Particulate microembolism during cardiac operation

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.

Prevention of major perioperative neurological dysfunction—a personal perspective

Neurological dysfunction following cardiac surgical procedures has many causes. We have reduced perioperative neurological dysfunction to very low levels with protocols related to five potential causes of perioperative stroke. The five areas we have concentrated upon are: 1) components and use of the heart-lung machine; 2) air embolization; 3) intrinsic cerebrovascular disease; 4) atheroemboli from the ascending aorta and; 5) clot emboli from the left ventricle. We have employed methods of operation of the heart-lung machine which minimize the risk of microemboli or air emboli. Air evacuation manoeuvres are employed in every patient at the termination of cardiopulmonary bypass. A brain protection protocol which employs pharmacological brain protection, as well as increased oxygen-carrying capacity and perfusion pressure, is used in patients with cerebrovascular disease and patients with atheromatous ascending aorta. Applying these protocols, we have performed 690 consecutive cardiac surgical procedures with strokes occurring in three patients (0-4%). There was one stroke in 558 patients (0.2%) having coronary artery bypass grafting. Stroke occurred in one of 48 high risk patients (2%) in whom the brain protection protocol was used. There were no apparent episodes of air embolization or embolization of clot from the left ventricle.

Platelet damage and haemolysis during bubble oxygenator perfusion with and without arterial line filter, compared to membrane oxygenator perfusion

We determined to what extent a 27 micron depth filter (Bentley Polyfilter bypass blood filter PF427, Bentley Lab., Irvine, California, USA) in the arterial line of a bubble oxygenator (BO) system is responsible for the difference in haemocompatibility between this BO system and a membrane oxygenator (MO) system in which no arterial line filter is used. We studied three groups of patients subjected to long perfusions of approximately three hours: BO perfusion with ( n = 8) and without ( n = 8) the arterial line filter and MO perfusion ( n = 10) without filter. Platelet and erythrocyte damage were evaluated at seven sampling points during perfusion. Also pre- and postoperative bleeding times and postoperative blood loss and blood transfusions up to 18 hours after perfusion were determined.

We found that the 27 micron depth filter in the arterial line impairs the haemocompatibility of the BO only to a small extent; the MO remains haematologically superior over the BO even when the arterial line filter is absent from the BO circuit.

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.

Lessons learned on the path to a healthier brain: dispelling the myths and challenging the hypotheses

Neurologic dysfunction remains the most significant complication associated with cardiopulmonary bypass (CPB). The insidious change of cognitive decline has been perceived as a key factor that has contributed to the shift to percutaneous intervention for coronary disease. Current neuropsychologic testing provides the most sensitive means of demonstrating clinically relevant cerebral damage of this nature. Through extensive experience in randomized clinical trials of over 900 patients undergoing CPB, our team has addressed several key hypotheses related to the embolic/ischemic nature of cerebral injury in cardiac surgery, using this testing. In the first temperature study, patients randomized to hypothermia with passive re-warming had a lower incidence of neurocognitive deficit when compared with those patients who were actively re-warmed to 37°. In order to clarify the role of the hypothermia as opposed to the re-warming process, a second temperature study was completed. In the hypothermic group, patients were cooled and maintained at 34° with no active re-warming whereas, in the normothermic group, the patients were kept at 37° throughout the perioperative period. No difference in neurocognitive outcome in the two groups was seen, implying that the benefit seen in the first temperature study was related not to the hypothermia, but rather to the absence of active re-warming. In the cardiotomy study, patients were randomized to either a control group in which their cardiotomy blood was returned unprocessed, or a treatment group in which this blood was sequestered and processed with centrifugal washing and fat filtration. No significant difference in neurocognitive outcome was found in these two groups. On the other hand, there was a significant increase in bleeding and transfusion requirements in the treatment group. Many of our daily practices in CPB management are based upon assumptions from observational studies without sound reference to evidence-based medicine. Our recent studies have challenged our assumptions related to ischemia and embolic events during CPB. They have also confirmed that, when high standards in trial design are applied, the results can have universal implications in terms of our practice. Perfusion (2007) 22, 153—160.

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.

Circulating non-hematological cells during cardiopulmonary bypass: new findings in cardiac surgery procedures

BACKGROUND

Several factors have been historically advocated to explain the coagulative and inflammatory disorders following cardiopulmonary bypass (CPB). In this paper, we describe the presence of circulating non-hematological cells, introduced within the bloodstream during CPB. We defined the origin of the cells and tested their impact on coagulation.

