Ultrasound detection of micro-emboli in the middle cerebral artery during cardiopulmonary bypass surgery

The occurrence of neurological sequelae following cardiopulmonary bypass (CBP) surgery has stimulated interest in refining the techniques of extracorporeal circulation. Air micro-emboli originating from the oxygenator have been postulated as one source of cerebral damage. Since controversy still exists regarding the merits of bubble versus membrane oxygenators, this has prompted investigators to devise methods to determine the amount of micro-emboli produced during CPB. In this study, 27 patients undergoing CPB surgery for coronary artery disease (21) or valve replacement (6) were examined. The surgical and anaesthetic techniques were standardised in all patients except for the type of oxygenator used. A bubble oxygenator was used in 17 patients (Bentley Bio-10, William Harvey or Dideco) and a membrane oxygenator with a 25 microns filter in the remaining 10 patients (Bentley BOS CM50). Transcranial pulsed Doppler ultrasound was used to obtain blood velocity signals from the middle cerebral artery throughout CPB. A flow disturbance index (FDI) was defined which provided a representative index of the number of micro-emboli passing the ultrasound transducer. The FDI indicated the presence of gaseous micro-emboli during insertion of the aortic cannula in 22 of the 27 patients. In the 17 patients with a bubble oxygenator, the FDI ranged from 4-39. In the 10 patients with a membrane oxygenator, the FDI was always 0. Variation of gas flow rates in 3 patients with bubble oxygenators showed a change in the FDI from 4 +/- 4 at a flow rate of 2 l/min to 17 +/- 9 at 5 l/min.(ABSTRACT TRUNCATED AT 250 WORDS)     

The detection of microemboli in the middle cerebral artery during cardiopulmonary bypass: a transcranial Doppler ultrasound investigation using membrane and bubble oxygenators

Twenty-seven patients were examined who were undergoing cardiopulmonary bypass (CPB) surgery with either a bubble oxygenator or a capillary membrane oxygenator. The latter incorporated an arterial filter and bubble trap. A noninvasive Doppler ultrasound technique is described for monitoring irregularities in the Doppler flow signals attributable to gaseous microemboli detected in the middle cerebral artery during CPB. The ultrasound index for detecting gaseous microemboli (MEI) indicated the presence of such microemboli in 22 of the 27 patients during insertion of the aortic cannula. Measurements during CPB showed the MEI ranged from 4 to 39 in the 17 patients with a bubble oxygenator. However, all 10 patients with a membrane oxygenator had an MEI of 0. Varying the gas flow rates in 3 patients with bubble oxygenators showed a change in MEI from 4 +/- 4 (SD) at a flow rate of 2 L/min to 17 +/- 9 at a flow rate of 5 L/min. This observation supports the assumption that the MEI is providing quantitative information regarding the presence of gaseous emboli in the middle cerebral artery.     

Cardiopulmonary bypass without systemic heparinization. Performance of heparin-coated oxygenators in comparison with classic membrane and bubble oxygenators

