Hollow Fiber Membrane Oxygenator Research Articles

Effect of nitric oxide upon gas transfer and structural integrity of a polypropylene membrane oxygenator.

Gaseous nitric oxide (NO) may act as a membrane passivator during cardiopulmonary bypass by inhibition of platelet and leukocyte adhesion, activation, and aggregation. However, NO and its by-product nitrogen dioxide (NO2) are potently reactive and may be capable of degradation of membrane oxygenator constituents in an oxygen-rich environment. To test these concepts, nine polypropylene hollow fiber membrane oxygenators received 224 +/- 10 ppm NO and 6.7 +/- 1.7 ppm NO2 in 73% oxygen (O2), and six oxygenators received 73% O2, while being perfused with heparinized thrombocytopenic bovine blood for 6 hours. Oxygenators were used for measurement of O2 and carbon dioxide (CO2) transfer rates, structural integrity by pulsing with 22 psi water at 0.5 Hz for 6 hours, and scanning electron microscopic (SEM) examination of structural integrity. Transfer rates between groups at 0, 1, 3, and 6 hours revealed no differences in O2 or CO2. No oxygenator failed hydraulic tests of structural integrity or exhibited "wet-out" during bypass. No evidence of material degradation was shown in the SEM appearance of oxygenators. There were no differences in hematologic values. These data support the safety of gaseous NO in polypropylene membrane oxygenators for limited-term cardiopulmonary bypass.

Extracorporeal membrane oxygenation for adult cardiac support: the allegheny experience

Background. A mix of cardiac assist options is necessary to meet the diverse indications for cardiac support in a comprehensive heart failure program. At our institution, an adult extracorporeal membrane oxygenation (ECMO) system comprising a centrifugal pump and hollow fiber membrane oxygenator is used for short-term and temporary cardiac assist. Methods. Between December 1991 and August 1997, 82 adult cardiac patients were supported on ECMO. Indications for cardiac assist included postcardiotomy cardiogenic shock (PCCS, 55 patients), high-risk cardiology intervention (27 patients), perioperative cardiac graft failure (4 patients), and emergency cardiac resuscitation (6 patients). Data for analysis were collected by prospective completion of standardized ECMO report forms and retrospective review of hospital charts. Results. The ECMO system was inexpensive to operate, uncomplicated to implant, and adaptable for diverse indications. Survival in PCCS was 20 of 55 patients (36%), with an increased survival rate of 56% (18 of 32 patients) in patients with PCCS after isolated coronary bypass. Catheter-based revascularizations were successfully performed in 26 of 27 (96%) high-acuity patients temporarily supported by ECMO, and 23 of 27 patients (85%) survived to discharge. Survival in the cardiac graft failure group was 2 of 4 (50%). No patient supported on ECMO for cardiac resuscitation survived. Conclusions. ECMO provides good cardiopulmonary and end-organ support; survival rates are similar to or higher than those seen with centrifugal pump support in comparable patient populations.

Cerebral microemboli during cardiopulmonary bypass: increased emboli during perfusionist interventions

Background. Microemboli to the cerebral circulation occur during cardiopulmonary bypass (CPB) and can contribute to postoperative neurologic dysfunction. Cerebral microemboli are known to occur during specific surgical interventions, but the source of a large proportion of emboli remains unexplained. We investigated whether interventions by the perfusionist could account for the appearance of cerebral microemboli.Methods. Transcranial Doppler ultrasonography was used to continuously monitor the middle cerebral artery of 18 patients undergoing coronary artery bypass grafting. The CPB circuit consisted of a softshell venous reservoir, a hollow-fiber membrane oxygenator, and a 32-μm arterial filter. The mean embolic rate was calculated for three time periods: (1) during surgical interventions (aortic cannulation and decannulation, cross-clamp application and removal, CPB start and end, and start of cardiac ejection); (2) during perfusionist interventions (blood sampling and drug administration into the venous reservoir); and (3) during baseline (all other time periods during CPB).Results. Microemboli were detected in all patients (mean ± standard deviation, 207 ± 142 per patient, median, 132). The number of emboli per minute was significantly (p < 0.001) higher during perfusionist interventions (6.9 ± 4.5) than during surgical interventions (1.5 ± 1.5) or during baseline (0.4 ± 0.5). Drug administration resulted in a higher embolic rate than blood sampling.Conclusions. Interventions by the perfusionist account for a large proportion of previously unexplained cerebral microemboli during CPB. These emboli likely represent air bubbles that are not eliminated by the arterial line filter. Although further studies of additional types of CPB circuits are required, we believe that air in the venous reservoir should be avoided whenever possible to minimize the risk of neurologic injury.

