Influence of oxygenator type on the prevalence and extent of microembolic retinal ischemia during cardiopulmonary bypass. Assessment by digital image analysis

We have previously reported the occurrence of microembolic ischemia in the retina during cardiopulmonary bypass, as revealed by fluorescein angiography. This method has been extended by digital image analysis to include quantification of the extent of retinal ischemia and has been applied to a prospective comparative study of 64 patients undergoing elective coronary operations with either a bubble or a membrane oxygenator. Patients with diabetes or clinically evident cerebrovascular disease were excluded. Bypass procedures were standardized in all cases with pulsatile flow and a 40 microns arterial line filter (Pall EC Plus). Thirty patients had bypass with a bubble oxygenator (Harvey H1700) and 34 patients had bypass with a flat sheet membrane oxygenator (COBE CML). In each case retinal fluorescein angiograms were obtained preoperatively and 5 minutes before the end of bypass and were processed with a digital image analyzer (Context Vision GOP-302). Microembolic perfusion defects were identified by digital subtraction of preoperative and end-bypass angiograms and their total area was computed. Results. In the bubble oxygenator group retinal perfusion defects indicative of microembolism occurred in all 30 (100%) patients. In contrast, over half the patients in the membrane oxygenator group had normal retinal perfusion, and the prevalence of perfusion defects (44%; 70% confidence limits 34% to 54%) was significantly less than in the bubble group (p less than 0.001). In addition, those patients in the membrane group had significantly fewer lesions (median 0; 70% confidence limits 0 to 1) than patients in the bubble group (median 2; 70% confidence limits 2 to 2; p less than 0.001) and also had significantly smaller total areas of retinal ischemia (median 0 mm2; 70% confidence limits 0 to 0.16 mm2) than the bubble group (median 0.22 mm2; 70% confidence limits 0.21 to 0.27 mm2; p less than 0.001). There was no relationship between the extent of retinal ischemia and bypass time, arterial blood gas concentrations, volume of cardiotomy suction or donor blood returned to the pump, or recent medication with aspirin. Inferences. Digital image analysis of retinal fluorescein angiograms may provide a method of quantifying microembolic ischemia in the central nervous system during cardiopulmonary bypass. Flat sheet membrane oxygenation appears to provide significantly better protection against microembolic ischemia than bubble oxygenation.     

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.     

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.     

Cerebral microembolism during cardiopulmonary bypass. Retinal microvascular studies in vivo with fluorescein angiography

To observe microembolic events in the central nervous system during cardiopulmonary bypass, we subjected 21 patients undergoing elective coronary operations to retinal fluorescein angiograms 5 minutes before cardiopulmonary bypass was discontinued. Patients with diabetes or clinically evident cerebrovascular disease were excluded. Bubble oxygenation and nonpulsatile perfusion were used for bypass. After 31 to 167 minutes of cardiopulmonary bypass, all 21 (100%) patients had retinal microvascular occlusions indicative of microembolism. Control fluorescein angiograms obtained preoperatively and in five patients immediately before bypass but after aortic cannulation showed retinal perfusion. During bypass there was a mean of 3.5 (range 1 to 7) blocked arterioles of less than 50 micron caliber and a mean of 6.3 (range 1 to 10) focal areas of capillary nonperfusion per 30-degree field of retina centered on the macula per patient. Repeat studies 30 minutes after discontinuation of bypass showed partial reperfusion with occlusions in four of the five (80%) patients and a decrease in the mean total microembolic count from 12.6 to 4.8 (38%). In later studies at a median of 8 days postoperatively, only two of 16 (12.5%) patients had persistently occluded retinal vessels. The total microembolic count did not correlate with bypass time (r = 0.14) and was not reduced by arterial line filtration with a Pall 40 micron filter (Ultipore) in a subgroup of 11 patients. Twenty patients completed four standardized psychometric tests. Retinal microvascular occlusions were more numerous in those patients with a psychometric deficit (n = 7) than in those with no deficit (n = 13; p = 0.075). In a dog model of cardiopulmonary bypass, eight of nine (88.9%) had retinal microvascular occlusions after 10 to 90 minutes of bypass. Retinal histologic studies revealed intravascular platelet-fibrin microaggregates 20 to 70 micron in diameter and focal ischemic changes in seven of the nine (77.8%) dogs. Six dogs undergoing sham bypass had normal retinal perfusion and histologic findings. This study demonstrates a very high incidence of microvascular occlusions in the territory of the internal carotid artery during bypass consistent with a microembolic origin. The clinical significance of these findings is uncertain.     

