A Peripherally Inserted Central Catheter (PICC line) is a long, thin, flexible tube inserted into a vein in the upper arm, with the tip advanced until it rests in a large central vein near the heart. This device provides reliable, long-term intravenous access for administering medications, fluids, and nutrition. Utilizing the catheter for procedures like drawing blood requires strict adherence to precise procedural guidelines. Improper technique can compromise the integrity of the blood sample, leading to inaccurate laboratory results, or it can cause damage to the catheter itself.
PICC Line Structure and Lumen Function
PICC lines are categorized by the number of internal channels, known as lumens, allowing for simultaneous use of the line for multiple therapies. Multi-lumen PICCs (e.g., double or triple-lumen devices) have entirely separate internal pathways running from the external ports to distinct exit points inside the vein. This design ensures that incompatible medications or fluids can be infused without mixing until they reach the bloodstream.
The exit points of these lumens are staggered along the catheter’s tip and are named based on their distance from the external access hub. The distal lumen exits at the very tip of the catheter, farthest from the insertion site. The proximal lumen exits closest to the insertion site, while a medial lumen is positioned between the two. Each lumen is often externally distinguished by colored clamps or hubs.
Selecting the Correct Lumen for Blood Sampling
The preferred channel for drawing a blood sample from a multi-lumen PICC line is the distal lumen. This choice is based on two primary advantages that ensure a quality sample and maintain catheter function. The distal port’s position minimizes the risk of aspirating intravenous fluids or medications infusing through the other lumens. If a sample is drawn too close to an infusion port, the blood specimen can be diluted or contaminated, leading to inaccurate test results.
Furthermore, the distal lumen often has a slightly larger internal diameter (gauge) than the other ports. A larger gauge facilitates a smoother, faster flow of blood into the collection syringe or vacuum tube. This improved flow reduces the negative pressure required for aspiration, minimizing the risk of causing hemolysis (the rupture of red blood cells). If a single-lumen PICC is used, that specific port must be used for blood sampling.
Maintaining Sample Integrity and Preventing Complications
To ensure sample integrity, the blood draw procedure involves several precise steps starting with line preparation. Before aspiration, the chosen lumen must be flushed with 10 milliliters of normal saline solution, using a 10-milliliter or larger syringe. This larger syringe size generates less pressure, protecting the catheter from excessive force that could lead to damage or rupture. This initial flush clears any residue of previous medications or clotting agents from the line.
The next step involves withdrawing and discarding a waste sample of blood, usually 5 to 10 milliliters. This waste volume clears the catheter tubing of the saline flush and any residual diluted blood mixture, ensuring the final specimen collected for testing is undiluted. Once the waste is discarded, the required volume of blood is collected into the appropriate laboratory tubes following the correct order of draw.
After all samples are collected, the PICC line must be thoroughly re-flushed with another 10 milliliters of saline using a pulsating or “push-pause” technique. This technique creates turbulence within the lumen, helping to dislodge any blood cells or debris adhering to the inner walls of the catheter. The procedure concludes with a positive pressure flush, where the clamp is closed while the last milliliter of fluid is injected. This prevents blood from flowing back into the catheter tip and causing an occlusion. If difficulty is encountered during aspiration or injection, forcing the syringe should be avoided, as this indicates a potential complication like catheter occlusion.