Clinical use of a Dacron wool filter during perfusion for open-heart surgery

A microscopic view of gaseous microbubbles passing a filter screen

PURPOSE

The aim of this study was to investigate the filtration efficacy of a 38-µm 1-layer screen filter based on Doppler registrations and video recordings of gaseous microbubbles (GME) observed in a microscope.

METHODS

The relative filtration efficacy (RFE) was calculated from 20 (n = 20) sequential bursts of air introduced into the Plasmodex® primed test circuit.

RESULTS

The main findings indicate that the RFE decreased (p = 0.00), with increasing flow rates (100-300 mL/min) through the filter screen. This reaction was most accentuated for GME below the size of 100 µm, where counts of GME paradoxically increased after filtration, indicating GME fragmentation. For GME sized between 100-250 µm, the RFE was constantly >60%, independently of the flow rate level. The video recording documenting the GME interactions with the screen filter confirmed the experimental findings.

CONCLUSIONS

The 38-µm 1-layer screen filter investigated in this experimental setup was unable to trap gaseous microbubbles effectively, especially for GME below 100 µm in size and in conjunction with high flow rates.

Haematological effects of a depth absorption arterial line filter during extracorporeal circulation

An arterial line filter (Swank High Flow 6000) was used during extracorporeal circulation (ECC) in 21 of 45 patients undergoing coronary artery bypass grafting, to study haematological effects. The mean age was 60 (41-69) years. All patients had obstructions of at least three coronary artery branches. Average ECC and aortic crossclamp times, drainage via chest tubes until the first day after surgery, total transfusions of blood products and haemolysis did not differ in the two groups. After 90 minutes of ECC, leukocyte counts were significantly lower in the filter group whereas haematocrit, counts of erythrocytes, lymphocytes and platelets, platelet volume, fibrinogen concentration and fibrinopeptide A were similar. Release of β-thromboglobulin and platelet factor 4 were significantly higher in the filter group. No clinically significant adverse haematological effects were observed with use of the arterial line filter, although there were indications of more pronounced platelet damage in the filter group.

Analysis of microembolic particles originating in extracorporeal circuits

Silicone tubing is utilised increasingly in extracorporeal circulation (ECC), particularly for prolonged bypass in cases of left ventricular failure following open heart surgery. We compared the spectrum of particle formation in the EC circuit, due to roller pump damage, resulting from wear of silicone tubing with that of polyvinyl chloride (PVC) tubing. The EC circuit was primed with plasmalyte solution for pump runs of up to 24 hours. Samples of the perfusate were taken from either system at prefixed times. Number and size of the particles were determined by means of a Coulter counter, while their chemical composition was analysed by X-ray dispersion (EDXA). The tubing was examined by scanning electron microscopy. When using PVC tubing, the amount of particles of all sizes rose above acceptable standards shortly after activating the roller pump. Following this early upsurge, the number of particles continued to increase for the remainder of the pump run, albeit at a more moderate rate. The silicone tubing continuously generated a marked quantity of particular matter at a steadily increasing rate. Electron microscopic examination of the silicone tubing revealed multiple particles emanating from the inner surface of the tube. The results suggest that filtration of the initial priming fluid may be advisable before connecting the patient to an EC circuit using PVC tubing. The multitude of particles liberated by the silicone tubing implies that its usage in ECC should be curtailed. Utilisation of noncrushing head pumps is recommended in ECC.

The scientific evidence of arterial line filtration in cardiopulmonary bypass

BACKGROUND

The indication for arterial line filtration (ALF) is to inhibit embolisation during cardiopulmonary bypass. Filtration methods have developed from depth filters to screen filters and from a stand-alone component to an integral part of the oxygenator. For many years, ALF has been a standard adopted by a majority of cardiac centres worldwide. The following review aims to summarize the available evidence in support for ALF and report on its current practice in Europe.

