A Peripherally Inserted Central Catheter, commonly known as a PICC line, provides a form of long-term intravenous access. This thin, flexible tube is inserted into a peripheral vein, typically in the upper arm, and advanced until its tip rests in a large central vein near the heart, often the superior vena cava. A double lumen PICC line contains two separate internal channels within the single catheter body. This design allows for the simultaneous administration of two different fluids or medications without them mixing until they reach the bloodstream. Understanding which of the two external ports should be used for specific medical needs ensures both safety and treatment efficacy.
Identifying the Separate Lumens
The two lumens of a double lumen catheter are structurally distinct, and their functionality is determined by where they exit the catheter tip. The lumen that exits the catheter closest to the insertion site is called the proximal lumen. Conversely, the lumen that extends farthest into the vein, with its opening near the catheter tip, is referred to as the distal lumen. The distal lumen is typically the larger of the two channels and terminates closest to the heart. Manufacturers often use color-coding to differentiate the two ports, though the terms proximal and distal define the true functional difference.
Standard Rules for Port Assignment
The fundamental principle governing port assignment is the separation of incompatible fluids and the prioritization of continuous, life-sustaining infusions. The distal lumen is generally preferred for continuous, high-concentration infusions because of its location at the catheter tip. Medications like Total Parenteral Nutrition (TPN) or vasopressors that require rapid dilution are usually routed through this port. The proximal lumen is typically reserved for intermittent medications, routine intravenous fluids, or bolus injections. This separation prevents potential chemical interactions, such as precipitation, that could occur if incompatible medications were to mix within the catheter itself.
Specialized Use for Blood Draws
Obtaining blood samples from a double lumen PICC line requires a specific protocol to ensure accurate lab results. The distal lumen is the designated port for drawing blood samples in most cases. This is because the distal lumen often has the largest internal diameter, which ensures an adequate flow rate and reduces the risk of catheter collapse during aspiration. Before drawing a sample, any ongoing infusions must be temporarily stopped, and the line is flushed with saline to clear residual medication. A small volume of blood, known as the waste sample, is withdrawn and discarded before the actual sample is collected. This crucial step removes contaminants that could lead to inaccurate lab values, and the line must be flushed again before any infusions are restarted.