Fluid fluorocarbon as oxygenator in experimental extracorporeal circulation

Improvement of gas transfer by hemosome

Intravascular oxidation is a respiratory assist method used to treat acute respiratory distress syndrome (ARDS). However intravascular oxidation through higher gas exchange is needed for successful clinical applications. In this study, an attempt was made to improve the gas exchange of an intravascular lung assist device by decreasing the level of damage to the blood through the microencapsulation of hemoglobin. The results showed that a hemosome 0.8 microm in diameter could be produced by microencapsulating the hemoglobin extracted from fresh bovine blood with the phospholipids extracted from egg yolk. The oxygen saturation curve of hemosome was S-shaped, which is similar to that found in normal blood, and the P50 was 24 mmHg. The oxygen saturation in the mixed solution of hemosome and blood at a 1:4 (v/v%) ratio was similar to that of normal blood. The gas exchange of the blood-hemosome mixed solution was more effective than whole blood. Therefore, the hemosome solution is expected to improve oxygen transfer.

Oxygenator anatomy and function

The natural lung is the organ responsible for oxygen and carbon dioxide exchange between the blood and the outside environment. This function is accomplished by the large surface area and high permeability of the gas exchange interface, the alveolar-capillary membrane. These same features are fundamental to the design of an artificial lung, or oxygenator. Additional lung-like features essential to the design of an ideal oxygenator include the ability to achieve balanced oxygen and carbon dioxide exchange with minimal blood damage and blood activation. The purpose of this review is to present the past and current developments of the oxygenator designs in terms of the structural and functional features of the natural lung as well as the limitations in the ability to mimic the features of the lung because of the lack of appropriate technology.

Fluorocarbon emulsions

Perfluorocarbon emulsions have been the topic of intense investigation for many years and presently there are still no absolute indications for their use in clinical practice. The relatively disappointing results of the early clinical studies, as a consequence of using low concentrations of a relatively underdeveloped emulsion, have been responsible for a largely negative impression and it is now essential that the newer second generation emulsions should be judged individually with regard to their efficacy and toxicity under different circumstances. Technological advancement in the fields of chemistry and detergent/emulsifier research will continue and new formulations are being developed which which will require to be tested in models in the laboratory. In the future, this class of drugs will continue to be the topic of intense investigation and their mechanisms of action, which are undoubtedly more complex than the simple carriage of dissolved gases in solution, will be clarified. However, whether fluorocarbon emulsions will ever be used as a 'blood substitute' as was originally anticipated is doubtful.

Afterword: bottom-line status report: CAN current trends in membrane gas transfer technology lead to an implantable intrathoracic artificial lung?

For at least 170 years, attempts have been made to alleviate inadequate gas exchange of patients with respiratory failure. Major milestones in the struggle to assist failing natural lungs to achieve adequate blood gas exchange include utilization of oxygen inhalation therapy, mechanical ventilatory assistance, and development of both extracorporeal and intracorporeal mechanical blood gas exchangers. Current state-of-the-art technology related to mechanical membrane blood gas exchangers has produced highly efficient gas transfer membranes and designs capable of replacing all the gas transfer functions of the natural lungs by a mechanical oxygenator-CO2 remover that can fit into a unilateral thoracic cavity. The possibility thus exists of moving extracorporeal mechanical blood oxygenators into the body as an implantable intracorporeal artificial lung. Problems impeding the development of an implantable, intrathoracic artificial lung have been identified, and at least partially successful attempts to solve them have been reported. The conclusion drawn is that the appropriate answer to the question posed in the title of this communication is affirmative. Reasons for this conclusion include the persistent widespread major need for better relief from respiratory failure, the advanced state-of-the-art of mechanical blood gas exchanger technology, and the incompletely tapped ingenuity of the human mind.

Hollow fiber hemodialyzers for partial respiratory support

Acute respiratory failure is still characterized by a high mortality rate, in spite of the development of ingenious treatment modalities involving mechanical ventilation and extracorporeal respiratory support. The coexistence of renal failure further complicates the outlook for respiratory failure patients. In this paper the development of the blood oxygenator and current aspects of its application are described. The concept of applying dialysis membranes for partial respiratory support is presented. An experimental animal model which was performed with A-V cannulation using dialysis membranes for partial respiratory support and simultaneous dialysis is analyzed. It is concluded that dialysis membranes are efficient for blood gas exchange and that their use in the management of the above-mentioned types of critically ill patients is promising.

