Time for new concepts about measurement of complement activation by cardiopulmonary bypass?

Fifty-one patients admitted for routine coronary bypass operations were randomized to cardiopulmonary bypass with a membrane oxygenator (Capiox) or a bubbler (Polystan or William Harvey). Complement activation was measured using enzyme immunoassays for concentrations of C3 activation products and the terminal complement complex. From 5.8 to 8.1 arbitrary units (AU)/mL (medians), the plasma concentrations of C3 activation products increased by 119.9 AU/mL (Capiox), 124.6 AU/mL (Polystan), and 79.5 AU/mL (William Harvey) to a peak at closure of the sternum (not significant when related to baseline concentrations). The increase in C3 activation products and baseline C3 activation were linearly correlated (R2 = 0.30; p less than 0.0001). From 5.5 to 6.1 AU/mL, the plasma terminal complement complex concentrations increased by 45.2 AU/mL (Capiox), 15.4 AU/mL (Polystan), and 17.4 AU/mL (William Harvey) to a peak before termination of cardiopulmonary bypass. Maximal terminal (C5-C9) activation was significantly higher in the membrane oxygenator group (p less than 0.0001) and showed no relationship to C3 activation. Measurement of C3 activation only gives no information about C5-C9 activation. At present, terminal complement complex quantitation is probably the best index of C5-C9 activation during cardiopulmonary bypass.     

Different oxygenators for cardiopulmonary bypass lead to varying degrees of human complement activation in vitro

Complement activation was studied in vitro with six different membrane and bubble oxygenators for cardiopulmonary bypass. There was a similar increase in terminal (C5 to C9) activation with all oxygenators (p less than 0.001), ranging from 281% (117% to 444%) to 453% (225% to 680%) after 60 minutes (median and 95% confidence intervals). C3 activation was not observed with a hollow fiber membrane and a soft shell bubble oxygenator. On the other hand, a capillary membrane, a sheet membrane, a nonporous membrane, and a hard shell bubble oxygenator all induced a similar increase in C3 activation (p less than 0.01), ranging from 107% (23% to 346%) to 272% (88% to 395%) after 60 minutes. The differences in C3 activation could not be explained by the blood contact materials or any other single factor known to induce activation, which suggests that overall complement activation during cardiopulmonary bypass is a multifactorial effect. The tubing set per se induced only minor C3 activation but contributed to the overall formation of terminal complement complex. The study further indicates that an arterial line blood filter prevents activated neutrophils from being reinfused to the patient and should be used regardless of type of oxygenator.     

Complement activation during cardiopulmonary bypass. Comparison of bubble and membrane oxygenators

A prospective randomized trial involving 91 patients undergoing cardiopulmonary bypass compared the effects of bubble oxygenators (with and without methylprednisolone sodium succinate) and membrane oxygenators on complement activation and transpulmonary sequestration of leukocytes. Patients were divided as follows: Group I, 30 patients, bubble oxygenator; Group II, 31 patients, bubble oxygenator and methylprednisolone sodium succinate (30 mg/kg); Group III, 30 patients, membrane oxygenator. In Group I, C3a increased from 323 +/- 171 ng/ml during cardiopulmonary bypass to 1,564 +/- 785 ng/ml at 25 minutes after bypass (p less than 0.0001). A significant decrease in C3a was found in Groups II and III compared to Group I (p less than 0.0001). C5a did not change significantly during cardiopulmonary bypass in any group. Reestablishment of pulmonary circulation at the end of bypass produced significant transpulmonary leukocyte sequestration in Group I; the median cell difference was 1,700/microliter. Transpulmonary sequestration was significantly (p less than 0.0001) less in Group II (median cell difference = 200/microliter) and in Group III (median cell difference = 400/microliter) than in Group I. We conclude that cardiopulmonary bypass with a bubble oxygenator alone initiates significantly (p less than 0.0001) more C3a activation and leukocyte sequestration than when methylprednisolone sodium succinate (30 mg/kg) is given 20 minutes before the start of cardiopulmonary bypass with a bubble oxygenator or when a silicone membrane oxygenator is used.     

