paediatric peripheral nerve blocks

16 March 2012 No. 9

PAEDIATRIC PERIPHERAL NERVE BLOCKS

Veena Ramson

Commentator: C Mitchell Moderator: M Naidoo

Department of Anaesthetics

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CONTENTS

INTRODUCTION……………………………………………………………………….. 3

BENEFITS……………………………………………………………………………… 4

REQUIREMENTS FOR A SUCCESSFUL BLOCK………………………………… 6

INDICATIONS FOR PNB’S…………………………………………………………… 9

CONTRAINDICATIONS……………………………………………………………….. 9

A PRACTICAL APPROACH TO SOME COMMON BLOCKS……………………. 10

UPPER EXTREMITY BLOCKS………………………………………………………. 10

LOWER EXTREMITY BLOCKS……………………………………………………… 15

PERIPHERAL NERVE BLOCKS OF THE TRUNK………………………………… 20

ULTRASOUND GUIDED PERIPHERAL NERVE BLOCKS……………………… 22

CONTROVERSIES………………………………………………………………......... 23

CONCLUSION…………………………………………………………………………. 26

REFERENCES…………………………………………………………………………. 27

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INTRODUCTION When Koller initially discovered in 1884 that cocaine can be used as a local anesthetic[1], he used it for eye surgery, and Corning in 1885 injected it into the epidural space[2], August Bier subsequently followed suit in 1898 by using cocaine as a spinal anesthetic[3]. Of Bier‟s 6 subjects, two were children. He immediately abandoned its use when he found all subjects had postoperative vomiting and headache. Interestingly, he even tried it on himself and his assistant; but they too had vomiting and headache for 4 days[1]. The true pioneers of peripheral nerve blocks are undoubtedly William Stewart Halstead and his assistant, Richard John Hall. These two surgeons described how they blocked various sensory nerves in themselves, and the technique of inferior alveolar nerve and antero-superior dental nerve blocks have been attributed to them[4]. Halstead‟s research, however, was halted by the fact that all of the surgeons who were involved in these experiments became addicted to cocaine. Halstead seems to have been the only one in his team to have recovered from this addiction; and went on to become a professor of surgery at Johns Hopkins medical school. [4] Paediatric surgical advancements between the 1950s and 1960s saw sporadic reports of developments in regional anesthesia, but names of anaesthetists like Harry Curwen and Adrian Bösenberg both from Durban, South Africa, have been at the forefront of the development of paediatric regional anesthesia, with Prof Bösenberg still currently active in promoting paediatric neuro-axial and peripheral nerve block techniques. Peripheral nerve blocks (PNBs) are generally regarded as safer than neuro-axial techniques. However, the same decision-making process regarding neuro-axial techniques applies to peripheral nerve blocks. These include informed consent from the parents, the age of the patient, the child‟s general condition, the presence of coexisting problems (CVS, respiratory), the severity of the injury and resultant pain, the anaesthetist's competence in performing the block, and if there are any contraindications to performing a block. The anaesthetist also needs to make sure that the block is performed in an appropriate facility with correct equipment, monitoring, and nursing care that is readily available. In 1994, the French Language Society of Paediatric Anesthesiologists (ADARPEF) collected data from 85,412 procedures, of which 24,409 were regional blocks (PNB's accounted for 38% of these blocks). They found that the overall complication rate of regional anaesthesia was 1.5 per 1000, but it was actually 0 following PNBs. Pursuant to this study, anaesthetists have been encouraged to use PNBs, where appropriate, instead of central blocks, and subsequently the use of PNBs, especially in older children, has increased. A follow-up study by the same society in 2010, served to reemphasize the safety of PNBs.[5, 6]

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PNBs can be extremely challenging for the unskilled anaesthetist, as soft tissue and bony landmarks are either poorly defined, or change as the child develops. Also, the risk of toxicity is greater in children. This warrants the use of the smallest effective dose of anesthetic to achieve optimal results. Small children are generally uncooperative, and for this reason, most blocks are done under sedation or general anesthesia. The advent of advanced equipment and aids made specifically for children have increased the success rate of these blocks and have maximized their benefits.

BENEFITS

Analgesia There is no doubt that PNBs provide excellent pain relief. These blocks are an effective alternative to systemic analgesics. The choice between single shot blocks or the use of peripheral nerve catheters dictates the duration of action of the block together with the local anaesthetic used. PNBs are especially useful when systemic opioids are contraindicated (children at risk of respiratory depression from opioids, children with chronic pain that have become tolerant to the analgesic effects of opioids).