Performance characteristics of heparin-coated hollow-fiber membrane oxygenators (COATED HFMO, n = 5) were evaluated in an open-chest dog model without systemic heparinization. Four other oxygenators were evaluated with standard systemic heparinization (300 IU/kg, activated clotting time more than 400 seconds): a standard hollow-fiber membrane oxygenator (HFMO, n = 5), an inversed hollow-fiber membrane oxygenator (IHFMO, n = 5), a plate membrane oxygenator (PLATE MO, n = 5) and a bubble oxygenator (BUBBLE O, n = 5). The 25 dogs (36 +/- 12 kg) were perfused after cavo-aortic cannulation for 6 hours with a mean flow of 100 ml/kg body weight. At the end of perfusion without systemic heparin, heparin-coated equipment was replaced in three animals with standard uncoated equipment for control studies. Besides continuous hemodynamic evaluation with Mikro-Tip pressure transducers (Millar Instruments, Inc., Houston, Texas), a standard battery of analyses was performed before, after mixing, and every 30 minutes during bypass. All animals could be perfused in accordance with the protocol. Blood-gas values (pH, arterial oxygen tension, and arterial carbon dioxide tension) were maintained within physiologic ranges for all groups. After 6 hours of perfusion, plasma hemoglobin levels were as follows: 0.57 +/- 0.51 gm/L for COATED HFMO without systemic heparinization versus 2.65 +/- 1.02 gm/L for HFMO (p less than 0.05), 1.77 +/- 0.48 gm/L for IHFMO (p less than 0.05), 1.96 +/- 0.41 gm/L for PLATE O (p less than 0.05), and 1.5 +/- 0.40 gm/L for BUBBLE O (p less than 0.05) with systemic heparinization. Platelet levels were highest for COATED HFMO with 47% +/- 36% without systemic heparinization versus 33% +/- 9% for HFMO, 12% +/- 2% for IHFMO, 36% +/- 17% for PLATE O, and 19% +/- 12% for BUBBLE O with systemic heparinization. Activated clotting time for COATED HFMO without systemic heparinization was 135 +/- 75 seconds before bypass, 207 +/- 21 seconds after mixing, and 131 +/- 20 seconds after 4 hours of perfusion. There was no statistically significant increase of plasma heparin levels in the group perfused without systemic heparin. Determination of fibrin split products during perfusion without systemic heparinization did not show a significant increase. At the end of perfusion all devices were disconnected and gently rinsed with saline: There were no macroscopic clots in the COATED HFMO group perfused without systemic heparin. However, uncoated equipment introduced for control in animals perfused without systemic heparin showed major clotting.(ABSTRACT TRUNCATED AT 400 WORDS)     

Extended ex vivo preservation of the heart and lungs. Effects of acellular oxygen-carrying perfusates and indomethacin on the autoperfused working heart-lung preparation

The autoperfused working heart-lung preparation has been proposed as a method for long-term heart-lung preservation. We investigated the effects of acellular oxygen-carrying perfusates (study 1) and the effect of donor pretreatment with indomethacin (study 2) on the working ex vivo heart-lung block. In study 1 perfusion with stroma-fee hemoglobin resulted in significantly reduced survival (118 +/- 46 minutes) compared with autologous blood (561 +/- 125 minutes, p less than 0.05) or perfluorocarbon (438 +/- 114 minutes, p less than 0.05). Decrease in survival with stroma-free hemoglobin perfusate is associated with a marked decrease in left ventricular performance and a significant increase in pulmonary vascular resistance. Perfusion with autologous blood is associated with a significant increase in pulmonary vascular resistance after 240 minutes of explantation, which is significantly delayed by perfusion with perfluorocarbon. Perfusion for 6 hours with blood pretreated with indomethacin (study 2) resulted in a decrease in the concentration of prostacyclin and thromboxane A2 metabolites but an increase in the prostaglandin/thromboxane A2 metabolite ratio. This is associated with abrogation of the increase in pulmonary vascular resistance (12,787 +/- 1682 dynes/sec/cm-5, T = 0; 13,134 +/- 2654 dynes/sec/cm-5, T = 360 minutes) observed in preparations perfused with autologous blood (13,194 +/- 1942 dynes/sec/cm-5, T = 0; 24,768 +/- 3325 dynes/sec/cm-5, T = 360 minutes, p less than 0.05). We conclude that alteration of the cellular and humoral components of autologous blood may prove advantageous for increasing the utility of the autoperfused working heart-lung preparation as a preservation technique.     

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 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.     