METHODS

We collected peripheral arterial blood samples in twenty consecutive coronary artery bypass graft cases at four different surgical moments and assessed the presence and nature of circulating cells with the use of the CELLSEARCH® Test, immunocytochemistry and immunofluorescence, evaluating the expression of cytokeratin and calretinin. The effect of the circulating non-hematological cells on coagulation was tested in vitro, using the ROTEM assay.

RESULTS

A mean of 263.85 ± 57.5 (median 258.5) cells were present in the samples following the suction of blood from the surgical field while all the other samples were negative (zero cells) (p<0.00001). Immunologic tests confirmed the mesothelial origin of the cells. The ROTEM® assay of the blood samples contaminated by the mesothelial cells presented longer clotting times (53.4 ± 8.2 secs 48.3 ± 8.9 sec, p=0.05), longer clot formation times (137.1 ± 31.5 sec vs 111.9 ± 25.2 sec, p=0.009), smaller alfa angle amplitudes (66.7 ± 9.1° vs 71.1 ± 5.1°, p=0.04) and maximum clot firmness times (59.0 ± 5.4 sec vs 61.9 ±4.6 sec, p=0.004) than the controls.

CONCLUSION

The presence of circulating non-hematological cells during CPB with a mesothelial immunophenotype alters in vitro coagulation assays. This finding can help to further understand the pathophysiology of CPB.

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.

Coronary artery surgery: cardiotomy suction or cell salvage?

Coronary artery bypass grafting (CABG) today results in what may be regarded as acceptable levels of blood loss with many institutions avoiding allogeneic red cell transfusion in over 60% of their patients. The majority of cardiac surgeons employ cardiotomy suction to preserve autologous blood during on-pump coronary artery bypass surgery; however the use of cardiotomy suction is associated with a more pronounced systemic inflammatory response and a resulting coagulopathy as well as exacerbating the microembolic load. This leads to a tendency to increased blood loss, transfusion requirement and organ dysfunction. Conversely, the avoidance of cardiotomy suction in coronary artery bypass surgery is not associated with an increased transfusion requirement. There is therefore no indication for the routine use of cardiotomy suction in on-pump coronary artery surgery.

The Cardiotomy Trial

Background— Reinfusion of unprocessed cardiotomy blood during cardiac surgery can introduce particulate material into the cardiopulmonary bypass circuit, which may contribute to postoperative cognitive dysfunction. On the other hand, processing of this blood by centrifugation and filtration removes coagulation factors and may potentially contribute to coagulopathy. We sought to evaluate the effects of cardiotomy blood processing on blood product use and neurocognitive functioning after cardiac surgery.

Methods and Results— Patients undergoing coronary and/or aortic valve surgery using cardiopulmonary bypass were randomized to receive unprocessed blood (control, n=134) or cardiotomy blood that had been processed by centrifugal washing and lipid filtration (treatment, n=132). Patients and treating physicians were blinded to treatment assignment. A strict transfusion protocol was followed. Blood transfusion data were analyzed using Poisson regression models. The treatment group received more intraoperative red blood cell transfusions (0.23±0.69 U versus 0.08±0.34 U, P =0.004). Both red blood cell and nonred blood cell blood product use was greater in the treatment group and postoperative bleeding was greater in the treatment group. Patients were monitored intraoperatively by transcranial Doppler and they underwent neuropsychometric testing before surgery and at 5 days and 3 months after surgery. There was no difference in the incidence of postoperative cognitive dysfunction in the 2 groups (relative risk: 1.16, 95% CI: 0.86 to 1.57 at 5 days postoperatively; relative risk: 1.05, 95% CI: 0.58 to 1.90 at 3 months). There was no difference in the quality of life nor was there a difference in the number of emboli detected in the 2 groups.

Conclusions— Contrary to expectations, processing of cardiotomy blood before reinfusion results in greater blood product use with greater postoperative bleeding in patients undergoing cardiac surgery. There is no clinical evidence of any neurologic benefit with this approach in terms of postoperative cognitive function.

