Control of breathing using an extracorporeal membrane lung.

Various amounts of carbon dioxide were removed through an extracorporeal membrane lung in spontaneously breathing lambs. The decrease in alveolar ventilation was proportional to the fraction of total carbon dioxide removed by the membrane lung. When extracorporeal CO2 removal approximated CO2 production (VCO2), alveolar ventilation almost ceased. Pulmonary ventilation can be controlled by extracorporeal carbon dioxide removal.

Use of the spiral coil membrane oxygenator during open heart surgery in infants and children.

The spiral coil membrane oxygenator was used without an arterial line filter during short term total cardiopulmonary bypass in 50 infants and children. The compact oxygenator proved to be efficient and reliable, was easy to operate in a simple perfusion circuit, has a high flow rate to priming volume ratio and eliminated gaseous emboli. During perfusion, platelet counts and fibrinogen concentrations descreased 51 and 31% respectively. Coagulation studies in eight infants less than 15 kilograms perfused with the membrane oxygenator system did not differ from those in 7 infants perfused by a bubble oxygenator system.

Clinical evaluation of a microporous membrane oxygenator.

1. The microporous membrane oxygenator has a maximum priming volume of 400 ml. and transfers up to 250 ml. of O2. 2. CO2 transfer is excessive when ventilating the oxygenator with 100% O2. CO2 should be added to the ventilating gas. 3. The oxygenator has performed satisfactorily in 90 cases of cardiac surgery with perfusion time up to nine hours. 4. Precautions are described to prevent possible accumulation of water vapor in the oxygenator.

Interactions of synthetic and natural surfaces with blood in the physiological environment.

Efforts to explain blood compatibility with synthetic and natural surfaces based on a single parameter or a single biological test procedure have either been unsuccessful or led to misleading generalizations. The problem reflects the complex interdependence between material's properties, the composition and properties of blood, and in vivo biorheological conditions. Among the initial events that occur when materials contact blood is the very rapid adsorption of plasma proteins; this process effectively influences the subsequent interactions with the formed blood elements, especially the platelets with the proteinated surfaces. In the case of natural surfaces, when the endothelium is damaged, collagen may become exposed that may cause the activation, adhesion, and aggregation of platelets leading to thrombosis. Current evidence indicates that the platelet-aggregating ability of collagen depends on its "multimeric" or fibrillar structure, rather than on the activation of the platelet-bound enzyme system. Under normal conditions, the flowing blood is probably not in direct contact with endothelial cells that line the blood vessel walls, but with an adsorbed layer of plasma proteins. Should a formation of a multilayer of plasma proteins occur following the initial adsorption of a monolayer, this process could be influenced by changes in the solubility of the proteins, especially fibrinogen, the solubility of which is quite low in plasma. The hypothesis is proposed that such changes may be intimately related to the electrical properties of proteins present in the vascular wall and in blood. It is possible that these properties play a much greater role in thrombogenesis and in the problem of blood compatibility than is currently appreciated. Considering synthetic polymers, a number of these have been prepared that exhibit little adverse effects on blood components and, at the same time, retain their physical properties for various periods of time in the physiological environment. These combined biological and physical properties make them useful for various prosthetic and other biomedical applications in surgery and therapy.

Increased oxygen pressure to improve the efficiency of membrane oxygenators.

Increased O2 pressure was used in a specially constructed oxygenator to test the concept of improved oxygen transfer with hyperbaria. Three membranes were tested: 5-mil Silastic, 1-mil copolymer, and 0.5-mil Teflon. Results are analyzed in terms of pressure, venous saturation, and flow. The 5-mil Silastic proved to be the most reliable and efficient at all levels of saturation and pressure. Oxygen transfers up to 100 cc/m2/min were recorded at lower venous saturations. Normal pCO2 differentials were maintained at atmospheric pressure but decreased as pressure increased. For the Silastic and copolymer membranes, peak efficiency for O2 transfer was at oxygen pressure 3 lb/in2, or 140 mmHg. This usually required a blood pressure of over 300 mmHg using an average blood layer of 0.5 mm. Changes of pressure were more critical than flow, although O2 transfer was found to increase up to flows of 1200 cc/min/m2. Pressure levels of 0-30 lb/in2 were tested. Teflon was most efficient at pressures of 10-15 lb/in2, and did not transfer CO2 in detectable amounts at these pressure levels. Plasma hemoglobin, WBC, and platelets were not seriously altered when studied over 4-hour periods at constant pressures.