Reduced complement activation with heparin-coated oxygenator and tubings in coronary bypass operations.

Complement activation after cardiopulmonary bypass is correlated with postoperative organ dysfunction. Heparin coating of the entire blood-contact surface of the cardiopulmonary bypass circuit has proved to reduce complement activation in vitro. A membrane oxygenator and tubing setup coated with functionally active heparin was compared with an uncoated, otherwise identical setup in 20 patients undergoing routine coronary bypass operations. The concentrations of C3 activation products and the terminal complement complex were measured in sensitive and specific enzyme immunoassays. Peak concentrations of C3 activation products were 90.1 (74.7 to 107.4) AU/ml (medians and 95% confidence intervals) and 52.4 (35.7 to 76.4) AU/ml with the uncoated and coated setups, respectively (p = 0.02). The corresponding concentrations of the terminal complement complex were 26.2 (20.1 to 37.5) AU/ml and 13.7 (11.1 to 25.1) AU/ml (p = 0.03). Blood loss from the mediastinal drains during the first 12 postoperative hours was 533 (416 to 975) ml in patients treated with the uncoated setup and 388 (313 to 579) ml in the coated treatment group (p = 0.06) and was significantly correlated with peak concentrations of the terminal complement complex (p = 0.01). There were no differences in neutrophil counts nor platelet numbers between the treatment groups. The approximate 45% reduction in complement activation with the heparin-coated cardiopulmonary bypass device indicates a substantial improvement of biocompatibility.     

A Comparison of the Effects of Membrane and Bubble Oxygenators on Platelet Counts and Platelet Size in Elective Cardiac Operations

To compare the effects of membrane and bubble oxygenators on platelet counts and the size of circulating platelets, serial hematocrits, platelet counts, and platelet sizing were measured in 23 patients undergoing elective cardiac operations. In 10 patients a bubble oxygenator was used and in 13, a SciMed membrane oxygenator. The two groups were statistically similar with respect to age, weight, time on bypass, and mean blood flow rates during bypass.It was found that platelet counts, when corrected for hemodilution, did not fall from control levels during or up to 24 hours after cardiopulmonary bypass in either group. In both groups, the relative number of platelets per gram of hemoglobin increased slightly during and after bypass, and this increase was significant in the bubble oxygenator group. The average size of circulating platelets increased only in the bubble oxygenator group, and then only in the one-day postoperative sample. These findings suggest that the membrane oxygenator offers no advantage with respect to preservation of platelets during cardiopulmonary bypass lasting up to 2 to 3 hours.     

Inflammatory system activation during cardiopulmonary bypass as an indicator of biocompatibility: a randomized comparison of bubble and membrane oxygenators

As the exposure of blood to foreign material during cardiopulmonary bypass (CPB) leads to triggering of inflammatory systems, the inflammatory response was used as an indicator of the biocompatibility of oxygenators. Activation of complement and neutrophil granulocytes during CPB was studied in 96 patients undergoing coronary bypass, with randomized comparisons between four different oxygenators, two of bubble and two of membrane type. Seven patients undergoing thoracotomy without CPB served as controls. During CPB there was significant complement activation, measured as changes in the ratio C3d/C3, with no demonstrable difference between the bubble and membrane oxygenator groups. Such change was not seen in the controls. Neutrophil granulocytes released significant amounts of the granule proteins lactoferrin and myeloperoxidase during CPB, but not during thoracotomy without CPB. The plasma concentrations of lactoferrin and myeloperoxidase were significantly lower in the membrane oxygenator groups, possibly indicating better biocompatibility. The strong inflammatory response with both oxygenator types, however, indicates that presently used CPB devices have unsatisfactory biocompatibility.     

