Blood heart-lung machine

Anesthesiology and intensive care medicine (control of blood damage in a heart-lung machine)... 

The hypothalamic temperature controller (Bl) can be inactivated by neuroleptics (p. 236), without impairment of other centers. Thus, it is possible to lower a patient s body temperature without activating counter-regulatory mechanisms (thermogenic shivering). This can be exploited in the treatment of severe febrile states (hyperpyrexia) or in open-chest surgery with cardiac by-pass, during which blood temperature is lowered to 10°C by means of a heart-lung machine. 

It is indicated in hypovolaemic shock, loss of blood and plasma (e.g., trauma, burns, preoperative autologous blood or plasma donation), and for priming the heart-lung machine. In addition, it can be used as a vehicle for various drugs. 

The need for infant heart-lung machines and their require-ments are discussed. Bubble, disk, and membrane oxygenators are compared. Membrane oxygenators are essentially non-traumatic to blood and make possible extended perfusion of the hypoxic infant. 

Thrombotic complications are frequently encountered when blood is exposed to the surfaces of hemodialysis devices, heart-lung machines, arterial grafts, artificial heart components and other prosthetic devices. The blood platelets are particularly vulnerable to these adverse effects which may include a decrease in platelet count, shortened platelet survival and attendant higher platelet turnover, and altered platelet function. However the interaction of platelets with an artificial surface exposed to blood must be preceded by the interaction of the molecular components of plasma, particularly the plasma proteins, with the surface (1,2). This is due to the prepon-... 

Prevention of thrombus formation is important in clinical applications where blood is in contact such as hemodialysis membranes and tubes, artificial heart and heart-lung machines, prosthetic valves, and artificial vascular grafts. In spite of the use of anticoagulants, considerable platelet deposition and thrombus formation take place on the artificial surfaces [Branger, 1990]. 

Heparin has been used in medicine and surgery for nearly 40 years and in this time has maintained a well-earned reputation as an effective and safe drug [1]. I may claim a share in this as I was a member of the research team at the University of Toronto which developed heparin for clinical use. The major clinical uses of heparin are for the prevention of thrombosis and the prevention of clotting of blood. Thrombosis is the complex plugging of blood vessels which can occur in veins after operation and child-birth and can occur in arteries as the result of diet, age and stress. Clotting of blood is a serious problem in the use of heart-lung machines, artificial kidneys, etc. and the prevention of this by heparin is most important. My presentation reviews points about this drug which indicates its actions are due to its polyelectrolyte nature. 

An example of gas permeation in a membrane is use of a polymeric membrane as an oxygenator for a heart-lung machine to oxygenate blood. In this biomedical application, pure O2 gas is on one side of a thin membrane and blood is on the other side. Oxygen diffuses through the membrane into the blood and CO2 diffuses in a reverse direction into the gas stream. 

The convenient properties of liquid and solid dimethylpolysiloxanes (thermal and chemical stability, hydrophobicity, anti-adhesive behavior, etc.) make them suitable for a variety of technical applications in medicine. Especially pure preparations (Silastic ) have been used to construct artificial limbs, gullets, cardiac valves, trachea, etc., and in face-lifting. Silicon rubber breast implants, which are filled with a polysiloxane gel, have been used cosmetically. Synthetic arteries impregnated with silicon do not break or cause coagulation, they are flexible, and they are well tolerated immunologically. Silicones prevent the formation of foam in equipment for artificial blood circulation (heart-lung machines). The surfaces of such equipment, and of the... 

With the help of ion-selective electrodes and the proper calibration, the ion activity at the indicating electrode position can be monitored directly and continuously. According to Friedman [249], who was the first to carry out continuous blood pNa and pK measurements, one can distinguish between static and dynamic flow measurements. Static measurements are those such as ion activity measurements in the stomach or on the surface of the skin. In vivo flow measurements are primarily ion activity measurements in bloodstreams, either in the flow circuit of a heart-lung machine, or also post-operatively by means of vein shunts. 

Nonetheless, there is great interest in the continuous monitoring of blood pH, pNa, pK and pCa. Perkins et al. [250] report on the importance of maintaining a specific calcium ion level in the blood circuit of a heart-lung machine. Here the danger exists that the free calcium ion level may be lowered too much (complex formation) by the usual citrate addition. If this is counteracted by the addition of more calcium, too high a calcium level may result. Either occurrence can cause the heart to stop. 

Aviator Charles Lindbergh worked with physician Alexis Carrel, a noted pioneer of vascular surgery, to find a means of oxygenating blood other than the lungs. They created a basic oxygen-exchange device that led to the development of the heart-lung bypass machine for artificial circulation. 

Although red blood cells (erythrocytes) play only a minimal role in wound healing and blood-biomaterial interactions, the contact of red blood cells with the material can lead to hemolysis. Hemolysis is the breakage of the erythrocyte s membrane with the release of intracellular hemoglobin. Normally, red blood cells live for 110-120 days. After that, they naturally break down and are removed from the circulation by the spleen. Some diseases and medical devices cause red blood cells to break too soon requiring the bone marrow to accelerate the regeneration of red blood cells (erythropoesis). Medical devices for hemodialysis, heart-lung-bypass machines or mechanical heart valves induce more hemolysis than smaller implants like stents or catheters [201]. 

Heart Valves. The cardiopulmonary bypass machine, which allows blood flow to bypass the heart and lungs, is also used in other surgical procedures, such as valve repair and replacement, repairs of septal defects and congenital heart defects, and heart transplantation. Surgeons repair or replace heart valves in 99,000 operations per year in the United States. The... 

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