From the spinning disc to the membrane oxygenator for open-heart surgery

Gibbon's rotating cylinder could not be enlarged to oxygenate an animal larger than a cat. The spinning disc oxygenator, introduced in 1947, had the capacity to perfuse a dog and the potential to increase oxygenation capacity by addition of more discs. When centers began to do three to four open-heart operations per day, the disposable bubble oxygenator was more practical. Bubble size was optimized to decrease the flow of oxygen relative to the blood flow and reduce trauma to blood. The bubble oxygenator is the type most commonly used today. Use of deep hypothermia with whole blood at an esophageal temperature of 10 degrees C was initially complicated by brain damage due to aggregation of white blood corpuscles and platelets. The introduction of hemodilution permitted safe utilization of hypothermic perfusion. Perfusion of infants should not be carried out at hematocrit below 25 ml/100 m. Early membrane oxygenators used nonporous silicone, or modified silicone membranes. High priming volumes, high pressure drop and marginal gas transfer efficiency characterized these devices. Recent advances in membrane technology have spawned a new generation of membrane oxygenators utilizing microporous polypropylene. In these new oxygenators, with either microporous hollow fibers or sheet membrane, the gas transfer characteristics are far superior to those of types produced in the past. The hollow-fiber devices typically have larger surface areas and higher pressure drop than in the new state-of-the-art flat plate models. An evaluation of one of these new-generation membrane oxygenators gave optimal oxygen and carbon dioxide exchange at a gas flow of 1 l/min of 60% oxygen in air at 30 degrees C and 2 l/min of 80% oxygen in air at normal temperature and rewarming for an adult. Today, after almost 40 years of oxygenator development, these new membrane device can offer better platelet preservation and reduced blood trauma as compared with types developed in the past. The new membrane oxygenators are fast becoming the preferred choice for use in infants and in protracted perfusion.     

Experimental studies on extracorporeal membrane oxygenation (ECMO) perfusion for respiratory insufficiency associated with pulmonary hypertension

Some types of neonatal respiratory insufficiency may be associated with severe pulmonary hypertension. This paper evaluates two methodologies of ECMO perfusion in the treatment of such serious respiratory insufficiency. Pulmonary hypertension was prepared in dogs by administering small pieces of gelatin sponge into the main pulmonary artery. The two methodologies of perfusion were venoarterial bypass (VAB) and venovenous bypass (VVB). Prior to ECMO perfusion, oxygen supplementation during perfusion and hemodynamics were examined. Oxygen supplementation was satisfactory in both VAB and VVB. With VAB, the mean pulmonary artery pressure (mPAP) was significantly dropped from 33.8 +/- 3.1 mmHg to 28.4 +/- 6.2 mmHg, the pulmonary blood flow (PBF) being significantly declined from 1.39 +/- 0.21 L/min to 1.07 +/- 0.15 L/min. With VVB, mPAP was significantly dropped from 33.9 +/- 6.2 mmHg to 29.1 +/- 5.1 mmHg, the pulmonary vascular resistance (PVR) being significantly decreased from 1983.1 +/- 656.0 dynes.sec.cm-5 to 1740.4 +/- 635.9 dynes.sec.cm-5. It is considered that VAB renders PBF decline, which induces a drop in PAP, while VVB accelerates a flow of well-oxygenated blood in the pulmonary artery, which results in a decline in PVR and then a drop in PAP. VVB as well as VAB is useful in the treatment of neonates with respiratory insufficiency who present with pulmonary hypertension.     

Comparing oxygen transfer performance between three membrane oxygenators: effect of temperature changes during cardiopulmonary bypass