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.     

Significance of the concentrated red cell and albumin priming method with particular reference to anaphylatoxin generation.

Anaphylatoxins generated by cardiopulmonary bypass were observed in basic and clinical studies (n = 120 in the latter). In vitro immunoglobulin fractions denatured by oxygen bubbling produced C4a, C3a, and C5a, but albumin identically treated did not. Therefore concentrated red cells with albumin were used to prime homologous blood for clinical application during cardiopulmonary bypass. Complement levels were compared with type of oxygenator (bubble or membrane) and the ratio of primed homologous blood to circulating autologous blood volume. With the bubble oxygenator at a low ratio of homologous to autologous blood (arbitrarily defined as less than 20%), C3a levels during cardiopulmonary bypass tended to be lower in the concentrated red cells plus albumin priming group than in the ordinary priming group (p less than 0.1, at 60 and 90 minutes of cardiopulmonary bypass). C4a and C3a levels increased less after protamine administration with concentrated red cells plus albumin priming (p less than 0.05, p less than 0.01, respectively, 90 minutes after protamine) than with ordinary priming. Such changes in the membrane oxygenator group were less remarkable. Thus C3a levels were approximately the same in both oxygenator groups primed with concentrated red cells plus albumin. The higher the homologous to autologous ratio, the steeper the C4a and C3a increase from the beginning of cardiopulmonary bypass with the bubble oxygenator. This tendency was less remarkable in the membrane oxygenator group. Early postoperative pulmonary function was improved by concentrated red cells plus albumin priming, especially in the bubble oxygenator group. In conclusion, (1) oxygenator systems primed with concentrated red cells plus albumin produced less anaphylatoxin than those with homologous blood, especially with the bubble oxygenator, and (2) our clinical results support the importance of immunoglobulin denatured by oxygen bubbling in anaphylatoxin generation (by means of the classical pathway), as shown by our in vitro study.     

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.     

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.     

Magnetic resonance imaging of the brain before and after open heart operations.

Magnetic resonance imaging of the brain was performed in 29 adult male patients before and 1 week after elective coronary artery bypass grafting to study the cerebral effect of cardiopulmonary bypass. The mean age of the patients was 60 years (range, 45 to 69 years). During cardiopulmonary bypass, either a bubble oxygenator without an arterial line filter (n = 9), a bubble oxygenator with a depth adsorption filter (n = 10), or a flat-sheet membrane oxygenator without a filter (n = 10) was used. The mean bypass time was 88 minutes (standard deviation, 31 minutes) and did not differ significantly between the three groups. Preoperative magnetic resonance imaging revealed high signal intensity foci on T2-weighted images (white matter abnormalities) in 17 (59%; 95% confidence limits, 39% to 76%) of the 29 patients, all of which were nonspecific and of the common type considered to be related to aging, and all were unchanged at the postoperative examination. Preoperative and postoperative frontal horn indices, bicaudate diameters, and third ventricle widths did not differ significantly regardless of oxygenator type or whether or not an arterial line filter was used during cardiopulmonary bypass. Two patients (7%; 95% confidence limits, 1% to 23%), both receiving bubble oxygenation (1 without a filter and 1 with an arterial line filter) sustained a cerebral infarction during cardiopulmonary bypass.     