Pressure drop, shear stress, and activation of leukocytes during cardiopulmonary bypass: a comparison between hollow fiber and flat sheet membrane oxygenators

The membrane oxygenator is known to be superior to the bubble oxygenator, but little information is available about the difference between the hollow fiber and flat sheet membrane oxygenators with regard to pressure drop, shear stress, and leukocyte activation. In this study, we compared these 2 types of membrane oxygenators in patients undergoing cardiopulmonary bypass (CPB) surgery with special focus on leukocyte activation and pressure drop across the oxygenators. Plasma concentration of elastase, a marker indicating leukocyte activation, increased to 593+/-68% in the flat sheet oxygenator group versus 197+/-42% in the hollow fiber oxygenator group (p<0.01) at the end of CPB compared to their respective baseline concentrations before CPB. Pressure drop across the oxygenator was significantly higher in the flat sheet group than in the hollow fiber group throughout the entire period of CPB (p<0.01). High pressure drop across the oxygenator as well as the calculated shear stress was positively correlated with the release of elastase at the end of CPB (r = 0.760, p<0.01, r = 0.692, p<0.01). However, this positive correlation existed in the flat sheet oxygenator but not in the hollow fiber oxygenator. Clinically, both membrane oxygenators have satisfactory performance in O2 and CO2 transfer. These results suggest that a higher pressure drop across the flat sheet oxygenator is associated with more pronounced activation of leukocytes in patients undergoing cardiopulmonary bypass.     

Complement activation in extracorporeal circulation. Comparison of nylon versus polyester bubble oxygenators

Complement activation during cardiopulmonary bypass is well known and may influence postoperative morbidity. As nylon can particularly induce complement activation, its influence was assessed by measuring total haemolytic complement and B, C3 and C4 factors, during cardiopulmonary bypass with bubble oxygenators for coronary surgery, comparing "nylon" circuits (20 patients, Bentley BOS 10) versus "polyester" circuits (19 patients, Shiley S 100 A). Complement activation began with induction of anaesthesia and surgical procedures, B, C3 and C4 levels falling significantly (respectively 15, 17 and 20% from baseline values). The alternative pathway was activated before the classical pathway. Complement activation continued during cardiopulmonary bypass, with no more consumption of complement factors (slight variations of about 0 to 3% of the levels found after anaesthetic induction and surgical procedures). No statistically significant difference appeared between the two groups. This suggested that nylon did not significantly increase complement activation during cardiopulmonary bypass. The bubble oxygenator material cannot therefore be considered as a criterion for choosing the type of equipment.     

Sequestration of glyceryl trinitrate (nitroglycerin) by cardiopulmonary bypass oxygenators

The effectiveness of glyceryl trinitrate (nitroglycerin) in controlling myocardial ischemia and blood pressure during coronary artery bypass graft surgery is frequently lost during surgery, possibly as a result of drug sequestration by the cardiopulmonary bypass circuit. The objective of this study was to utilize a gas-liquid chromatographic assay to determine the extent of removal of glyceryl trinitrate from the priming fluid by the bubble and membrane oxygenators. The apparatus was maintained at either 25 or 37 degrees C, the two extreme temperatures experienced by the patient during bypass surgery. At apparent steady state, the circulating glyceryl trinitrate concentration was decreased by 20.6%, 46.6%, and 67.3% with the Maxima membrane oxygenator, Cobe membrane oxygenator, and Bentley bubble oxygenator, respectively. The three-layer defoaming filters that are used in the Bentley bubble oxygenator were studied by immersing each of the three filters in fluid containing 60 nM glyceryl trinitrate and monitoring the drug concentration in Plasmalyte. The filters sequestered approximately 90% of the glyceryl trinitrate from the bathing solution of which 31% was recovered with a single methanol wash of the polyurethane filter. These data demonstrate that the different oxygenators used in the cardiopulmonary bypass circuit remove glyceryl trinitrate to varying degrees from the circulating fluid.     

