A midline is a long peripheral IV catheter placed into a peripheral vein, terminating near the axillae, distal to the shoulder.  The same veins accessed for PICC placement in the upper arm are also used when inserting a midline.
Midlines are a great solution for patients with difficult IV access receiving non-vesicant and non-irritant therapy.
Midlines are contraindicated when there is a history of venous thrombosis, restricted blood flow to the extremities, and renal disease requiring peripheral vein preservation.