Cardiopulmonary bypass is a surgical procedure that uses a machine to perform the functions of the heart and lungs. It enables a surgeon to open and repair the heart without interrupting its essential functions.

The machine contains tubes that mimic the function of the main blood vessels that carry blood to and from the heart. It also has parts that mimic the pumping action of the heart muscle and the oxygenation action of the lungs.

Although the procedure is relatively safe, some serious complications, such as stroke and bleeding, can occur.

This article discusses cardiopulmonary bypass, including how it works, why someone may need it, recovery, and possible complications. It also examines the difference between the procedure and extracorporeal membrane oxygenation (ECMO).

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A cardiopulmonary bypass is a surgical procedure that uses a machine to perform the blood-circulating function of the heart. It also performs lung functions, including adding oxygen to the blood and removing excess carbon dioxide. Another name for the device is a heart-lung machine.

The procedure has become the standard treatment method for many heart surgeries. Temporarily diverting blood from the heart and lungs into the machine enables a surgeon to operate on a nonbeating heart. It permits the repair of the heart without stopping its vital function of pumping warm oxygenated blood throughout the body.

The cardiopulmonary bypass machine has the following parts:


Cannulas are tubes that connect a person to the machine and the machine back to the person. The tubes connecting someone to the machine are called venous cannulas, which take oxygen-poor blood. Tubes that connect the machine back to an individual are called arterial cannulas, which bring oxygen-rich blood back to the body.

Reservoir container

The reservoir container collects the blood that the venous cannulas drain from the heart. It allows the operative team — including a surgeon, anesthesiologist, and perfusionist — to accurately measure the volume of drained blood and manage the blood’s electrolyte and chemical content. Electrolytes are minerals in the blood that have an electric charge.


The machine has pumps that propel the blood forward to the oxygenator and ultimately back to the body.


The oxygenator functions as an artificial lung, which adds oxygen and removes carbon dioxide from the blood. A heat exchanger that regulates blood temperature integrates with the oxygenator.

Cardiopulmonary bypass can provide the following benefits:

  • helps with blood loss during surgery and returns blood to the person
  • allows the heart to be still, not beating, so surgeons can operate
  • protects the muscular tissue of the heart
  • prevents distension, or swelling, of the heart during surgery
  • offers safety nets and standby pathways

The above functions can be of use during various surgical procedures that may include:

  • aneurysm surgery
  • coronary artery bypass grafting
  • heart valve repair or replacement
  • heart transplant
  • lung transplant

Below are the basic steps of the procedure:

  1. Blood drains from the heart through the venous cannula into the reservoir container. The height difference between the person having the surgery and the reservoir means that drainage occurs through the force of gravity.
  2. The pump propels the drained blood into the oxygenator, where it receives oxygen.
  3. The machine returns oxygenated blood to the individual in two places in the aorta, the main artery that transports blood to all body parts.

A person can ask their doctor what to expect during recovery. Recovery can depend on several factors, including:

  • the person’s age
  • the type and duration of surgery
  • co-occurring conditions

Factors that can delay recovery include a prolonged surgery duration and an extended length of time using the heart-lung machine. Doctors define a delayed recovery as not regaining consciousness within 12 hours after anesthesia.

Cardiopulmonary bypass is relatively safe if the duration of the surgery is not overly long.

However, complications may occur, which may be mechanical or systemic. Mechanical complications are due to problems the machine may cause, while systemic complications stem from harmful physiological responses within the person’s body to the procedure.

Mechanical complications

Mechanical complications may include:

  • bleeding
  • plaque dislodgement, where fatty deposits move to other areas of the body
  • dissection, or disruption of a blood vessel’s inner lining
  • inadequate return of venous blood
  • air embolisms
  • blood clot formation
  • oxygenation failure

Systemic complications

Systemic complications may include:

  • dysfunction of platelets, the fragments of blood that enable typical blood clotting
  • low blood pressure and inflammation, which can cause acute kidney injury
  • cerebral injury, which can lead to conditions ranging from stroke to a hindered ability to think
  • injury to the heart muscle, which can have serious consequences
  • arrhythmias, or an irregular rate or rhythm of someone’s heartbeat
  • injury to the lungs, which can result in serious breathing problems

Like the cardiopulmonary bypass machine, an ECMO machine temporarily provides the functions of the heart and lungs.

Doctors may recommend specific types of ECMO on an individual basis. The venoarterial ECMO is for heart and lung problems, and a venovenous ECMO is for lung problems only.

However, cardiopulmonary bypass is appropriate for only short-term use during surgery. In contrast, ECMO is a means of life support that a person can use for 1–3 weeks. Doctors order this when someone has a life threatening condition that prevents their heart and lungs from functioning properly.

A cardiopulmonary bypass is a machine that performs the functions of the heart and lungs during heart surgery. Doctors use it in many operations on the heart.

The machine has venous and arterial cannulas that transport the blood to and from the person undergoing surgery. It also has parts that perform the heart’s pumping function and the lungs’ functions of oxygenating and removing carbon dioxide from the blood.

The procedure is relatively safe, but there is a small risk of serious complications.

People should not confuse it with ECMO, a means of life support for those whose heart and lungs are not functioning.