The fact that these children are pain-free, improves the psychological profile of both the child and the family. This, of course, has a ripple effect, in that a calm, cooperative child, who is not tugging at drains and dressings, decreases the burden on the nursing staff in the recovery room, as well as the ward. Certain categories of children, where general anaesthesia may be dangerous, benefit from the use of PNBs. These include ex-prems, children with neuromuscular disorders, cardiac, respiratory or metabolic problems, or in the case of malignant hyperthermia, as well as in the emergency situation where there is a risk of aspiration. Children are generally admitted to have fractures reduced in theatre, rather than in the emergency room, purely because the pain is debilitating. PNBs can obviate this practice (in older children). Reduction in Depth of Anaesthesia PNBs are usually performed in conjunction with general anaesthesia in children. This results in a reduction in the required depth of anaesthesia. This is especially important in small children, where the immature organ systems are particularly sensitive to general anaesthetic agents, and their depressant effects. When volatile agents are used, neonates, infants and young children experience dose-dependent and agent-related depression of cardio-respiratory function as well as blunting of central control of ventilation.

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The reduction in the need for deeper levels of anaesthesia (lower MAC) has its benefits:

The need for intubation and positive pressure ventilation is decreased (as would be needed with deep anaesthesia where children are bound to become apnoeic).

The use of muscle relaxants is decreased.

Emergence is faster and duration of stay in recovery is decreased.

Appetite returns earlier.

The risks associated with deeper planes of anaesthesia are reduced (cardiac, respiratory and CNS depression, metabolic upsets).

Hemodynamic Stability It is unlikely for PNBs to cause haemodynamic instability, unless it has been complicated by intravascular injection or local anaesthetic toxicity, whereas general anaesthetic agents are well known to cause exaggerated responses especially during induction, intubation and extubation. Post-operative Ventilation Respiratory depression caused by opiates often necessitates prolonged postoperative ventilation. Opiates also blunt the central respiratory drive‟s response to hypercapnia. In contrast, bupivacaine directly stimulates the respiratory centre. The use of PNBs, thus, reduces the length of post op ventilation, which translates into fewer post-operative complications (eg. pneumonia, hypoxemia). Neuroprotection General anaesthetic agents are implicated in causing apoptosis of the immature brain[7]. This implies that the use of PNBs will decrease the damage caused by general anaesthetic agents. Butterworth et al.[8] have suggested that local anaesthetic agents may have a neuro-protective effect in adults, demonstrated by decreased cognitive dysfunction. Perhaps this can be extrapolated to children. Unfortunately, a study to this effect may be difficult in children. Neuroendocrine Stress Response and Immunomodulation Surgical stress and pain affect hormonal, autonomic, metabolic, inflammatory, immunologic, and neurobehavioral function. A severe stress response leads to extensive release of catabolic hormones like catecholamines, cortisol and glucagon which has been shown to worsen outcomes in the paediatric population; especially neonates [8-10].

The use of regional anaesthesia has been shown to decrease these hormone levels, thereby improving outcomes [11-13]. Studies have more significantly shown that regional techniques are superior to systemic opioids in providing analgesia more effectively and for a longer duration [14,

15].

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Local anaesthetics are also implicit in immunomodulation, and have been noted to influence inflammatory cell response (polymorphonuclear leukocytes, monocytes and macrophages). This is of particular importance in sick infants who may be prone to a disregulated inflammatory response, which may manifest as ARDS, SIRS, MOF[16]. Natural killer cells are stimulated by local anaesthetics, which is an important part of the host defence mechanism.

REQUIREMENTS FOR A SUCCESSFUL BLOCK The performance of a successful block depends on the following:

Patient selection and parent‟s permission

Skill in performing blocks: only anaesthetists skilled in performing PNBs in children should be performing them or teaching them

Supportive surgeons: The surgeon‟s cooperation is of paramount importance when discussing these blocks with parents, as lack of consensus makes the parents wary of the anaesthetist, and subsequent performance of these blocks becomes a contentious issue.

Appropriate assistance: There should, ideally, be a second anaesthetist monitoring the patient's airway and general anaesthetic. This is not hard to achieve in the academic setting, but may prove to be a challenge if the anaesthetist is working alone.

