Fundamentals of Regional Anesthesia Using Nerve Stimulation in the Dog

Introduction

The first demonstration of electrical nerve stimulation was performed as early as 1780 by Luigi Galvani on a frog. Galvani touched the nerves of the frog's spinal cord with metal electrodes which caused contractions of the leg muscles. Perthes in 1912 and Pearson in 1955 demonstrated that nerves could be identified by electrostimulation, but it was the work of Greenblatt et al. in 1962 [1] that introduced the nerve stimulator into clinical practice.

During the 1980’s, the characteristics of an ideal nerve stimulator were studied and defined [2,3]. The use of a nerve stimulator allows for exact needle location without eliciting paraesthesia [4]

Until very recently, regional techniques have been confined to neuraxial (epidural/ spinal) approaches. However, peripheral nerve blockade has been shown to provide effective analgesia with potentially less morbidity than neuraxial techniques [5]. Although controversial, a number of randomized controlled studies in people suggest that regional techniques provide superior pain relief, faster postoperative recovery and reduced hospital stay than do systemic opioids [6,7]. In studies comparing regional and general anaesthesia, more effort and more interventions are required during general anaesthesia than during regional anaesthesia to produce equivalent outcomes. But the important question is whether the benefits associated with regional anaesthesia lead directly to measurable clinical improvements such as lower mortality and morbidity rates and better outcome from surgery.

Possibly, the key features of regional anaesthesia, combined with new less invasive surgical techniques and ward routines (encouraging early nutrition, increased mobility), make it possible to reduce the incidence and severity of complications, delayed recovery and may reduce hospital stay.

Physiology of Electrical Nerve Stimulation

Electrical impulses reaching a nerve are transmitted along the nerve fibres. If the nerve contains motor fibres, the electrical current will induce axon membrane depolarization and contractions of the effector muscle will be observed. This is the underlying principle of electrical nerve stimulation utilised in peripheral regional anaesthesia. The intensity of the current needed to produce a motor twitch is inversely proportional to the square of the distance between the needle tip and the nerve. When a nerve block is performed with a nerve stimulator, a muscle twitch obtained at low output indicates that the needle tip is close to the nerve. This in turn translates into a better success rate as the precision of the injection is augmented [8]. Recently, the inclusion of ultrasound-guided techniques may improve the quality of the block and reduce even more the possibility of complications [9].

The factors determining the stimulus threshold of the nerve are:

Rheobase (mA) (Fig. 1)

The minimal electric CURRENT of very long duration that is required to stimulate a nerve where further lengthening of duration does not further reduce the current required.

Figure 1. Low speed thin fibers (pain) in blue have a higher chronaxy than high-speed thick fibers (motor) in red. 2002 B. Braun Medical Inc., (accessed at www.bbraunusa.com/stimuplex/pens1.html).

Chronaxy (ms)

The minimum DURATION of a stimulus required to stimulate a nerve fibre at a current of twice rheobase.

Chronaxy measures the excitability of the different types of nervous tissue, i.e. the duration of an effective electrical stimulus required to elicit a response. Stimulation of selective motor and sensory fibres occurs when the duration of the stimulus (pulse duration) is within chronaxy (Table 1).

Polarity of Stimulating Electrodes

Nerves need twice the current to respond to an electrical stimulus when the adjacent electrode is the anode (positive red lead) than when it is the cathode (negative black electrode).

Density of Current in the Biological Tissues

Two factors influence this:

1. Distance of the electrode from the nerve.
   The further the electrode is from the nerve the more current is required to stimulate the nerve (Coulomb’s law). Conversely, when a predetermined low current is used, the electrode can be systematically repositioned until a nerve stimulus results. At this point, it can then be assumed that the electrode is close to the nerve.
2. Cross-sectional area of the electrode transmitting the current (Fig. 2)
   Insulated needles have higher CURRENT DENSITY at the un-insulated tips. Additionally, this higher current density at the tip of the needle increases the accuracy of nerve location.

Figure 2. Insulated needles provide a high density current area at the un-insulated tip and in turn a more precise nerve location.

Complications (Table 2)

Auroy in 1997 [10] evaluated a multicentre series of regional anaesthetics to measure the incidence and characteristics of associated serious complications in human patients. A total of 21,278 peripheral nerve blocks were analyzed in this study. The incidence of complications was as follows: three cardiac arrests (1.4/10,000), one death (0.5/10,000), sixteen seizures (7.5/10,000), four neurological injuries (1.9/10,000) and four radiculopathies (1.9/10,000).