Haematological characteristics of a new membrane oxygenator: the Cobe CML

The new Cobe CML membrane oxygenator is more compact than other membrane oxygenators and has a combined venous and cardiotomy suction reservoir. Its size makes it as easy to use as a bubble oxygenator. The studies reported here were designed to show whether the excellent haemocompatibility found with other types of membrane oxygenators had ben compromised by the changes introduced in the Cobe CML oxygenator. Platelet number and function (ADP induced aggregation) plasma betathromboglobulin concentration and plasma haemoglobulin concentration were studied in nine patients where the Cobe CML oxygenator had been used and these were compared with ten patients managed with a Shiley S-100 bubble oxygenator. We conclude that the constructional changes of the Cobe CML oxygenator do not affect the haemocompatibility of this type of membrane oxygenator and that it remains significantly better than the Shiley S-100 bubble oxygenator.     

Deleterious effects of cardiopulmonary bypass. A prospective study of bubble versus membrane oxygenation

A number of hematologic and immunologic parameters that reflect erythrocyte and platelet damage and host defense mechanisms against infection were studied in 20 patients undergoing cardiopulmonary bypass during coronary operations. The patients were randomly assigned to a group in which a bubble oxygenator or a hollow-fiber membrane oxygenator was used. Hemolysis, thrombocytopenia, and significant release of beta thromboglobulin occurred in patients from the bubble oxygenator group and, to much lesser extent, in patients from the membrane oxygenator group. Polymorphonuclear leukocytes and monocytes from bubble oxygenator patients demonstrated increased generation of reactive oxygen species in the resting state and in the presence of the stimulating agents N-formyl-methionyl-leucyl-phenylalanine, concanavalin A, and opsonized zymosan, as compared with cells from membrane oxygenator patients. No difference was found between bubble and membrane oxygenator patients in the time of occurrence or intensity of leukopenia during bypass, of leukocytosis at the end of bypass, nor in the rate of complement activation, as assessed by quantitation of plasma C3a antigen. Complement activation was dependent on the alternative pathway. Immunoglobulin M concentration significantly decreased during bypass in both groups of patients. The serum opsonizing capacity for endotoxin and serum bactericidal activity for Serratia marcescens were decreased in both groups, mainly because of hemodilution, although they were additionally affected by bubble oxygenation. Several deleterious hematologic consequences of cardiopulmonary bypass can be minimized by the use of a membrane oxygenator. However, complement activation remains a potential risk factor even in membrane oxygenator patients and requires further investigation to obtain better hemocompatible materials for cardiopulmonary bypass circuits.     

Membrane oxygenator prevents lung reperfusion injury in canine cardiopulmonary bypass

The effect of blood activation on lung reperfusion injury during cardiopulmonary bypass was investigated in 20 dogs with the use of a bubble oxygenator (n = 10) or a membrane oxygenator (n = 10). In the bubble oxygenator group, significant leukocyte and platelet right to left atrium gradients were found 15 minutes after lung reperfusion (p less than 0.05, p less than 0.01) accompanied by a sharp increase in plasma malondialdehyde concentration 5 minutes after lung reperfusion, whereas no significant right to left atrium gradient of leukocytes or platelets nor significant increase in plasma malondialdehyde concentration was observed in the membrane oxygenator group. In both the bubble oxygenator and membrane oxygenator group, similar mild to moderate lung histological changes were found before lung reperfusion. After lung reperfusion, however, more endothelial cell swelling (p less than 0.05), leukocyte (p less than 0.01) and platelet (p less than 0.01) accumulation in lung capillaries, leakage of erythrocytes into the alveolar space (p less than 0.05), and type I cell damage (p less than 0.05) were found only in the bubble oxygenator group. Eventually, a significantly higher lung water content was found in the bubble oxygenator group than in the membrane oxygenator group (p less than 0.01) after cardiopulmonary bypass. This study indicated that lung injury during cardiopulmonary bypass starts mainly after lung reperfusion, which was correlated with lung leukocyte and platelet sequestration associated with different types of oxygenators.     

