Medical care often requires direct access to a patient’s bloodstream for various treatments, leading to the use of different vascular access devices. These devices provide a way to deliver medications, fluids, and nutrients directly into the veins. Understanding the specific type of access device used is important for both treatment efficacy and patient safety.
What Are Midline Catheters?
A midline catheter is a type of intravenous access device inserted into a peripheral vein, typically in the upper arm, and advanced until the tip rests in a larger, more central vein, but not reaching the central circulation. These catheters are generally longer than standard peripheral intravenous (IV) lines, ranging from 15 to 25 centimeters (6 to 10 inches) in length. Unlike a short peripheral IV, which is usually only a few centimeters long and terminates in a superficial vein, a midline extends deeper. However, it differs significantly from a central venous catheter (CVC) or a peripherally inserted central catheter (PICC), which are designed to have their tips located in the superior vena cava, a major vein near the heart. Midline catheters serve to provide intravenous access for an intermediate duration, usually between one and four weeks.
Why Blood Samples Are Not Drawn From Midlines
Drawing blood samples from a midline catheter is generally not recommended due to several factors that can compromise the sample’s integrity, the catheter’s function, and patient safety.
The small lumen of midline catheters makes them susceptible to damage during forceful aspiration for blood collection. This suction can cause catheter walls to collapse or adhere, leading to occlusion or weakening of the device. This damage can shorten the catheter’s lifespan, requiring early removal and replacement.
Drawing blood through a long, narrow lumen can stress red blood cells, leading to hemolysis, the rupture of red blood cells and release of their contents into the plasma. This can alter laboratory test results, particularly for substances like potassium, lactate dehydrogenase, and bilirubin, leading to inaccurate readings and potentially incorrect clinical decisions. Even a small amount of hemolysis can render a blood sample unreliable for analysis.
Sample dilution is another concern, which can skew laboratory values. Midline catheters primarily contain intravenous fluids or medications for infusions. Even after flushing, residual infusate can mix with aspirated blood, diluting the sample and leading to falsely low concentrations of blood components. This dilution makes it difficult to obtain accurate measurements of blood constituents, compromising the diagnostic utility of the sample.
Drawing blood from a midline also increases the risk of introducing microorganisms into the catheter or bloodstream. Each access risks bacterial contamination, potentially leading to catheter-related bloodstream infections. These infections are serious complications, requiring additional treatment and potentially prolonging hospital stays. Preserving the patency and sterility of the midline for continuous infusion is important.
When Midline Catheters Are Used
Midline catheters are a valuable option for patients requiring intravenous access for a duration longer than a standard peripheral IV can safely provide, but who do not need a central line. They are frequently utilized for administering prolonged courses of intravenous antibiotic therapy, often lasting for several weeks. Patients needing sustained hydration due to an inability to tolerate oral fluids may also benefit from a midline catheter. These devices are also suitable for the continuous infusion of certain non-irritating medications, such as some pain management drugs. They serve as an important bridge between the short-term capabilities of peripheral IVs and the long-term, more invasive nature of central venous catheters, offering a less complex alternative for intermediate-term treatment needs.
How Blood Samples Are Collected With a Midline Present
When a patient has a midline catheter in place and a blood sample is required, healthcare providers will typically use alternative methods to ensure accuracy and patient safety.
The most common and preferred method is peripheral venipuncture. This involves drawing blood from a separate vein, usually in the opposite arm or hand that does not have the midline catheter, using a standard needle and syringe or vacuum tube system. This approach avoids any compromise to the midline catheter or the integrity of the blood sample.
If a patient has a central venous catheter (e.g., PICC line or central line), blood samples can often be safely drawn from these devices. Central lines are designed with larger lumens and materials that can withstand the negative pressure of blood aspiration without damage or hemolysis. This method is usually efficient and minimizes additional needle sticks. The choice of method depends on the patient’s overall vascular access and clinical needs.