Since blockade of sodium channels affects action potential propagation throughout the body, it is not surprising that local anaesthetics may produce system toxicity. Central nervous system symptoms usually occur before cardiovascular changes. Blockade of inhibitory pathways allows facilitatory neurons to discharge without the normal negative input. Consequently, excitatory pathways function in an opposed manner, leading to signs and symptoms of excitation. Further increases in plasma levels will depress excitatory neuronal activity, producing signs of depression.

Local anaesthetics depress myocardial automaticity and reduce the duration of the refractory period. Myocardial contractility and conduction velocity are depressed leading to bradyarrhythmias, myocardial depression and possibly myocardial collapse. Treatment of local anaesthetic toxicity is not in the scope of this article and will not be discussed, however, two good sources can be found at [11,12].

Temporary dysaesthesias, localized tenderness and haematoma formation are regarded as trivial complications of short duration. However, benefits such as haemodynamic stability, early discharge and enhanced pain control are sufficient reasons to encourage increasing interest in peripheral regional techniques. Neurologic complications following peripheral nerve block can be caused by one or more of the following factors:

• Mechanical trauma to the nerve
• Intra-neuronal (intra-fascicular) injection
• Neuronal ischemia
• Inadvertent needle placement into unwanted locations
• Neurotoxicity of local anaesthetics
• Drug error
• Infection

The intensity of the stimulating current, resistance to injection and stimulating needle design are some of the elements involved in preventing neuronal damage.

Chan, Brull et al. 2007 [13] evaluated the minimum stimulating current associated with intraneural needle placement in the brachial plexus in pigs. They found that the minimum current able to elicit a motor response was 0.43 mA (range 0.12 - 1.8 mA) and concluded that a motor response above 0.5 mA does not necessarily exclude an intraneural injection. Kapur (2007) [14] studied the neurological outcome after intraneural injections in the sciatic nerve in the dog. They found that the worst outcomes were associated with high injection pressures (20 - 38 psi, ~ 138 - 262 KPa) whereas intraneural injections associated with moderate pressures (<12psi, ~ 82.7 KPa) had a longer than expected duration but no adverse effects. All perineural injections were associated with low injection pressures (<5 psi, ~ 34.5 KPa).

Needle trauma remains an important factor. Trauma may damage blood vessels associated with a nerve, cause extra- or intra-neural haematoma or oedema and lead to degenerative changes or discontinuity of fibres [15] as well as cause direct fascicular trauma.

The use of a short bevel needle (e.g. 30 - 45° angle) may help identify tissue planes and may reduce the likelihood of impaling a nerve [15]. Additionally, the use of a nerve stimulator and/or ultrasound-guided techniques helps to objectively assess the proximity of the needle tip to the nerve.

Local anaesthetic agents in concentrations used clinically are not known to be neurotoxic when applied extra-neurally [15]. Nerve injury caused by local anaesthetic appears to be related to increased hydrostatic pressure and physical disruption of nerve fibres and not cytotoxicity [16]. Infection after injection of local anaesthetics, according to the author’s knowledge, is very rare and, to date, has not been implicated as a cause of peripheral nerve damage.

Post-block neuropathy may also be associated with confounding factors such as tourniquet ischaemia, neuropathy due to positioning of the patient or nerve damage following surgery. In one study of 3996 patients [17], no patient had permanent neurologic injury attributed to the regional anaesthetic technique itself. Interestingly, the only variable that showed a significant predictive association with post-operative nerve injury was tourniquet pressure greater than 7.54 psi (52 kPa, 400 mmHg).

The symptoms of a nerve lesion after peripheral nerve block may usually become apparent within 48 hours. The intensity and duration of symptoms may also vary with the severity of the injury. In human subjects, these may vary from a light, intermittent tingling and numbness to a persistent, painful paraesthesia, neuropathic pain, sensory loss, and/or motor weakness lasting for several months or years. In general, it is safe to say that following peripheral nerve anaesthesia, if sensory and/or motor function remains depressed beyond the expected duration of action of the local anaesthetic, potential causes for the neurologic deficits should be investigated. The treatments more commonly prescribed for these paraesthesias, neuropathic pain and other deficits include tricyclic antidepressants (amitriptyline), serotonin reuptake inhibitors (paroxetine), anticonvulsants (gabapentin), opiods (tramadol) and capsaicin ointment.