Comparison of bubble and membrane oxygenators in short and long perfusions.

Eighty patients had cardiopulmonary bypass (CPB), half having short (109 +/- 11 minutes) perfusions and half having long (188 +/- 14 min) perfusions. Twenty patients in each group were perfused with bubble oxygenators (Bentley, Harvey, or Galen) and 20 with membrane oxygenators (Modulung or Teflo). Hemodilution to a hematocrit value of 22.5% +/- 1.4% and hypothermia to 28 degrees +/- 2 degrees C were used in all patients. Complete hemograms, sequential multiple analyzer 18 tests, coagulation profiles, blood gases and pH, three immunoglobulins, and two complement fraction proteins were sampled as follows: three times before perfusion, one to ten times during perfusion, 1 hour immediately after perfusion, and 4, 24, and 48 hours postoperatively. Data in concentration terms were compared statistically and reported as mean and standard error for each subset. Additionally, rates of gain or loss were calculated in terms of quantity per liter of blood pumped per minute. During perfusion for both duration sets, use of a membrane oxygenator resulted in greater pump flows (4.55 +/- 0.15 L/min versus 3.75 +/- 0.11 L/min), lower total peripheral resistances (1,125 +/- 63 dynes.sec.cm-5 versus 1,652 +/- 115 dynes.sec.cm-5), and greater urinary outputs (9.4 +/- 1.1 ml/min versus 2.2 +/- 0.6 ml/min) than in the bubble oxygenator subsets. Comparisons of measured and calculated data in the immediate postperfusion interval showed no differences between bubble and membrane oxygenator subsets for short perfusions. In long perfusions, the membrane subset had lower plasma hemoglobin and white cell concentrations and generation rates, smaller (3 to 8 1/2 times) losses of IgG, IgM, C3 and shed blood necessitating less transfusion, and greater C4 losses. The membrane oxygenator systems used were more complex and costly and offered no advantages for short perfusion in adults. In anticipated long perfusions or where bleeding may be a problem, a membrane oxygenator appears more efficacious than bubble systems. For perfusions of less than 2 hours, membrane oxygenators had no biochemical or hematologic advantage over the bubble devices used in this study.     

Oxygenation strategy and neurologic damage after deep hypothermic circulatory arrest. I. Gaseous microemboli.

OBJECTIVES: Recent studies suggest that myocardial reperfusion injury is exacerbated by free radicals when pure oxygen is used during cardiopulmonary bypass. Partial replacement of the oxygenator gas mixture with nitrogen, however, such as has already been adopted clinically in many centers, could increase the risk of gaseous nitrogen microembolus formation and therefore of brain damage because of the low solubility of nitrogen, particularly under conditions of hypothermia. METHODS: Ten 7- to 10-kg piglets were cooled for 30 minutes to 15 degrees C on cardiopulmonary bypass and then rewarmed for 40 minutes to 37 degrees C. In 5 piglets cardiopulmonary bypass was normoxic and in 5 it was hyperoxic. In each group 3 bubble oxygenators without arterial filters and 2 membrane oxygenators with filters were used. Cerebral microemboli were monitored continuously by carotid Doppler ultrasonography (8 MHz) and intermittently by fluorescence retinography. RESULTS: Embolus count was greater with lower rectal temperature (P <.001), use of a bubble oxygenator (P <.001), and lower oxygen concentration (P =.021) but was not affected by the temperature gradient between blood and body during cooling or rewarming. CONCLUSIONS: Gaseous microemboli are increased with normoxic perfusion, but this is only important if a bubble oxygenator without a filter is used.     

