A midline catheter is an intravenous (IV) catheter used in healthcare to deliver medications and fluids directly into a patient’s bloodstream. Unlike typical short IVs, its design allows for use over a longer period. Understanding its precise anatomical location and the significance of this placement is important for patient care.
What is a Midline Catheter?
A midline catheter is a peripheral intravenous catheter, inserted into a vein away from the body’s center. It is typically placed in an upper arm vein, such as the basilic, cephalic, or brachial veins. These catheters are longer than standard peripheral IVs, usually 10 to 20 centimeters.
Healthcare professionals use midlines for IV therapy expected to last longer than a few days but not requiring central vein access. Midline catheters are often chosen for administering less irritating medications or for hydration.
Insertion is performed by trained professionals, frequently using ultrasound guidance to ensure proper vein selection and placement. This guidance helps cannulate deeper, larger arm veins that better accommodate the catheter.
Where Midline Catheters End
The tip of a midline catheter terminates in a large peripheral vein in the upper arm. This location is below the axillary line (armpit area) and remains outside the chest cavity. Common veins where the tip may reside include the axillary, subclavian, or brachiocephalic veins, but it always ends before reaching the superior vena cava (SVC). The SVC is a large vein that empties into the heart, marking the beginning of the central venous system.
This distinction is important: a midline catheter is not a central venous catheter because its tip does not enter a central vein. Its placement in a larger peripheral vein allows for better blood flow around the catheter tip, which helps dilute medications more effectively. This increased dilution helps reduce the risk of irritation to the vein walls, known as phlebitis, compared to smaller, more superficial veins.
How Midlines Differ From Other Catheters
Midline catheters differ from both short peripheral IVs and peripherally inserted central catheters (PICC lines). Standard peripheral IVs are short catheters, typically inserted into smaller, superficial veins in the hand or forearm, and are generally used for short-term therapy, usually lasting only a few days. Midlines are longer and placed in larger, deeper veins, allowing them to remain in place for weeks.
PICC lines, in contrast, are also inserted into peripheral veins of the arm, but their tip is advanced much further. A PICC line’s tip terminates in a central vein, the superior vena cava, which lies within the chest cavity, or sometimes even closer to the heart at the cavoatrial junction.
This central placement allows PICC lines to deliver medications that are highly irritating or have extreme pH or osmolarity, which would damage peripheral veins. Midlines are not suitable for these types of medications because their tips are not in the central circulation where rapid dilution occurs.
Why Midline Placement Matters
The placement of a midline catheter offers several advantages for patient care. Because the catheter tip remains in a peripheral vein and does not extend into the central circulation, midlines carry a lower risk of complications associated with central lines. These include pneumothorax during insertion or central line-associated bloodstream infections.
While providing benefits over standard IVs, such as less phlebitis and a longer functional life, midlines balance risk and utility. The termination point in a larger peripheral vein allows for the safe administration of various medications, including certain antibiotics and fluids for hydration, which might be too irritating for smaller peripheral veins.
This placement also enables midlines to remain in place for an extended period, commonly from one to four weeks, with some even lasting up to 30 days or longer if no complications arise. This longer dwell time reduces the need for frequent IV insertions, improving patient comfort and preserving veins.