Interscalene block 2018-07-22T06:39:51+00:00

INTERSCALENE BLOCK

Level of difficulty

Intermediate

Indications

Anaesthesia & Analgesia for shoulder, clavicle (Lateral 2/3 – combine with superficial cervical plexus), acromioclavicular and upper arm surgery, as well as manipulation of dislocated shoulder.

Anatomy

Formation of Brachial Plexus

Brachial plexus in Interscalene groove

The brachial plexus is formed by the ventral rami of C5 – T1 nerve roots. The C5 – C7 roots travel very superficially in the groove between scalenus anterior and medius muscles (interscalene groove). The C5 & C6 roots combine to form the upper trunk of the brachial plexus, and the C7 root continues as the middle trunk. Both trunks are involved in supplying sensation to the shoulder, distal clavicle and upper arm – therefore brachial plexus block at the interscalene level is essential for adequate anaesthesia and analgesia in the above indications. In the majority of individuals, and accounting for wide variations in body habitus and neck circumference, the roots will lie at a depth of 1-3 cm and often lie on top of one another within the groove (C5-C7). This can aid identification of each root however anatomy and therefore sono-anatomy can vary greatly, particularly in the elderly where the scalene muscles and therefore interscalene groove can be difficult to delineate. Identification of nerve roots and vertebral level can therefore be done by tracing roots proximally and identifying the corresponding transverse process. C5 & C6 transverse processes have a bifid appearance owing to the presence of both anterior and posterior tubercles (C5 larger posterior; C6 larger anterior); whereas C7 has only a posterior tubercle (easy to identify).

Scanning Technique

Place the probe transversely in the supraclavicular fossa to obtain a view of the brachial plexus as for supraclavicular block. Identify the subclavian artery and the brachial plexus lateral and superficial to the vessel. Scan cephalad maintaining the plexus in view, visualise the appearance of the scalenus muscles, and the plexus divisions now forming their roots within the interscalene groove. As described above they can be typically seen stacked in a line on top of the other within the groove (C5-C7 superficial to deep) appearing as hypoechoic circles/ovals. Identification of the vertebral level and roots is also advised particularly if anatomy is indistinct. C5 and C6 roots are typically together at level of C6 (C6 may be split into two, thereby 3 hypoechoic circles may be visible at this level). C7 root is visible at the C7 transverse process level. Identify the vascular structures when selecting the optimal image and prior to needling by using colour Doppler, it is a highly vascular area. Identification of the phrenic nerve is also possible on the surface of scalenus anterior

Interscalene Brachial Plexus

Phrenic nerve

Video Neck Scanning

Block Performance

  • Probe: High-frequency linear probe (15-10Hz)
  • Settings: Nerve
  • Depth: 1 – 4cm
  • Needle: 50 mm short-bevel nerve block needle
  • Position: Supine with head turned contralaterally (typical). Some clinicians employ a variable degree of lateral positioning (block side up!) stating improved visualisation as well as room for needling.
  • Needle technique: In plane (Lateral to medial – typical, medial to lateral), out of plane
  • Needle tip position: adjacent and slightly below C6 root within the groove. Initially Inject 1-2ml of anaesthetic to ensure spread within groove around roots and not in belly of scalenus medius. There is an interscalene fascial layer to pierce to ensure the needle tip has entered the groove.
  • Drug choice: for longer lasting nerve blocks, bupivacaine O.25% to 0.5%. For short-duration blocks, lidocaine 1 to 2% may be employed
  • Drug Volume: Analgesia (low volume 5-10ml), Anaesthesia (higher volume 15-20ml)

Inplane-Lateral to Medial approach

Inplane-Medial to Lateral approach

Out of Plane approach

Testing Block Success

  • It may be possible to demonstrate adequate surgical anaesthesia after 5-10 minutes, however, some blocks may take significantly longer to establish (up to 40 minutes). Three components for the block should be tested. Motor- by asking the patient to abduct and flex the arm at the shoulder, Sensory- by checking loss of cold sensation over the area of surgery, Proprioception- by demonstrating loss of sense of joint position and motion