A Prospective Randomized Study of Membrane versus Bubble Oxygenators in Children

We studied 60 children, 2 weeks to 10 years old, prospectively by randomly assigning them to a SciMed membrane oxygenator or Harvey bubble oxygenator. Variables of cardiopulmonary bypass (CPB) were closely controlled: prime, circuit configuration, flow rate, and blood gases. Blood variables measured at eight intervals before, during, and after operation were as follows: seven plasma proteins, free hemoglobin, formed elements, and clotting functions. Preoperatively and postoperatively, we evaluated brain function (psychological testing), renal function (creatinine clearance), and pulmonary function (compliance changes and postoperative shunt fraction). Postoperative blood loss, fever, and length of hospitalization were also evaluated. We compared 302 variables by computer program.No difference (p > 0.05) between the two groups was found in any variable related to CPB or organ function (pulmonary, renal, or cerebral) or in hematological variables except free hemoglobin. After 5 and 60 minutes of CPB and the next day, it was significantly lower (p < 0.05) in the group with a membrane oxygenator. Safety, cost, and convenience, not physiology, should be the major factors in considering membrane versus bubble oxygenators for cardiac operations in children.     

Retinal microembolism and neuropsychological deficit following clinical cardiopulmonary bypass: comparison of a membrane and a bubble oxygenator. A preliminary communication

To observe and quantify cerebrovascular microembolic events in the central nervous system during cardiopulmonary bypass, 40 patients having elective uncomplicated coronary surgery had retinal fluorescein angiograms 5 min before bypass was discontinued. Each patient also had 10 neuropsychological tests before and after surgery. A Harvey H1700 bubble oxygenator was used for 23 patients and a Cobe CML sheet membrane oxygenator was used for 17 patients. All 23 (100%) of patients in the bubble oxygenator group had retinal microvascular occlusions consistent with microembolism compared to 8/17 (47%) in the membrane oxygenator group (P less than 0.001). In those retinas with occlusions, the mean resultant area of non-perfusion was less in the membrane oxygenator group (0.11 mm2; n = 8) than in the bubble oxygenator group (0.29 mm2; P less than 0.01). Arterial PO2 levels during bypass were similar in both groups at moderate hypothermia, but the mean PaO2 during rewarming was higher in the bubble oxygenator group (27 kPa) than in the membrane group (13 kPa; P less than 0.001). Neuropsychological deficits were more common and more severe after bubble oxygenation than after membrane oxygenation, but in this small patient group, the difference was not statistically significant. We conclude that flat sheet membrane oxygenation during cardiopulmonary bypass may confer significant protection against cerebrovascular microembolism.     

Comparative evaluation of a new disposable rotating membrane oxygenator with bubble oxygenator.

The comparative in vivo performance of adult-size bubble and rotating membrane oxygenators was evaluated during closed-chest cardiopulmonary bypass for six hours in two groups of dogs. The results show that the rotating membrane oxygenator is efficient in oxygen and carbon dioxide transfer with minimal trauma to blood, while platelet destruction and hemolysis were marked with the bubble oxygenator. Cerebral, cardiac, and respiratory complications were frequent with the bubble oxygenator and absent with the membrane oxygenator.     

Generation of platelet-derived microparticles in patients undergoing cardiac surgery is not affected by complement activation

OBJECTIVE: The mechanisms causing the presence of platelet-derived microparticles in the circulation are unknown. In vitro platelets release platelet-derived microparticles in response to complement activation. This study evaluates the relationship between complement activation and levels of circulating platelet-derived microparticles in patients undergoing cardiac surgery. METHODS: Prospectively, 71 patients were included who underwent elective coronary artery bypass grafting with cardiopulmonary bypass. The patients were randomly allocated to one of the 3 groups: uncoated oxygenator, UnModified Surface (n = 25) or oxygenator coated with either BioPassive Surface (n = 25) or BioActive Surface (n = 21). Platelet-derived microparticles and terminal complement complexes were determined before bypass and after induction of anesthesia, 15 minutes after the start of cardiopulmonary bypass, at the end of cardiopulmonary bypass, and 30 minutes after administration of protamine sulfate. RESULTS: Demographic and cardiopulmonary bypass data were similar for the 3 groups. At the end of cardiopulmonary bypass, platelet-derived microparticle numbers were decreased in all 3 groups. No significant differences were observed among the groups at any sampling point. At the end of cardiopulmonary bypass, terminal complement complex concentrations were increased in all groups (P <.001), and significant differences among the groups were present (P =.002). CONCLUSIONS: Despite significant complement activation, no increase in numbers of circulating platelet-derived microparticles was found in the systemic blood of patients undergoing cardiac surgery with cardiopulmonary bypass. Thus complement activation in vivo does not necessarily affect generation of platelet-derived microparticles.     

