In some examples, a device includes a catheter and a sheath. The catheter includes a catheter body and an expandable balloon positioned on the catheter body. The sheath includes a sheath body including a wall defining a lumen configured to receive the expandable balloon, the wall defining a channel extending longitudinally at least partially between a proximal end of the sheath body and a distal end of the sheath body, and a sheath insert configured to close the channel. The sheath insert includes a septum configured to be removably received within the channel, and a flange extending from the septum and configured to retain the septum within the channel when the septum is received within the channel.