Oxygenator
Encyclopedia
An oxygenator is a medical device that is capable of exchanging oxygen
and carbon dioxide
in the blood of human patient in surgical procedures that may necessitate the interruption or cessation of blood flow in the body, a critical organ or great blood vessel. These organs can be the heart
, lung
s or liver
, while the great vessels can be the aorta
, pulmonary artery
, pulmonary veins or vena cava. An oxygenator is typically utilized by a perfusionist
in cardiac surgery
in conjunction with the heart-lung machine
. However, oxygenators can also be utilized in extracorporeal membrane oxygenation
in neonatal intensive care units by nurses.
For most cardiac operations such as coronary artery bypass grafting, the cardiopulmonary bypass is performed using a heart-lung machine (or cardiopulmonary bypass machine). The heart-lung machine
serves to replace the work of the heart during the open bypass surgery. The machine replaces both the heart's pumping action and the lungs' gas exchange function. Since the heart is stopped during the operation, this permits the surgeon to operate on a bloodless, stationary heart.
One component of the heart-lung machine is the oxygenator. The oxygenator component serves as the lung, and is designed to expose the blood to oxygen and remove carbon dioxide. It is disposable and contains about 2-4 m² of a membrane permeable to gas but impermeable to blood
, in the form of hollow fibers. Blood flows on the outside of the hollow fibers, while oxygen flows in the opposite direction on the inside of the fibers. As the blood passes through the oxygenator, the blood comes into intimate contact with the fine surfaces of the device itself. Gas containing oxygen and medical air is delivered to the interface between the blood and the device, permitting the blood cells to absorb oxygen molecules directly.
does not completely prevent clotting or the activation of complement
, neutrophils, and monocytes, which are the principal mediators of the inflammatory response. This response produces a wide range of cytotoxins, and cell-signaling proteins that circulate throughout the patient's body during surgery and disrupt homeostasis
. The inflammatory responses can produce microembolic particles. A greater source of such microemboli are caused by the suction of sugical debris and lipids into the CPB circuit.
Microparticles obstruct arterioles that supply small nests of cells throughout the body and, together with cytotoxins, damage organs and tissues and temporarily disturb organ function. All aspects of cardiopulmonary bypass, including manipulation of the aorta by the surgeon, may be associated with neurological symptoms following perfusion. Physicians refer to such temporary neurological deficits as “pumphead syndrome.” Heparin-coated blood oxygenators are one option available to a surgeon
and a perfusionist
to decrease morbidity associated with CPB to a limited degree.
Heparin-coated oxygenators are thought to:
Mirow et al. 2001 examined the effects of heparin-coated cardiopulmonary bypass systems combined with full and low dose systemic heparinization in coronary artery bypass patients. The researchers concluded that:
Ovrum et al. 2001 compared the clinical outcomes of 1336 patients with the Carmeda Bioactive Surface and Duraflo II coatings. The researchers concluded that:
Statistics and conclusions from more studies are available here. Clearly, heparin-coated blood oxygenators exhibit some advantages over non-coated oxygenators. Some hospitals use heparin-coated oxygenators for the large majority of their cases requiring cardiopulmonary bypass. It is unclear whether most surgeons actually reduce the amount of systemic heparin used when their patients are being perfused with heparin-coated oxygenators. Ultimately, each surgeon makes this decision based upon the needs of individual patient.
Although they offer advantages, these oxygenators are not widely regarded by surgeons as revolutionary breakthroughs in cardiopulmonary bypass. This is attibutable to the fact that most of the morbidity associated with CPB is not caused by the contact between the blood with the oxygenator. The leading cause of hemolysis and microemboli is the return of blood suctioned from the surgical field to the CPB circuit. This blood has come into contact with air, lipids and debris that can significantly increase system inflammatory response. Surgeons are instead looking to off-pump cardiac procedures, wherein surgery is performed on beating hearts, as the next “big thing” in open heart surgery.
Coated circuits have not been proven to alter surgical outcomes in any statistically significant manner. Furthermore, coated circuits are significantly more expensive than conventional circuits.
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
in the blood of human patient in surgical procedures that may necessitate the interruption or cessation of blood flow in the body, a critical organ or great blood vessel. These organs can be the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
, lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s or liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, while the great vessels can be the aorta
Aorta
The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...
, pulmonary artery
Pulmonary artery
The pulmonary arteries carry deoxygenated blood from the heart to the lungs. They are the only arteries that carry deoxygenated blood....