In vivo evaluation of a phosphorylcholine coated cardiopulmonary bypass circuit

A complete phosphorylcholine coated cardiopulmonary bypass circuit, including the Dideco D901 oxygenator, was tested for gas transfer, blood path resistance, and biocompatibility in a standardized setting. Blood compatibility was tested by measuring complement and platelet activation. Three dogs (mean body weight 28 +/- 3 kg) were placed on cardiopulmonary bypass at a flow rate of 600 mL/min during 6 hours. The animals were weaned from cardiopulmonary bypass and sacrificed electively after 7 days. Oxygen and carbon dioxide transfer were 26.6 +/- 2.4 mL/min and 33.0 +/- 1.9 mL/min, respectively. Mean pressure drop across the oxygenator was 52.6 +/- 0.2 mmHg. The respective baseline values for thromboxane B2, prostaglandin E2 and platelet factor 4 were 1817 +/- 283 pg/mL, 12783 +/- 2109 pg/mL, and 0.35 +/- 0.08 IU/mL. Thromboxane B2 and prostaglandin E2 increased slightly to 2881 +/- 868 pg/mL and 18083 +/- 3144 pg/mL at 30 minutes of bypass, whereas platelet factor 4 values remained stable curing the procedure. Concentrations of complement split products C5a were only mildly increased. After use scanning electron microscopy was performed on the inner housing, heat exchanger, and outer surface of the hollow fibers. No thrombi nor organized cellular deposits were found on any of the components. Phosphorylcholine coating of CPB seems to be very promising regarding platelet activation and complement activation.     

Evaluation of Membrane Oxygenators and Reservoirs in Terms of Capturing Gaseous Microemboli and Pressure Drops

An increasing amount of evidence points to cerebral embolization during cardiopulmonary bypass (CPB) as the principal etiologic factor of neurologic complications. In this study, the capability of capturing and classification of gaseous emboli and pressure drop of three different membrane oxygenators (Sorin Apex, Terumo Capiox SX25, Maquet QUADROX) were measured in a simulated adult model of CPB using a novel ultrasound detection and classification quantifier system. The circuit was primed with 1000 mL heparinized human packed red blood cells and 1000 mL lactated Ringer's solution (total volume 2000 mL, corrected hematocrit 26–28%). After the injection of 5 mL air into the venous line, an Emboli Detection and Classification Quantifier was used to simultaneously record microemboli counts at post‐pump, post‐oxygenator, and post‐arterial filter sites. Trials were conducted at normothermic (35°C) and hypothermic (25°C) conditions. Pre‐oxygenator and post‐oxygenator pressure were recorded in real time and pressure drop was calculated. Maquet QUADROX membrane oxygenator has the lowest pressure drops compared to the other two oxygenators (P < 0.001). The comparison among the three oxygenators indicated better capability of capturing gaseous emboli with the Maquet QUADROX and Terumo Capiox SX25 membrane oxygenator and more emboli may pass through the Sorin Apex membrane oxygenator. Microemboli counts uniformly increased with hypothermic perfusion (25°C). Different types of oxygenators and reservoirs have different capability of capturing gaseous emboli and transmembrane pressure drop. Based on this investigation, Maquet QUADROX membrane oxygenator has the lowest pressure drop and better capability for capturing gaseous microemboli.