A Peripherally Inserted Central Catheter (PICC line) is a long, thin tube inserted into an arm vein, with its tip resting near the heart. It provides a reliable way to administer medications, fluids, nutrition, and draw blood samples, reducing the need for repeated needle sticks. Selecting the appropriate channel, or “lumen,” for blood draws is important for accurate test results and patient safety.
Understanding PICC Lumens
PICC lines can have one, two, or three separate internal channels, known as lumens. Each lumen extends the full length of the catheter and has its own external port, allowing for independent use. Lumens are described by their position relative to the catheter’s tip and the heart.
The “distal lumen” is furthest from the insertion site and closest to the heart. In multi-lumen PICCs, the “medial lumen” is between the proximal and distal openings. The “proximal lumen” is closest to the insertion site and furthest from the heart. These distinct channels enable various medical tasks, including administering different medications simultaneously or performing blood draws.
Preferred Lumen for Blood Draws
When drawing blood from a multi-lumen PICC line, the distal lumen is generally the preferred site. This choice is standard practice, helping ensure the integrity and accuracy of the blood sample and optimizing laboratory results.
Why the Distal Lumen is Preferred
The preference for the distal lumen stems from several factors that contribute to the quality of the blood sample. Its placement closest to the central circulation allows for a more representative sample of systemic blood, minimizing localized variations that could affect test results.
The distal lumen typically has the largest internal diameter. This wider channel facilitates smoother blood flow during collection, reducing the risk of hemolysis (red blood cell rupture) that can compromise sample integrity.
Using the distal lumen also helps minimize contamination or dilution of the blood sample. Other lumens are often used for continuous infusions, which could potentially mix with the blood sample. The distal lumen is frequently designated for blood draws, reducing interference from infusing substances and ensuring the collected sample accurately reflects the patient’s current physiological state.
The better flow characteristics also contribute to a reduced risk of clotting within the lumen. Maintaining an unobstructed lumen is important for successful blood draws and the overall longevity of the PICC line.
Alternative Lumen Considerations
If the distal lumen cannot be used for blood draws due to occlusion, poor blood return, or active use for an uninterrupted infusion, alternative lumens may be considered. The order of preference, if the distal lumen is unavailable, is the medial lumen (if present), followed by the proximal lumen.
When using an alternative lumen, specific precautions are important. Thoroughly flush the alternative lumen with saline to clear any infusing medications or fluids before drawing blood. A discard volume, typically 3-5 mL of blood, should be withdrawn and discarded prior to collecting the sample to remove any diluted or contaminated blood within the catheter.
Despite these precautions, samples collected from non-distal lumens might carry a slightly higher potential for dilution or medication interference. If no lumen yields a good sample, repositioning the patient or contacting a healthcare professional for further assessment and troubleshooting may be necessary.