Proper equipment and monitoring: Adult equipment and needles are not meant for children. There are now regional block kits and short bevelled sheathed needles that are specifically made for the paediatric population. As most PNBs are performed in the anesthetized child in theatre, standard monitoring and equipment are usually available. They are still a necessity if these blocks are performed outside the operating room.

Nursing policies: The child's discharge from the recovery room depends on each hospital„s individual practice. Some require return of motor function before the child is discharged, while others stipulate a specific time-period (15 to 30 minutes). Discharge to the ward, versus discharge directly home remains a controversial issue. Some centres in the US and UK discharge patients directly home, even with residual sensory and motor blockade, and sometimes with peripheral indwelling catheters still left in situ. If an anaesthetist were to decide the latter, the following needs to be taken into cognizance: a) The parents need to be able to follow instructions and fully understand

what his required of them. b) They need to accept responsibility for early discharge. c) They must be taught and be able to provide protection of the numbed and

weakened body parts from injury at home.

Anatomical considerations: Target nerves in children are smaller, closer to adjacent vascular structures, and more superficial than adults. Although it is not the subject of this talk, it is interesting to note that neuraxial blockade in children less than 8 years do not

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cause the same haemodynamic instability as adults, hence; there is no need to volume load younger children.[17]

Pharmacology: The anaesthetist needs to be aware of the choice of anaesthetics available, the correct dosages, as well as the toxic range of the drugs used. Table 1 & 2 Children are unique in the following way: a) They have a higher volume of distribution of local anaesthetics compared

to adults. This results in lower peak plasma levels. This implies that children can tolerate larger doses (mg/kg basis) and peak plasma concentrations are generally below the toxic threshold.

b) Infants less than 6 months have depressed hepatic metabolism, as well as serum binding proteins (α1 glycoprotein) about half that of older children and adults. This means that there will be higher free fraction and higher peak plasma concentration of local anaesthetic. Toxicity can therefore occur at much lower blood levels. It is recommended that the anaesthetic dose should be decreased by 50% in this age group.

Table 1: Recommended local anaesthetic (volumes) [18]

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Table 2: Recommended Dose (body weight)[19]

Drug Onset Max Dose

(without adrenaline)

Max Dose

(with adrenaline)

Continuous infusion Duration

(without Adrenaline)

Duration

(with Adrenaline)

Bupivacaine 10-15 min 2mg/kg 2.5mg/kg 0.25mg/kg/hr 3-12 hrs 4-12 hrs

Levobupivacaine 10-15 min 2.5mg/kg 2.5mg/kg 0.25mg/kg/hr 3-12 hrs 4-12 hrs

Ropivacaine 10-15 min 3mg/kg 4mg/kg 0.4mg/kg/hr 3-12 hrs 4-12 hrs

Lignocaine 5-10 min 3mg/kg 7mg/kg ? up to 2mg/kg/hr* 1-2 hrs 2-4 hrs

Prilocaine 5-10 min 6mg/kg 8mg/kg Not suitable 1-2 hrs 2-4 hrs

*not substantiated

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INDICATIONS FOR PNB’S [20]

CONTRAINDICATIONS

Contraindications are similar to those in adults:

Parent/ patient (older children) refusal

Coagulopathy

Infection at the needle insertion site

Generalized sepsis

True local anaesthetic allergy

Abnormal superficial landmarks

Risk of compartment syndrome

Progressive neurologic disease - relative contraindication mostly due to medicolegal concerns

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A PRACTICAL APPROACH TO SOME COMMON BLOCKS General principles

a) 3 basic principles that were developed in the 1980's still holds true[21-23]: 1. Finding the depth of the nerve involves knowing the patient‟s anatomy and

getting a “feel” of the different anatomical layers 2. Advancement of the needle with gentle and careful pressure on the

syringe plunger in order to appreciate resistance and loss of resistance 3. NEVER inject anaesthetic against resistance

b) Peripheral blocks last longer than single shot central neuraxial blocks c) It takes about 30 minutes for the block to be optimally effective d) PNBs allow for catheter insertion and continuous administration of local

anaesthetic infusion postoperatively. e) Nerve stimulators should be capable of delivering 0.2 to 2 mA of current.

Remember, that the negative terminal is attached to the needle, and the positive is placed onto the patient ("negative to needle" or "black to block” & “positive to patient “).

f) It is generally considered that the needle is in or close to the nerve sheath if contractions disappear at 0.5mA current. Conventional teaching suggests that the persistence of twitches below the 0.5mA current implies that the needle is intraneural, but this is not necessarily true[24, 25]

g) Aseptic technique is best practice for any invasive procedure.

