Royal National Orthopaedic Hospital, Stanmore, UK

In 1912 L.Eloesser¹ stated that any part of the body subserved by a simple combination of nerves which anatomical course admits be reached by a needle without damage to adjacent structures, are amenable to regional anaesthesia (RA).

This statement remains in force, with the advantage that nowadays, we are able to see those nerves, the needle and the adjacent structures, making RA safer and more effective.

The upper limb’s innervation comes mainly from the brachial plexus (BP) and most of the surgeries on the upper limb can be done under RA alone.

Different approaches of the BP, provide different surgical anaesthesia/analgesia because nerves emerge from the BP at different levels along its course. A thorough knowledge of the BP anatomy is essential to succeed.

The BP is formed by the ventral primary rami of cervical nerves 5 to 8 (C5-C8) and the first thoracic nerve (T1) with variable contributions from the fourth cervical (C4) and the second thoracic (T2) nerves.²

These ventral primary rami form the roots, which become trunks named according to their vertical arrangement within the interscalene groove (IS) where the interscalene block (ISB) is performed.

The C5 and C6 roots unite to form the superior trunk (ST), which at the supraclavicular fossa, gives the supraescapular nerve (SSN). This nerve courses deep to the omohyoid muscle heading posterior to the supraspinous fossa and provides innervation to the glenohumeral and acromioclavicular joint and the humeral head and neck.³

The C7 root becomes the middle trunk (MT) and the C8 and T1 roots form the inferior trunk (IT), which is rarely reached by the local anaesthetic (LA) deposited with ISB.

The three trunks continue under the clavicle and over the first rib where each one separates into anterior and posterior divisions. These divisions are located posterolateral to the subclavian artery (SA), which is a valuable anatomic landmark when performing supraclavicular BP blockades (SNB).

Further distally, the divisions reorganize into three cords, defined by their relationship to the axillary (subclavian) artery (AA) at the infraclavicular fossa. The lateral cord (LC) is lateral to the AA, the posterior cord (PC) is posterior and the medial cord (MC) is located medial. The infraclavicular BP blockade (ICB) targets these cords. A safe approach is found at the coracoid process where the subscapularis muscle, but not the lung, can be found posterior to the neurovascular bundle.²

In the infraclavicular fossa, the axillary nerve (AN), subscapular nerves (NS) and the lateral pectoral nerve (LPN), branch and head to the shoulder to contribute on its innervation.⁴

The musculocutaneous nerve (MscN), the medial antebrachial cutaneous nerve (MABCN) and the medial cutaneous nerve (MBCN) also branch here, but run with the vessels to enter the axilla.²

Further separation of the cords gives the terminal nerves. The radial nerve (RN), the ulnar nerve (UN) and median nerve (MN) run in close proximity to the AA in the axilla above the conjoint tendon (CJT) while the MscN runs separately. The CJT is an essential landmark when performing AXB as beyond its lateral border each nerve follows their own course.²

Nerves can be approached at any level on their course. The choice of a specific technique and LA type, volume and concentration should be made based on the surgical area to be covered including the tourniquet and whether surgical anaesthesia or analgesia is required. The duration of surgery, patient position, patient characteristics/morbidities and anaesthesiologist experience should be balanced.

Choice of LA The choice of LA is decided according to the desired speed of onset, block intensity and duration.

The mass of LA rather than concentration or volume, seems to be the most important determinant of onset and duration. However, clinical studies have suggested there is a threshold beyond which duration and onset of block do not change.⁵ Therefore, if an analgesic block is required, the use of low concentrations should be considered against higher concentrations with the aim of reducing the risk of LAST and nerve damage.

Adjuvants and Continuous infusion catheters

Single shot BP blocks have limited duration. Perineural continue infusions by indwelling catheters are an excellent option to prolong analgesia,⁶ however, its use is limited by the need of trained staff and appropriate setup to provide the adequate care.

Many adjuvants have been used in an attempt to prolong analgesia, however none of the adjuvants studied have proven a clear benefit exempt of risks.^7–9

Shoulder Surgery The shoulder innervation is mainly supplied by the SSN and the AN, with small contributions from the LPN and NS,⁴ therefore to provide good cover of the shoulder the BP should be approached before the SSN branches.

ISB is the preferred technique.¹⁰ ISB aims the roots/trunks but when enough volume is deposited here, further spread and blockade of the supraclavicular nerves of the superficial cervical plexus is achieved, providing cutaneous cover of the cape of the shoulder.¹¹ Unfortunately, the phrenic nerve running anterior to the anterior scalene muscle, is consistently blockade too, leading to hemi-diaphragmatic paralysis (HPD).¹²

In patients with pre-existing pulmonary compromise or having bilateral shoulder surgeries, alternative diaphragm-sparing techniques should be considered.