Oxygenator exhaust capnography as an index of arterial carbon dioxide tension during cardiopulmonary bypass using a membrane oxygenator

We have studied the relationship between the partial pressure of carbon dioxide in oxygenator exhaust gas (PECO2) and arterial carbon dioxide tension (PaCO2) during hypothermic cardiopulmonary bypass with non- pulsatile flow and a membrane oxygenator. A total of 172 paired measurements were made in 32 patients, 5 min after starting cardiopulmonary bypass and then at 15-min intervals. Additional measurements were made at 34 degrees C during rewarming. The degree of agreement between paired measurements (PaCO2 and PECO2) at each time was calculated. Mean difference (d) was 0.9 kPa (SD 0.99 kPa). Results were analysed further during stable hypothermia (n = 30, d = 1.88, SD = 0.69), rewarming at 34 degrees C (n = 22, d = 0, SD = 0.84), rewarming at normothermia (n = 48, d = 0.15, SD = 0.69) and with (n = 78, d = 0.62, SD = 0.99) or without (n = 91, d = 1.07, SD = 0.9) carbon dioxide being added to the oxygenator gas. The difference between the two measurements varied in relation to nasopharyngeal temperature if PaCO2 was not corrected for temperature (r2 = 0.343, P = < 0.001). However, if PaCO2 was corrected for temperature, the difference between PaCO2 and PECO2 was not related to temperature, and there was no relationship with either pump blood flow or oxygenator gas flow. We found that measurement of carbon dioxide partial pressure in exhaust gases from a membrane oxygenator during cardiopulmonary bypass was not a useful method for estimating PaCO2.      

Blood conservation with membrane oxygenators and dipyridamole

Cardiopulmonary bypass induces platelet activation and dysfunction, which result in platelet deposition and depletion. Reduced platelet numbers and abnormal platelet function may contribute to postoperative bleeding. A membrane oxygenator may preserve platelets and reduce bleeding more than a bubble oxygenator, and the antiplatelet agent dipyridamole may protect platelets intraoperatively and reduce bleeding postoperatively. A prospective randomized trial was performed in 44 patients undergoing elective coronary artery bypass grafting to assess the effects of the membrane oxygenator and dipyridamole on platelet counts, platelet activation products, and postoperative bleeding. Patients who were randomized to receive a bubble oxygenator and no dipyridamole had the lowest postoperative platelet counts, the greatest blood loss, and the most blood products transfused. Platelet counts were highest and blood loss was least in patients randomized to receive a membrane oxygenator and dipyridamole (p less than .05). A bubble oxygenator with dipyridamole and a membrane oxygenator without dipyridamole resulted in intermediate postoperative platelet counts and blood loss. Arterial thromboxane B2 and platelet factor 4 concentrations were elevated on cardiopulmonary bypass in all groups. Both the membrane oxygenator and dipyridamole were independently effective (by multivariate analysis) in preserving platelets. Optimal blood conservation was achieved with a membrane oxygenator and dipyridamole.     

Complement activation with bubble and membrane oxygenators in aortocoronary bypass grafting

Thirty-three patients admitted for coronary bypass grafting were randomized to cardiopulmonary bypass with a bubble oxygenator (Cobe or Polystan) or a membrane oxygenator (SciMed). Plasma concentrations of C3 activation products and the terminal complement complex were measured using enzyme immunoassays. Both variables increased almost linearly after onset of cardiopulmonary bypass, with maximal concentrations at closure of the sternum. From a baseline of 7.5 to 12.0 arbitrary units (AU)/mL (medians), the concentrations of C3 activation products increased by 117.5 AU/mL (Cobe), 120.5 AU/mL (Polystan), and 213.3 AU/mL (SciMed). The increase in the membrane group was significantly higher than in the two bubble oxygenator groups (p less than 0.01). From a baseline of 0.9 to 1.3 AU/mL, the concentrations of terminal complement complex increased by 5.4 AU/mL (Cobe), 6.6 AU/mL (Polystan), and 7.7 AU/mL (SciMed) (differences not significant). The higher C3 activation caused by the membrane oxygenator may be explained by differences in flow profile and surface area in contact with blood. The study cannot confirm the general assumption that membrane oxygenators lead to lower complement activation than do bubble oxygenators.     

Postperfusion lung syndrome. Comparison of Travenol bubble and membrane oxygenators.