UPPER EXTREMITY BLOCKS

www.esra-learning.com

[26]

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Brachial Plexus Anatomy[27] The brachial plexus runs from cervical spine, through the neck, the axilla and into the arm. With the exception of the intercostobrachialis nerve, all nerves in the upper extremity stem from the brachial plexus. The roots of the brachial plexus include C5 to T1, with minor contributions from C4 and T2. The nerve roots enter the interscalene groove between the scalenous anterior and scalenous medius muscles. C5 and C6 nerve roots form the upper trunk. C7 continues as the middle trunk. C8 and T1 unite to form the lower trunk. The trunks are sheathed by the prevertebral fascia and lie in the same plane as the subclavian artery. The upper and middle trunks lie above the subclavian artery, while the lower trunk lies posterior to the subclavian artery, near the first rib. Each trunk divides into anterior and posterior divisions. The anterior divisions of the upper and middle trunks form the lateral cord. The anterior division of the lower trunk is forms the medial cord. The posterior divisions of all the trunks form the posterior cord. Cords: The lateral, medial and posterior cords derive their names from their relation to the second part of the axillary artery behind the pectoralis minor muscle. Branches: several branches are derived from the brachial plexus and can be divided into those derived from the roots, the trunks and the cords. From the roots: C5 contributes to the phrenic nerve and branches to the levator scapulae muscle. C5-7 branch to the serratus anterior. C8 and T1 branch to the rhomboids and levator scapulae. The trunk of c5-6 gives of the suprascapular nerve which ultimately contributes to the supraspinatus and infraspinatus. The lateral cord branches to the lateral pectoral nerve, the musculocutaneous nerve and the lateral head of the median nerve. The medial cord branches to the medial pectoral nerve, the medial cutaneous nerve of the arm and forearm and the medial heads of the median and ulnar nerves. The posterior cord divides into the upper and lower subscapular nerves, the nerve to the latissimus dorsi, the axillary nerve to the shoulder joint, which innervate the deltoid and teres minor and the radial nerve. Except for the innervations of the skin over the upper part of the shoulder (C3, C4) and the upper part of the medial arm (T2), all motor and sensory innervations to the upper extremity is derived from the brachial plexus.

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Brachial Plexus Blocks

a) Axillary Approach (at level of trunks, blocks C5 to T1)[28] Without a nerve stimulator

Landmarks: Identify the axillary artery within the axilla. Technique: Using the non-dominant hand, fix the axillary artery against the humerus. Direct the needle tip just superior to the artery, and stop when a slight “give” or loss-of-resistance is felt. Inject half the local anaesthetic dose. The needle is then withdrawn just beneath the skin and then directed inferiorly, and the remainder of the drug is injected.

Peripheral nerve stimulator technique

The nerve stimulator is used to identify the nerve bundles, and the current is decreased to at least 0.5 mA. Again, half the dose is injected at each nerve bundle.

NB: The intercostobrachial nerve, which runs subcutaneously, is not covered by the axillary block, and this is significant if a tourniquet is being used. Therefore, reserve 3 to 5 ml of the local anaesthetic used for your block & inject a subcutaneous ring of anaesthetic high around the inner aspect of the arm.

Pediatric peripheral Nerve Blocks; Allison Kinder, MD

[29]

Complications

The artery can be punctured accidentally, therefore, it is important to constantly aspirate throughout the procedure. Should this occur, continue advancing the needle while aspirating until there is no longer any blood being withdrawn. After injection of the local anaesthetic, maintain pressure in the artery for at least 2 to 5 minutes to prevent haematoma formation (and subsequent nerve compression).

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b) Interscalene Approach (at level of the roots, blocks, C4 to T1; especially C4 to C7) [28]

Landmarks Identify the lateral border of sternocleidomastoid muscle, the interscalene groove which is found posterior to the SCM at the level of the cricoid cartilage.

Technique Insert a towel under the shoulders, and tilt the head slightly to the contralateral side and extend it slightly. Keeping the needle perpendicular to the skin, insert it into the interscalene groove at the level of the cricoid cartilage (C6). Direct the needle laterally if bone is encountered. The PNS is used in the same manner as described above. Again, negative aspiration of blood must be confirmed before injection.