Pearls & Pitfalls

  • Positioning: ensure both patient’s and your comfort, as well as that there is enough room to manoeuvre and align the needle. May require slight lateral positioning to achieve this, particularly in patients with short large necks.
  • Communication: ensure patient is aware that you may rest a hand against thier face. This often happens when blocking from the top end rather than the side.
  • Tip repositioning: often not required if spread is good at above insertion point. There may however be muscular bridges crossing the groove which prevent spread around the roots. If spread around C5 & C6 is not adequate then repositioning between C5 and C6 or even superficial to C5 may be required.
  • Phrenic n palsy: High volume blockade or insertion points superficial to C5 route will invariably result in blockade of the phrenic nerve as local anaestheic spreads over the ventral surface of Scalenus anterior. Low volume blockade and needle tip positioning adjacent to or just below C6 will tend to avoid it.
  • Additional blockade of the superficial cervical plexus: advised in arthroscopic surgery to cover the posterior port site, as well as for clavicle surgery. It will also certainly be required in when low volume interscalene blockade is used.
  • Intercostobracheal nerve: T2, cutaneous branch of an intercostal nerve, innervates the upper medial arm, and potentially part of the shoulder. Must be supplemented if a brachial plexus block is used
  • Vertebral artery: Injections deep to C6 should be done with caution due to risk of puncturing the vertebral a (which becomes visible anterior to C7 transverse process using Doppler). If possible keep the transverse process out of view in the needling image.
  • If the hypoechoic area representing the spread of local anaesthetic from the tip of the needle is not seen during injection, stop injecting and reposition the needle position needs to be readjusted. The main concern is vascular injection if injectate spread is not seen.

Video of Interscalene catheter insertion

Continuous interscalene block (CISB) may also be performed for procedures with anticipated ongoing pain. The in-plane or out-of-plane approach may be used for siting CISB.

Injection of 0.5-1ml of local anaesthetic through the needle to distend the interscalene groove is recommended to facilitate the ease of catheter advancement.

Local anaesthetic spread can be observed in real time during catheter injection to help confirm correct positioning.

Side Effects

The following are classified as side-effects rather than complications because they are likely to be present with any successful ISB and are temporary and resolve with resolution of the block

  • Ipsilateral hemidiaphragm paresis is a common sequelae to an interscalene block
  • Recurrent laryngeal nerve blockade may occur, leading to hoarseness and swallowing difficulty.
  • Horner’s syndrome often occurs due to the proximity of the sympathetic cervical chain.

Complications

Respiratory complications

  • Permanent damage to phrenic nerve and diaphragm function
  • Pnemothorax

Neurological complications

  • Neuropathy may be a consequence either of intra-neural injection or direct trauma to the nerve by the needle. However, nerve injury is much more frequently due to surgical trauma. Injection of local anaesthetics in the vertebral artery or even in the small cervical vessels can lead to neurotoxicity.  Epidural or spinal injection is a described complication and should be suspected if sensory defect of the contra lateral upper limb occurs

Contraindications

Absolute contraindications to interscalene blockade are patient refusal and severe local infection

A successful interscalene block also usually results in blockade of the ipsilateral phrenic nerve and thus ipsilateral diaphragmatic paresis.  It is important therefore never to block both sides at the same time.

Caution should be exercised in the following circumstances and in general they constitute relative contraindications for an interscalene block:

  • Contralateral phrenic palsy
  • Contralateral pneumothorax
  • Contralateral pneumectomy
  • Severe COPD

Ultrasound guided block may be judiciously performed in coagulopathic patients as the vascular anatomy can be identified and avoided.

References

  1. Applying ultrasound imaging to interscalene brachial plexus block. Chan VW: Reg Anesth Pain Med 2003; 28: 340-3.
  2. Ultrasonographic guidance improves the success rate of interscalene brachial plexus blockade. Kapral S, Greher M, Huber G, Willschke H, Kettner S, Kdolsky R, Marhofer P.   Reg Anesth Pain Med

2008;33:253-8.