A midline intravenous (IV) catheter is a specialized vascular access device designed for patients requiring IV therapy for a moderate length of time. This type of line serves as an intermediate solution, bridging the gap between a short, standard peripheral IV and a long-term central line. It is a long, flexible catheter inserted into a vein in the upper arm, providing reliable access for treatments that last longer than a few days. The catheter tip does not reach the central circulation near the heart, offering a stable, less frequently replaced option for intermediate-duration medical needs.
Structure and Insertion of a Midline IV
A midline catheter is a long, thin tube typically constructed from a flexible material like polyurethane. These devices generally range in length from 15 to 25 centimeters, making them significantly longer than a standard short peripheral catheter. Insertion usually occurs in the upper arm, targeting larger veins such as the basilic, cephalic, or brachial veins, often performed using ultrasound guidance for accuracy and patient safety.
The defining characteristic of the midline is the final placement of its tip, which is situated at or near the level of the axilla, or armpit. The tip remains distal to the shoulder, meaning it does not enter the central veins of the chest. Because the tip terminates in a peripheral vessel, the midline is classified as a peripheral access device. This peripheral tip location is a key factor in determining the type of solutions and medications that can be safely administered.
Specific Therapies Requiring a Midline
The midline catheter is intended for treatments lasting from one to four weeks, providing stable access that avoids the need for repeated needle sticks. It is specifically indicated for long courses of intravenous therapies that are known to be safe for peripheral infusion. Common uses include the administration of non-vesicant antibiotics for infections like cellulitis or pneumonia, prolonged intravenous hydration, and certain types of pain management protocols.
The larger veins in the upper arm provide greater blood flow, which helps dilute medications and reduces the risk of vein irritation, or phlebitis. However, a midline cannot be used for all types of intravenous solutions. Highly irritating solutions, total parenteral nutrition (TPN), or medications with an extreme pH (below 5 or above 9) or high osmolarity (greater than 900 mOsm/L) are contraindicated. These solutions require a central line because they can cause severe damage to the peripheral veins where the midline catheter tip rests.
How Midlines Differ from PICC and Peripheral IVs
The choice of vascular access device depends heavily on the planned duration of therapy and the specific properties of the infused medication. Standard peripheral IVs are the most common device, characterized by their short length, typically three to six centimeters, and insertion into smaller veins in the hand or forearm. They are only reliable for short-term use, generally lasting a few days before requiring replacement.
Midlines offer an intermediate solution, providing reliable access for a medium duration of a few weeks. The most significant difference lies in the catheter tip’s termination point; the midline tip remains in the peripheral circulation below the axilla. In contrast, a Peripherally Inserted Central Catheter (PICC) is much longer, with the tip threaded all the way into a large central vein, such as the superior vena cava, located just above the heart.
This central termination point allows the PICC line to be used for long-term treatments, sometimes lasting months, and for caustic medications like certain chemotherapies or TPN that require rapid dilution. Both midlines and PICCs are typically inserted using ultrasound guidance to ensure accurate placement, whereas peripheral IVs are usually placed using a standard, non-guided technique.
Lifespan and Maintenance Procedures
A major advantage of the midline catheter is its extended dwell time, which can typically last for up to 28 days, depending on the patient’s clinical status and institutional policy. This longer lifespan significantly reduces the discomfort and potential complications associated with frequent catheter replacements. Proper maintenance is necessary to ensure the line remains functional and free from infection throughout its use.
Routine care involves regular flushing of the catheter with a sterile saline solution, often in a pulsatile manner, to prevent blood clots or medication residue from blocking the line. The dressing covering the insertion site must be kept clean and dry, with sterile changes performed at least weekly or immediately if soiled or loose. Patients and caregivers must also monitor the site for signs of complications that require immediate medical attention:
- Localized pain
- Swelling
- Redness
- Warmth (indicating infection or thrombosis)