Frank H. Netter

[30] Complications

If the needle is directed too cephalad, anaesthetic is injected into the intervertebral foramen, which produces a high spinal block, and results in associated complications.

Horner's syndrome, vagus nerve injury, recurrent laryngeal nerve injury, phrenic nerve paralysis Some experts have reported phrenic nerve paralysis occurs up to 100% of the time, which results in paralysis of the hemidiaphragm[31]. It is for this reason that interscalene blocks are usually contraindicated in patients with COAD and respiratory compromise.

Pneumothorax and vertebral artery injection are also possible complications.

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c) Parascalene Approach Dalens described this technique in 1995 as an alternative to interscalene blocks in order to minimize the risk of intravascular injection, intrathecal injection, and pneumothorax.[28]

Landmarks

Chassaignac's tubercle (the transverse process of C6 vertebra - extend a line from the cricoid cartilage to the posterior border of sternocleidomastoid) and the midpoint of the clavicle.

Technique As with the interscalene block, turn the head slightly to the opposite side, and raise the shoulders by placing a towel between the scapulae. Draw a line between the two points described above and identify the junction between the upper two thirds and lower one third. This will be the point of insertion of the needle, which is then directed posteriorly until muscle contractions are elicited by the nerve stimulator.


[29]

Complications The same as for interscalene blocks:

Phrenic nerve injury

Intravascular (vertebral artery injury)

High/total spinal block

Horner‟s Syndrome

d) Infraclavicular Approach The infraclavicular approach was first described by Prithvi Raj in 1973 [32], as an alternative to the axillary approach. Since then there have been many modifications, with the lateral vertical infraclavicular brachial plexus (LVIBP) approach described by Fleischmann[33], and more recently, the lateral sagittal approach being described by Gürkan[34].

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The differences in each description of the infraclavicular techniques refer mostly to the point of insertion of the needle in relation to the coracoid process and the angulation of the needle, with the vertical approach describing the needle angulation as being 90° or vertical, while the lateral sagittal approach recommends puncturing the skin starting at a 15 °-20° angle and moving dorsally to about 30°. The lateral sagittal approach has been found to be the safer in children, as the chance of pneumothorax is the less with this technique in this population[34]

Landmarks

Coracoid process, clavicle Technique

The child is placed supine with the head turned in the opposite direction. Palpate the coracoid process and insert the stimulating needle 0.5 cm distal to the coracoid process at an angle of about 15-20° to the sagittal plane in a caudal direction, while aspirating for blood and/or air. Once muscle twitches in the fingers/wrist are obtained, LA is injected.

Sedeek, et al;Anesthesia & Analgesia; July 2007

[35]

Complications

Complications using this approach are unusual.

Pneumothorax or vascular puncture can occur, but these risks should be less than other techniques.

LOWER EXTREMITY BLOCKS Selectively blocking the lower extremities confers the advantage of providing a longer duration of analgesia (10 to 12 hours cf. 2 to 4 hours with caudal/epidural techniques). Patients can still weight-bear on at least one leg, which helps with mobility in older children as well as relieves the burden on nursing staff and the parents. Older children generally become more distressed after experiencing numbness and paralysis that occurs with neuraxial techniques (even if adequately counselled pre-operatively), and this problem is partially obviated by PNBs.

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Lumbar and Sacral Plexus Anatomy:

Adapted from European Society For Regional Anaesthesia[36]

Adapted from James F. Thompson[37]

The lumbar plexus is formed by the anterior rami of lumbar nerves L1-L4 with some innervation from T12. It divides into the femoral, the lateral femoral cutaneous, and the obturator nerves. The femoral nerve provides motor innervation to the quadriceps femoris muscles and sensation to the anterior and medial thigh. The saphenous nerve, which is a branch of the femoral nerve, provides innervation below the knee to the medial aspect of the lower leg and foot. The lateral femoral cutaneous nerve innervates the lateral thigh, and the obturator nerve provides motor innervation to the leg adductors with some sensation to the lower medial thigh and knee.