METHOD

The principles and application of ALF in Europe was investigated using a survey conducted in 2014. The scientific evidence for ALF was examined by performing a systematic literature search in six different databases, using the following search terms: "Cardiopulmonary bypass AND filters AND arterial". The primary endpoint was protection against cerebral injury verified by the degree of cerebral embolisation or cognitive tests. The secondary endpoint was improvement of the clinical outcome verified elsewise. Only randomised clinical trials were considered.

RESULTS

The response rate was 31% (n=112). The great majority (88.5%) of respondents were using ALF, following more than 10 years of experience. Integrated arterial filtration was used by 55%. Of respondents not using ALF, fifty-four percent considered starting using integrated arterial filtration. The systematic literature database search returned 180 unique publications where 82 were specifically addressing ALF in cardiopulmonary bypass. Only four out of the 82 identified publications fulfilled our inclusion criteria. Of these, three were more than 20 years old and based on the use of bubble oxygenation.

CONCLUSION

ALF is a standard implemented in a majority of cardiopulmonary bypass procedures in Europe. The level of scientific evidence available in support of current arterial line filtration methods in cardiopulmonary bypass is, however, poor. Large, well-designed, randomised trials are warranted.

White particulate matter: report of the ad hoc industry review group

BACKGROUND

In January 2003, blood center personnel in the American Red Cross, Southern Region in Atlanta, noticed whitish particulate material (WPM) that had not been observed previously in several units of red blood cells (RBCs). An expert panel was formed to evaluate studies of the material and make appropriate recommendations

STUDY DESIGN AND METHODS

The expert panel reviewed information provided by several investigations and organizations. This included: background information, and experiences relating to WPM; WPM composition; factors promoting WPM formation; risk of WPM (if any) to patients; and recommendations to prevent future occurrences.

RESULTS

WPM is derived from blood. No data suggest that external contamination or collection set components contribute to WPM development. A major constituent of WPM is platelets (PLTs). WPM is most commonly observed in RBCs that have been subjected to a hard spin without PLT separation. WPM is rarely, if ever, observed in RBCs that have been subjected to leukoreduction.

CONCLUSIONS

(1) WPM is not new, can be prevented, and can be removed. (2) WPM contains PLTs, white blood cells, fibrin, and cellular debris. (3) Changes in blood handling are not necessary. (4) WPM may be more frequent when higher g forces are used in component preparation. (5) Enhanced visual inspection of blood components need not be continued. (6) It appears that WPM may not form in RBC collected using automated devices. (7) WPM did not pose a risk to patients but should be avoided.

A brief history of blood filtration: clot screens, microaggregate removal, and leukocyte reduction

A historical perspective of the evolution of blood filtration is presented. Topics addressed include recognition of aggregates in blood as mediators of morbidity, targeted for removal with gross clot screens, and evolution through the implementation of universal leukocyte reduction. Future directions for the development of blood filters are also described.

Investigation on the ability of an ultrasound bubble detector to deliver size measurements of gaseous bubbles in fluid lines by using a glass bead model

Detectors based on ultrasonic principles are today's state of the art devices to detect gaseous bubbles that may be present in extracorporeal circuits (ECC) for various reasons. Referring to theoretical considerations and other studies, it also seems possible to use this technology to measure the size of detected bubbles, thus offering the chance to evaluate their potential hazardous effect if introduced into a patient's circulation. Based on these considerations, a commercially available ultrasound bubble detector has been developed by Hatteland Instrumentering, Norway, to deliver bubble size measurements by means of supplementary software. This device consists of an ultrasound sensor that can be clamped onto the ECC tubing, and the necessary electronic equipment to amplify and rectify the received signals. It is supplemented by software that processes these signals and presents them as specific data. On the basis of our knowledge and experience with bubble detection by ultrasound technology, we believe it is particularly difficult to meet all the requirements for size measurements, especially if these are to be achieved by using a mathematical procedure rather than exact devices. Therefore, we tried to evaluate the quality of the offered bubble detector in measuring bubble sizes. After establishing a standardized test stand, including a roller pump and a temperature sensor, we performed several sets of experiments using the manufacturers software and a program specifically designed at our department for this purpose. The first set revealed that the manufacturer's recommended calibration material did not meet essential requirements as established by other authors. Having solved that problem, we could actually demonstrate that the ultrasonic field, as generated by the bubble detector, has been correctly calculated by the manufacturer. Simply, it is a field having the strongest reflecting region in the center, subsequently losing strength toward the ECC tubing's edge. The following set of experiments revealed that the supplementary software not only does not compensate for the ultrasonic field's inhomogeneity, but, furthermore, delivers results that are inappropriate to the applied calibration material. In the last set of experiments, we were able to demonstrate that the signals as recorded by the bubble detector heavily depend upon the circulating fluid's temperature, a fact that the manufacturer does not address. Therefore, it seems impossible to resolve all these sensor related problems by ever-increasing mathematical intervention. We believe it is more appropriate to develop a new kind of ultrasound device, free of these shortcomings. This seems to be particularly useful, because the problem of determining the size of gaseous bubbles in ECC is not yet solved.

