Cooling catheters are inserted into a femoral vein. Cooled saline solution is circulated through either a metal coated tube or a balloon in the catheter. The saline cools the persons whole body by lowering the temperature of a persons blood. Catheters reduce temperature at rates ranging from  per hour. Through the use of the control unit, catheters can bring body temperature to within  of the target level. Furthermore, catheters can raise temperature at a steady rate, which helps to avoid harmful rises in intracranial pressure. A number of studies have demonstrated that targeted temperature management via catheter is safe and effective.
Adverse events associated with this invasive technique include bleeding, infection, vascular puncture, and deep vein thrombosis (DVT). Infection caused by cooling catheters is particularly harmful, as resuscitated people are highly vulnerable to the complications associated with infections. Bleeding represents a significant danger, due to a decreased clotting threshold caused by hypothermia. The risk of deep vein thrombosis may be the most pressing medical complication.
Deep vein thrombosis can be characterized as a medical event whereby a blood clot forms in a deep vein, usually the femoral vein. This condition may become potentially fatal if the clot travels to the lungs and causes a pulmonary embolism. Another potential problem with cooling catheters is the potential to block access to the femoral vein, which is a site normally used for a variety of other medical procedures, including angiography of the venous system and the right side of the heart.  However, most cooling catheters are triple lumen catheters, and the majority of people post-arrest will require central venous access. Unlike non-invasive methods which can be administered by nurses, the insertion of cooling catheters must be performed by a physician fully trained and familiar with the procedure. The time delay between identifying a person who might benefit from the procedure and the arrival of an interventional radiologist or other physician to perform the insertion may minimize some of the benefit of invasive methods' more rapid cooling.