, pulmonary veins or vena cava. An oxygenator is typically utilized by a perfusionist
Perfusionist
A perfusionist, also known as a clinical perfusionist or a cardiovascular perfusionist, is a specialized health professional who operates the heart-lung machine during cardiac surgery and other surgeries that require cardiopulmonary bypass....
in cardiac surgery
Cardiac surgery
Cardiovascular surgery is surgery on the heart or great vessels performed by cardiac surgeons. Frequently, it is done to treat complications of ischemic heart disease , correct congenital heart disease, or treat valvular heart disease from various causes including endocarditis, rheumatic heart...
in conjunction with the heart-lung machine
Heart-lung machine
Cardiopulmonary bypass is a technique that temporarily takes over the function of the heart and lungs during surgery, maintaining the circulation of blood and the oxygen content of the body. The CPB pump itself is often referred to as a heart–lung machine or "the pump"...
. However, oxygenators can also be utilized in extracorporeal membrane oxygenation
Extracorporeal membrane oxygenation
In intensive care medicine, extracorporeal membrane oxygenation is an extracorporeal technique of providing both cardiac and respiratory support oxygen to patients whose heart and lungs are so severely diseased or damaged that they can no longer serve their function...
in neonatal intensive care units by nurses.
For most cardiac operations such as coronary artery bypass grafting, the cardiopulmonary bypass is performed using a heart-lung machine (or cardiopulmonary bypass machine). The heart-lung machine
Heart-lung machine
Cardiopulmonary bypass is a technique that temporarily takes over the function of the heart and lungs during surgery, maintaining the circulation of blood and the oxygen content of the body. The CPB pump itself is often referred to as a heart–lung machine or "the pump"...
serves to replace the work of the heart during the open bypass surgery. The machine replaces both the heart's pumping action and the lungs' gas exchange function. Since the heart is stopped during the operation, this permits the surgeon to operate on a bloodless, stationary heart.
One component of the heart-lung machine is the oxygenator. The oxygenator component serves as the lung, and is designed to expose the blood to oxygen and remove carbon dioxide. It is disposable and contains about 2-4 m² of a membrane permeable to gas but impermeable to blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
, in the form of hollow fibers. Blood flows on the outside of the hollow fibers, while oxygen flows in the opposite direction on the inside of the fibers. As the blood passes through the oxygenator, the blood comes into intimate contact with the fine surfaces of the device itself. Gas containing oxygen and medical air is delivered to the interface between the blood and the device, permitting the blood cells to absorb oxygen molecules directly.
Rationale
Operations which involve uncoated CPB circuits require a high dose of systemic heparin. Although the effects of heparin are reversible by administering protamine, there are a number of side effects associated with this. Side effects can include allergic reaction to heparin resulting in thrombocytopenia, various reactions to the administration of protamine and post-operative hemorrhage due to inadequate reversal of the anticoagulation. Systemic heparinHeparin
Heparin , also known as unfractionated heparin, a highly sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule...
does not completely prevent clotting or the activation of complement
Complement system
The complement system helps or “complements” the ability of antibodies and phagocytic cells to clear pathogens from an organism. It is part of the immune system called the innate immune system that is not adaptable and does not change over the course of an individual's lifetime...
, neutrophils, and monocytes, which are the principal mediators of the inflammatory response. This response produces a wide range of cytotoxins, and cell-signaling proteins that circulate throughout the patient's body during surgery and disrupt homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
. The inflammatory responses can produce microembolic particles. A greater source of such microemboli are caused by the suction of sugical debris and lipids into the CPB circuit.
Microparticles obstruct arterioles that supply small nests of cells throughout the body and, together with cytotoxins, damage organs and tissues and temporarily disturb organ function. All aspects of cardiopulmonary bypass, including manipulation of the aorta by the surgeon, may be associated with neurological symptoms following perfusion. Physicians refer to such temporary neurological deficits as “pumphead syndrome.” Heparin-coated blood oxygenators are one option available to a surgeon
Surgeon
In medicine, a surgeon is a specialist in surgery. Surgery is a broad category of invasive medical treatment that involves the cutting of a body, whether human or animal, for a specific reason such as the removal of diseased tissue or to repair a tear or breakage...
and a perfusionist
Perfusionist
A perfusionist, also known as a clinical perfusionist or a cardiovascular perfusionist, is a specialized health professional who operates the heart-lung machine during cardiac surgery and other surgeries that require cardiopulmonary bypass....
to decrease morbidity associated with CPB to a limited degree.