Recently, a new oxygenator (Dideco 903 [D903], Dideco, Mirandola, Italy) has been introduced to the perfusion community, and we set about testing its oxygen transfer performance and then comparing it to two other models. This evaluation was based on the comparison between oxygen transfer slope, gas phase arterial oxygen gradients, degree of blood shunting, maximum oxygen transfer, and diffusing capacity calculated for each membrane. Sixty patients were randomized into three groups of oxygenators (Dideco 703 [D703], Dideco; D903; and Quadrox, Jostra Medizintechnik AG, Hirrlingen, Germany) including 40/20 M/F of 68.6 +/- 11.3 years old, with a body weight of 71.5 +/- 12.1 kg, a body surface area (BSA) of 1.84 +/- 0.3 m(2), and a theoretical blood flow rate (index 2.4 times BSA) of 4.4 +/- 0.7 L/min. The maximum oxygen transfer (VO(2)) values were 313 mL O(2)/min (D703), 579 mL O(2)/min (D903), and 400 mL O(2)/min (Quadrox), with the D903 being the most superior (P < 0.05). Oxygen (O(2)) gradients were 320 mm Hg (D703), 235 mm Hg (D903), and 247 mm Hg (Quadrox), meaning D903 and Quadrox are more efficient versus the D703 (P < 0.05). Shunt fraction (Qs/Qt) and diffusing capacity (DmO(2)) were comparable (P = ns). Diffusing capacity values indexed to BSA (DmO(2)/m(2)) were 0.15 mL O(2)/min/mm Hg/m(2) (D703), 0.2 mL O(2)/min/mm Hg/m(2) (D903), and 0.18 mL O(2)/min/mm Hg/m(2) (Quadrox) with D903 outperforming D703 (P < 0.0005). During hypothermia (32.0 +/- 0.3 degrees C), there was a lower absolute and relative VO(2 )for all three oxygenators (P = ns). The O(2) gradients, DmO(2) and DmO(2)/m(2), were significantly lower for all oxygenators (P < 0.01). Also, Qs/Qt significantly rose for all oxygenators (P < 0.01). The oxygen transfer curve is characteristic to each oxygenator type and represents a tool to quantify oxygenator performance. Using this parameter, we demonstrated significant differences among commercially available oxygenators. However, all three oxygenators are considered to meet the oxygen needs of the patients.     

Development of a new silicone membrane oxygenator for ECMO.

Two types small and efficient ECMO oxygenators were developed utilizing the most up to date hollow fiber technology. Newly silicone hollow fibers possess sufficient mechanical strength while maintaining ultra thin walls of 50 micro meter. Two types of oxygenators were made with this fiber. The fiber length for the type 1 module is 150mm with a priming volume 194 cc (surface area 1.3 m(2)) and type 2 has a fiber length of 100 mm with a 144 cc priming volume (the surface area 0.8 m(2)). The studies were performed at 0.5, 1.0 and 2.0 L/min of blood flow and these oxygenators demonstrated. O(2) gas transfer rate of 69+/-4 ml/min/L for type 1 and 68+/-6 ml/min/L for type 2. The CO(2) gas transfer rate was 25+/-2 ml/min/L for type 1 and 32+/-2 ml/min/L for type 2. These results demonstrate type 2 oxygenator has similar gas exchange capabilities to those of Kolobows' oxygenator which has about 2.0 times larger surface area. Additionally, comparative hemolysis tests were preformed with this new oxygenator and the Kolbow. The NIH value was 0.006 (g/100 L) for the type 1 oxygenator and 0.01 (g/100 L) for the Kolbow oxygenator. These results suggested that this ECMO oxygenator had sufficient gas exchange performance in spite of being smaller and induced minimal blood damage.     

Hematological advantage of a membrane oxygenator over a bubble oxygenator in long perfusions

To determine whether the large volumes of cardiotomy suction which occur during long perfusions can obscure the hematological advantage of the membrane oxygenator (MO) over the bubble oxygenator (BO), we studied 23 patients undergoing a coronary artery bypass grafting operation with an expected perfusion time of 3 hours (MO group, N = 10, SciMed spiral coil; BO group, N = 13, Shiley 100-A). During MO perfusion we found significantly higher platelet numbers, better platelet function (adenosine diphosphate-induced platelet aggregation), and less hemolysis (plasma hemoglobin), than during the BO perfusion. After the MO perfusion we measured significantly shorter bleeding times (Simplate II) and fewer transfusions of blood products. However, blood loss and whole-blood transfusions 18 hours after perfusion did not differ significantly between both groups. So in coronary artery bypass grafting operations with long perfusion times (mean, 3 hours), the MO still causes significantly less platelet and erythrocyte damage than the BO, despite the large volumes of cardiotomy suction known to occur during these operations.     