The sacral plexus is derived from the anterior rami of L4 to S3 and gives rise to the posterior cutaneous nerve of the thigh and the sciatic nerve. The sciatic nerve is a mixed motor and sensory nerve to the posterior aspect of the thigh and the most of the lower leg. As the sciatic nerve travels down the posterior thigh, it divides into the common peroneal nerve and posterior tibial nerve. a) Lumbar Plexus Block (Psoas Compartment Block)

Various methods have been suggested to find the optimal point of needle insertion, and the complexities in demarcating this point has been one of the reasons why anaesthetists have been reluctant to perform these blocks. I found this method described by Scheupfer in 2005 to be one of the simplest. A 100% success rate was described in his study involving more than 100 children.[38]

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Landmarks: Spinous process of L4, the posterior superior iliac spine Technique:

The child is placed in the lateral decubitus position with the hip joints flexed 90°. Draw a line from the spinous process of L4 to the PSIS. Demarcate the junction of the medial 2/3 and the lateral 1/3 of this line. This is the point of needle insertion. The needle is advanced until quadriceps muscle twitches in the thigh are elicited. Needle penetration should be limited to 20 mm.

Schuepfer,G et al; Paediatric Anaesthesia 2005.

[38]

Complications:

retroperitoneal haemorrhage

renal haematoma

total spinal

epidural injection

Many of the above complications have been due to injection sites that have been too caudal or too medial, and with the above technique, most of these problems are eliminated.[39]

b) Femoral Nerve Block (L2 to L4) Landmarks: The femoral triangle: Vein – Artery – Nerve (medial to lateral)

Technique:

Palpate the femoral artery about half to 1 cm below the inguinal ligament, and aim the needle laterally and slightly cephalad, which is where the femoral nerve lies within the femoral triangle. A distinct pop is felt when the needle pierces the fascia lata. A PNS should elicit contractions in the quadriceps- commonly known as "a patellar kick". Inject local anaesthetic slowly; ensuring intermittently that no blood is aspirated.

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Femoral Nerve Anatomy; AnaesthesiaMD blogspot

[40]

Complications Femoral artery puncture - in which case and pressure for 5 minutes to avoid haematoma formation. c) Sciatic Nerve Block

Landmarks: This depends on the approach used to access the sciatic nerve – the posterior approach or the Raj Block technique. If a posterior approach is used, the child is placed in a lateral position; then the landmarks used would be the midpoint of a line drawn from the tip of the coccyx to the greater trochanter. If the child is placed in a supine position, with the hip and knee flexed, the needle insertion would be the midpoint of the line joining the ischial tuberosity and greater trochanter (Raj Block)[41] Technique

Posterior Approach: Dalens et al.[39] modified Labat‟s technique[42] to come up with the following approach. The child is placed in the lateral position and the upper leg flexed at the hip and knee. The needle is inserted at the midpoint of the line that extends from the greater trochanter of the femur to the tip of the coccyx. Needle entry is perpendicular to the skin. It can be slightly angulated towards the lateral ischial tuberosity.

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[29]

Complications

Vascular puncture of gluteal blood vessels. The Raj Block [41] This block is performed with the child supine and the leg to be blocked held in flexion at the hip and knee. Insert the needle at the midpoint between the greater trochanter and the ischial tuberosity within the sciatic groove. With flexion of the hip in this manner, the Raj technique makes the sciatic nerve more superficial. This increases the likelihood of a successful block, which can be a challenge in obese children and adolescents.

Pediatric peripheral Nerve Blocks; Allison Kinder, MD[29]

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PERIPHERAL NERVE BLOCKS OF THE TRUNK Anatomy The iliohypogastric and ilioinguinal nerves originate from the lumbar plexus and traverse the transversus abdominis muscle. The iliohypogastric nerve then courses between the transversus and internal oblique muscles while the ilioinguinal nerve passes between internal oblique and external oblique. Sensation of the skin over the inguinal region is from the iliohypogastric nerve. The ilioinguinal nerve supplies sensory innervation to the skin on the superomedial aspect of the thigh. a) Ilioinginal / Iliohypogastric Nerve Block

Landmarks: Anterior superior iliac spine, the umbilicus and the inguinal ligament Technique:

Draw a line between the ASIS and the umbilicus. Then, divide the line into 4 equal parts such that the junction of the lateral 1/4 and the medial 3/4 can be found. Pierce this point with a short bevelled needle perpendicular to the skin until loss of resistance his felt. This loss of resistance assumes that the external oblique aponeurosis has been breached. Inject local anaesthetic into this layer. Insert the needle deeper until a second “pop” is felt. This implies that the internal oblique has been penetrated. The rest of the local anaesthetic is injected here.


[29] NYSORA

[43]

Complications

Femoral nerve block has been reported up to 8.8% of the cases [44]

Rapid absorption of the LA, leads to high plasma levels, especially in young children [45] .