To examine the role of the oxygenator in the postperfusion lung syndrome, we studied 16 patients undergoing aorta-coronary bypass with a bubble oxygenator and 14 similar patients with a membrane oxygenator both before and for 2 days after the operation. To maintain the same pulmonary artery occluded pressure and hemoglobin level at the end of the surgical procedure, significantly more blood was required in the bubble than in the membrane group. Postoperative pulmonary dysfunction in the bubble group was characterized by increased pulmonary vascular resistance (PVR) and lung water. The increase in lung water was present after bubble oxygenation on three successive measurements, whereas there was no increase in lung water above control value at any measurement time in the membrane group. The bubble group had a significantly greater increase in PVR at the immediate postoperative study time than did the membrane group. PVR returned to control value for the duration of study. These differences in lung water and PVR measurements may be related to greater blood component trauma with a Travenol bubble oxygenator than with a membrane lung.     

Rapid cardiopulmonary support for children with complex congenital heart disease

BACKGROUND: Extracorporeal membrane oxygenation has limitations in children with congenital heart disease (prolonged setup times, increased postoperative blood loss, and difficulty during transport). We developed a miniaturized cardiopulmonary support circuit to address these limitations. PATIENTS AND METHODS: The cardiopulmonary support system includes a preassembled, completely heparin-coated circuit, a BP-50 Bio-Medicus centrifugal pump, a Minimax plus membrane oxygenator, a Bio-Medicus flow probe, and a Bio-trend hematocrit/oxygen saturation monitor. Short tubing length permits a 250-mL bloodless prime in less than 5 minutes. From 1995 to 1997, 23 children with congenital heart disease were supported with this technique. RESULTS: Overall survival to discharge was 48% (11 of 23 patients). Survival to discharge was 80% (4 of 5) in the preoperative support group, 20% (1 of 5) in the postoperative failure to wean from cardiopulmonary bypass group, 44% (4 of 9) in the group placed on support postoperatively after transfer to the intensive care unit, and 50% (2 of 4 patients) in the nonoperative group. Neonatal cardiopulmonary support survival to discharge was 46% (6 of 13 patients). CONCLUSIONS: This pediatric cardiopulmonary support system is safe and effective. Advantages over conventional extracorporeal membrane oxygenation include rapid setup time, decreased postoperative blood loss, and simplified transport.     

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.     

The safety and efficacy of ten percent pentastarch as a cardiopulmonary bypass priming solution. A randomized clinical trial.

Ten percent pentastarch is a low-molecular-weight hydroxyethyl starch with greater oncotic pressure and shorter intravascular persistence than 6% hetastarch. To evaluate its safety and efficacy as a component of cardiopulmonary bypass priming solution, we prospectively studied 90 patients undergoing coronary artery bypass grafting or valve replacement necessitating cardiopulmonary bypass (bubble oxygenator and moderate systemic hypothermia). Sixty patients were randomized to receive 75 gm of either 10% pentastarch (group P) or 25% albumin (group A), and 30 patients received lactated Ringer's solution alone (group C). Intravascular colloid osmotic pressure during cardiopulmonary bypass was highest with either of the colloid primes (15-minute measurement: group P, 15.7 +/- 2.2 mm Hg (mean +/- standard deviation); group A, 15.2 +/- 2.0 mm Hg; group C, 11.3 +/- 1.7 mm Hg; p less than 0.05, groups P and A compared with group C). This was associated with a lower volume requirement during cardiopulmonary bypass to maintain the venous reservoir (group P, 333 +/- 318 ml; group A, 483 +/- 472 ml; group C, 1332 +/- 1013 ml; p less than 0.05, groups P and A compared with group C). Urine output during cardiopulmonary bypass was similar in each group. Net intraoperative fluid balance was lowest in the colloid groups (groups P and A, 5.7 +/- 1.4 L; group C, 6.9 +/- 1.3 L; p less than 0.05, groups P and A compared with group C). Cardiac index shortly after weaning from cardiopulmonary bypass was greatest in group P (group P, 3.2 +/- 0.9; group A, 2.8 +/- 0.8; group C, 2.7 +/- 0.6 dyne.sec.cm-5; p less than 0.05, group P compared with group C). Changes in alveolar-arterial oxygen gradients, shunt fraction, and effective compliance were similar in all groups. During cardiopulmonary bypass, pentastarch appeared to cause the greatest degree of hemodilution, as suggested by the lowest hemoglobin, factor VII and IX levels and platelet count. The activated partial thromboplastin time was significantly prolonged during and immediately after cardiopulmonary bypass in group P relative to groups A and C (p less than 0.05), although there were no significant differences in the activated clotting time before cardiopulmonary bypass, during cardiopulmonary bypass, or after heparin neutralization. As well, clinical indices of hemostasis, including mediastinal drainage, red cell, platelet, and fresh frozen plasma requirements, and reoperation for excessive postoperative bleeding, were similar. We conclude that pentastarch, when used in cardiopulmonary bypass prime, is as safe as either albumin or Ringer's solution alone.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effect of oxygenator type and bypass flow pattern on the P(a-ET)CO2 gradient.