Heparin-coated oxygenators are thought to:
- Improve overall biocompatibility and host homeostasis
- Mimic the natural endothelial lining of the vasculature
- Reduce the need for systemic anticoagulation
- Better maintain platelet count
- Reduce adhesion of plasma proteins
- Prevent denaturation and activation of adhered proteins and blood cells
- Avoid complications resulting from an abnormal pressure gradient across the oxygenator
Surgical outcomes
Heparin coating is reported to result in similar characteristics to the native endothelium. It has been shown to inhibit intrinsic coagulation, inhibit host responses to extracorporeal circulation, and lessen postperfusion, or “pumphead,” syndrome. Several studies have examined the clinical efficacy of these oxygenators.Mirow et al. 2001 examined the effects of heparin-coated cardiopulmonary bypass systems combined with full and low dose systemic heparinization in coronary artery bypass patients. The researchers concluded that:
- Heparin-coated extracorporeal circuits with reduced systemic heparinization lead to significantly increased thrombin generation.
- Postoperative bleeding was reduced with low systemic heparinization, but the reduction was not significant.
Ovrum et al. 2001 compared the clinical outcomes of 1336 patients with the Carmeda Bioactive Surface and Duraflo II coatings. The researchers concluded that:
- Duraflo II patients required less heparin to keep the target activated clotting time
- Effects on renal function and platelets were similar
- Incidences of perioperative MI, stroke, and hospital mortality were similar
- Reduced incidence of postoperative atrial fibrillation compared to identical uncoated controls
- Overall clinical results were favorable in both groups
Statistics and conclusions from more studies are available here. Clearly, heparin-coated blood oxygenators exhibit some advantages over non-coated oxygenators. Some hospitals use heparin-coated oxygenators for the large majority of their cases requiring cardiopulmonary bypass. It is unclear whether most surgeons actually reduce the amount of systemic heparin used when their patients are being perfused with heparin-coated oxygenators. Ultimately, each surgeon makes this decision based upon the needs of individual patient.
Although they offer advantages, these oxygenators are not widely regarded by surgeons as revolutionary breakthroughs in cardiopulmonary bypass. This is attibutable to the fact that most of the morbidity associated with CPB is not caused by the contact between the blood with the oxygenator. The leading cause of hemolysis and microemboli is the return of blood suctioned from the surgical field to the CPB circuit. This blood has come into contact with air, lipids and debris that can significantly increase system inflammatory response. Surgeons are instead looking to off-pump cardiac procedures, wherein surgery is performed on beating hearts, as the next “big thing” in open heart surgery.
Coated circuits have not been proven to alter surgical outcomes in any statistically significant manner. Furthermore, coated circuits are significantly more expensive than conventional circuits.
See also
- Cardiac SurgeryCardiac surgeryCardiovascular surgery is surgery on the heart or great vessels performed by cardiac surgeons. Frequently, it is done to treat complications of ischemic heart disease , correct congenital heart disease, or treat valvular heart disease from various causes including endocarditis, rheumatic heart...
- Cardiothoracic surgeryCardiothoracic SurgeryCardiothoracic surgery is the field of medicine involved in surgical treatment of diseases affecting organs inside the thorax —generally treatment of conditions of the heart and lungs .-Cardiac / Thoracic:...
- Coronary artery bypass surgeryCoronary artery bypass surgeryCoronary artery bypass surgery, also coronary artery bypass graft surgery, and colloquially heart bypass or bypass surgery is a surgical procedure performed to relieve angina and reduce the risk of death from coronary artery disease...
- Extracorporeal membrane oxygenationExtracorporeal membrane oxygenationIn intensive care medicine, extracorporeal membrane oxygenation is an extracorporeal technique of providing both cardiac and respiratory support oxygen to patients whose heart and lungs are so severely diseased or damaged that they can no longer serve their function...
- Heart-lung machineHeart-lung machineCardiopulmonary bypass is a technique that temporarily takes over the function of the heart and lungs during surgery, maintaining the circulation of blood and the oxygen content of the body. The CPB pump itself is often referred to as a heart–lung machine or "the pump"...
- Membrane oxygenatorMembrane oxygenatorA membrane oxygenator is a device used to add oxygen to, and remove carbon dioxide from the blood. It can be used in two principal modes: to imitate the function of the lungs in cardiopulmonary bypass , and to oxygenate blood in longer term life support, termed extracorporeal membrane oxygenation,...
- PerfusionistPerfusionistA perfusionist, also known as a clinical perfusionist or a cardiovascular perfusionist, is a specialized health professional who operates the heart-lung machine during cardiac surgery and other surgeries that require cardiopulmonary bypass....
- Neonatal Intensive Care UnitNeonatal intensive care unitA Neonatal Intensive Care Unit —also called a Special Care Nursery, newborn intensive care unit, intensive care nursery , and special care baby unit —is an intensive care unit specializing in the care of ill or premature newborn infants.The problem of premature and congenitally ill infants is not a...
- ThrombinThrombinThrombin is a "trypsin-like" serine protease protein that in humans is encoded by the F2 gene. Prothrombin is proteolytically cleaved to form thrombin in the first step of the coagulation cascade, which ultimately results in the stemming of blood loss...