Abdominal wall perforation [46] and colonic injury can occur [47, 48]

The nerves can extremely close to the peritoneal cavity (1-2mm); inadvertent intraperitoneal injections can occur

Noxious stimuli like traction on the peritoneal sac can still be felt.

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Without ultrasound guidance a correct needle placement has been reported to occur only in 14% of cases [49]

The New Kid on the Block... 1. TRANSVERSUS ABDOMINIS PLANE BLOCK [50]

The transversus abdominis plane block or TAP block, is based on the anatomy of the lower intercostal nerves which supply the abdominal wall, in that it runs in the plane between the internal oblique muscle and the transverses abdominis. This block has garnered a lot of interest in the last 10 years due to the number of proposed advantages: Technically simple Highly effective analgesia Opioid sparing effect Long duration of action (30 - 36 hour), Minimal side effects compared to neuraxial techniques (e.g. hypotension, motor

block).

Landmarks: The “Triangle of Petit” - age is bordered by the external oblique anteriorly, the iliac crest inferiorly, and the latissimus dorsi muscle posteriorly. Technique:

A “two-pop” technique, with a blunt needle, has been described; which refers to the needle penetrating the external oblique and internal oblique fascia to enter the plane between the internal oblique and the transverses abdominis. Local anaesthetic is then injected. The intercostal nerves must be blocked before they give off the lateral cutaneous branches; therefore injection must be posterior to the mid axillary line

Triangle of Petit

[50]

NYSORA

[43]

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Complications

Intrahepatic injection [51]

Intraperitoneal injection,

Bowel haematoma

Transient femoral nerve palsy.

Local anaesthetic toxicity due to the large volumes of anaesthetic used, especially if bilateral blocks are performed

Intravascular injections - as with all regional techniques

This block abolishes somatic sensation, but deep visceral pain is still appreciable, and bilateral blocks are needed for midline incisions (eg. caesarian sections)

ULTRASOUND GUIDED PERIPHERAL NERVE BLOCKS In the review published over 3 years ago, Marhofer et al.(12) suggested that ultrasound guided regional anaesthesia (USGRA) offers several potential advantages: 1. Direct visualization of nerves: The assumption that this may make the use of

PNS‟s obsolete, is up for debate. Koscielniak-Nielsen‟s meta-analysis in 2008[52] revealed that, while USGRA is useful for blocks involving superficial nerve structures (the interscalene, supraclavicular, axillary, inguinal, popliteal, elbow/forearm), there have been no studies that report a 100% success rate in identifying all nerves, and has summarized that there are 8-18% of patients where nerve structures would not be adequately visualized, and would require confirmation with nerve stimulation.

2. Direct visualization of anatomical structures: especially blood vessels (most commonly the axillary artery and the femoral artery), bones, muscle, fascias, and tendons. This is especially important in children, where the target nerve could be 1-2mm away from vascular structures.

3. Real-time control of needle advancement: This may reduce the number of attempts at performing the block and shorten the time taken to perform the block. There is also the supposition that the risk of complications, especially vascular puncture, would be decreased, but this is not necessarily true. Studies indicate that there is a 4-5% chance of vascular injury, despite using ultrasound.[53]

4. Assessment of LA spread around the nerves and immediate supplementation with further injections in case of insufficient spread of drug. This may improve the efficacy of the block, shorten the latency period, prolong duration of analgesia (which has been found to be significantly increased in children rather than adults), reduce the dose of LA used and decrease the risk of overdose.

5. Avoidance of muscle twitches: This may reduce block discomfort.

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CONTROVERSIES

With litigation being on the mind of most anaesthetists, controversial issues have arisen as a result:

1. Block Needles and its Placement

The best needle design remains a controversial issue. Since 1977, short‐bevelled needles have been recommended and used for peripheral nerve blocks based on the concept that they are less likely to cause penetrating nerve injuries[54].

But Rice and McMahon found that short‐bevelled needles caused more severe and frequent nerve injury which required a longer recovery time[55]. “Pencil‐point” needles have been shown to decrease the incidence and severity of spinal headaches in children (compared with “cutting point needles”)[56, 57], but there is no research on PPN‟s and its effect when used in peripheral nerve blocks.

