Blood extracorporeal oxygenators

All of the above-mentioned blood oxygenators are used outside the body, and hence are referred to as extracorporeal oxygenators. They are mainly used for heart surgery, which can last for up to several hours. However, blood oxygenators are occasionally used extracorporeally to assist the pulmonary function of the patients in acute respiratory failure (ARF) for extended periods of up to a few weeks. This use of extracorporeal oxygenators is known as extracorporeal membrane oxygenation (ECMO). 

Cardiopulmonary bypass—The use of extracorporeal devices to pump blood and oxygenate the blood while the heart or lungs are not functional. Extracorporeal membrane oxygenation (ECMO) is a form of long-term cardiopulmonary b5 pass that is typically used for days to weeks. 

Lung. No implantable, artificial lung exists, and transplantation of this organ is relatively rare. Much work has been done, however, on extracorporeal oxygenators, which are used in over 100,000 operations each year. These oxygenators add fresh oxygen to the blood and permit removal of carbon dioxide. Several designs have... 

Frankenfeld. Li, and Asher" 49 4 have described an apparatus quite similar to dial shown in Fig. 19.4-6B for the extracorporeal oxygenation of blood. Bubbles of gaseous Oj. encapsulated in a fluorocarbon membrane, rise ihrongh oxygen-depleted blood. As they do so oxygen diffuses from the membrane into the blood while CD2 differes in the opposite direction and is swept ont. This process was reviewed earlier. 1" The key to its potential success is the use of fluorocarbons in the membrane phase.11,45 4 Fluorocarbons are uniquely compatible with human blood and circumvent the damage to blood cells which is encountered with conventional devices. 

In the oxygen-independent Type III reactions the excited/sensi-tized psoralen donates its excitation energy directly to, or reacts with, the target compound. This occurs if the substrate and the target compound (e.g., DNA) are already in close proximity or intercalated. The reactions will proceed very rapidly via the excited singlet state, and are, typically, cyclization reactions or electron-transfer between the sensitizer and the target. In addition, the psoralen can be ionized, either directly or via the excited state, and react with the target compound in the form of a radical cation. Furocoumarins are also employed in treatment of cutaneous T-cell lymphoma and some infections connected with AIDS, by so-called photopheresis processes [71, 74-76]. In this case, peripheral blood is exposed to, e.g., photoactivated (sensitized) 8-methoxypsoralen (8-MOP) in an extracorporeal flow system. This... 

BELS The Berlin extracorporeal Hver support system consists of a three-dimensional accmnulation of approx. 500 g pig liver cells. These cells are linked by means of capillaries and provided with oxygen independently of the patient s blood, so that they function and stay vital for several weeks. (89)... 

The presence of an extracorporeal bypass circuit results in large heat losses from the blood. Thus an integral heat exchanger is essential to regulate the patient s body temperature. To decrease the oxygen demand during surgery, the patient s body temperature is often maintained at 5°C-10°C below normal body temperature. 

Figure 9 Degree of platelet retention in unheparinized rabbits undergoing simulated extracorporeal membrane oxygenation (ECMO) whose extracorporeal blood conduits are lined with MAHMA/NO-containing PVC to inhibit platelet adhesion ( ) as compared with controls whose tubing is made of undiazeniumdiolated PVC ( ). [Adapted from Reference 13 with permission.]...

Extracorporeal blood gas exchange is only one method of treating the hypoxic infant. Hypothermia and hyperbaric oxygenation, alone and in conjunction with extracorporeal blood gas exchange, have been used to lower or to meet the metabolic requirements of the infant. 

Extracorporeal medical machines (e.g., artificial kidney, pump-oxygenator) perfused with blood have been an effective part of the therapeutic armamentarium for many years. These devices all rely on systemic heparinization to provide blood compatibility. Despite continuous efforts to improve anticoagulation techniques, many patients still develop coagulation abnormalities with the use of these devices (1-3). Even longer perfusion times may occur with machines such as the membrane oxygenator. In such cases, the drawbacks of systemic heparinization are multiplied (4). A number of ap-... 

Figure 1. Proposed heparin circuit. The extracorporeal device could be a renal dialysis unit or a pump-oxygenator. The heparinase reactor could be part of a blood filter to be used either continuously (in which case heparin would, be added, continuously at the start of the circuit) or at the end of an operation. Heparin could thus be confined to the extracorporeal circuit.

At present, synthetic blood filters are routinely placed at the effluent of extracorporeal devices such as the pump-oxygenator or artificial kidney to remove clots or aggregates formed during the perfusion. The filters used in oxygenators can be as large as 2 L, whereas those used in renal dialysis are only several milliliters. With further development, heparinase could be immobilized to polymers in these filters. In this case, the filter could remove both clots and heparin. 

A fluorosensor for monitoring blood gases and pH in an extracorporal loop is commercially available [125]. Arterial or venous oxygen and carbon dioxide pressure, pH, and temperature can be determined continuously during cardiopulmonary bypass surgery. The system consists of a microprocessor-based instrument, bifurcated fiber-optic cables, and a disposable sensor head with fluorescent spots sensitive to the respective analytes. 

Wo Implantable, artificial lungs exist at this time hut some research has been done on polymeric membranes that could be used In such a device. Extracorporeal blood oxygenators are, however, used In excess of 100,000 times a year (l) and contain a thin, polymeric membrane thru which O2 and CO2 are exchanged. These oxygenators, which exist in several different styles are widely used In by-pass and other operations. The main polymers used are silicone rubber but poly(alkyIsulfones) and some others show promise (l, 50, 5l). 

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