Cardiopulmonary Bypass Using the Landé-edwards Membrane Oxygenator and the Rygg-Kyvsgaard Perfusion Apparatus

The Landé-Edwards membrane oxygenator was used in ten total body perfusions. A modified Rygg-Kyvsgaard perfusion apparatus was employed in a gravity drainage circuit. No technical difficulties could be attributed to the oxygenators. The gas exchange was satisfactory in all cases. No signs of haematological disorders occurred. Postoperative complications were slight and transitory among the eight survivors. The two deaths were due to myocardial infarction.     

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.     

The Type of Aortic Cannula and Membrane Oxygenator Affect the Pulsatile Waveform Morphology Produced by a Neonate-Infant Cardiopulmonary Bypass System In Vivo

Although the debate still continues over the effectiveness of pulsatile versus nonpulsatile perfusion, it has been clearly proven that there are several significant physiological benefits of pulsatile perfusion during cardiopulmonary bypass (CPB) compared to nonpulsatile perfusion. However, the components of the extracorporeal circuit have not been fully investigated regarding the quality of the pulsatility. In addition, most of these results have been gathered from adult patients, not from neonates and infants. We have designed and tested a neonate-infant pulsatile CPB system using 2 different types of 10 Fr aortic cannulas and membrane oxygenators in 3 kg piglets to evaluate the effects of these components on the pulsatile waveform produced by the system. In terms of the methods, Group 1 (Capiox 308 hollow-fiber membrane oxygenator and DLP aortic cannula with a very short 10 Fr tip [n =2]) was subjected to a 2 h period of normothermic pulsatile CPB with a pump flow rate of 150 ml/kg/min. Data were obtained at 5, 30, 60, 90, and 120 min of CPB. In Group 2 (Capiox 308 hollow-fiber membrane oxygenator and Elecath aortic cannula with a very long 10 Fr tip [n =7]) and Group 3 (Cobe VPCML Plus flat sheet membrane oxygenator and DLP aortic cannula with a very short 10 Fr tip [n =7]), the subjects' nasopharyngeal temperatures were reduced to 18°C followed by 1 h of deep hypothermic circulatory arrest (DHCA) and then 40 min rewarming. Data were obtained during normothermic CPB in the pre- and post-DHCA periods. The criteria of pulsatility evaluations were based upon pulse pressure (between 30 and 40 mm Hg), aortic dp/dt (greater than 1000 mm Hg/s), and ejection time (less than 250 ms). The results showed that Group 1 produced flow which was significantly more pulsatile than that of the other 2 groups. Although the same oxygenator was used for Group 2, the quality of the pulsatile flow decreased when using a different aortic cannula. Group 3 did not meet any of the criteria for physiologic pulsatility. In conclusion these data suggest that in addition to a pulsatile pump, the aortic cannula and the membrane oxygenator must be chosen carefully to achieve physiologic pulsatile flow during CPB.     

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.     

Comparison of dopamine and dobutamine therapy during intraaortic balloon pumping for the treatment of postcardiotomy low-output syndrome

