During an open-heart surgery (such as valve or bypass surgery), the heart-lung machine is used to take over the functions of the heart and lungs. Also known as a cardiopulmonary bypass machine, it allows the surgeon to carefully stop the heart while the vital organs continue to receive blood and oxygen. When patients are on the heart-lung machine, very delicate work can be performed by surgeons without interference from bleeding or the heart’s pumping motion.

When first used successfully in humans in 1955, the machine was a revolutionary piece of equipment. Today, the heart-lung machine is used in about 1 million cardiac surgeries every year, including surgeries to the coronary arteries, heart valves and other structures of the heart. The heart-lung machine has a very low complication rate, approaching 1 percent for certain surgeries.

Newer medical technology is being developed that may someday replace the heart-lung machine in some circumstances. These technologies include systems that allow surgeons to operate on a beating heart, without use of the heart-lung machine. Known as off-pump surgery, this is used when surgeons are operating on the coronary arteries.

During an open-heart surgery (such as valve or bypass surgery), the heart-lung machine takes over the functions of the heart and lungs. Also known as a cardiopulmonary bypass machine, it allows the heart to can be carefully stopped and drained of blood. Surgeons can then operate in a blood-free, quiet surgical field. The heart-lung machine allows surgeons to perform complicated surgeries without the interference of a beating heart.

The heart-lung machine basically consists of a pump (to replace the heart) and a bubble oxygenator (to replace the lungs). Acting as a mechanical heart and lungs, it keeps oxygen-rich blood flowing throughout the body after the patient’s heart has been carefully stopped. In a process called perfusion, the machine receives the patient’s blood, removes the carbon dioxide and other waste products, adds oxygen, warms (or cools) the blood and pumps it back through the body. Cooling the blood lowers body temperature. This helps protect the body's organs while the heart-lung machine is in use. After the surgery is completed, the heart is restarted, the heart-lung machine is stopped and the machine is disconnected from the patient.

The heart-lung machine can perform other tasks. For example, it can directly deliver medications into the recirculated blood. It can also minimize blood loss by vacuuming up and recirculating any blood that may get into the surgical field.

The first step in using a heart-lung machine during open-heart surgery is to give the patient a drug called heparin, which is a powerful anticoagulant. Heparin reduces the blood’s ability to clot, reducing the risk of clots forming in the heart-lung machine and within the tubes placed in the heart. Once the medication has taken effect, a tube (cannula) from the heart-lung machine is placed in the upper-right chamber of the heart (the right atrium), which receives oxygen-poor blood from the body. Another cannula is placed in the aorta, a large artery that carries oxygen-rich blood from the heart to the rest of the body. By setting up the machine in this way, oxygen-poor blood drains into the machine, receives fresh oxygen and is returned to the aorta to be carried to the rest of the body.

Once the machine is functioning, the surgeon can carefully stop the heart with medications in order to perform the necessary surgery. A patient may remain on the heart-lung machine for several hours, though surgeons typically try to limit the amount of time patients are on bypass.  When the surgery is complete, the surgeon will restart the heart. Once the surgical team is satisfied that the heart is beating strongly again, the tubes are removed from the right atrium and the aorta. To reverse the effects of the heparin given at the beginning of the process, the patient will be administered another medication called protamine.

Throughout this process, the heart-lung machine is operated by a perfusionist, one of several medical specialists on hand in the operating room during open-heart surgery. While the heart is stopped and the machine is working, the perfusionist continually monitors blood pressure, blood oxygen levels, carbon dioxide levels, blood temperature and breathing.

Since its first use in humans in 1955, the heart-lung machine has been used in millions of open-heart surgeries. Nevertheless, there are risks associated with use of the machine. The complication rate is between 1 and 4 percent, depending on the kind of surgery.

The major risks associated with the heart-lung machine include:

• Blood clots. These may form as the machine processes blood and in extreme cases may cause stroke, heart attack or kidney failure upon return to the body’s bloodstream.
  
  
• Postpericardiotomy syndrome. A severe inflammatory response that may damage many of the body’s systems and organs.
  
  
• The reintroduction of fat and debris from the surgical field through the use of suction.
  
  
• Cardiac arrest.

Problems with temporary confusion or memory loss have also been reported in some cases. To avoid these risks, new surgical techniques called beating heart (or off-pump) surgeries have been developed, in which the heart beats throughout the operation and the heart-lung machine is not used. Some types of beating heart surgery are minimally invasive, requiring only small incisions. Other versions involve opening the chest. Today, about 25 percent of coronary artery bypass surgeries are performed without use of the heart-lung machine.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their treatment options. The following questions related to the heart-lung machine may be helpful:

1. Will a heart-lung machine be used during my surgery?
   
   
2. How common is the use of a heart-lung machine with my type of surgery?
   
   
3. What are my risks with the heart-lung machine?
   
   
4. How long will I be on the heart-lung machine?
   
   
5. What will happen if my heart does not function when they remove me from the bypass machine?
   
   
6. What specialists will be used during my surgery?
   
   
7. Are there any other alternatives available to me?
   
   
8. Will by recovery be any more or less difficult if a heart-lung machine is used?
   
   
9. Do I need any special preparations for surgery using a heart-lung machine?
   
   
10. Will I need to change my medications prior to my surgery?
    
    
11. How long will it take me to recover from the surgery?
    
    
12. Could a heart-lung machine affect my pregnancy in any way?