The rationale for fat filtration during cardiac surgery

Improved filter technology may enable the removal of specific substances such as lipids from the blood. Lipids form a heterogeneous group of compounds, but during surgery, the main interest is focussed on triglycerides, glycerol and free fatty acids. Fat emboli have been demonstrated in the brain after cardiac surgery and are associated with ischaemic brain injury. Fat emboli have also been demonstrated in lung and kidney tissue. Lung tissue and leucocytes are especially vulnerable to the effects of free fatty acids. The surgical wound suction blood during cardiac surgery contains a considerable quantity of microemboli. Therefore, as a first step to determining the place of fat filtration during cardiac surgery, the use of a fat removal filter for surgical wound suction blood is advocated.

Processing scavenged blood with a cell saver reduces cerebral lipid microembolization

BACKGROUND

Microembolization during cardiopulmonary bypass (CPB) can be detected in the brain as lipid deposits that create small capillary and arteriolar dilations (SCADs) with ischemic injury and neuronal dysfunction. SCAD density is increased with the use of cardiotomy suction to scavenge shed blood. Our purpose was to determine whether various methods of processing shed blood during CPB decrease cerebral lipid microembolic burden.

METHODS

After hypothermic CPB (70 minutes), brain tissue from two groups of mongrel dogs (28 to 35 kg) was examined for the presence of SCADs. In the arterial filter (AF) group (n = 12), shed blood was collected in a cardiotomy suction reservoir and reinfused through the arterial circuit. Three different arterial line filters (Pall LeukoGuard, Pall StatPrime, Bentley Duraflo) were used alone and in various combinations. In the cell saver (CS) group (n = 12), shed blood was collected in a cell saver with intermittent preocessing (Medtronic autoLog model) or a continuous-action cell saver (Fresenius Continuous Auto Transfusion System) and reinfused with and without leukocyte filtration through the CPB circuit.

RESULTS

Mean SCAD density (SCAD/cm2) in the CS group was less than the AF group (11 +/- 3 vs 24 +/- 5, p = 0.02). There were no significant differences in SCAD density with leukocyte filtration or with the various arterial line filters. Mean SCAD density for the continuous-action cell saver was 8 +/- 2 versus 13 +/- 5 for the intermittent-action device.

CONCLUSIONS

Use of a cell saver to scavenge shed blood during CPB decreases cerebral lipid microembolization.

Longer duration of cardiopulmonary bypass is associated with greater numbers of cerebral microemboli

BACKGROUND AND PURPOSE

Many patients who undergo cardiac surgery assisted with cardiopulmonary bypass (CPB) experience cerebral injury, and microemboli are thought to play a role. Because an increased duration of CPB is associated with an increased risk of subsequent cerebral dysfunction, we investigated whether cerebral microemboli were also more numerous with a longer duration of CPB.

METHODS

Brain specimens were obtained from 36 patients who died within 3 weeks after CPB. Specimens were embedded in celloidin, sectioned 100 microm thick, and stained for endogenous alkaline phosphatase, which outlines arterioles and capillaries. In such preparations, emboli can be seen as swellings in the vessels. Cerebral microemboli were counted in equal areas and scored as small, medium, or large to estimate the embolic load (volume of emboli).

RESULTS

With increasing survival time after CPB, the embolic load declined (P<0.0001). (Lipid emboli are known to pump slowly through the brain.) Also with increasing time after CPB, the percentage of large and medium emboli became lower (P=0.0034). This decline is consistent with the concept that the emboli break into smaller globules as they pass through the capillary network. A longer duration of CPB was associated with increased embolic load (P=0. 0026). For each 1-hour increase in the duration of CPB, the embolic load increased by 90.5%.

CONCLUSIONS

Thousands of microemboli were found in the brains of patients soon after CPB, and an increasing duration of CPB was associated with an increasing embolic load.

Cardiotomy suction: a major source of brain lipid emboli during cardiopulmonary bypass

BACKGROUND

Brain injury remains a significant problem in patients undergoing cardiac surgery assisted by cardiopulmonary bypass (CPB). Autopsy brain specimens of patients after cardiac operations with CPB reveal numerous acellular lipid deposits (10 to 70 microm) in the microvasculature. We hypothesize that these small capillary and arterial dilatations result from a diffuse inflammatory response to CPB or from emboli delivered by the bypass circuit. This study was undertaken to determine which aspect of CPB is most clearly associated with these dilatations.

METHODS

Thirteen dogs were studied in four groups: group I (n = 3), right-heart CPB; group II (n = 2), lower-extremity CPB; group III (n = 3), hypothermic CPB; and group IV (n = 5), hypothermic CPB with cardiotomy suction. All dogs in all groups were maintained on CPB for 60 minutes and then euthanized. Brain specimens were harvested, fixed in ethanol, embedded in celloidin, and stained with the alkaline phosphate histochemical technique so that dilatations could be counted.