Changes in pre-bypass and post-bypass P(a-ET)CO2 gradients were evaluated regarding the type of bypass flow (pulsatile or nonpulsatile) and oxygenator (membrane or bubble). Duration of bypass and hemodynamic changes were analyzed also to determine their possible influence on PaCO2, PETCO2, and P(a-ET)CO2. A total of 36 adult patients undergoing cardiopulmonary bypass were anesthetized using a sufentanil-pancuronium-oxygen technique. Patients were divided into three groups based on the type of oxygenator and pump flow: group 1 (control group) consisted of a bubble oxygenator with nonpulsatile flow (BN), group 2 consisted of a bubble oxygenator with pulsatile flow (BP), and group 3 consisted of a membrane oxygenator with nonpulsatile flow (MN). Cardiac parameters (MAP, CI, SVR, and PVR) PaCO2, PETCO2, and P(a-ET)CO2 were determined pre-bypass and post-bypass following steady-state conditions. For the entire group there was a trend for the P(a-ET)CO2 gradient to increase in the post-bypass period (pre-bypass = 3.5 +/- 0.5 mm Hg, post-bypass = 4.3 +/- 0.5 mm Hg.). However, this increase was not statistically significant. Pulsatile flow (group 2) demonstrated a significant correlation with the change in P(a-ET)CO2 gradients from the pre-bypass to the post-bypass period (r = 0.85) when compared with the other two groups (group 1: r = -0.09 and group 3: r = 0.37). Thus, the P(a-ET)CO2 gradient tended to remain constant from the pre-bypass to the post-bypass period in group 2, whereas it increased in groups 1 and 3. Changes in MAP, CI, SVR, and PVR and the duration of CPB did not influence the P(a-ET)CO2 gradient.     

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.     

Biocompatibility of extracorporeal circulation with autooxygenation.

Platelet damage, complement activation and neutropenia during cardiopulmonary bypass are the result of blood contact with artificial surfaces, mainly in the oxygenator. To evaluate biocompatibility of this kind of bypass we compared two techniques of extracorporeal circulation in 40 patients undergoing elective coronary bypass operations. In 20, a standard technique with a bubble oxygenator was used (group 1), and in the remaining 20 patients with autooxygenation, the patients' own lungs were included in the perfusion circuit (group 2). Several blood samples were taken before, during and after perfusion to estimate the corrected platelet numbers and pulmonary leucocyte sequestration in all patients, and additionally in 6 patients from each group, complement C3a and C5a anaphylatoxins were measured (radioimmunoassay). At the end of cardiopulmonary bypass, the decline of platelet number corrected to haematocrit platelet number in group 1 was significantly higher than in group 2 (P less than 0.01). There was a significant increase in circulating white blood cells when compared to pre-bypass time in both groups (P less than 0.05). However, comparison of differences between leucocyte counts in the blood of the patients' right and left atria showed enhanced leucocyte sequestration in group 1, 1.46 +/- 0.5 x 10(3)/mm3 vs only 0.34 +/- 0.2 x 10(3)/mm3 in group 2. The C3a rose progressively during extracorporeal circulation: in group 1 from 268 +/- 46 ng/l to 521 +/- 65 ng/l, and in group 2 from 244 +/- 46 ng/l to 418 +/- 34 ng/l (P less than 0.05). No characteristic changes in C5a activation were observed in either group.(ABSTRACT TRUNCATED AT 250 WORDS)