Continuous interscalene block is popular for shoulder surgery, but there are several challenges when performing this continuous block. The interscalene catheter is susceptible to incidental dislodgement and migration due to movement of the head and neck. Another important consideration is phrenic nerve involvement; the phrenic nerve is susceptible to being incidentally anaesthetised with local anaesthetic during interscalene block, owing to its close proximity to the interscalene groove. We present two cases: firstly, a case demonstrating an interscalene catheter insertion approach that provides an effective spread of local anaesthetic perineurally within the interscalene groove, with the additional benefit of preventing catheter dislodgement. Secondly, we present a case in which ultrasound-guided interscalene catheter insertion resulted in phrenic nerve palsy in an asthmatic patient, where dilution or ‘wash-off’ of local anaesthetic with normal saline and repositioning of the catheter under ultrasound guidance resulted in rapid recovery of respiratory function and adequate pain control.