An enzymatic membrane reactor for extracorporeal blood oxygenation

The potential use of the enzyme catalase to oxygenate blood was investigated. A microcalorimetric technique was used to study the kinetics of oxygen generation in human blood serum at 25 and 37°C. Experiments carried out in serum and in phosphate buffer provided the apparent rate constants for the enzymatic and non-enzymatic oxygen-generation reactions. A simplified mathematical model was then developed to analyse the behavior of a hollow-fiber membrane oxygenator with catalase covalently bound to the membrane surface. The model was used to simulate an extracorporeal oxygenation treatment and outline differences with current devices.

Biocompatibility of a silicone-coated polypropylene hollow fiber oxygenator in an in vitro model

Background. A silicone-coated microporous hollow-fiber membrane oxygenator has been developed to prevent plasma leakage during long-term use. The objective of this study was to evaluate the biocompatibility of the oxygenator. Methods. A silicone-coated oxygenator was compared with an uncoated oxygenator in an in vitro model of cardiopulmonary bypass. Simulated circulation was maintained for 6 h at 37°C. Results. Platelet counts decreased significantly ( p < 0.05) and leukocyte counts tended to decline; however, the differences between groups were not significant. Concentrations of C3a increased significantly in both groups ( p < 0.05), but levels were significantly less in the silicone-coated oxygenator ( p = 0.008). In contrast, concentrations of C4a, β-thromboglobulin, and granulocyte elastase increased significantly ( p < 0.05), but the differences between groups were not significant. Conclusions. Silicone coating over a microporous hollow-fiber membrane may improve biocompatibility by reducing C3a activation.

Albumin in the cardiopulmonary bypass prime: how little is enough?

Previous studies have demonstrated high transoxygenator pressures with noncoated hollow-fiber membrane oxygenators. These reports have been associated with dramatic platelet count drops during cardiopulmonary bypass (CPB). It has also been shown that adding human albumin to the prime of the bypass circuit reduces, if not eliminates, these problems. This study was conducted to determine what is the smallest amount of albumin added to the prime that will still display its protective effects. Eighty patients undergoing nonemergency open-heart surgery were randomly divided into four groups. Groups I and II received the Sarns Turbo 440 oxygenator with 0.0375 g of albumin/100 ml of prime and 0.125 g of albumin/100 ml of prime, respectively, added to the pump prime. Groups III and IV received the Medtronic Maxima-PRF oxygenator with 0.0375 g of albumin/100 ml of prime and 0.125 g of albumin/100 ml of prime, respectively, added to the pump prime. Pre-CPB, on CPB (15-20 min after the initiation of bypass) and warming hemoglobin, hematocrit and platelet counts were drawn on all patients. Net platelet count drop, which accounted for hemodilutional effects, was calculated for all specimens and compared to previous results obtained from the test oxygenators without albumin in the prime. The net platelet count drops for the study groups were as follows: Sarns oxygenator with no albumin in the prime = 11.8+/-12.5%; Sarns oxygenator with 0.0375 g of albumin/100 ml prime = -3.7+/-10.8%; Sarns oxygenator with 0.125 g of albumin/100 ml prime = -2.0+/-12.6%; Medtronic oxygenator with no albumin in the prime = 20.1+/-14.5%; Medtronic oxygenator with 0.0375 g albumin/100 ml prime = -6.9+/-8.7%; and Medtronic oxygenator with 0.125 g albumin/100 ml prime = -14.0+/-12.4%. Our results illustrate that adding as little as 0.0375 g albumin/100 ml prime (3 ml of 25% solution/2000 ml of prime) to the pump prime illicits the beneficial effects of surface coating on platelet loss during CPB.

