A dialysis catheter is a specialized medical device used to establish temporary or semi-permanent vascular access for hemodialysis. Unlike an arteriovenous fistula or graft, which are surgically created beneath the skin, the dialysis catheter is a visible, external tube inserted directly into a large central vein. This device serves as a conduit to allow a continuous, high-volume flow of blood to and from the dialysis machine during treatment.
The Physical Structure of a Dialysis Catheter
The visible portion of a dialysis catheter consists of flexible tubing, typically made from soft, biocompatible materials like polyurethane or silicone. This tubing is designed with a dual-lumen structure.
The dual channels are color-coded: one port is generally red, signifying the “arterial” lumen that withdraws blood from the body to send to the machine. The second port is typically blue, designating the “venous” lumen that returns the filtered blood to the patient. These external connection points, known as hubs, are where the lines from the dialysis machine attach. They must be secured with clamps when not in use to prevent blood loss and air entry.
The catheter’s tip, which resides inside the vein, is engineered to maximize blood flow and minimize the chance of filtered blood immediately mixing with unfiltered blood. This is accomplished by staggering the tips of the two lumens, often by a few centimeters. The lumen size is also notably larger than typical intravenous lines to accommodate the high flow rates, ranging between 200 and 500 milliliters per minute, necessary for effective dialysis treatment.
Non-Tunneled Versus Tunneled Catheters
Dialysis catheters are categorized into two main types. A non-tunneled catheter is designed for short-term use, typically for acute or emergency dialysis needs. This type is inserted directly into the vein, and the tubing exits the skin close to the entry point, secured only by sutures and a dressing.
A tunneled catheter, in contrast, is built for long-term or intermediate use, often while a more permanent access like a fistula is maturing. Its distinguishing feature is a subcutaneous tunnel, meaning the catheter is inserted into the vein and then passed under the skin for a distance of several centimeters before it finally exits the body. This tunneling process provides a physical barrier that helps reduce the risk of infection compared to non-tunneled access.
A tunneled catheter also incorporates a small felt ring, known as a Dacron cuff, positioned beneath the skin in the tunnel. Tissue grows into this cuff over time, which serves two purposes: it anchors the catheter securely in place and further helps to block the entry of bacteria along the catheter track. Due to this tunneling, the external portion of the catheter is often seen emerging from the chest wall, well away from the vein entry site in the neck.
Placement Sites and Context of Use
Dialysis catheters are inserted into large central veins to ensure adequate blood flow, with the most common site being the internal jugular vein in the neck. When placed here, the tubing of the catheter is typically taped and dressed on the chest or neck, with the external hubs resting outside the dressing. The right internal jugular vein is often preferred due to the straighter path it offers to the heart.
Other placement sites include the femoral vein in the groin, which is generally reserved for emergency or temporary access, and the subclavian vein beneath the collarbone, which is used less often due to a higher risk of complications. Regardless of the site, the goal is for the catheter tip to sit ideally at the junction of the superior vena cava and the right atrium of the heart to optimize blood return and flow.
A catheter is often chosen over a permanent access method, like a fistula or graft, when a patient requires immediate hemodialysis, such as in cases of acute kidney injury. It is also used as a temporary bridge while a newly created permanent access is healing and maturing for use, or if a patient’s veins are not suitable for a fistula or graft.