A midline catheter is a specialized intravenous access device used for patients requiring intermediate-term intravenous therapy. It is longer than a standard peripheral IV line but shorter than a central line. Its function is to provide a reliable pathway for administering non-irritating medications and fluids directly into the bloodstream. Midlines reduce the need for multiple needle sticks over several weeks, offering a more stable option than frequently replaced standard IVs.
Anatomical Placement and Insertion Technique
Midline catheters are always placed in one of the large veins of the upper arm, such as the basilic, cephalic, or brachial veins. Clinicians commonly choose these veins for insertion due to their size and accessibility. The catheter is threaded through the vein and kept short, typically between 8 to 20 centimeters in length.
The midline’s tip rests in a large peripheral vein at or below the axilla (armpit), remaining in the upper arm and shoulder region. It deliberately avoids the main central circulation near the heart. Insertion is performed using ultrasound guidance, allowing the clinician to visualize the vein in real-time. This technique enhances precision and minimizes the risk of hitting nearby nerves or arteries.
Clinical Reasons for Choosing a Midline
A midline catheter is selected when a patient requires intravenous access lasting longer than a standard peripheral IV can reliably provide. Standard IVs often fail or cause complications like phlebitis after only a few days. Midlines are intended for therapies lasting from 6 days up to four weeks, such as extended courses of antibiotics or long-term hydration.
Midlines are particularly beneficial for individuals with difficult venous access. Placing the catheter in a larger, deeper vein provides a more durable and stable site for infusion. Utilizing this single, reliable access point reduces patient discomfort and preserves smaller, superficial veins for future use.
Midline Versus Central Line Distinction
The distinction between a midline catheter and a central line, such as a Peripherally Inserted Central Catheter (PICC), rests entirely on the final location of the catheter tip. A PICC line is inserted in the arm but is advanced until its tip resides in the superior vena cava near the heart, placing it in the central circulation. In contrast, the midline catheter’s tip stops in the peripheral venous system of the arm, remaining below the shoulder.
This difference in tip location dictates the types of medications that can be safely administered. Because a midline terminates in a smaller vein, it cannot handle highly concentrated solutions or medications with extreme pH levels or high osmolarity. Vesicant drugs (which cause tissue damage if they leak) and solutions like Total Parenteral Nutrition (TPN) must be delivered through a central line. This ensures rapid dilution in the large volume of blood near the heart. Administering these high-risk medications through a midline risks severe vein irritation and damage, known as chemical phlebitis.
Duration of Use and Patient Care
Midline catheters are an intermediate-term solution, typically used for 14 to 28 days, depending on clinical needs and institutional guidelines. The catheter remains in place until the prescribed therapy is completed or a complication necessitates removal. Maintenance involves specific steps to ensure the site remains sterile and the catheter functions properly.
The insertion site is covered with a transparent dressing that must be changed every seven days, or immediately if soiled or loose. To prevent blood clots, the catheter must be flushed with sterile saline solution:
- Before and after each use.
- At regular intervals when not in use.
Patients and caregivers must monitor the insertion site closely for signs of complications. These include localized swelling, redness, pain, or drainage, which could indicate a developing infection or phlebitis.