Delayed Horner's syndrome during a continuous infraclavicular brachial plexus block.

Horner's syndrome is a potential, albeit rare, feature of continuous infraclavicular brachial plexus local anesthetics infusion, mainly the result of anatomical considerations. Horner's syndrome may be described as an "unpleasant side effect" because it has no clinical consequences in itself. Nevertheless, patient discomfort and anxiety may reduce acceptance of the analgesic technique. Reassurance and close clinical monitoring of the patient are essential to enhance patient's safety and acceptance of the technique.