FRCA Notes

Interscalene Brachial Plexus Block

Resources

  • Interscalene blocks aim to anaesthetise the trunks of the brachial plexus as they exit the interscalene groove
  • There is also an effect on the proximal nerve roots, and nerves which exit proximally from the plexus such as the suprascapular nerve
  • The roots of the brachial plexus arise from the ventral rami of the C5 - T1 spinal nerves
    • Some patients may have pre-fixed plexuses, arising instead from C4 - C8 (up to 26%)
    • Others may have post-fixed plexuses, arising from C6 - T2 (2.5%)

  • The roots fuse to form the:
    • Superior trunk: C5 & C6
      • C6 often bifurcates into two fascicles within a common epineurium, before joining C5 to form the upper trunk
    • Middle trunk: C7
    • Inferior trunk: C8 & T1

  • The trunks exit in the interscalene groove between the anterior and middle scalene muscles
    • Sometimes C5 passes anteriorly to the anterior scalene muscle
    • Sometimes the superior trunk passes through the anterior scalene muscle

Nearby structures of note

  • Proximal branches such as the dorsal scapular nerve and long thoracic nerve travel within the middle scalene muscle and are at risk of injury
  • The carotid artery, vertebral artery and internal & external jugular veins lie medially, and run perpendicular and in close proximity to the nerve roots
  • The subclavian artery runs parallel to the trunks of the brachial pexus at the level of C8/T1, although is both anterior and inferior
  • The transverse cervical, thyroid and suprascapular arteries, which arises from the thyrocervical trunk of the subclavian artery, lie in close proximity to the scalene muscles
  • The apex of the lung lies antero-inferiorly to the trunks

Distribution of anaesthesia

  • Good coverage of the distal clavicle, shoulder and proximal upper arm
    • C5-C7 dermatomes reliably covered
    • Distal clavicle, humerus, radius and lateral three digit osteotomes typically covered

  • Misses the lower trunk (C8 - T1 rami) in up to 50% of cases, unless injection occurs more distally
    • This leaves the ulnar nerve and median cutaneous nerve of the arm unblocked
    • Therefore less suitable for forearm and hand procedures

  • Low volume block misses the superficial cervical plexus and may need to be supplemented for arthroscopic shoulder surgery

Indications

  • Shoulder surgery in combination with superficial cervical plexus block to block the supraclavicular nerves
    • Either as the sole technique or as an analgesic supplement to GA
    • May still require posterior port site infiltration for arthroscopic shoulder surgery
    • Use of interscalene block for rotator cuff day surgery is associated with less pain, earlier ambulation, earlier discharge, fewer unplanned admissions and greater patient satisfaction

  • Surgery on the lateral two-thirds of the clavicle
  • Surgeries on the proximal humerus

Contraindications

General Specific
Patient refusal Contralateral respiratory impairments
Local anaesthetic allergy Significant pulmonary disease
Localised infection Contralateral vocal cord palsy
Lack of appropriate resources
Coaguloapthy
Pre-existing nerve injuries


Standard regional anaesthetic set-up

  • Patient consent obtained
  • Ensure appropriate equipment available
  • Ensure adequate staffing i.e. trained assistant
  • Access to resuscitation equipment including intralipid
  • IV access obtained
  • Monitoring in situ
  • Correct LA dosing calculated
  • Stop Before You Block moment

Positioning/equipment/ergonomics

  • Ultrasound (high frequency linear array) ± peripheral nerve stimulator ± pressure monitoring
    • Ultrasound associated with fewer needle passes, lower volumes of local anaesthetic and better post-operative analgesia

  • Patient awake or asleep, supine but sat up 30° (or semi-lateral decubitus)
  • Head turned to contralateral side, exposing the ipsilateral neck
  • Ultrasound on contralateral side with ergonomic set-up at anaesthetists discretion
  • High-frequency linear array ultrasound transducer
  • 50mm echogenic short-bevel needle
  • Full aseptic precautions

Local anaesthetic

  • Minimum effective volume of local anaesthetic for post-operative analgesia is as little as 0.9ml when using ultrasound
  • More commonly 8-15ml of local anaesthetic (e.g. 0.2% ropivacaine, 0.25% levobupivacaine) is used for analgesia
  • Higher volumes (15-20ml) of higher concentration (e.g. 0.75% ropivacaine) anaesthetic are required to guarantee an effective block for awake surgery

