Hemidiaphragmatic Paralysis After Interscalene Block

Hemidiaphragmatic paralysis after interscalene block is loss of ipsilateral diaphragm movement from phrenic nerve blockade, generally lasting for the duration of the block, rarely longer.

Epidemiology. Almost 100% of usual interscalene blocks, with 25% to 45% fall in lung function. Prolonged paralysis beyond block duration is reported in about 1 in 1,000 to 1 in 4,000 (case series), possibly from nerve injury or compression by haematoma.

Risk factors. Large volume (over 15 mL), obesity, pre-existing lung disease, contralateral diaphragm disease, supine or lateral position and continuous catheter infusion.

Pathophysiology.

Anterior spread of local anaesthetic to the phrenic nerve interrupts motor signals to the hemidiaphragm. Permanent injury follows direct neural trauma, ischaemia or compressive haematoma.

Reduced breath sounds and dullness at the ipsilateral base, shortness of breath on exertion or lying flat, paradoxical abdominal motion, desaturation and basal atelectasis. Symptoms often resolve within 24 hours.

Red flags.

• Dyspnoea at rest.
• Hypercapnia or fatigue.
• Persistence beyond 48 hours.

Diaphragm ultrasound (M-mode excursion under 10 mm or paradoxical movement) is the preferred bedside test. Chest radiograph shows hemidiaphragm elevation. Spirometry (fall in forced vital capacity of over 20% when supine) and sniff test provide support. Nerve conduction of the phrenic nerve when persistent.

Differential diagnosis.

• Pneumothorax.
• Pleural effusion.
• Atelectasis.
• Phrenic nerve injury from surgery.
• Neuralgic amyotrophy.
• Neuromuscular disease.

Reassure and monitor in most. Sit upright, give oxygen to saturation of 94% to 98%, and encourage incentive spirometry. Use bilevel positive airway pressure for hypercapnic failure.

• Paracetamol: 1 g orally every 6 hours; maximum 4 g daily; reduce in hepatic impairment or under 50 kg.

Persistent paralysis beyond 3 months: respiratory physician review, sniff test and dynamic imaging; consider diaphragm plication for symptomatic permanent paralysis after 6 to 12 months.

Prevention. Use diaphragm sparing techniques (superior trunk, low volume interscalene, suprascapular nerve and axillary nerve block), and avoid interscalene block when respiratory reserve is poor.

Monitoring. Oxygen saturation, respiratory rate and symptoms for 24 hours, with follow up spirometry in persisting symptoms.

Referral and escalation. Respiratory and thoracic surgical review for persistent paralysis.