Techniques

Various factors may markedly affect the onset time for peripheral nerve blocks. These include the concentration and volume of anaesthetic agent injected [19], the use of additives such as clonidine [20], a double injection technique [21], the type of evoked motor response obtained i.e. dorsi vs. ventral flexion of the foot when performing a sciatic nerve block [22] and the intensity of the current at which peripheral nerve stimulation is achieved [23].

Front Limb Blocks

Figure 3. Thoracic limb dermatome map.

Brachial Plexus Block

Anatomy

The brachial plexus is formed by the ventral branches of the cervical spinal (C6, C7, C8) and the first thoracic (T1) nerves. After the roots have passed through the intervertebral foramina and intertransversius musculature, the cords emerge through and cross the ventral border of the scalenus muscle where they spread out over a fairly large area and extend to the thoracic limb by traversing the axillary space. Specific nerves exit the plexus. These include from cranial to caudal the cranial pectoral, suprascapular, subscapular, axillary, musculocutaneous, radial, median and ulnar nerves.

The axillary artery and vein and subscapular vein lie ventromedial to the caudal portion of the brachial plexus.

Distribution of Anaesthesia - Technique

The patient should lie in lateral recumbency with the limb to be blocked uppermost. Landmarks include the scapulo-humeral joint, trachea, jugular vein and the axillary artery. The puncture site is located cranial to the acromium and medial to the subscapularis muscle. The pulse of the axillary artery can be palpated. Care should be taken not to puncture the external jugular vein, axillary artery, axillary vein or subscapular vein which are to be found in this region. The direction of insertion of the stimulating needle should be caudal, with a discrete dorsal orientation relative to the body axis (Fig. 4). Recommended peripheral nerve locator settings: 1 mA, 1 - 2 Hz. After a few centimetres, the musculocutaneous nerve is reached which becomes evident by contractions of the biceps brachii muscle and flexion of the elbow (Table 3). Current should then be decreased to 0.5 mA and the same response elicited. The intensity then should be decreased to 0.2 mA before injecting local anaesthetic and check absence of response to avoid intra-neural injection. Additionally, a test injection of 1 ml of the solution (Raj test) should cause the motor response to cease thus indicating that the nerve has been displaced away from the needle by the injectate; this rules out the possibility of making an intra-neural injection. However, quite possibly, the injection of an electrolyte, such as local anaesthetic, can dissipate the current ceasing nerve stimulation [24] (if water for injection is injected, muscular twitch does not disappear). Due to the high vascularity of the area and potential for inadvertent intravascular injection, the local anaesthetic solution should be injected slowly, with frequent aspiration. No resistance should be noted during injection.

Figure 4. Positioning of the needle should be cranio-caudal, with a discrete dorsal orientation relative to the body axis. The musculocutaneous nerve is the most cranial nerve within the brachial plexus. Adapted from Popesko’s Atlas of Topographical Anatomy of the Domestic Animals [25].

Choice of Local Anaesthetic

The choice of type and concentration of local anaesthetic should be based on whether the block is planned for surgical anaesthesia or pain management (Table 4).

Recommended volume to be injected: 0.25 - 0.3 ml/kg [30] (Fig. 5).

Figure 5. Cadaver dissection after a brachial plexus block using methylene blue solution. A volume of 0.3 ml/kg was used.

Complications (Table 5)

Intravascular injection, haemorrhage, pneumothorax, lung laceration, cervicothoracic or "stellate" ganglion block with associated Horner’s syndrome. Additionally, unilateral blockade of the phrenic nerve may also occur. The latter does not appear to compromise pulmonary function in conscious or anaesthetised dogs [31]. Stradling et al. [32] showed that acute bilateral paralysis of the diaphragm in awake dogs did not impair ventilation because of a marked increase in rib cage expansion due to an increase in intercostal and accessory muscle activity. However, Kowalski et al. in 1992 [33] demonstrated how anaesthetised dogs with induced bilateral phrenic nerve paralyisis developed paradoxical respiration with negative inspiratory intra-abdominal pressures.

Radialis, Median and Ulnar Blocks

Anatomy

The radial nerve emerges between the medial and lateral heads of the triceps and brachialis muscle in the lateral aspect of the front limb just proximal to the elbow joint. It soon then divides into its deep and superficial branches.