A reduction of the LA dose and/or its deposition outside the BP sheath^{13 14} or instead, the use of SCB, anterior approaches of SNN alone or a ST block, have proven to reduce the incidence of HPD providing similar analgesia to ISB.^15–17 Negligible risk of HDP has only been shown by costoclavicular block and the combination of ICB and posterior approach of the SNN, however the analgesia provided need further evaluation.¹²

To perform ISB I use a traceback technique. The patient is positioned supine with the head facing the contralateral side. The probe is placed on the supraclavicular fossa to identify the subclavian artery (SA) and the BP posterolateral. The probe is swept cephalad following the BP until the unique shape of the C7 transverse process (TP) lacking the anterior tubercle but showing a large posterior tubercle is distinguished. Every other cervical TP holds anterior and posterior tubercles (U-shaped) and can be identify sweeping the probe upward.¹⁸

The roots found exiting the TP are followed downwards between the middle and anterior scalene muscle and away for the vertebras where the ISB is performed.

The needle is introduced in plane from posterolateral to anteromedial, aiming to deposit the LA on the lateral border of the BP sheath. Careful should be taken to avoid any hyperechoic structure within the middle scalene as the Dorsal scapula nerve and the Long thoracic nerves run inside it.¹⁹

10–20ml are usually recommended.

Upper arm surgery The innervation of the upper arm is supported by the same nerves supplying the shoulder. In addition, the MBCN and the nerve the intercostobrachial nerve (ICBN), branch of T2, provide cutaneous innervation to medial aspect of the upper arm.²

If the surgery field goes further distally, the RN and MscN need to be blocked as they supply the proximal and distal part of the humerus respectively.³

SCB or ICB are good options to provide analgesia for the upper arm. However, if the surgery field includes the shoulder, the blockade of SNN and/or supraclavicular nerves should be ensured. If an ICB is performed, this has to be achieved by a separated injection.²⁰

The ICBN block is usually not required, however, if needed, its blockade can be performed by a LA deposition above the Latissimus dorsi muscle at 2–4cm from the AA.²¹

To perform a SCB, position the patient supine and place the probe over the supraclavicular fossa to identify the SA and the clusters of nerves posterolateral and superficial to it. The BP is crossed by different vessels at this level (the dorsal scapular artery, transverse cervical artery or suprascapular artery). The first rib and pleura should be identified and avoided, however, due to its proximity, there is a risk of pneumothorax.

The needle is inserted in plane, from lateral to medial to deposit the LA below the SA over the first rib and over the BP to accomplish a complete blockade. Volumes of 25ml- 30ml are usually required.²²

To perform an ICB, the probe is place at or medial to the coracoid process underneath the clavicle to identify the AA and cords in close proximity to the it. The abduction of the arm usually helps bringing the BP more superficial. The lung should be left away from the needle’s trajectory, therefore avoiding the risk of pneumothorax.

The needle is inserted in plane, from cephalad to caudad, aiming to deposit the LA bellow the AA (6 o’clock) where the PC is located to get a U shape around the AA. If there is no adequate spread to the LC and MC, redirection of the needle to the LC (9 o’clock) and MC (3 o’clock) should be performed.

If a SSN is required to supplement the ICB, this could be performed anteriorly under the omohyoid muscle, or posteriorly, at the level of the supraspinatus fossa.³

Elbow, forearm and hand surgery:

For surgery at the elbow and below, we need to achieve the blockade of the RN, UN, MN, MscN, MABCN and MBCN.

Similar success rates have been found with SCB, ICB and AXB for these surgeries,²³ however, AXB holds a low rate of complications and very superficial position.

To perform an AXB the patient is positioned with the arm abducted 90 degrees at the shoulder. I use a traceback technique starting with the probe at the mid-humerus to identify the AA and trace it proximally until the CJT of the Latissimus dorsi and Teres major is identified below it.

There is a lot of variability on the nerves’ location around the AA in the axilla, but also changes on the arm position or pressure on the probe may lead to further fluctuation.

To ensure their identity, the nerves can be traced distally, however, as a rule, the MN usually is found in the anterolateral quadrant, the UN in the anteromedial and the RN in the posteromedial.²⁴ The MscN runs separate between the Biceps and Coracobrachialis muscle.

The MCBN and MACBN are not easily distinguishable but they can be found running medial to the axillary vein and between this and the AA respectively.²⁵

The needle is inserted in plane from lateral to medial targeting the conjoint tendon below the AA to deposit LA around the RN. The needle is then withdrawn and redirect to the MN and UN. Lastly, the needle targets the MscN. 25–30ml of LA are usually required to ensure the blockade of all the nerves.

To provide anaesthesia of the hand, nerves can be block along the forearm.²⁶

On its course along the arm, the MN remains in close proximity to the AA. Proximally, the MN is usually lateral to it but cross to be located medially in the antecubital fossa. If the nerve is target in the forearm to provide hand anaesthesia, this should be done at least 5 cm proximally to the wrist crease, as the palmar cutaneous nerve usually branches there.

The UN diverges from the AA and run superficially to pass through the condylar groove in the elbow and course along the medial aspect of the ulnar artery in the forearm where can be safely targeted.

The RN descends posterior to the humerus and turns anterior to the lateral epicondyle in the antecubital fossa. Its superficial branch joins the lateral side of the radial artery in the forearm to supply the dorsum of the hand.

The MscN is positioned lateral to the Biceps tendon in the antecubital fossa and continues as the lateral cutaneous nerve of the forearm.

The blockade of these nerves can be also used to supplement other blocks as ‘recue blocks’ or in combination to short acting proximal BP blocks to prolong analgesia with minimal motor block.

References

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