Treatment of postcardiotomy low-output syndrome includes intraaortic balloon pumping (IABP), volume loading, pharmacological afterload reduction, and stimulation with an inotropic agent. This study compares the effectiveness of combined nitroprusside and dopamine therapy and nitroprusside and dobutamine therapy in 12 patients requiring IABP postoperatively. Serial hemodynamic measurements were made before and during infusion of nitroprusside and after administration of the combined therapy (N = 6 in each group). Prior to pharmacological therapy, cardiac index was 1.47 +/- 0.31 L/min/m2 and systemic vascular resistance (SVR) was 3,114 +/- 1,350 dynes sec cm-5 in patients subsequently given dopamine, and 1.59 +/- 0.38 L/min/m2 and 2,661 +/- 405 dynes sec cm-5, respectively, in those given dobutamine. With infusion of nitroprusside, both groups showed significant reduction in SVR. Nitroprusside plus either inotropic agent resulted in augmentation of cardiac index and an additional reduction in SVR, both changes being greater in the group given dopamine. Larger doses of dobutamine than dopamine were needed to achieve similar hemodynamic improvement. We conclude that the addition of an inotropic agent to vasodilator therapy during IABP results in a greater increase in cardiac index and a greater decrease in afterload than a vasodilator alone. In addition to its beneficial effect on renal perfusion at the dose required to effect these improvements, dopamine appears a better inotropic agent than dobutamine for postcardiotomy low-output syndrome.     

A prospective comparison of bubble and membrane oxygenators in short and long perfusions

In operations with perfusion times longer than 90 min, a hollow-fibre membrane oxygenator causes less damage to red cells and platelets than a standard bubble oxygenator. There is also a trend towards less post-operative pulmonary shunting when a membrane oxygenator is employed.     

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.     

Bubble and membrane oxygenators--comparison of postoperative organ dysfunction with special reference to inflammatory activity

Bubble and membrane oxygenators (2 types of each) were compared in a randomized study of 96 patients undergoing coronary bypass grafting. Cardiac performance, assessed from postoperative need of inotropic support, was significantly better in the membrane oxygenator group. After perfusion lasting more than 2 hours, respiratory function, measured as alveolar-arterial oxygen pressure gradient, was less compromised in that group and renal function, quantified as postoperative rise of serum creatinine was less disturbed. Cerebral function, studied in terms of psychometric test results and concentration of adenylate kinase in cerebrospinal fluid, did not differ between the bubble and membrane oxygenator groups. In investigations concerning changes in inflammatory activity during bypass, complement activation could not be related to the mentioned clinical parameters. Release of the neutrophil granulocyte factors lactoferrin and myeloperoxidase was greater in the bubble oxygenator group and correlated to impaired cardiac and renal performance, but not to pulmonary or cerebral dysfunction.     

In Vivo Uptake and Elimination of Isoflurane by Different Membrane Oxygenators during Cardiopulmonary Bypass

Background: Volatile anesthetics are frequently used during cardiopulmonary bypass (CPB) to maintain anesthesia. Uptake and elimination of the volatile agent are dependent on the composition of the oxygenator. This study was designed to evaluate whether the in vivo uptake and elimination of isoflurane differs between microporous membrane oxygenators containing a conventional polypropylene (PPL) membrane and oxygenators with a new poly-(4-methyl-1-pentene) (PMP) membrane measuring isoflurane concentrations in blood.

Methods: Twenty-four patients undergoing elective coronary bypass surgery with the aid of CPB were randomly allocated to one of four groups, using either one of two different PPL-membrane oxygenators for CPB or one of two different PMP-membrane oxygenators. During hypothermic CPB, 1% isoflurane in an oxygen-air mixture was added to the oxygenator gas inflow line (gas flow, 3 l/min) for 15 min. Isoflurane concentration was measured in blood and in exhaust gas at the outflow port of the oxygenator. Between-group comparisons were performed for the area under the curve (AUC) during uptake and elimination of the isoflurane blood concentrations, the maximum isoflurane blood concentration (Cmax), and the exhausted isoflurane concentration (FE).

Results: The uptake of isoflurane, expressed as AUC of isoflurane blood concentration and a function of FE, was significantly reduced in PMP oxygenators compared to PPL oxygenators (P < 0.01). Cmax was between 8.5 and 13 times lower in the PMP-membrane oxygenator groups compared to the conventional PPL-membrane oxygenator groups (P < 0.01).