Phrenic-Sparing Regional Anaesthesia for Shoulder Surgery

• The phrenic nerve (C3-5) lies on the anterior surface of anterior scalene, close to the C5/6 roots at the level of an interscalene block, before moving medially away from the plexus lower in the neck
• Interscalene block is effective because it targets C5/6 before the nerves to the shoulder diverge
• However, the proximity of the nerve and the interscalene brachial plexus explains why the phrenic nerve is so often blocked
• Moving the injection distally improves phrenic sparing but progressively misses parts of the shoulder innervation

• Classic large-volume interscalene blocks cause hemidiaphragmatic paresis in essentially all patients, with around a 25-30% fall in vital capacity and FEV₁ reduced by up to 40%
• Most patients with normal reserve compensate using intercostal and accessory muscles and remain asymptomatic
• Problems arise when paresis combines with pain, supine posture, opioids, atelectasis or cardiorespiratory disease

• Dyspnoea and hypoxaemia ± new oxygen requirement
• Prolonged recovery stay, delayed day-case discharge, unplanned admission
• Need for non-invasive ventilation, higher-level care or, rarely, intubation

• Pre-existing lung disease: COPD, moderate to severe asthma, restrictive lung disease, home oxygen
• Obesity and obstructive sleep apnoea
• Heart failure
• Contralateral phrenic nerve palsy or previous pneumonectomy
• Low baseline room-air SpO₂, advanced age, ASA III or above
• Planned continuous catheter technique, which prolongs any phrenic involvement

• Phrenic-sparing blocks are good analgesic blocks but are not quite as effective as interscalene block in the early post-operative period
• Less complete analgesia could lead to increased opioid requirements in a patient cohort least able to tolerate OIVI
• Analgesia and surgical anaesthesia are different goals and most phrenic-sparing/distal techniques provide analgesia only and thus GA is still required
• Ultimately, if the patient can tolerate phrenic nerve involvement then interscalene block remains the preferred option

• Pulse oximetry is insensitive to hemidiaphragmatic paresis
• Point-of-care diaphragmatic ultrasound before and 15-30 minutes after the block is a simple and more accurate bedside test
• Maximal inspiratory pressure has been proposed as a pre-operative risk marker but remains investigational

• No single technique is best for every patient and "phrenic sparing" is a spectrum rather than an all-or-nothing goal
• Even distal techniques do not completely eliminate the risk

• The best-established strategy: reducing volume from 20 ml to 5 ml reduced paresis from 100% to around 45% without compromising analgesia
• Ultrasound guidance allows lower volumes than nerve stimulation

• With a fixed 20 ml, halving bupivacaine from 0.25% to 0.125% reduced paresis from 78% to 21% with acceptable analgesia
• Does not guarantee sparing when large volumes are used

• Injecting outside the interscalene fascia reduced paresis from 90% to 21% in one study
• Greater distance from the plexus may reduce block density and reliability

• Reducing the mass of local anaesthetic may shorten block duration
• These modifications reduce but do not eliminate phrenic involvement

• Follow C5 and C6 distally in the interscalene groove to where they fuse to form the superior trunk
• Inject proximal to the departure of the suprascapular nerve, which runs laterally beneath omohyoid
• Identify the suprascapular and transverse cervical arteries first, as their course is variable
• In-plane, posterolateral to anteromedial, hydrodissecting around the trunk with 10-15 ml
• Covers the major shoulder innervation; useful where the interscalene view is poor (e.g. short neck)
• Improves respiratory function in some studies but is not phrenic-free

• Similar shoulder analgesia to interscalene block, with less Horner's syndrome
• Phrenic block risk is not appreciably different in meta-analysis, which limits its role, although targeting superior trunk components may help
• May miss the suprascapular nerve, which leaves the plexus more proximally

• Arises from the superior trunk (C5,6) and runs posterolaterally beneath the inferior belly of omohyoid
• Passes through the suprascapular notch beneath the superior transverse scapular ligament, runs deep to supraspinatus in the supraspinous fossa with the suprascapular artery, then curves around the spinoglenoid notch
• Supplies the superior and posterior capsule, acromioclavicular joint, supraspinatus and infraspinatus

• Linear probe in the supraclavicular fossa: identify subclavian artery, plexus and the inferior belly of omohyoid
• The nerve lies just lateral to the plexus, deep to omohyoid
• In-plane, lateral to medial; around 5 ml (e.g. ropivacaine 0.5%) into the fascial plane beneath omohyoid
• Still at the level of the supraclavicular block, so spread to the phrenic nerve remains possible