Performance

  • Structures identified, especially making note of nearby arterial vasculutare and nerves including phrenic nerve and proximal branches of the plexus
  • Typical 'traffic light' appearance of C5 - C7 roots (sometimes C6 as two roots) between the anterior and middle scalene
  • Transduced position approximately lateral across the neck at the level of the cricoid cartilage
  • Postero-lateral to antero-medial, in-plane needle approach

  • May feel a pop as the prevertebral fascia is pierced
  • Needle orientated to space between roots rather than at roots directly
  • If nerve stimulation used, motor response in the shoulder, arm or forearm indicates correct placement in the interscalene groove
    • If nerve stimulation occurs below 0.5mA consider withdrawing needle slightly as may be intraneural
  • If pressure monitor used, a high pressure (>15psi) indicates needle-nerve contact

  • Performing a periplexus technique (as opposed to intraplexus technique) is associated with similar block efficacy but may reduce risk of nerve injury
  • Consider tracing the plexus down towards the subclavian artery; if correct placement of LA within the plexus sheath then should see spread down to here

  • Higher incidence of prolonged nerve dysfunction than other peripheral nerve blocks; up to 14% at 10 days post-block

Unilateral phrenic nerve blockade

  • Spread of local anaesthetic over scalenus anterior blocks the phrenic nerve almost universally, especially if landmark techniques and/or high volumes (>10-20ml) are used
  • Smaller volumes (e.g. 5ml) and/or lower insertion sites may lead to lower incidence of phrenic nerve blockade (13 - 50%), although potentially compromise block efficacy

  • Leads to hemi-diaphragmatic paralysis and a 15-40% reduction in FEV1
  • This may lead to dyspnoea ± more pronounced respiratory failure, especially if:
    • Existing airway or respiratory disease, including contralateral issues (e.g. pneumothorax) or bilateral issues (e.g. COPD)
    • Obesity
    • Existing contralateral phrenic nerve palsy

  • Not reliably detected by pulse oximetry due to physiological compensation and may be asymptomatic
  • Intra-operative oxygen supplementation may be required
  • Suitable planning for post-operative monitoring ± ventilatory support is required for higher risk patient
  • Long-term phrenic nerve dysfunction occurs in 1 in 2,000 patients due to compressive neuropathy

Horner's syndrome

  • Arises in approximately 50% of patients due to sympathetic stellate ganglion blockade
  • Leads to the triad of ipsilateral:
    • Ptosis (may be partial)
    • Constricted pupil (miosis)
    • No thermal sweating (anhidrosis)
  • Often spontaneously resolves within hours without intervention beyond reassurance

Other

  • Epidural or intrathecal spread via the dural cuff of a nerve root, which can lead to adverse central neurological symptoms including seizures or indeed a total spinal anaesthetic
  • Recurrent laryngeal nerve block leading to hoarse voice, often not clinically consequential
  • Vertebral artery injection
  • Injury to dorsal scapular nerve (lies within middle scalene muscle) ± the long thoracic nerve which sometimes accompanies it
  • Pneumothorax
  • Direct needling of the cervical spinal cord

Generic


  • Catheter-based techniques facilitating continuous infusion of local anaesthetic may be required for major surgery, where post-operative pain outlasts the analgesic effect of single-shot interscalene block
  • Compared to single-shot techniques, they are associated with:
    • Less shoulder pain at rest
    • Less dynamic shoulder pain
    • Reduced opioid consumption
    • Greater patient satisfaction

  • Placement of a catheter facilitates ambulatory regional analgesia although requires appropriate patient selection framework and a robust follow-up system to be successful
  • Examples of regimens include a 25-35ml 0.25% levobupivacaine followed by an infusion rate of 3-5ml/hr of 0.1% levobupivacaine

  • Complications are low, although can be significant if there is catheter dislodgement
  • As such, it is imperative to:
    • Robustly check the catheter tip position during insertion
    • Fix the catheter securely including use of specialist anchor dressings, surgical glue or tunnelling