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Interscalene block: side effects

An ipsilateral phrenic nerve block occurs in almost 100% and leads to a 25% reduction in pulmonary function. This procedure is therefore contraindicated in anyone with respiratory insufficiency or a contralateral nerve palsy. Risk of pneumothorax is remote but real. Recurrent laryngeal nerve is occasionally blocked as well, and this can lead to hoarseness and complete airway obstruction in patients with an existing vocal cord palsy (thus ask about hoarseness or previous neck surgery). Slight caudad direction of the needle reduces the risk of accidental epidural, subarachnoid, or vertebral artery injection. Meticulous aspiration is a requirement. As with all peripheral nerve blocks, permanent neurologic injury is possible, but rare

The Bezold-Jarisch reflex results in unmyelinated vagal afferent stimulation in response to noxious ventricular stimuli (chemical or mechanical), leading to the triad of hypotension, bradycardia, and coronary vasodilation (mediated via increased parasympathetic tone as well as by ANP and BNP). In the setting of shoulder surgery, it is postulated that the combination of increased levels of circulating epinephrine combined with the sitting position may irritate the left ventricle, leading to the massive parasympathetic outflow that accompanies the Bezold-Jarisch reflex. It is also thought that perioperative beta blockade may increase the incidence of this dangerous reflex. The Bezold-Jarish reflex (bradycardia and hypotension following sudden loss of cardiac stimulation) occurs in 15-30% of patients and can be treated by volume, atropine, and ephedrine.

Interscalene Block: Side Effects

  • Diaphragmatic hemiparesis from ipsilateral phrenic nerve block (100% incidence, 25% reduction in pulmonary function)
  • Pneumothorax
  • Permanent neurologic injury
  • Blockade of vagus, recurrent laryngeal, and cervical sympathetic nerves (Horner’s syndrome)
  • Epidural or subarachnoid injection
  • Vertebral artery injection
  • Severe hypotension and bradycardia (Bezold-Jarisch reflex)


  1. W F Urmey, K H Talts, N E Sharrock One hundred percent incidence of hemidiaphragmatic paresis associated with interscalene brachial plexus anesthesia as diagnosed by ultrasonography. Anesth. Analg.: 1991, 72(4);498-503 PubMed Link
  2. W F Urmey, M McDonald Hemidiaphragmatic paresis during interscalene brachial plexus block: effects on pulmonary function and chest wall mechanics. Anesth. Analg.: 1992, 74(3);352-7 PubMed Link
  3. N Fujimura, H Namba, K Tsunoda, T Kawamata, K Taki, M Igarasi, A Namiki Effect of hemidiaphragmatic paresis caused by interscalene brachial plexus block on breathing pattern, chest wall mechanics, and arterial blood gases. Anesth. Analg.: 1995, 81(5);962-6 PubMed Link
  4. J G D’Alessio, R S Weller, M Rosenblum Activation of the Bezold-Jarisch reflex in the sitting position for shoulder arthroscopy using interscalene block. Anesth. Analg.: 1995, 80(6);1158-62 PubMed Link