The median and ulnar (cranial and caudal) nerves run along the brachial artery (cranial to the nerves) and vein (medial to the nerves). They supply the pronator teres, pronator quadratus, flexor carpi radialis and flexor digitorum.

Distribution of Anaesthesia - Technique

Blockade of the three nerves will provide anaesthesia for procedures involving the carpus and manus (front paw).

With the dog in either lateral or dorsal recumbency and leg to be blocked uppermost, the puncture sites should be clipped and aseptically prepared. The puncture site for radialis nerve block will be in the lateral aspect of the limb, between the long head of the triceps and the brachialis muscle, proximal to the elbow joint (Fig. 6). The nerve is very superficial at this location. With the peripheral nerve locator set at 1 mA and 1 - 3 Hz radialis response characterized by extension of the carpus (extensor carpi twitch) should be elicited. Appropriate nerve stimulation is then sought at 0.3 - 0.5 mA. After aspiration, 1ml test and absence of resistance to injection, local anaesthetic can be injected.

In the medial aspect of the limb, the pulse of the brachial artery can be palpated just proximal to the elbow joint between the biceps brachialis and the medial head of the triceps (Fig. 6). The puncture site will be caudal to the artery. With the peripheral nerve locator set at 1 mA and 1 - 3 Hz median nerve response characterized by flexion and pronation of the antebrachium (flexor carpi, pronator teres twitch), or ulnar response characterized by flexion of the forepaw (flexor carpi), should be elicited. Appropriate nerve stimulation is then sought at 0.3 - 0.5 mA. After aspiration, 1 ml test and absence of resistance to injection, local anaesthetic can be injected. Local anaesthetic deposited here will block both nerves.

Figure 6. (Right) Puncture site for the radialis nerve is marked between the long head of the triceps and the brachialis muscle, proximal to the elbow joint in the lateral aspect of the front limb. (Left) The puncture site for the median and ulnar nerves is located in the medial aspect of the leg, between the biceps and the medial head of the triceps caudal to the brachialis artery shown on the left limb in this picture.

Pelvic Limb Blocks

Figure 7. Pelvic limb dermatome map.

Psoas Compartment Block (Lumbar Plexus)

Anatomy

The lumbar plexus is situated within the psoas muscle. It is formed by the ilioinguinal, lateral cutaneous femoral, genitofemoral, femoral, saphenous and obturator nerves. These nerves emerge between the fourth and sixth lumbar vertebra (Fig. 8). This compartment is limited ventrally by the aponeurosal continuation of the fascia iliaca, thus producing a true sheath which allows diffusion of local anaesthetics within the sheath. The psoas muscle is attached to the lateral surfaces and transverse processes of the lumbar vertebrae so that as soon as the roots of the lumbar plexus emerge from the intervertebral foramina, they become embedded in the psoas major muscle. The femoral nerve arises from the cranial part of the lumbar plexus (L4 - L6) and follows a course through the psoas muscle, then out through the femoral canal to the quadriceps femoris muscle. The femoral nerve is accompanied by the external iliac artery and vein and, on entering the thigh, it runs in a position between the sartorius and pectineus muscles. The saphenous nerve (cutaneous and muscular branches) comes off the femoral nerve at the level of the coxo-femoral joint.

Figure 8. Lumbar plexus anatomy showing needle placement between L5 and L6 in the vicinity of the femoral nerve. Adapted from Miller’s Anatomy of the Dog [34].

Distribution of Anaesthesia - Technique

Anaesthesia of the hemipelvis, femur, femoro-tibial joint, medial femoro-tibial joint capsule, femoro-tibial intra-articular structures, skin of the dorso-medial tarsus and first digit. Allen et al. [35] reported that the addition of a sciatic nerve block to a femoral nerve block did not further improve analgesic efficacy in procedures involving the knee joint in humans. However, Ben-David et al. [36] showed that sciatic nerve block is necessary in order to achieve complete analgesia after total knee arthroplasty. In one study by Farny et al. in 1994 [37] and using a combination of psoas compartment and sciatic nerve blocks for lower limb anaesthesia in people, complete sensory blockade was obtained in 40 out of 45 patients (89%). The author finds that the addition of a sciatic nerve block to either psoas compartment or femoral nerve blocks augments the quality of the analgesia for procedures involving the knee such as TPLO or extracapsular cruciate repair.

