Procedure Therapeutic Hypothermia
The medical procedure for inducing therapeutic hypothermia falls into one of two categories: invasive and non-invasive.
Big strides in medically induced hypothermia have opened the doors for new patient treatments. The procedure for therapeutic hypothermia varies according to the problem being treated. And new procedures are developed as new needs arise.
The principal invasive therapeutic hypothermia procedure is the cooling catheter. In this procedure, a catheter is inserted in the femoral vein and maneuvered near the heart. Once the catheter reaches the heart, saline solution is circulated through the catheter. A control unit regulates the temperature of the saline solution.
The main advantages of cooling catheters over other cooling methods are that they can cool more precisely and can reduce temperature more rapidly. Catheter users claim to reduce temperature by as much as 4 degrees Celsius per hour. The sophisticated temperature control units can maintain body temperature within 0.1 degree Celsius of the desired temperature. This high degree of accuracy helps doctors avoid the adverse effects of deep hypothermia that may arise with less precisely controlled temperature reductions. When it is time to raise the body’s temperature again, the catheter procedure allows it to be done slowly and steadily, reducing the possibility of harmful rises in intracranial pressure.
However, this invasive technique has been associated with bleeding, infection, vascular puncture, and deep vein thrombosis. Infection is particularly harmful because cardiac arrest patients are especially vulnerable to immunological failures and the complications associated with infections. Bleeding too can be especially dangerous in therapeutic hypothermia patients because the blood’s clotting threshold is heightened. Even more alarming is deep vein thrombosis, which seems to be relatively common in catheter cooling procedures. One study found that deep vein thrombosis increased 33 percent if a catheter was left in place for up to four days, and 75 percent if the catheter was kept active for more than four days. Deep vein thrombosis is a medical event in which a blood clot forms in a deep vein, usually the femoral artery. The clot may break loose, travel to the hear or lungs, and cause serious complications or even death.
Catheters make the femoral vein unavailable to doctors for use in other medical procedures. The catheter procedure also requires the supervision of a doctor, while a non-invasive therapeutic hypothermia procedure can be performed by anyone, even lay persons. This makes it possible to perform a non-invasive therapeutic hypothermia procedure earlier in the treatment process.
The most common non-invasive procedure for inducing therapeutic hypothermia is called the water blanket. A water blanket is a two-layer plastic bag that contains water. It is connect by tubes to a control unit that cools and circulates the water. The water blanket is placed over the patient’s entire body and the cool water lowers body temperature. The skin is not penetrated, and nursing professionals can perform this procedure.
However, water blanks have several undesirable qualities. They are prone to leaking, which can pose a serious electrical shock hazard. Also, water blankets are labor intensive because they require nearly continuous monitoring. Water blankets provide very imprecise temperature control, so nursing staff must constantly monitor the patient’s core temperature and continually adjust the temperature and flow rate of the cooling water. Water blankets tend to overshoot the target temperature of 32 degrees Celsius, and may induce dangerously deep hypothermia. The whole-body covering of a water blanket hinders application of other medical treatment.
A newer procedure for therapeutic hypothermia is called "Arctic Sun". It attempts to combine the non-invasive benefits of water blanks with the speed and precision of catheter cooling. The Arctic Sun device consists of several gel pads, connectors, and a control unit. The gel pads adhere to about 40 percent of the patient's body, leaving most of the body open to other medical treatment. The adherence of the gel pads also increases the efficiency of the cooling effect versus a water blanket loosely laid over the body. Water is pulled through the gel pads rather than pushed, reducing pressure and the risk of leakage. The Arctic Sun device can cool a body at the rate of 1.5 degrees Celsius per hour, and maintain body temperature within 2 degrees Celsius of the desired temperature.
One serious complaint about the Arctic Sun is the very rare occurrence of skin injury. One recent article even documents a case in which skin was removed.
Procedures for therapeutic hypothermia will continue to improve, pursuing the goals of rapid cooling and precision temperature maintenance.