Macroemboli and microemboli during cardiopulmonary bypass

Macroscopic and microscopic emboli of gas, biologic aggregates, and inorganic debris can occur during cardiac operations with cardiopulmonary bypass and may result in end-organ ischemia. In the current era pump-generated embolism is a diminishing cause of perioperative neurologic injury, which now appears to be related mostly to atheroembolism from manipulation of the atherosclerotic ascending aorta, and presents a continuing technical challenge to the surgeon.

Brain embolic phenomena associated with cardiopulmonary bypass

Various biologic and non-biologic materials may be embolized to the brain after the use of cardiopulmonary bypass (CPB) pumps during open heart surgery but their relative frequency and importance are uncertain. Among the nonbiologic materials, Antifoam A, which contains organosilicates and silicon, continues to be employed as an additive to prevent frothing. Recent improvements in filtration and oxygenation techniques have clearly reduced the incidence of large emboli and complications like stroke but other neurologic sequelae following open heart surgery are common and in many cases poorly explained. A recently developed histochemical technique for the demonstration of the endothelial alkaline phosphatase (AP) was employed in a post-mortem study of brains from 8 patients and 6 dogs dying within a few days after open heart surgery employing cardiopulmonary bypass perfusion. Brains from 38 patients and 6 dogs who were not subjected to heart surgery were studied as controls with the same technique. The AP-stained slides are suitable for both light microscopic examination of the thick celloidin sections as well as a subsequent processing for high-resolution microradiography. Small capillary and arteriolar dilatations (SCADs) were seen in the test subjects/animals but not controls. SCADs were seen in all parts of the brain. Approximately 50% of the SCADs showed birefringence when examined with polarized light. SCADs are putative embolic phenomena and the exact nature and source of the embolic material is under investigation. A glycolipid component is indicated by preliminary studies. SCADs are difficult to find in routine paraffin sections and most if not all of the offending material seems to be dissolved during processing.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral blood flow during cardiopulmonary bypass in man: effect of arterial filtration

Cerebral blood flow was recorded in 39 patients undergoing cardiac surgery by intraarterial injection of xenon 133. There were three subgroups of patients: 10 patients had a 20 micron arterial filter (Johnson) and 11 a 40 micron filter (Pall), and 18 had no arterial filtration. All patients had a 40 micron (Pall) filter in the coronary suction line. Significant changes in cerebral blood flow occurred during extracorporeal circulation (p less than 0.0001). For all patients cerebral blood flow increased from a resting prebypass level of 30 to 46 and 57 ml/100 g a minute during initial and stable hypothermic extracorporeal circulation respectively. Both measurements were obtained at 26 degrees C and the recordings were made on average 12 and 55 minutes after the extracorporeal circulation was started. During rewarming cerebral blood flow increased to 64, 53, 41, and 36 ml/g a minute at 31 degrees, 33 degrees, 35 degrees, and 37 degrees C respectively, and when measured four and 16 minutes on average after bypass it was 44 and 41 ml/100 g a minute. This general brain hyperperfusion was noticed in all patients with a high enough mean blood pressure to produce hyperaemia. Interposing 20 and 40 micron arterial filters reduced cerebral blood flow but did not prevent this hyperaemia. The cerebral autoregulation, which maintains a constant cerebral blood flow within wide limits of perfusion pressures, was not affected by arterial filtration. The lower limit of blood pressure at which a further reduction in blood pressure was followed by a reduction in cerebral blood flow was around 60 mm Hg in all three groups.