Experimental evaluation of the Dideco D903 Avant 1.7 hollow-fibre membrane oxygenator.

Membrane oxygenators have now gained wide acceptance. A new hollow-fibre membrane oxygenator, the Dideco D903 Avant 1.7, with an optimized membrane surface (1.7 m2) and a wavy blood flow pattern, was tested for gas transfer and blood path resistance in a standardized setting with surviving animals. Three calves (mean body weight 63.29 +/- 2.9 kg) were connected to cardiopulmonary bypass by jugular venous and carotid arterial cannulation, classic roller pump and the Dideco D903 oxygenator with a mean flow rate of 53 +/- 0.1 ml/kg/min for 6 h. After this time, the animals were weaned from the CPB and thereafter from the ventilator. After 7 days, the animals were killed electively. Blood gas analysis was performed before bypass, after mixing (10 min) and then hourly for the 6 h of perfusion. Further samples were taken 30 min (spontaneous breathing) and 60 min after bypass (extubated). Physiological blood gas values could be maintained throughout perfusion in all animals. Mean arterial oxygen saturation varied between 99.3% and 99.7% for the arterial side of the oxygenator compared to 64.6% and 71% for the venous side. The highest mean pressure drop through the oxygenator was 54 mmHg. Postbypass blood gas analysis showed physiological values and no evidence of major lung trauma or pulmonary oedema in relation to the 6 h perfusion. The hollow-fibre membrane oxygenator, Dideco D903, offers excellent gas exchange capabilities and a low pressure drop under experimental conditions, despite reduced membrane surface area. The post mortem examination did not show any deleterious lesion.

Experimental Evaluation of the Medtronic Maxima Forte Hollow Fiber Membrane Oxygenator

A new hollow fiber membrane oxygenator, the Medtronic Maxima Forté, was tested for gas transfer, blood path resistance and blood handling characteristics in a standardized setting with surviving animals. Three calves (mean body weight: 71±9.6 kg) were placed on cardiopulmonary bypass at a mean flow rate of 50 ml/kg/min for six hours. The circuit included the Maxima Forté oxygenator. The animals were weaned from cardiopulmonary bypass and then from the ventilator. After seven days, the animals were sacrificed electively. Physiologic blood gas values could be maintained throughout perfusion in all animals. Mean pressure drop through the oxygenator varied between 49 mmHg and 66 mmHg. The respective baseline values for red blood cell count, white blood cell count and platelets were 8.90±1.26 106/mm3, 7.46±3.17 103/mm3 · and 680±216 l03/mm3. Red blood cell and platelet counts dropped slightly to 7.26±1.61 106/mm3 and 400±126 l03/mm3 at the end of the bypass, whereas the white blood cell count increased up to 9.13±5.25 103/mm3. All three cell lines returned to near their baseline values after seven days. Blood trauma evaluated as a function of plasma hemoglobin (plasma Hb) and lactate dehydrogenase (LDH) showed stable values during all the perfusion time. Both peaked at 24 hours before returning to their baseline values at seven days. LDH showed a statistically significant variation: 3255 ± 693 IU at 24 hours versus 2029 ± 287 IU at baseline (p = 0.04). The variation of plasma Hb was not statistically significant (93.5 ± 7.7 µmol/1 at 24 hours versus 77.3 ± 52.3 µmol/1 at baseline) indicating a weak effect of the perfusion on blood trauma. The Medtronic Maxima Forté hollow fiber membrane oxygenator offered good gas exchange capabilities, a low pressure drop, and low blood trauma over a prolonged perfusion time of six hours in this evaluation.

Testing neonate-infant membrane oxygenators with the University of Texas neonatal pulsatile cardiopulmonary bypass system in vitro.