There is also much debate on the extent and site of injury caused by block needles, and researchers have gone on to define intraneural injury as being extra- or intrafascicular, with most researchers acknowledging that intraneural injury (on the basis of type of needle used, the pressure used to inject the anaesthetic and the direction the needle entered the nerve) does occur during PNB – the incidence of which is 0.4 in 1000- and is a modifiable risk factor[58].

Organisational layers of the nerve

[59]

Interestingly, there is also research to suggest that intraneural injections have no adverse consequence, and in fact that peripheral nerve stimulators are unable to detect intraneural placement of needle with currents as low as 0.2mA[24, 60, 61]. Despite the above, all anaesthetists are aware that the risk of neuropraxia is a known complication of manipulation to a nerve, and obviously should be avoided. Other causes of perioperative nerve injury are listed below.

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Barrington et al; Current Opinion in Anesthesiology 2011

[58]

2. Test Dose The use of adrenaline incorporated into the local anaesthetic as a test dose, is an issue that still has not been resolved. Since the vast majority of blocks are performed in children who are under general anaesthesia or are heavily sedated, early signs of accidental intravascular injection is impossible to appreciate.

There are 2 methods suggested for detecting accidental intravascular injection[62]: a) Blood in the needle on aspiration or if spontaneous backflow is detected b) Heart rate changes associated with intravascular injection of adrenaline. The major drawbacks of the above 2 techniques is that aspiration is often not sensitive enough in children - negative aspiration has still yielded intravascular injection, and CVS changes are subject to other factors, such as the type of general anaesthetics used, and the depth of anaesthesia. Tanaka and Varghese [63, 64] have suggested the use of ECG changes (ie. T-wave amplitude and ST segment changes of >25% irrespective of the ECG lead used) as being a more sensitive indicator. T-wave amplitude changes occur first, followed by heart rate changes and finally blood pressure is affected. The underlying mechanism of this phenomenon is still unknown.

3. Awake versus Asleep (“Double anaesthetic, double the risk”)

This controversy is based on a report by Benumof and Bromage in 1998[65], where an adult female suffered permanent paraplegia as a result of epidural insertion whilst asleep. This statement has subsequently been discredited, with most regional anaesthesia societies advocating that the child be asleep or heavily sedated during performance of a block, as this is indeed a safer option.

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4. Peripheral Blocks and Anticoagulation Spinal haematoma is the most catastrophic complication of regional blocks due to bleeding into a fixed incompressible space.

The risk following nerve plexus and peripheral techniques are still unknown. There have, however, been 26 cases of major bleeding reported after psoas compartment or lumbar sympathetic block and/or in the presence of antiplatelet agents or anticoagulant use. Of these 26, 13 patients were anticoagulated perioperatively. Nearly all these patients received enoxaparin within 24 hrs of performing the block or were on NSAID‟s.

These case reports indicate that the neurological fallout from these injuries is not the most significant complication[66-70] – in fact, it is the major blood loss in anticoagulated patients that is more important; which was either requiring of blood transfusions or resulted in death (1 patient out of 13 reported cases). In patients that did have neurological deficit, complete recovery occurred in 6-12 months. The reason for neurological deficit reversal is the fact that the haemorrhaging occurs into expandable sites as opposed to bleeding into closed spaces with neuraxial blockade. Although the latest ASRA guidelines on Neuraxial Anaesthesia and Anticoagulation recommends that the same guidelines should be used for both neuraxial techniques and plexus/peripheral techniques[66, 67], many critics believe that treating plexus/peripheral blocks in the same manner as neuraxial techniques may be unnecessarily restrictive for techniques involving superficial and compressible vasculature. Whatever the opinion of the anaesthetist, individualization of each case is paramount in weighing the risks and benefits of performing these procedures.

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ASRA Consensus Conference on Neuraxial Anesthesia and Anticoagulation, Reg Anesth Pain Med 2003

[66]

CONCLUSION The majority of the popular peripheral block techniques are easy to perform, but some less experienced anaesthetists consider the risk too great, and therefore opt not to offer them, especially in the face of potential adverse medico-legal implications, and lack of evidence in defence of the anaesthetist. The best choice for each patient needs to be examined, and ultimately a peripheral technique may or may not be appropriate, which is why cases need to be individualized with careful consideration to patient and surgical factors, there must be meticulous attention to detail and careful monitoring is needed. Ultrasound guided nerve blocks are at the forefront of ongoing improvements in technique and equipment for use in children, and with regular audits and record-keeping, the practice of peripheral techniques should grow to benefit more infants and children.

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