Hemoperfusion is a treatment technique in which large volumes of the patient's blood are passed over an adsorbent substance in order to remove toxic substances from the blood. Adsorption is a process in which molecules or particles of one substance are attracted to the surface of a solid material and held there. These solid materials are called sorbents. Hemoperfusion is sometimes described as an extracorporeal form of treatment because the blood is pumped through a device outside the patient's body.
The sorbents most commonly used in hemoperfusion are resins and various forms of activated carbon or charcoal. Resin sorbents are presently used in Europe but not in the United States; since 1999, all hemoperfusion systems manufactured in the United States use cartridges or columns containing carbon sorbents. A newer type of cartridge containing an adsorbent polymer has been undergoing clinical tests in the United States since the summer of 2002.
Hemoperfusion has three major uses:
- to remove nephrotoxic drugs or poisons from the blood in emergency situations (A nephrotoxic substance is one that is harmful to the kidneys.)
- to remove waste products from the blood in patients with kidney disease
- to provide supportive treatment before and after transplantation for patients in liver failure
Hemoperfusion is more effective than other methods of treatment for removing certain specific poisons from the blood, particularly those that bind to proteins in the body or are difficult to dissolve in water. It is used to treat overdoses of barbiturates, meprobamate, glutethimide, theophylline, digitalis, carbamazepine, methotrexate, ethchlorvynol, and acetaminophen, as well as treating paraquat poisoning. Paraquat is a highly toxic weed killer that is sometimes used by people in developing countries to commit suicide.
A hemoperfusion system can be used with or without a hemodialysis machine. After the patient has been made comfortable, two catheters are placed in the arm, one in an artery and one in a nearby vein. After the catheters have been checked for accurate placement, the catheter in the artery is connected to tubing leading into the hemoperfusion system, and the catheter in the vein is connected to tubing leading from the system through a pressure monitor. The patient is given heparin at the beginning of the procedure and at 15–20-minute intervals throughout the hemoperfusion in order to prevent the blood from clotting. The patient's blood pressure is also taken regularly. A typical hemoperfusion treatment takes about three hours.
Hemoperfusion works by pumping the blood drawn through the arterial catheter into a column or cartridge containing the sorbent material. As the blood passes over the carbon or resin particles in the column, the toxic molecules or particles are drawn to the surfaces of the sorbent particles and trapped within the column. The blood flows out the other end of the column and is returned to the patient through the tubing attached to the venous catheter. Hemoperfusion is able to clear toxins from a larger volume of blood than hemodialysis or other filtration methods; it can process over 300 mL of blood per minute.
In emergency situations, preparation of the patient may be limited to cleansing the skin on the inside of the arm with an antiseptic solution and giving a local anesthetic to minimize pain caused by the needles used to insert the catheters.
The hemoperfusion system is prepared by sterilizing the cartridge containing the sorbent and rinsing it with heparinized saline solution. The system is then pressure-tested
Normal results include satisfactory clearance of the toxic substance or waste products from the patient's blood. The success of hemoperfusion depends in part, however, on the nature of the drug or poison to be cleared from the blood. Some drugs, such as the tricyclic antidepressants, enter the tissues of the patient's body as well as the bloodstream. As a result, even though hemoperfusion may remove as much as 80% of the drug found in the blood plasma, that may be only a small fraction of the total amount of the drug in the patient's body.
The risks associated with hemoperfusion are similar to those for hemodialysis, including infection, bleeding, blood clotting, destruction of blood platelets, an abnormal drop in blood pressure, and equipment failure. When hemoperfusion is performed by a qualified health professional, however, the risks are minor compared to the effects of poisoning or organ failure.
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Rebecca Frey, Ph.D.