Microemboli observed in deaths following cardiopulmonary bypass surgery: silicone antifoam agents and polyvinyl chloride tubing as sources of emboli

Refractile foreign particles within clear vacuoles were observed in capillaries of 17 patients who underwent cardiopulmonary bypass surgery, died, and were autopsied at the George Washington University Hospital from December 1978 through April 1981. The postoperative survival time ranged from less than one day to more than eight months. The approximate maximal diameter of the individual particles was 10 micrometer and that of the vacuoles 60 micrometer. The particle-droplet complexes showed affinity for hydrophobic stains. In all 17 cases, the kidneys were involved in combination with several other organs. In two patients, the emboli were associated with microinfarcts in one or more organs. Scanning electron microscopy (SEM) of the polyvinyl chloride tubing used during four cardiopulmonary bypasses showed spallation and shredding of the luminal surface in the areas exposed to the roller pump heads. This suggested that fragments of polyvinyl chloride might be the particles in the emboli. Another possible source was the antifoam agent used in the bubble oxygenator. Scanning electron microscopy x-ray microprobe analysis of the foreign material within capillaries of several organs showed it to be strongly positive for silicon but not for chlorine. Therefore, it was concluded that the microemboli were droplets of antifoam agent, the refractile particles corresponding to the particulate silica component and the vacuoles corresponding to the dimethylpolysiloxane liquid component. Since x-ray microprobe analysis of the microemboli did not reveal a strong chloride peak, there is as yet no evidence that polyvinyl chloride fragments were involved in the microembolism. The morphologic findings reported here indicate that antifoam microembolization continues to complicate cardiopulmonary bypass surgery and must, therefore, be considered a potential cause of postoperative morbidity. The consequence of the fragments of polyvinyl chloride tubing released into the circulation remains to be established.

The blood volume and the renin-angiotensin-aldosterone system following open-heart surgery

The circulating blood volume changes, plasma electrolytes, aldosterone as well as plasma-renin-activity (PRA) were studied in 14 patients following open-heart surgery with cardiopulmonary bypass (CPB) and in 14 patients following cardiac surgery without CPB. In both the groups a postoperative decrease of circulating blood volume was observed. This decrease occurred in spite of the positive fluid balance, and so a shift of fluid from vascular to extravascular compartment was likely. In the bypass group the plasma aldoserone level rose immediately after the operation and reached the peak on the first postoperative day. In the non-bypass group the aldosterone level started to fall after the operation, and reached the lowest level on the third postoperative day. The pattern of the postoperative PRA changes was almost identical with the aldosterone level changes in both the groups studied, which suggests that the activation of renin-angiotensin-aldosterone axis might be responsible for the observed plasma aldosterone changes.

The effect of a nylon mesh blood filter in the arterial line during extracorporeal circulation

Forty patients with different cardiac diseases underwent perfusion with the Shiley bubble oxygenator without a filter in the arterial line (Group A). This group was compared with a similar group of patients (Group B), in whom an Intersept nylon mesh filter was used in the arterial line. There were no differences according to age, weight or duration of perfusion between the two groups. The average postoperative bleeding via the chest tubes was 361 ml/m2 B.S.A./24 hours in group A compared with 414 in group B (p less than 0.05). One patient in the filter group died on the table because of myocardial failure, while the remaining 79 patients could leave hospital alive. One patient in each group showed impaired consciousness, but no other neurological complications were recorded in the patients. There were no significant differences in haematocrit, B-haemoglobin or leucocyte counts after 15 min, 1 hour, at the end of perfusion or 1 hour, respectively 24 hours postoperatively. The platelet count after 1 hour of perfusion was 55.8 x 10(9)/l in the filter group compared with 80.4 x 10(9)/l in group A (p less than 0.05), there were, however, no significant differences in B-platelet counts at the end of perfusion or later. Our study showed that a nylon mesh filter in the arterial line can reduce the platelet count. As no measureable advantages were found in the filter group we cannot recommend an arterial line filter.

