Pneumothorax is seen most commonly with which approach of brachial block:-

In supraclavicular approach of brachial block as pleura is in close vicinity. The anterior rami of C5 to T1 form the brachial plexus, which exits the cervical spine to form the superior, middle, and inferior trunks that travel between the anterior and middle scalene muscles. Each trunk divides into an anterior and posterior branch, which subsequently rejoins to form the lateral, posterior, and medial cords as it travels distally to the clavicle. The supraclavicular approach blocks the brachial plexus from the distal trunks to the proximal cords but often is targeted at the divisions level. General complications to peripheral nerve blockade apply to supraclavicular blocks including risk for infection, bleeding, and neuropathy. With the advent of ultrasonography, constant visualization of the needle tip, first rib, and pleura can decrease the risk for pneumothorax. Common, self-limited, side effects associated with other proximal brachial plexus blockade include hoarseness due to an ipsilateral laryngeal nerve block, Horner syndrome from stellate ganglion block, and hemidiaphragmatic paresis from a phrenic nerve blockade.