RESULTS

All dogs completed the protocol. The mean density of dilatations per square centimeter for each group was as follows: group I, 1.77 +/- 0.77; group II, 4.17 +/- 1.65; group III, 4.54 +/- 1.69; and group IV, 46.5 +/- 14.5. In group IV (cardiotomy suction), dilatation density was significantly higher than in group III (hypothermic cardiopulmonary bypass) (p = 0.04) and all other groups (p = 0.04).

CONCLUSIONS

Blood aspirated from the surgical field and subsequently reinfused into dogs undergoing CPB produces a greater density of small capillary and arterial dilatations than CPB without cardiotomy suction, presumably because of lipid microembolization.

Leukocyte depletion results in improved lung function and reduced inflammatory response after cardiac surgery

Leukocyte depletion during cardiopulmonary bypass has been demonstrated in animal experiments to improve pulmonary function. Conflicting results have been reported, however, with clinical depletion by arterial line filter of leukocytes at the beginning of cardiopulmonary bypass. In this study, we examined whether leukocyte depletion from the residual heart-lung machine blood at the end of cardiopulmonary bypass would improve lung function and reduce the postoperative inflammatory response. Thirty patients undergoing elective heart operations were randomly allocated to a leukocyte-depletion group or a control group. In the leukocyte-depletion group (n = 20), all residual blood (1.2 to 2.1 L) was filtered by leukocyte-removal filters and reinfused after cardiopulmonary bypass, whereas in the control group an identical amount of residual blood after cardiopulmonary bypass was reinfused without filtration (n = 10). Leukocyte depletion removed more than 97% of leukocytes from the retransfused blood (p < 0.01) and significantly reduced circulating leukocytes (p < 0.05) and granulocytes (p < 0.05) compared with the control group. Levels of the inflammatory mediator thromboxane B2 determined at the end of operation (p < 0.05) were significantly lower in the depletion group than in the control group, whereas no statistical differences in interleukin-6 levels were found between the two groups. After operation, pulmonary gas exchange function (arterial oxygen tension at a fraction of inspired oxygen of 0.4) was significantly higher in the leukocyte-depletion group 1 hour after arrival to the intensive care unit (p < 0.05) and after extubation (p < 0.05). There were no statistical differences between the two groups with respect to postoperative circulating platelet levels and blood loss, and no infections were observed during the whole period of hospitalization. These results suggest that leukocyte depletion of the residual heart-lung machine blood improves postoperative lung gas exchange function and is safe for patients who are expected to have a severe inflammatory response after heart operations.

Techniques for avoiding neurologic injury during adult cardiac surgery

The mechanisms and pathophysiology of perioperative neurologic injury are reviewed. The principle mechanisms of the ischemic injury are gaseous and particulate emboli and hypoperfusion caused by cerebrovascular occlusive disease. The contribution of the cardiopulmonary bypass circuit to the development of ischemic injury is discussed. The important role of the surgeon in preventing particulate and gaseous microemboli and macroemboli is described and techniques for avoiding hypoperfusion in the presence of occlusive cerebrovascular disease are presented. Patients at greatest risk of perioperative neurologic injury are elderly patients with atherosclerotic aorta, cerebrovascular disease, and previous neurologic abnormalities. The pump oxygenator may be the cause of neurologic injury by generation of emboli, hypoperfusion, and perfusion accidents. The principles of perfusion safety are presented. Massive air embolization may occur from the heart-lung machine or from the heart. Methods of preventing massive air embolus including techniques of bypass and air removal from the heart are discussed. The management of massive air embolus is thoroughly described. The detection of cerebrovascular disease is discussed and the management of the patient with cerebrovascular disease described. Atherosclerosis of the ascending aorta is a major risk factor for perioperative neurologic injury. Methods of detection and management are thoroughly described. Prevention of embolization from intracardiac debris and clot is described.

