Central venous catheters, also known as central venous access devices (CVADs) or central lines, have become a mainstay for patients requiring intravenous (IV) administration of medications and other therapies.
Unlike peripheral intravenous catheters typically inserted into the veins of the hand or forearm, central access devices are inserted into large veins in the central circulation. The tip of a central venous catheter is generally threaded into the internal or external jugular veins or into the lower third of the vena cava (superior or inferior) that leads to an area just above the right atrium. At the time of insertion, a chest x-ray is done to confirm proper tip location and catheter position and to make sure that there is no pneumothorax.
Unlike peripheral catheters, a central line, depending on the type, can remain in place for more than a year. Central lines are especially beneficial for patients who have chronic diseases and require long-term intravenous therapy.
A central line is indicated for patients who need:
- parenteral nutrition
- chemotherapy or other vesicant or irritating solutions
- blood products
- IV medications or solutions (when peripheral access is limited)
- central venous pressure monitoring
A lumen is a hollow channel within a tube. Some central catheters have just one lumen while others have multiple lumens.
A single-lumen catheter consists of a tube or lumen ending in a hub that can either be connected to tubing for a continuous infusion of fluid or medication or capped and used for intermittent infusions. A single-lumen central venous catheter is used for patients who need an infusion into a large, central vein. When a single-lumen catheter is in place for infusing parenteral nutrition, it cannot be used to sample blood or to transfuse blood. This is because blood cells tend to adhere to the lumen and impede the flow of the nutrition solution.
A multi-lumen catheter (MLC) increases the advantages of a single-lumen catheter. An MLC has separate color-coded ports to identify the different lumens. Each lumen opens separately from the other lumens at the distal end of the catheter or along various areas of the catheter. This means that solutions do not mix as they travel through the catheter. With a multi-lumen catheter in place, several treatments can be performed via a single central line insertion site. The number of lumens within an MLC varies from two to four. For example, an MLC with three separate tubes (lumens) combined into one catheter is called a triple-lumen catheter. The multiple ports allow for administration of medications, blood infusions, blood sampling, fluid replacement, and pressure monitoring. Any one, any two, or all three may be capped and filled with heparinized saline or saline solution for intermittent use.
Distinguishing the portsA fairly common MLC configuration is three ports, commonly labeled and used as follows:
- distal port (16-gauge lumen): The largest lumen; used for central venous pressure monitoring or high volume or viscous fluids, colloids, medications
- medial port (18-gauge lumen): Used for parenteral nutrition, medications
- proximal (18-gauge lumen): Used for blood sampling, medications, blood component administration
The configurations vary, though. For example, a central catheter with two proximal lumens and one distal lumen is available. Always become familiar with particular MLC catheter you are accessing. Check the manufacturer’s instructions and how the lumens are labeled (color-coded, labeled by size, labeled by their proximal-medial-distal relationship). And, follow your facility’s procedures for labeling each lumen according to how it is used (for drawing blood samples, infusing fluids, infusing parenteral nutrition).
Also, keep in mind that the designation of proximal, medial, or distal relates to the holes or eyelets at different places along the part of the catheter that sits in the superior vena cava. The first hole is the proximal port (closest to the tip that sits inside the patient’s vein). The next hole is the medial opening, and the next is the distal. In other words, you cannot tell by glancing at the external portion of the catheter which is the proximal, medial, or distal lumen. You have to depend on how the manufacturer labels the lumens.
Types of central linesFour types of central venous access catheters are available (and are detailed in another accepted practice section of this module):
- implanted port
- peripherally inserted central catheter (PICC)
It can be challenging to sort out the various names you’ll hear for central venous access devices, including Hickman, Port-A-Cath, Groshong, and Broviac. These are trade names for various catheters that often become “household words” in the particular practice setting. It is easier to say, “We’ll need a Hickman” than to say, “We’ll need a tunneled central catheter.” Keep in mind, though, that the key to understanding central venous access devices and their uses is to understand that they are all one of the four basic types listed above. The number of lumens does not define its type, either, only that it allows multiple uses. In any case, the provider will work with the patient to decide to use a central catheter and then decide which type of catheter to use, depending on the type of therapy the patient needs and the length of time it will continue. It is important to know the type of catheter you are accessing so that you can manage the patient’s intravenous therapy correctly.
General principles for all central lines
Syringe size. Excessive pressure from the syringe you use to deliver therapy through a central line can rupture the catheter. Therefore, use only 10-mL or larger syringes and avoid excessive force when flushing the lines or administering medications. Flushing with larger syringes creates less pressure; smaller syringes create more pressure.
Flushing. Flushing with preservative-free, sterile 0.9% sodium chloride solution helps ensure and maintain patency of all types of central venous access devices. Your facility’s policies will specify flushing procedures to perform after catheter placement, before fluid infusion, and before and after blood sampling and drug, blood-product, and parenteral nutrition infusions. When flushing a central venous access device catheter, use a pulsing (push – stop – push – stop) flush to create turbulence that helps clear blood and medications from the line. Use a volume of flush solution that is at least twice the volume capacity of the catheter and add-on devices. (On average, a tunneled catheter has an internal volume of 1.5 to 2 mL, while a PICC holds 0.5 to 1 mL.) If you meet resistance or cannot aspirate blood, take further steps to assess the catheter’s patency before you administer medications and solutions. Do not flush the catheter forcefully. (See the accepted practice section on troubleshooting.)
Heparin flushing. Most central venous access devices require heparin flushing. However, valve-tip or closed-end valve catheters such as a Groshong incorporate a valve that opens from positive or negative pressure, as is generated by flushing or aspirating. Otherwise, the valve remains closed to keep blood from entering the catheter. These types of valves require only saline flushes. Flushing with heparin helps ensure and maintain patency of the central venous access device. Heparin is available in several concentrations. Check your facility’s policies to determine the concentration and volume of heparin required for the specific device as well as the frequency of the flush. The goal is not systemic anticoagulation; it is catheter patency.
Clamping. If central lines are not clamped, air might enter the patient’s central circulation, causing an air embolus. Keep central catheters clamped when not in use. This includes the time in between syringe changes. Use the small plastic clamp attached to the central line for clamping. A catheter with a valved or closed tip such as a Groshong does not require clamping.
Fluid displacement needleless connectors
Negative displacement devices let blood flow back into the catheter’s lumen when you disconnect the syringe or administration set. Blood reflux can lead to occlusions. When using a negative displacement device, it is important to use a positive-pressure flushing technique: Withdraw the syringe from the injection cap as you flush the last 0.5 mL of flush solution into the catheter. Or, flush all fluid into the catheter, maintain pressure on the syringe plunger, clamp the tubing between the catheter hub and the patient, then disconnect the syringe. Use a pressure flushing technique unless the device has a positive fluid displacement needleless cap. This device withholds a small amount of fluid to overcome blood reflux. When using a device with a needle-free positive fluid-displacement injection cap, do not use positive pressure flushing techniques. Disconnecting the administration set or syringe forces the reserved fluid into the catheter’s lumen. In this case, using a positive pressure flushing technique will cause blood reflux. Flush these devices only with saline and do not clamp the line.
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