Fluorocarbons. Current status and future applications

This article presents information on medical applications of fluorocarbons. These inert chemicals have a high solubility for the respiratory gases and, in emulsified form, are present in the oxygen-transporting plasma substitutes now undergoing clinical trials. Oxygen content is directly related to arterial partial pressure of oxygen (PaO2). Thus, although oxygen transport of Fluosol-DA 20% (FDA) is only 0.75 ml per 100 ml per 10 kPa, oxygen delivery at the tissues will be adequate in the presence of a high PaO2. FDA has a low viscosity at low shear rates and this, together with a very small emulsion particle size of 0.1 micron, helps provide improved tissue oxygenation in conditions of ischaemic hypoxia. Fluorocarbon plasma substitutes may be employed as 'blood', but may also be used for a wide range of purposes in clinical practice. This review describes some current and potential future applications.

Perfluorocarbon blood substitutes

The salient physicochemical properties of the fluorocarbons are briefly reviewed, including their solubility for the physiologically important gases and their properties relevant to formulation (nonmiscibility with water). The preparations used to date are described, including their properties and compositions, with some comment about the available knowledge of the properties of the constituents. A critical review of the biological aspects and the possible uses of fluorocarbon emulsions constitutes the main body of the manuscript. Gas-transporting capabilities are considered quantitatively. The biological effects of these preparations are reviewed in in vivo, whole body systems, with some in vitro evidence where appropriate. The usefulness of these preparations investigated to date are reviewed under the broad headings of cardiovascular system, radiology, intoxications, and organ preservation. Finally, the shortcomings and potential usefulness are discussed, with recommendations for potential modifications.

[Is there a possibility of paraplacental oxygenation of fetal blood? First results of an investigation with fluorocarbon (author's transl)]

By checking the cardiotropic effect on fetal rabbits we tried to find out weather there is a possibility of paraplacental oxygenation of fetal blood. Amniotic caves of nine fetal rabbits of 28th or 29th day of gestation are perfused with Perfluorobutyltetrahydrofuran (FX 80, 3 M Comp., St. Paul, Minn., USA) continuously. This was done by double blind investigation. The fetal heart rate is written by Hewlett-Packard-cardiotocograph. Therefore we use modificated EEG-electrodes. 48 h before we cut the spinal cord of the pregnant animals just for analgesie. So we exclude the influence of analgesics or narcotics. After complete interruption of uterine blood supply you can find an initial reduction of fetal heart rate. Using fluorocarbon we notice an increasing or stabilisation of fetal heart rate of all rabbit fetus. In comparison with control animals the difference is high significant. The cardial survival rate of four fetal rabbits treated with fluorocarbon is prolonged up to 50 min. During this time all "fluorocarbon fetus" never died earlier than the control animals. Lots of new questions are provoked by our results. One has to find an answer.

Human platelet and fluorochemical interaction

Since the fluorochemicals have become of interest for the development of artificial red blood cells, oxygenators, liquid breathing, and as a radiographic contrast medium, their interaction with biological substances is of importance. Fresh human platelets were placed in contact with four different fluorochemicals for a period of 50 min. The platelet function as measured by aggregation was determined before and after fluorochemical contact. Appropriate controls were also evaluated. No significant differences were found between the aggregation of platelets contacted with fluorochemicals and the aggregation of platelets from the same donor unexposed to fluorochemicals.

Survival of mammals breathing organic liquids equilibrated with oxygen at atmospheric pressure

Because oxygen and carbon dioxide are very soluble in certain silicone oils and fluorocarbon liquids, these liquids will support respiration of mammals. Mice and cats respiring silicone oil die shortly after return to air breathing, while those breathing fluorocarbon survive for weeks. The respiration of mice is optimally supported by these organic liquids at about 20 degrees C. In cats, arterial oxygenation is excellent, but there is some impairment of carbon dioxide elimination. All animals have suffered some pulmonary damage from breathing fluorocarbon liquids. Continued investigation of organic fluid respiration may lead to development of a safe method to support the respiration of man by liquids equilibrated with gases at atmospheric pressure.