Normothermic versus hypothermic cardiopulmonary bypass: central nervous system outcomes

The recent advent of "warm heart" surgery has resulted in reexamination of the neuroprotective effects of hypothermia in the setting of cardiopulmonary bypass (CPB). Hypothermia has been shown to confer significant protection in the setting of transient, but not permanent, ischemia. The mechanism of this neuroprotection is unclear at this time. Reduction in cerebral metabolic rate is believed to be less important compared with the effect of hypothermia on the release of excitatory neurotransmitters, catecholamines, or other mediators of cellular injury. It is for this reason that mild hypothermia (33-35 degrees C) is believed to confer significant neuroprotection. Two large randomized trials of warm versus cold heart surgery have been reported. Neither study found a difference in terms of neuropsychologic dysfunction. However, one study identified a threefold increase in strokes in the "warm" patients. The reasons for this difference are not clear; however, there were various differences in technique and patient population that may have been important. There are other reports of large series of patients undergoing normothermic bypass, with no increase in stroke rate over what is reported elsewhere in the literature. To date, the evidence would suggest that neuropsychologic function is not affected by CPB temperature, suggesting that the transient ischemia is not an important mechanism in this injury. Stroke after CPB is usually the result of permanent ischemia, and hypothermia's effect in this setting is minimal. It would seem unlikely that hypothermia offers anything more than modest benefits in the clinical situation where there is no circulatory arrest.

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)

Quantitation of particulate microemboli during cardiopulmonary bypass: experimental and clinical studies

An electronic particle-size analyzer (Coulter Counter ZM) was used to quantitate particulate microemboli 15 to 80 microns in size during cardiopulmonary bypass. Through both laboratory studies and clinical research, we confirmed three main causes of microemboli: (1) infusion of banked blood stored for more than 3 days; (2) use of cardiotomy reservoirs; and (3) use of bubble oxygenators. The regression equation between number of particles and blood storage time was Y = 3.7262X + 10.244 (r = 0.886; p < 0.01). The number of microemboli from cardiotomy reservoirs was 2.8 to 5.1 times that from other sources (p < 0.01). The number of solid particles from bubble oxygenators was 1.8 to 3.2 times that from membrane oxygenators (p < 0.01). Electron microscopy showed that a large number of solid particles more than 20 microns in size were formed during heart-lung bypass. They obstructed the microcirculation and damaged pulmonary capillary endothelial and alveolar epithelial cells. The degree of histological damage was related to the number and size of microemboli and the duration of pulmonary microcirculatory obstruction.

Perioperative stroke. Part II: Cardiac surgery and cardiogenic embolic stroke

The major mechanism of stroke in cardiac surgery is embolization. The risk is higher in intracardiac than in extracardiac surgery. The incidence of stoke associated with CABG is about 5%. The cerebral protective properties of isoflurane and thiopentone, acid-base management, and monitoring of cerebral perfusion during cardiopulmonary bypass are discussed. Prophylactic carotid endarterectomy for patients with asymptomatic carotid disease before cardiac surgery is not necessary. Symptomatic carotid disease increases the risk of stroke, and the management of patients who have both symptomatic coronary and carotid artery diseases is discussed. Cardiogenic embolism is probably responsible for many perioperative strokes. Patients with atrial fibrillation, valvular disease, and prosthetic heart valves are at high risk of cardiogenic embolism. Strokes associated with cardioversion, pacemaker insertion, coronary arteriography and angioplasty are explored.

The effect of arterial filtration on reduction of gaseous microemboli in the middle cerebral artery during cardiopulmonary bypass

Noninvasive in vivo detection of gaseous microemboli in the middle cerebral artery, by transcranial Doppler ultrasound, was used to determine the effect of filtration in the arterial catheter using 25- and 40-microns filters and bubble oxygenators in patients undergoing cardiopulmonary bypass surgery. Eighteen patients undergoing coronary artery bypass surgery were studied using a closed cardiac (unvented heart) model. Group 1 patients (no filters) had the highest incidence of gaseous microemboli, as indicated by the ultrasound microemboli index, at both high and low oxygen flow rates. Group 2 patients (40-microns filters) had a significantly lower microemboli index, particularly at low oxygen flow rates (t = 4.9, p less than 0.001). The 25-microns group patients had the lowest values of all. No microemboli were detected at low oxygen flow rates, and microemboli were detected in only 0.1% of the samples at high oxygen flow rates. Additionally, observations on vented hearts in 3 patients undergoing cardiac valve surgery indicate that the origin of gaseous microemboli may be air trapped inside the heart.

