Midline catheters (according to the European and Australian classifications) are peripheral venous access devices, placed by ultrasound guidance in deep veins of the arm, 15-25 cm long, so that their tip is usually located in the axillary vein soon before the clavicle, or in the subclavian vein just below the clavicle (hence the definition 'midclavicular').They are currently used widely in Europe (Italy, Spain, UK), specially in palliative care, though they are not popular in USA.
The expected length of a midline is maily related to its appropriate use (i.e., exclusively for infusion of peripherally compatible solutions).
Midline catheters should be in polyurethane, open-ended, non-valved, preferably power injectable. Silicon midlines are fragile, low-flow, difficult to replace over guidewire, and they should be abandoned. Valved midline have no proven advantage, but - on the contrary - have many specific disadvantages (such as high incidence of malfunction and high cost).
If a peripheral venous access is needed for a length of time shorter than one month, a mini-midline (long peripheral cannula: 6-15 cm) may also be appropriate.