Assessment of cerebral damage during open-heart surgery. A new experimental model

A new experimental technique for the assessment of cerebral cellular damage during extracorporeal circulation is described. It is based upon the direct measurement of the enzyme creatine phosphokinase (CPK) and the brain-specific isoenzyme CPK-B in cerebrospinal fluid of dogs submitted to conventional techniques of cardiopulmonary bypass (CPB). Highly significant elevations occur during a 60 min period of CPB in CSF levels of total CPK and CPK-B isoenzyme. These elevated levels persist at 24 hours postoperation, despite full clinical recovery in the dogs. In a comparative study of the effects of introducing a 40 micrometer arterial line screen filter during the period of CPB, there was a highly significant reduction in total CPK and CPK-B levels in the filtered group (p < 0.005).

The effect of shear, specific surface, and air interface on the development of blood emboli and hemolysis

Heparinized dog blood was exposed to shear and foreign surfaces in conicylindrical test cells. The cells were injection molded from polycarbonate and were filled using a technique that avoided contact of the blood with air. Particulate-matter formation was measured and was found to be dominated by the surface-to-blood-volume ratio and to be independent of shear rate. Hemolysis was also measured and was found to vary linearly with shear rate and to increase with increasing surface-to-blood volume ratio. Thus, at low shear rates and high specific surface conditions, the degree of hemolysis was found to be minimal while particulate-matter formation was high. The results suggest that the safety of extracoporeal perfusion procedures cannot be inferred from hemolysis measurements alone. In one series of tests, a gas-blood interface was generated at a rate equivalent to the rate of surface renewal in conventional disc oxygenators. The gas-blood interface failed to contribute significantly to the damage indices, which suggests that the apparent superiority of membrane oxygenators may be a result of factors other than the absence of a blood-gas interface.

Relationship between platelet count and cardiotomy suction return

A simple, inexpensive, accurate method of measuring the amount of blood returned by the cardiotomy suction system was devised and calibrated. Preoperative and postoperative platelet counts were obtained in 76 patients with congenital heart disease in whom the amount of cardiotomy suction return was measured. The mean percentage of total perfusate returned by the cardiotomy suction system was 8.9%. Both postoperative platelet count and the percentage change between preoperative and postoperative platelet counts correlated with the amount of blood returned by the cardiotomy suction system, time on bypass, and the percentage of total perfusate aspirated by the system.

Blood filter evaluation

Massive blood transfusion and extracorporeal circulation result in bombardment of the small pulmonary arterioles with micro-aggregates which are mainly composed of cellular degradation products, damaged platelets and leukocytes, fibrin strands, portions of cellular membrane and protein precipitates. Such amorphous material can cause patients to die of respiratory insufficiency without underlying chest trauma. Increasing amounts of stored blood are transfused to patients and extracorporeal circulation has become one of the most useful techniques for surgeons. Unfortunately, these procedures are often accompanied by disturbing post-operative consequences. This is because micro-aggregates invade the capillary network of several organs, especially lungs, kidneys, brain and retina. It is why blood filtration has recently gained added interest because of widespread efforts to minimise the number or emboli which are either transfused or reinfused to the patient through the blood return line.

