A central line, or central venous catheter, is a slender tube placed into a large vein, typically in the neck, chest, or groin, with the tip resting near the heart. This device is used to administer medications, fluids, and to draw blood samples without repeated needle sticks. Drawing blood from this catheter is a high-stakes procedure because improper technique can lead to severe complications, including life-threatening infection or diagnostic errors. Precision is paramount to ensure both patient safety and the integrity of the laboratory results.
Errors in Maintaining Aseptic Technique
Failing to maintain a sterile environment can introduce bacteria directly into the bloodstream, leading to a Central Line-Associated Bloodstream Infection (CLABSI). Proper hand hygiene must be performed thoroughly before donning gloves or beginning the procedure. Wearing gloves is not a substitute for washing hands.
A frequent error involves the inadequate scrubbing of the needleless connector or hub before accessing the line. This disinfection step, often called “scrub the hub,” requires vigorous mechanical friction for a minimum of five seconds using an approved antiseptic. Not allowing the antiseptic solution to air-dry completely after scrubbing compromises the disinfection process, as the agent needs time to eliminate microorganisms.
Contaminating the sterile field is another common lapse, such as accidentally touching connecting parts after they have been cleaned. Once the hub is disinfected, it must only be touched by the sterile syringe or luer-lock connection. Failing to replace needleless connectors or caps after the blood draw creates a pathway for bacterial entry. Drawing blood from a line site that shows signs of localized infection, like redness or swelling, without consulting a physician increases the risk of systemic infection.
Errors Compromising Sample Accuracy
Failing to discard an adequate volume of initial blood is necessary to clear the catheter of residual locking solution or infusing fluids. The line is often filled with saline or an anticoagulant like heparin, and if this is not flushed out, it will dilute the sample and contaminate the test results. The necessary discard volume is often five milliliters, though a larger volume may be required depending on the catheter type.
Drawing the sample too forcefully can cause damage to the blood cells, leading to hemolysis. High aspiration pressure physically stresses the red blood cells as they pass through the small catheter lumen, resulting in a sample that appears pink or red and yields falsely elevated potassium or lactate dehydrogenase levels. If resistance or turbulence is felt during aspiration, the technique should be adjusted immediately.
Attempting to draw a sample from a lumen that is actively being used for an infusion, especially one running intravenous fluids or medications, severely contaminates the sample. This leads to inaccurate drug levels or electrolyte readings. For example, a sample drawn from a line running a glucose solution will show an artificially high blood sugar result.
Improper sequencing of collection tubes is a common error that can cause cross-contamination of tube additives, which interferes with the lab assays. For instance, an anticoagulant from one tube, if drawn before a coagulation tube, can falsely alter the clotting time results. The standard order of draw must be followed to ensure the integrity of tests. After collection, failing to properly mix the sample tubes with their respective additives or mislabeling the tubes requires a repeat draw.
Errors Related to Line Maintenance and Patient Safety
Improper flushing technique immediately after the blood draw can compromise the long-term function of the line. The line must be flushed to clear residual blood that could clot and block the catheter, a complication known as occlusion. An error is using a slow, continuous push instead of the pulsatile or “push-pause” method, which uses turbulence to effectively clear the catheter walls.
Failing to clamp the line immediately after use or while changing caps or connectors is a safety mistake. Since the central line terminates in a large vein, an unsealed or unclamped line creates a direct route for air to enter the bloodstream. This ingress of air can lead to a venous air embolism, where a bubble of air travels to the heart and lungs, potentially causing circulatory collapse.
The improper locking procedure is the final step intended to maintain patency between uses. This involves using the wrong concentration or volume of locking solution, or failing to perform the lock entirely when indicated. Using a syringe smaller than 10 milliliters for flushing or locking is also an error, as the smaller diameter can generate excessive pressure inside the line, risking damage or rupture of the catheter. Accurate and timely documentation of the draw site, time, and any complications is a necessary safety step.