Doppler ultrasonic detection of particulate release during hemodialysis with cellulose hollow-fiber and sorbent suspension reciprocating dialyzers

Doppler ultrasound is a noninvasive technique for monitoring moving objects such as flowing blood while ignoring stationary objects such as shunt tubing. A Doppler system was investigated to determine its sensitivity in detecting particulate release in blood during hemodialysis. Seven hemodialysis procedures with dogs and six trials with humans were done using a sorbent suspension reciprocating dialyzer ( SSRD ). Two additional trials were done with humans using a cellulose acetate hollow-fiber dialyzer (HFD). A large increase (approximately twofold) was found in the reflected Doppler signal in outflowing blood from the SSRD and HFD in both dogs and humans. Numerous additional studies to characterize the nature of the particulate matter showed platelet aggregates in the dogs and fibrinogen-fibrin degradation products in the humans to be present in the outflowing blood. In vitro studies suggested microscopic air bubbles (less than 25 micron in diameter) may have contributed to the particulate matter detected during hemodialysis by this sensitive monitoring system.

Intravascular microaggregation and in vitro platelet aggregation in coronary artery disease

To investigate in vivo and in vitro microaggregation in coronary artery disease, we obtained blood samples from the coronary sinus (CS), pulmonary artery (PA), and aorta (AO) in patients undergoing cardiac catheterization. An electronic particle size analyzer was used to quantify microaggregates 13 to 81 mu in diameter in blood. In the first group of 58 patients, preformed circulating microaggregates and platelet responsiveness to ADP were assessed in AO and PA blood only. The coronary artery disease patients did not have significantly higher volumes of preformed in vivo aggregates in either AO or PA blood. However, the mean aggregate size in response to 0.2 microM ADP in vitro was larger in both AO and PA blood in patients with coronary disease [12.4 +/- 0.9 vs. 9.4 +/- 1.4 X 10(3) mu3 (AO); 12.5 +/- 0.9 vs. 8.3 +/- 0.7 0.7 X 10(3) mu3 (PA)]. In a second group of 46 patients, CS, AO and PA samples were compared using the same methods. The volume of microaggregates preformed in vivo was significantly greater in CS blood than in PA or AO blood in patients with and without coronary disease. The volume and mean size of aggregates induced by ADP in vitro were smaller in CS blood compared to PA. In conclusion, the volume of in vivo microaggregates is increased in CS blood, independent of coronary disease, but significant volumes are not found in PA or AO blood. Patients with coronary disease have more reactive platelets to in vitro aggregatory agents in AO and PA samples of similar hematocrit.

Defective platelet aggregation in patients undergoing surgical repair of cyanotic congenital heart disease

Fifteen patients undergoing cardiopulmonary bypass for repair of cyanotic congenital defects were examined for evidence of platelet aggregation abnormalities by means of electronic particle sizing. Eight patients with polycythemia whose hematocrits were greater than or equal to 50% before bypass were compared with 7 patients without polycythemia whose hematocrits were less than 50%. Patients also were compared with 11 healthy volunteers. Before bypass, platelets in blood from the patients with polycythemia formed markedly smaller platelet aggregates (8.9 +/- 0.8 X 10(3) mu 3; mean +/- standard error of the mean) in response to adenosine diphosphate than those of the other group of patients (21.7 +/- 1.9 X 10(3) mu 3; p less than 0.001) or healthy volunteers (25.8 +/- 2.1 X 10(3) mu 3; p less than 0.001). Mean platelet aggregate sizes were not different between patients without polycythemia and normal volunteers (p greater than 0.05). In samples taken after bypass, patients with polycythemia again had smaller aggregates than the other group of patients (p less than 0.005). This platelet defect is quantitatively related to polycythemia, and may be a mechanical effect of the excess erythrocytes.

Effect of blood microfilters on complement activity in human plasma

While many devices that come into direct contact with patients' blood have been shown to be safe with respect to their effects on the cellular components and coagulation system of blood, many have not been examined with respect to their potential to activate the complement system. We present evidence that suggests that a combination of nylon plus polypropylene, and a combination of polyester plus polypropylene, found in blood microfilters used to protect patients from gaseous and particulate embolism during cardiopulmonary bypass, produce significant (p less than 0.01, p less than 0.05, respectively) C3a generation during incubation in heparinized plasma. Filter mesh composed of nylon plus polypropylene produced significantly more (p less than 0.01) C3a than the polyester plus polypropylene combination.

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.