• Patient sitting, ideally with the hand on the contralateral shoulder to bring the scapula posterolaterally; operator behind the patient
• Probe just anterior to and parallel with the spine of the scapula; supraspinatus overlies the bony fossa ('hockey stick' appearance)
• Scan laterally towards the spinoglenoid notch, keeping a steep probe angle; the suprascapular notch is more anterior and carries a risk of pneumothorax
• Identify the suprascapular artery with colour Doppler; in-plane, medial to lateral
• 10 ml local anaesthetic (up to 15-20 ml described) deep to supraspinatus on the floor of the fossa; injectate lifts the muscle
• If the nerve is not seen, contact bone on the floor of the fossa, withdraw slightly and inject
• Nerve stimulation: supraspinatus and infraspinatus twitch
• The most reliably lung-sparing approach

• On its own, early analgesia is inferior to interscalene block (though better than intra-articular injection)
• No cutaneous analgesia; covers mainly the posterior shoulder

• Branch of the posterior cord; passes through the quadrangular space with the posterior circumflex humeral artery and wraps around the surgical neck of the humerus beneath deltoid
• Supplies the inferior capsule, deltoid, teres minor and skin over the deltoid
• 'Selective' distinguishes it from the axillary brachial plexus block

• Patient sitting (arm relaxed by the side) or lateral
• Probe on the posterior humerus just distal to the humeral head, where the shaft curves into the head
• In short axis, lateral and posterior deltoid form a 'donut' with the circumflex artery visible beneath posterior deltoid (colour Doppler); the nerve lies with it in the fascial plane between deltoid and teres minor
• In-plane through posterior deltoid, aiming for the posterior rather than lateral humerus to encourage medial spread
• 5-10 ml into or deep to the fascial compartment; the nerve itself need not be seen
• Nerve stimulation: deltoid or teres minor twitch

• Larger volumes (around 15 ml) spread proximally through the quadrangular space and can block the radial nerve
• General block risks: LAST, intravascular injection, nerve injury, infection, bleeding

• Combined suprascapular (usually posterior) and selective axillary nerve block; described by Price in 2007
• Blocks the two nerves that provide most of the joint's supply, peripherally around the joint
• Provides analgesia, not anaesthesia, so is used with GA and systemic analgesia
• Indications: arthroscopic surgery (growing evidence), open surgery where interscalene block is contraindicated or declined, rescue analgesia, chronic shoulder pain
• Consent: warn of possible early recovery pain (anterior capsule) requiring systemic analgesia

Several techniques aim to add the anterior shoulder supply (subscapular, lateral pectoral and musculocutaneous nerves) while staying away from the phrenic nerve. Evidence is mostly limited to small studies and case reports.

• Infraclavicular block covers the axillary, subscapular, musculocutaneous and lateral pectoral nerves
• One study in arthroscopic surgery showed similar 24-hour pain, opioid use and satisfaction to interscalene block, with no paresis (vs 68-88% with interscalene)
• Others report paresis in 10-15%
• Disadvantage: blocks much of the arm distal to the shoulder

• A more selective infraclavicular injection around the posterior cord (e.g. ropivacaine 0.5% 10 ml) may cover the axillary and subscapular nerves, with some spread to the lateral pectoral and musculocutaneous nerves
• Combined with a suprascapular block, this may approach interscalene-quality analgesia

• Subscapularis plane: arm adducted and externally rotated; probe in the coronal plane over the lesser tuberosity; in-plane, medial to lateral, ~15 ml over the ventral surface of subscapularis to block the axillary and subscapular nerves
• Combined with a 5 ml sub-omohyoid suprascapular block
• A PECS 1 injection (between pectoralis major and minor) can be added to block the lateral pectoral nerve if the acromioclavicular joint is involved

• Interscalene catheters extend analgesia but also extend phrenic involvement for the duration of the infusion
• A retrospective study of continuous interscalene analgesia for arthroplasty linked respiratory complications to higher BMI, older age, asthma, heart failure, lower baseline SpO₂ and ASA III or above
• Suprascapular nerve catheters are feasible; axillary nerve catheters are hampered by lying within the surgical field
• Perineural dexamethasone with a single shot may offer a useful compromise between duration and respiratory risk