Landmarks include the spinous process of L5 - L6 and transverse process of L5 (Fig. 9).

Figure 9. Sagittal orientation of the stimulating needle at the level of the fifth lumbar vertebra is shown.

The stimulating needle is advanced with a strictly sagittal orientation. In the event of contact with the transverse process of the 5th lumbar vertebra, the needle should be redirected in a caudal direction so as to pass over the transverse process until contractions of the femoral quadriceps muscle (anterior motion of the femur) show that the needle is in the direct vicinity of the nerve (Table 6) (Quadratus response may be firstly seen). When stimulation is obtained with current intensity of 1.5mA, the needle should be partially advanced to obtain the same response with a current of 0.8 - 1 mA (it has been postulated that injecting at lower currents may increase the incidence of epidural migration). The intensity should be decreased to 0.2 mA before injecting local anaesthetic and check absence of response to avoid injection into the dural sleeves which may result in spread into the epidural or spinal spaces. Additionally, a test injection of 1 ml of the solution should cause the motor response to cease thus indicating that the nerve has been displaced away from the needle by the injectate; this rules out the possibility of making an intra-neural injection. No resistance should be noted during injection. If no adverse effect is noted after one minute, then the rest of the dose may be administered.

Choice of Local Anaesthetic

The choice of type and concentration of local anaesthetic should be based on whether the block is planned for surgical anaesthesia or pain management (Table 7).

Recommended volume to be injected: 0.4 ml/kg [30] (Fig. 10).

Figure 10. Cadaver dissection of the lumbar plexus showing the femoral nerve stained with methylene blue solution. A volume of 0.4 ml/kg was injected.

The psoas muscle is a relatively loosely compacted muscle, therefore relatively large volumes are required to fill this space. Higher volumes result in more solid, complete and faster blockade, but may have a higher risk of toxicity. Alternatively, a continuous infusion of local anaesthetic (0.05 ml/kg/h) of bupivacaine 0.25% via a peripheral nerve catheter may be ideal for continuous postoperative analgesia.

Complications (Table 8)

The main complication with this approach is the potential risk of epidural migration of the injectate and subsequent bilateral blockade (Fig. 11). Farny, Girard et al. 1994 [37] reported an incidence of 9% in humans. Our experience is an incidence of 6%. Threshold current of 1 mA and turning the patient over on to the blocked side (blocked side down) immediately after blockade have been postulated to reduce this complication. Additionally, abdominal vena cava puncture, aortic puncture or viscous puncture may also be possible.

Figure 11. Epidural migration after a psoas compartment block with methylene blue solution.

Femoral Nerve Block

Anatomy

The femoral nerve arises from the cranial part of the lumbar plexus (L4 - L6) and follows a course through the psoas muscle. The femoral nerve is accompanied by the external iliac artery and vein. It enters the pelvic limb through the femoral canal in a position between the sartorius and pectineus muscles where it innervates the quadriceps femoris muscle. The saphenous nerve (cutaneous and muscular branches) branches off the femoral nerve at the level of the coxo-femoral joint just before leaving the iliopsoas muscle and parallel to the femoral artery and vein (Fig. 12).

Figure 12. Anatomy of the femoral triangle. Dog is in lateral recumbency with the leg abducted 900 and extended caudally.

Distribution of Anaesthesia (Table 9) - Technique

Anaesthesia of the femur, femoro-tibial joint, medial femoro-tibial joint capsule, femoro-tibial intra-articular structures, skin of the dorso-medial tarsus and first digit.

With the dog in lateral recumbency the limb to be blocked should be uppermost, abducted 90 degrees and extended caudally. Landmarks include the femoral triangle (limited caudally by the pectineus muscle, cranially by the sartorius muscle, medially by the rectus femoris and proximal by the iliopsoas muscle) (Fig. 13). The pulse of the femoral artery can be palpated. The puncture site is between the femoral artery and the medial belly of the sartorius muscle. The stimulating needle should be advanced towards the iliopsoas muscle with a 20 - 30° angle (Fig. 14). The femoral nerve is directly medial to the medial belly of the sartorius muscle (sartorius muscle twitch is often seen before quadriceps twitch) (Table 9). As an example, in a mid-sized breed (e.g. Labrador retriever), the femoral nerve is about 0.5 - 1 cm deep.