Haemostasis disorders in open heart surgery with extracorporeal circulation. Importance of the platelet function and the heparin neutralization

The main haemostasis changes observed in a screening study performed in 40 patients who underwent an open heart surgery with extracorporeal circulation (ECC) are: a significant drop in platelet count from the onset of the ECC to the third postoperative day, a decrease of platelet retention and aggregation during ECC with an 8-day persistently increased heparin-neutralizing activity in plasma but not in serum, a moderate decrease of plasma factors I, II, VII-X, X and XIII and a more important drop in factor V which disappears 24 h after ECC, a transitory increase of fibrinolysis during ECC and the lack of FDP elevation in the serum. These disorders require a very good neutralization of the heparin used during ECC. The ratio protamine/heparin can be established by a titration clotting time test. Protamine chloride seems to be more efficacious and to act more quickly than protamine sulfate for the neutralization. An overload in protamine can enhance the hemostatic, biological and clinical disorders. The preventive administration of platelet concentrate immediately after the heparin neutralization contributes to reduce the bleeding disorders related to the quantitative and qualitative platelet defects.

Banked blood microfiltration. II. Dacron-wool microfilter

It is well established that debris tends to accumulate in banked blood, the amount of debris increasing with storage time. If such a blood is transfused to a patient, it will be filtered by the capillary network of the lungs and could cause various intensities of microemboli. These can be prevented by microfiltration--the Swank IL200 transfusion filter made of Dacron wool is perfectly suitable. It removes more than 70% of the debris 29-100 mum size from four blood units and its efficiency for particle removal is greatly increased by lactate priming.

A Dacron wool packed-bed extracorporeal reactor: a kinetic study of immobilized Escherichia coli II L-asparaginase

An extracorporeal reactor containing a packed bed of Dacron fibers has been developed. Escherichia coli II L-asparaginase was coupled to the Dacron using gamma-aminopropyltriethoxysilane and glutaraldehyde. The preparation had an activity of 37 IU per gram of Dacron (37 degrees C). The apparent Km was studied as a function of the flow rate. The data indicated that the apparent Km approached the Km of the native enzyme at flow rates of about 300 mg/min. In vivo use of L-asparaginase immobilized on the Dacron indicated effective lowering of plasmatic L-asparagine levels.

A role of extracorporeal circuit in the post-perfusion thrombocytopenia: a scanning electronmicroscopic observation

Thrombocytopenia is one of the adverse effects of extracorporeal circulation (ECC) but the mechanism of which has not been fully understood. Blood-gas interface, mechanical agitation, rough surface of extracorporeal circuit and sequestration in the liver have been considered to be a cause of platelet loss. Extracorporeal circuit which provides large artificial surface for contact of blood has been blamed as the site of platelet destruction during oxygenation. However, the part of the oxygenator responsible for platelet loss has bot been located. This study was designed to identify the sites of extracorporeal circuit responsible for platelet loss during ECC with scanning electron microscopy (SEM) of the post-perfusion circuit. The accumulation of platelet aggregates was most pronounced at the defoaming net and blood filter where a sudden changes in velocity of blood flow take place. The aggregates were considered to be formed locally at these sites. However, there were no accumulation and/or adherence of platelet aggregates of significant degree at the other parts of the circuit, namely venous and arterial tubings, venous colum and arterial reservoir. Platelets seem to be removed from the circulation during each passage by defoaming net and blood filter. However the other parts of the circuit seem to be less blamed for the platelet loss. It was not possible to conclude whether the formation and trapping of platelet microaggregates at the defoaming net and blood filter or the destruction by oxygen bubbles is mainly responsible for the plateletloss during ECC.

Cardiopulmonary bypass. Microembolization and platelet aggregation

Particulate microemboli and in vitro platelet aggregation were studied in blood of patients during cardiac operations with an electronic particle size analyzer. A small gradient of microemboli developed on passage of blood through a bubble oxygenator but not through a membrane oxygenator. However, with both types of oxygenators, there was a sustained increase in the volume of microemboli in cardiotomy return blood which was much greater than in aterial blood. After cardiopulmonary bypass with both oxygenators, there was a comparable reduction in the volume of circulating platelets which exceeded that of the hemoglobin concentration, indicating platelet loss exceeded that that expected from hemodilution alone. However, the total volume and mean size of platelet aggregates induced in blood of patients after membrane oxygenation was significantly greater than similar measurements after bubble oxygenation. This study shows that membrane oxygenation reduces particulate microembolization and preserves platelet function in patients undergoing cardiac operations when compared to bubble oxygenation.