Reusable tubular membrane oxygenator for isolated organ hemoperfusion.

A reusable tubular membrane oxygenator is described for hypotraumatic hemoperfusion of isolated organs in physiological studies. The constructed oxygenator was of approximately 0.24-m2 effective surface area and contained 450 silicone rubber capillaries of 0.51-mm nominal ID, 34.9 cm long, fixed by conical-shaped, plastic blood headers at manifolds made from Dow-Corning MDX-4-4210 silicone elastomer. During ex vivo hemoperfusions in dogs at inlet hemoglobin saturations near 67%, oxygen transfer rates of the oxygenator increased serially, from 16.6 +/- 1.7 ml/min per m2 (mean +/- SD) at blood flows of 100 ml/min to 34.1 +/- 3.8 ml/min per m2 at flows of 500 ml/min. The oxygenator was thromboresistant and of much loss priming blood volume and wall compliance than the nonresuable Travenol membrane oxygenator of 0.26-m2 effective surface area. The tubular oxygenator was easily cleaned and reassembled, with reproducible oxygen transfer rates. It should prove useful for hemoperfusion studies in organs of moderate size, such as the isolated canine kidney, stomach, and pancreas.

[Experimental and clinical use of the mini-size bubble-bag thermooxygenator by the Rygg-Kyvsgaard method]. / Experimenteller und klinischer Einsatz des Mini-size-bubble-bag-Thermooxygenators nach Rygg-Kyvsgaard

The authors report on experimental and clinical use of the Mini-size-bubble-bag-thermooxygenator according to Rygg-Kyvsgaard. The advantages and possible applications are demonstrated. The Mini-size-bubble-bag-thermooxygenator is recommended for routine cardiosurgery on infants. The authors point at possibilities to use it in systems of extracorporeal circulation beyond cardiac surgery.

Improving the efficiency of a tubular membrane oxygenator.

The development of a tubular membrane oxygenator is described. Fine silicone rubber tubes are inserted into a large silicone rubber tube and sealed. Oxygen is blown through the fine tubes, blood flows through the large tube, and the gases are exchanged through the wall of the fine tubes. The efficiency of the device is improved by increasing the gas pressure, which is followed by bubble formation in the blood, and which is therefore unacceptable. By arranging the inside tubes in a wavy pattern and by repeatedly stretching them the efficiency is increased without side effects.

Clinical use of the membrane oxygenator.

Since April 1973 we have treated nine patients with extracorporeal membrane oxygenation (ECMO), utilizing the spiral coil membrane lung. One patient is a long-term survivor. All patients except one showed substantial improvement in peripheral arterial oxygen tension. Four adults and two neonates were treated for critical hypoxia. Two patients were treated for cardiac failure but failed to show improved myocardial function. Complications involving perfusion circuitry, cannulation, chronic systemic heparinization, thrombocytopenia, and renal failure have been managed with minimal difficulty. However, irreversible pulmonary, neurologic, hepatic, or gastrointestinal damage due to hypoxia present before the institution of ECMO was associated with lethal complications. The ECMO has supplied adequate oxygenation to this group of nine critically hypoxic patients. Institution of ECMO at an earlier date in patients with critical hypoxia would provide a higher likelihood of survival.

Dispersion-casting thin and ultrathin fabric-reinforced silicone rubber membrane for use in the membrane lung.