Platelet aggregation during and after cardiopulmonary bypass: effect of two different cardiotomy filters

Patients undergoing cardiopulmonary bypass with a membrane oxygenator were studied to determine the effects of two cardiotomy filters on platelet number and function. A Dacron wool filter removed significantly more microemboli than a 40 mu X 40 mu pore-mesh filter. Postoperatively, there were fewer platelets and a lower total volume of platelets in patients who had a Dacron wool filter in the extracorporeal circuit. However, the volume of adenosine diphosphate-induced aggregates was nearly identical in the two patient groups (p greater than 0.1). The study documents an increased number of circulating platelets after pore-mesh filtration, and suggests that the microaggregates reinfused during pore-mesh filtration represent aggregated platelets that dissociate and subsequently circulate in the patient but do not function.

Evaluation of a new cardiotomy blood filter

A new cardiotomy blood filter with a polycarbonate body, a polyester prefilter, and a nylon screen with 20 mu pores was compared with four other commercially available filters. The Optigard filter was found to function as a "surface filter," which effectively removes blood particles larger than its nominal pore size.

An ultrasonic analysis of the comparative efficiency of various cardiotomy reservoirs and micropore blood filters

The ability of 12 commercially available cardiotomy reservoirs to remove bubbles from aspirated blood was investigated by means of a simulated cardiopulmonary bypass circuit and an ultrasonic microbubble detector. Performance varied considerably. The number of gaseous microemboli remaining after passage of blood through the reservoir was reduced by (a) holding the blood in the reservoir, (b) reducing the volume of air mixed with the aspirated blood, and (c) using a reservoir that did not induce turbulence and that contained integral micropore filtration material. Further micropore filtration of the blood after passage through the cardiotomy reservoir was beneficial, and significantly more bubbles were extracted when the microfilter was sited below the reservoir than when it was placed in the arterial line.

Computerized discrimination of microemboli in extracorporeal circuits

A computerized ultrasonic particle detection system is capable of identifying microemboli in the 10 to 350 microgram. Data show that appropriate computer analysis of the reflecting signals allows discrimination of size and type of emboli. All extracorporeal circuits have microemboli with a large variation in size and number, depending upon the apparatus and how it is run.

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.

Pathology of hearts after aortocoronary saphenous vein bypass grafting for coronary artery disease, studied by post-mortem coronary angiography

A detailed pathological study was made in 10 patients dying up to 13 months after aortocoronary saphenous vein bypass grafting for coronary atherosclerosis. The coronary arteries and vein grafts were investigated by injection with a radio-opaque mass, radiography, dissection, and histology. The report is to some extent historical since the patients died during a period when the operation was first being introduced into two cardiothoracic hospitals. About 80 operations were performed during the time the 10 deaths occurred, a mortality of 12-5 per cent (including cases followed up to 13 months after operation). Seven of the patients were operated on for intractable angina and 3 with a view to aneurysmectomy. All the patients selected for operation were severely disabled despite medical treatment. The main cause of death was extremely severe coronary artery disease and its effects on the left ventricle; in one case, over two-thirds of the left ventricle had been destroyed by infarction before operation. Other causes or contributing causes of death were pulmonary embolism, myocardial infarction complicating angiography (ostial stenosis), and cerebral damage. Ten of the 14 vein grafts (71%) were patent at necropsy. A free flow of injection medium usually occurred between patent grafts and coronary arteries. Thrombosis of a graft was thought to have contributed to death in 3 patients, but not in a fourth who died of pulmonary embolism. Since thrombosis of grafts was usually secondary to poor run-off blood into severely atheromatous coronary arteries, this was also an indirect effect of the advanced coronary arterial disease. In one case, thrombosis followed severe chronic intimal thickening of a graft in place for 13 months. The study of these deaths emphasizes that in some patients the pathological changes in the coronary arteries and left ventricle are too severe for them to benefit from surgery. Vein grafts cannot be expected to distribute blood effectively through grossly narrowed coronary arteries. In addition, when a large part of the left ventricle is infarcted or scarred, it is almost certain that improving the blood supply by grafting will not result in significant regeneration of cardiac muscle. Since the time when this study was made, there have been few deaths among the many vein graft operations subsequently carried out in the hospitals involved. The two most important factors thought responsible for the improvement are the selection of cases more suitable for surgery by continued improvement of diagnostic techniques, and also the employment of more radical surgical procedures in the form of coronary endarterectomy and the insertion of more grafts per patient.