Intravenous access allows for the administration of fluids and medications directly into a patient’s bloodstream. Central lines and midline catheters are two types of devices often confused due to their similar appearance and function. This article clarifies their distinctions.
What is a Central Line?
A central line, also known as a central venous catheter (CVC), is a long, flexible tube inserted into a large vein. Common insertion sites include veins in the neck (internal jugular), chest (subclavian), or groin (femoral). Its tip terminates in a large central vein, typically the superior vena cava near the heart. This placement allows for rapid dilution of administered substances.
Central lines handle a wide range of medical substances, including those that are highly concentrated, irritating to smaller peripheral veins (such as certain chemotherapies or vasopressors), or require rapid and extensive dilution. They are also used for long-term infusions, frequent blood draws, and specialized monitoring.
What is a Midline Catheter?
A midline catheter is a thin, soft tube placed into a vein, typically in the upper arm. Unlike a central line, it is a peripheral access device. Its tip terminates in a peripheral vein in the upper arm or shoulder region, specifically below the armpit (axilla), and does not extend into a central vein near the heart.
Midlines are suitable for administering medications and fluids that are less irritating to veins. They offer a longer duration of use than standard peripheral intravenous (IV) catheters, which need replacement every few days. This makes them a good option for therapies lasting several days to a few weeks.
How They Differ and Why It Matters
The primary distinction between a central line and a midline catheter lies in the final resting place of their tips. A central line’s tip resides in a large central vein close to the heart, such as the superior vena cava, ensuring immediate dilution into the high-flow central circulation. In contrast, a midline catheter’s tip ends in a peripheral vein of the upper arm, remaining below the axilla and not reaching the central circulation. This difference in tip location dictates the types of substances that can be safely infused.
Central lines are necessary for highly concentrated solutions, medications that can damage smaller veins (vesicants), or those requiring continuous rapid dilution, such as certain chemotherapies or vasopressors. The large volume of blood flow in central veins quickly dilutes these substances, minimizing irritation and damage to the vessel lining. Midline catheters are restricted to medications compatible with peripheral infusion, having a near-neutral pH and lower osmolarity (not exceeding 500 mOsm/L). They are not used for vesicant medications or total parenteral nutrition (TPN).
Insertion sites also vary; central lines can be placed in the neck, chest, or groin, while midlines are primarily inserted into veins of the upper arm. While both devices can remain in place for extended periods, central lines are designed for longer-term access, potentially months to years. Midlines are used for intermediate durations, usually up to 30 days. Using the wrong device for a particular medication can lead to vein damage, complications, and ineffective treatment.
When Each is Used
Central lines are chosen for medical situations requiring robust and long-term intravenous access or the administration of specific types of medications. They are used for certain chemotherapy regimens, continuous infusions of vasopressors, and total parenteral nutrition. Central lines also allow for central venous pressure monitoring and frequent blood sampling.
Midline catheters are a suitable option when a patient needs intravenous therapy for an extended period, typically longer than a few days but less than a month. They are commonly used for prolonged courses of antibiotics, general hydration, or medications safe for peripheral veins that require longer access than a standard short IV. Midlines also benefit patients with difficult peripheral venous access, helping to preserve their veins and reduce the need for multiple punctures.