Pinholes in thin silicone rubber membrane have previously been traced to undispersed silica filer aggregates within the silicone rubber. This was overcome by centrifuging the dispersion to remove the aggregates prior to membrane fabrication. Thin (less than 75 mu) and ultra-thin (less than 25 mum) membrane could then be dispersion-cast. To facilitate handling and to increase mixing of blood in the membrane lung, it is often desirable to reinforce the silicone rubber membrane with fabric. Unfortunately, this process frequently introduces pinholes of its own. We have found than pinhole-free fabric-reinforced silicone rubber membrane can consistently be produced by the double-layer casting technique. First, the dispersion is cast onto aluminum foil, solvent evaporated, and partially cured. A second layer is next cast on top of it, followed by fabric. After solvent evaporation, final cure is under nitrogen using organic peroxide catalysts. This technique has permitted us to consistently cast strong pinhole-free membranes as thin as 9 mu.

Evaluation of fluorochemicals for liquid membrane oxygenation.

An attempt is being made to develop an oxygenator utilizing gaseous oxygen bubbles completely encapsulated with fluorochemical, thereby avoiding the detrimental changes induced by a blood-gas interface. After the feasibility of this method of oxygenation had been proved, the biocompatibility of the fluorochemicals was investigated. No significant changes in human red blood cells, fibrinogen, or platelets were induced by chronic in vitro contact with fluorochemical over a 24-hour peroid. There is no evidence that the fluorochemicals tested extract lipids from plasma. A device which allowed continuous formation of a blood-fluorochemical interface was utilized in vitro with human blood and in vivo with dogs. No significant alterations were induced by fluorochemicals in the human or animal blood or in the canine organs at autopsy. A prototype oxygenator is now undergoing evaluation. A method of analyzing for fluorochemical in blood and other protein solutions is presented.

Membrane vs bubble oxygenator: clinical comparison.

Numerous studies have demonstrated the superiority of membrane oxygenators (MO) over the bubble oxygenators (BO) when used for prolonged cardiopulmonary support. However, there is little information available evaluating the MO for routine, short-term cardiopulmonary bypass. In this study the 5MO314 Modulung-Teflo (MO) was compared to 5M30314 Miniprime Variflo (BO). The data of 91 patients (46 MO and 45 BO) were analyzed according to the duration of cardiopulmonary bypass (Group I less than 60 min., Group II 60-90 min. and Group III greater than 90 min.). Hemodynamic parameters, fluid and blood balance, as well as hematologic and blood gas studies were used for comparing the two oxygentors. The hemodynamic parameters were better, and the arterial blood gases were more physilogic with the MO. The postoperative blood loss was significantly less when using the MO. The other measurements documented the stability of the MO. All statements were based on statistical analysis with a DEC PDP-9 computer, using the MIIS language and operating system. Consequently, we are now using this MO for routine cardiopulmonary bypass.

Extracorporeal perfusion for acute respiratory failure: recent experience with the spiral coil membrane lung.

Selection criteria, clinical data, and physiological measurements obtained during five extracorporeal membrane lung perfusions for acute respiratory insufficiency are presented. Four patients died and 1 survived. A new technique of femoral artery cannulation to allow aortic arch perfusion is described. When properly monitored, this route provides improved oxygen delivery to the brain during venoarterial (VA) perfusion. The importance of monitoring the equivalent of carotid artery Po2 during VA perfusion is emphasized. Recognition of the effects of high cardiac output in limiting the quality of extracorporeal perfusion, plus the use of hypothermia to reduce output, are stressed. We have confirmed that perfusion can be accomplished with small quantities of heparin, so that bleeding is reduced, but thrombocytopenia and occasional hemorrhage continue to be persistent problems.

Nature of deposits in a tubular membrane oxygenator after prolonged extracorporeal circulation: a scanning electron microscope study.

Although silicone fibers are among the most compatible with tissue and blood, numerous deposits are observed after their prolonged usage in a capillary membrane oxygenator, even when the blood has been properly heparinized. The scanning electron microscope (SEM) study shows that the morphology of these deposits varies greatly, depending upon the part of the unit from which the sample is taken. The area close to the inlet is the most severely affected. The outlet zone is affected to a lesser degree, and the areas in between are only slightly affected.