Respiratory System: Oxygen Delivery System

The primary function of the respiratory system is to supply the blood with oxygen in order for the blood to deliver oxygen to all parts of the body. The respiratory system does this through breathing. When we breathe, we inhale oxygen and exhale carbon dioxide. This exchange of gases is the respiratory system's means of getting oxygen to the blood.

Respiration is achieved through the mouth, nose, trachea, lungs, and diaphragm. Oxygen enters the respiratory system through the mouth and the nose. The oxygen then passes through the larynx (where speech sounds are produced) and the trachea which is a tube that enters the chest cavity. In the chest cavity, the trachea splits into two smaller tubes called the bronchi. Each bronchus then divides again forming the bronchial tubes. The bronchial tubes lead directly into the lungs where they divide into many smaller tubes which connect to tiny sacs called alveoli. The average adult's lungs contain about 600 million of these spongy, air-filled sacs that are surrounded by capillaries. The inhaled oxygen passes into the alveoli and then diffuses through the capillaries into the arterial blood. Meanwhile, the waste-rich blood from the veins releases its carbon dioxide into the alveoli. The carbon dioxide follows the same path out of the lungs when you exhale.

The diaphragm's job is to help pump the carbon dioxide out of the lungs and pull the oxygen into the lungs. The diaphragm is a sheet of muscles that lies across the bottom of the chest cavity. As the diaphragm contracts and relaxes, breathing takes place. When the diaphragm contracts, oxygen is pulled into the lungs. When the diaphragm relaxes, carbon dioxide is pumped out of the lungs.

Heart-Lung Machines

Gale Encyclopedia of Surgery, (2004)
by Allison J.

Definition
The heart-lung machine is medical equipment that provides cardiopulmonary bypass, or mechanical circulatory support of the heart and lungs. The machine may consist of venous and arterial cannula (tubes), polyvinyl chloride (PVC) or silicone tubing, reservoir (to hold blood), bubbler or membrane oxygenator, cardiotomy (filtered reservoir), heat exchanger(s), arterial line filter, pump(s), flow meter, inline blood gas and electrolyte analyzer, and pressure-monitoring devices. Treatment provides removal of carbon dioxide from the blood, oxygen delivery to the blood, blood flow to the body, and/or temperature maintenance. Pediatric and adult patients both benefit from this technology.

Purpose
In the operating room , the heart-lung machine is used primarily to provide blood flow and respiration for the patient while the heart is stopped. Surgeons are able to perform coronary artery bypass grafting (CABG), open-heart surgery for valve repair or repair of cardiac anomalies, and aortic aneurysm repairs, along with treatment of other cardiac-related diseases.
The heart-lung machine provides the benefit of a motionless heart in an almost bloodless surgical field. Cardioplegia solution is delivered to the heart, resulting in cardiac arrest (heart stoppage).

The heart-lung machine is invaluable
In critical care units and cardiac catheterization laboratories, the heart-lung machine is used to support A heart-lung machine. ( Photograph by Albert Paglialunga. Phototake NYC. Reproduced by permission. ) and maintain blood flow and respiration. The diseased heart or lung(s) is replaced by this technology, providing time for the organ(s) to heal. The heart-lung machine can be used with venoarterial extracorporeal membrane oxygenation (ECMO), which is used primarily in the treatment of lung disease. Cardiopulmonary support is useful during percutaneous transluminal coronary angioplasty (PTCA) and stent procedures performed with cardiac catheterization. Both treatments can be instituted in the critical care unit when severe heart or lung disease is no longer treatable by less-invasive conventional treatments such as pharmaceuticals, intra-aortic balloon pump (IABP), and mechanical ventilation with a respirator.
Use of this treatment in the emergency room is not limited to patients suffering heart or lung failure. In severe cases of hypothermia, a patient's body temperature can be corrected by extracorporeal circulation with the heart-lung machine. Blood is warmed as it passes over the heat exchanger. The warmed blood returns to the body, gradually increasing the patient's body temperature to normal.

Tertiary care facilities are able to support the staffing required to operate and maintain this technology. Level I trauma centers have access to this specialized treatment and equipment. Being that this technology serves both adult and pediatric patients, specialized children's hospitals may provide treatment with the heart-lung machine for venoarterial ECMO.

Description
The pump oxygenator had its first success on May 6, 1953. Continued research and design have allowed the heart-lung machine to become a standard of care in the treatment of heart and lung disease, while supporting other non-conventional treatments.

Foreign surfaces of the heart-lung machine activate blood coagulation, proteins, and platelets, which lead to clot formation. In the heart-lung machine, clot formation would block the flow of blood. As venous and arterial cannulas are inserted, medications are administered to provide anticoagulation of the blood which prevents clot formation and allows blood flow through the heart-lung machine.

Large vessels (veins and arteries) are required for cannulation, to insert the tubes (cannulas) that will carry the blood away from the patient to the heart-lung machine and to return the blood from the heart-lung machine to the patient. Cannulation sites for venous access can include the inferior and superior vena cava, the right atrium (the upper chamber of the heart), the femoral vein (in the groin), or internal jugular vein. Oxygen-rich blood will be returned to the aorta, femoral artery, or carotid artery (in the neck). By removing oxygen-poor blood from the right side of the heart and returning oxygen-rich blood to the left side, heart-lung bypass is achieved.

The standard heart-lung machine typically includes up to five pump assemblies. A centrifugal or roller head pump can be used in the arterial position for extracorporeal circulation of the blood. The four remaining pumps are roller pump in design to provide fluid, gas, and liquid for delivery or removal to the heart chambers and surgical field. Left ventricular blood return is accomplished by roller pump, drawing blood away from the heart. Surgical suction created by the roller pump removes accumulated fluid from the general surgical field. The cardioplegia delivery pump is used to deliver a high potassium solution to the coronary vessels. The potassium arrests the heart so that the surgical field is motionless during surgical procedures. An additional pump is available for emergency backup of the arterial pump in case of mechanical failure.