Figure 13. Femoral nerve block landmarks: pectineus, sartorius and iliopsoas muscle, femoral artery and puncture site are marked.

Figure 14. Needle should be advanced towards the iliopsoas muscle with a 20 - 30° angle. The femoral nerve lies underneath the medial belly of the sartorius muscle.

Alternatively, an ultrasound-guided technique using a short axis view of the femoral nerve and an in-plane technique at the level of the femoral triangle may be used. The femoral nerve has a hyperechoic appearance and is located at seven o’clock relative to the femoral artery (Fig. 15).

Figure 15. Femoral artery (arrow) and femoral nerve (solid arrow).

Choice of Local Anaesthetic

The choice of type and concentration of local anaesthetic should be based on whether the block is planned for surgical anaesthesia or pain management (Table 10).

Recommended volume to be injected: 0.1 ml/kg (Fig. 16).

Figure 16. Cadaver dissection of the femoral triangle showing the femoral nerve (probe) stained with methylene blue solution. A volume of 0.1 ml/kg was injected.

Complications (Table 11)

The main complication with this approach is the potential risk of puncturing the femoral artery or vein.

Sciatic (Ischiatic) Nerve Block

Anatomy (Fig. 17)

The sciatic nerve is formed by L6, L7 and S1 roots and is composed of two branches: the tibial nerve (medially) and the common peroneal nerve (laterally). The division is variable. Occasionally, it is located as far proximally as the hip joint, while other times it may be as far distally as the popliteal space [34]. The sciatic nerve passes between the middle and the deep gluteal muscles and exits the pelvis through the greater sciatic foramen and descends protected by the greater trochanter of the femur. It then runs between the biceps femoris laterally and the semitendinosus muscle medially. In its proximal portion, it is accompanied by the caudal gluteal artery and vein which lie caudal to the nerve.

Figure 17. Sciatic nerve anatomy. Note the femoral greater trochanter, the ischiatic tuberosity and the puncture site marked in blue. Adapted from Popesko’s Atlas of Topographical Anatomy of the Domestic Animals [25].

Distribution of Anaesthesia

Caudolateral femorotibial joint capsule, lateral meniscus, tibia, tarsus, metatarsus (dorsal/peroneal component and plantar/tibial component aspects) and digits (except first and proximal aspect of second digits (Table 12). The sural nerve innervates the skin of the caudolateral aspect of the femorotibial join region. It is clinically relevant that blocking the proximal sciatic nerve will also block this nerve. Therefore, a combination of a proximal sciatic nerve block and a lumbar plexus block (psoas compartment or femoral nerve block) should be performed for complete analgesia of the leg.

Technique

Landmarks include the ischiatic tuberosity and the greater trochanter of the femur (Fig. 13). The patient is placed in lateral recumbency, with the leg to be blocked uppermost. In this position, the greater trochanter and the ischiatic tuberosity should be identified by palpation and a mark is made at each point. The puncture site is marked one third the distance along this GT-IT line, nearer to the greater trocanter (Fig. 18). The stimulation needle is inserted perpendicular to the skin with a discrete angle. Advancing the needle may result at first in contractions of the gluteal musculature, biceps femoris or vastus lateralis by direct muscle stimulation. In the event of bone contact, the needle should be withdrawn and redirected. Dorsiflexion (peroneal component) or plantar flexion (tibial component) of the foot with a stimulating current of 0.5 mA will be considered as positive response (Table 12). The intensity should be then decreased to 0.2 mA before injecting local anaesthetic and checking for the absence of response to avoid intraneural injection. Additionally, a test injection of 1 ml of the solution should cause the motor response to cease. No resistance should be noted during injection. If no adverse effect is noted after one minute, then the rest of the dose may be administered.

Choice of Local Anaesthetic (Table 13)

A sciatic block requires a relatively low volume of local anaesthetic to achieve anaesthesia of the entire trunk of the nerve. Systemic toxicity after sciatic blockade may be more common than after brachial plexus blocks because of the proximity of large vascular beds in the muscles.

Recommended volume to be injected: 0.05 ml/kg [30] (Fig. 18)

Figure 18. Cadaver dissection after a sciatic nerve block with methylene blue solution. Note that the biceps femoris muscle is being lifted. A volume of 0.05 ml/kg was used.

Complications (Table 14)