomography at the 4 th lumbar spine level from a 90-year-old female.Inferior vena cava is distended (indicated by the arrow), and there is a potential risk of inadvertent inferior vena cava puncture in this case.

Fig. 15 .
Fig. 15.The computed tomography at the 4 th lumbar spine level from a 76-year-old female.In this case, inferior vena cava is laterally deviated (indicated by the arrow), and there is a potential risk of inadvertent inferior vena cava puncture.