Prevention of neurological damage during open-heart surgery

A previous study of neurological damage related to open-heart surgery suggested that the onset of cardiopulmonary bypass is a time of particular hazard, and there is evidence that both microemboli from the extracorporeal circulation and inadequate cerebral perfusion may be contributory factors. Measures to eliminate or minimize these hazards have been introduced, and a clinical survey has been undertaken to evaluate their efficacy. There has been a very highly significant decrease in the incidence of neurological damage as judged by comparison with the results of a similar survey carried out before these measures were introduced. In spite of limitations imposed by differences in workload, perfusion techniques, and methods of data collection, it is concluded that the prophylactic measures have been responsible for the reduction in the incidence of neurological damage.

Platelet aggregation: effects of cardiopulmonary bypass

This study was designed to determine whether reduction in platelet aggregate microembolization during the first 30 minutes of cardiopulmonary bypass is due to thrombocytopenia or to decreased ability of platelets to aggregate. The total volume of platelet aggregates induced in blood by adenosine diphosphate (ADP) was measured with a Coulter counter. The volume of platelets in blood was calculated by multiplying hemocytometry platelet counts by the mean platelet volume. Immediately before cardiopulmonary bypass, the total volume of aggregates induced in blood by ADP (2muM) was reduced when compared to normal donors because of (1) a slight fall in the volume of platelets, and (2) reduction in the percentage by volume of platelets which aggregated. After 30 minutes on bypass, the volume of both platelets and aggregates fell, but a greater percentage of platelets aggregated. This indicates that reduction of platelet aggregate formation during cardiopulmonary bypass is due to thrombocytopenia. It also suggests that anesthesia, surgical trauma and heparinization alter platelet reactivity more than cardiopulmonary bypass.

Pulmonary insufficiency associated with pregnancy

Six obstetric patients with severe pulmonary insufficiency are presented. The volume respirator and quality intensive care remain the basis of treatment. Experience with extracorporeal oxygenation is discussed. The patients demonstrated the typical progression seen in lung disease. An acute, severe insult is followed by hypoxia and pulmonary insufficiency with ensuing pulmonary fibrosis. Serious infection, coagulopathies, and mechanical problems of ventilation add to the difficulty of treatment and the high mortality rate in what may be referred to as an adult respiratory distress syndrome. It is important for the clinician to take an aggressive approach in the management of severe respiratory insufficiency.

Simultaneous perfusion of both coronary arteries and drainage of the coronary sinus in the dog heart in situ

A technique is described for perfusion of the entire coronary arterial system of the dog heart in situ and for drainage of the coronary sinus blood. Both coronary arteries are cannulated without ligation of major ventricular branches and disconnected from the aorta. The cannulas are connected to an extracorporeal system allowing perfusion under controlled pressure, without ill effects to either the heart or the blood. The arterial perfusion system is fed from the femoral arteries of the dog. The coronary sinus is cannulated for draining the blood to a venous reservoir against a controlled pressure. From the reservoir the blood is pumped into a femoral vein. Thus a preparation is obtained in which the interdependency of coronary circulation and performance of the heart has been discontinued. Under careful monitoring of pressures and flows, and of blood temperature, blood gases and plasma electrolytes, the preparation has been kept in excellent condition for up to 7 hrs.

Ultrasonic identification of sources of gaseous microemboli during open heart surgery

An ultrasonic transducer was used to detect gaseous microemboli during open heart surgery. When placed over the carotid artery of patients during surgery it was recognized that gaseous emboli were released into the systemic circulation following recognizable surgical procedures and from the oxygenator during bypass. Fixation of the transducer on the arterial return from the oxygenator demonstrated that the two types of disposable bubble oxygenators and disc oxygenators tested delivered microbubbles in the arterial blood. Some factors affecting the number of bubbles released were recognized and are discussed. Case reports of two patients who received large volumes of gaseous microemboli from different sources are presented.