Neurologic complications are already well documented after cardiopulmonary bypass (CPB) procedures in neonates and infants. Physiologic pulsatile flow CPB systems may be the alternative to the currently used steady-flow CPB circuits. In addition to the pulsatile pump, a membrane oxygenator should be chosen carefully, because only a few membrane oxygenators are suitable for physiologic pulsatile flow. We have tested four different types of neonate-infant membrane oxygenators for physiologic pulsatility with The University of Texas neonate-infant pulsatile CPB system in vitro. Evaluation criteria were based on mean ejection time, extracorporeal circuit (ECC) pressure, and upstroke of dp/dt. The results suggested that the Capiox 308 hollow-fibre membrane oxygenator produced the best physiologic pulsatile waveform according to the ejection time, ECC pressure, and the upstroke of dp/dt. The Minimax Plus and Masterflo Infant hollow-fibre membrane oxygenators also produced adequate pulsatile flow. Only the Variable Prime Cobe Membrane Lung (VPCML) Plus flat-sheet membrane oxygenator failed to reach the criteria for physiologic pulsatility. Depending on the oxygenator used, the lowest priming volume of the infant CPB circuit was 415 ml and the highest 520 ml.

Development of a Silicone Hollow Fiber Membrane Oxygenator for ECMO Application

A new silicone hollow fiber membrane oxygenator for extracorporeal membrane oxygenation (ECMO) was developed using an ultrathin silicone hollow fiber, with a 300 microm outer diameter and a wall thickness of 50 microm. The hollow fibers were mechanically cross-wound on the flow distributor to achieve equal distribution of blood flow without changing the fiber shape. The housing, made of silicone coated acryl, was 236 mm long with an inner diameter of 60 mm. The surface area was 1.0 m2 for prototype 211, and 1.1 m2 for prototype 209. The silicone fiber length was 150 mm, and the silicone membrane packing density was 43% for prototype 211 and 36% for prototype 209. Prototype 211 has a priming volume of 208 ml, and prototype 209 has a priming volume of 228 ml. The prototype 211 oxygenator demonstrates a gas transfer rate of 120 +/- 5 ml/min (mean +/- SD) for O2 and 67 +/- 12 ml/min for CO2 under 2 L of blood flow and 4 L of O2 gas flow. Prototype 209 produced the same values. The blood side pressure drop was low compared with the silicone sheet oxygenator (Avecor, 1500ECMO). These results showed that this new oxygenator for ECMO had efficiency similar to the silicone sheet oxygenator that has a 50% larger surface area. These results suggest that the new generation oxygenator using an ultrathin silicone hollow fiber possesses sufficient gas transfer performance for long-term extracorporeal lung support.

Is condensation the cause of plasma leakage in microporous hollow fiber membrane oxygenators

Extracorporeal membrane oxygenators are comprised of large bundles of microporous hollow fiber membranes (HFMs) across which oxygen and carbon dioxide are transferred to and from blood. Long term use of extracorporeal oxygenators is limited by plasma leakage through the pores of the HFM walls, requiring replacement of the oxygenator. Condensation of water vapor on the pore walls is thought to be a possible precursor to plasma leakage. To explore this mechanism, a simple theoretical analysis is used to examine the temperature of the gas flow through the HFMs. For conditions representative of two commercially available oxygenators, the analysis predicts that the gas heats up to the temperature of blood flow outside of the fibers after passing through less than 0.5% of the fiber lengths. Once the gas temperature and hence the fiber wall temperature equilibrates with the blood, condensation of water vapor is no longer possible. In vitro testing of microporous HFMs under gas flow rates and temperature conditions similar to those of extracorporeal oxygenators but with the fibers submerged in water is also presented. The fibers showed negligible degradation in carbon dioxide transfer over a four-day period. These results of both the theoretical and experimental analyses indicate that the condensation of water vapor within the pores of the HFMs is unlikely to be the cause of plasma leakage in clinically used extracorporeal 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 degrees 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.

An In Vitro Comparison of Gas Transfer and Pressure Drop of the Bentley Duraflo Coated Spiral Gold and the Medtronic Carmeda Coated Maxima Hollow Fiber Membrane Oxygenators

Two models of heparin coated, hollow fiber membrane oxygenators were tested in vitro to compare gas transfer and transoxygenator pressure drop using an established protocol. Oxygen and carbon dioxide transfer rates were measured at blood flows of 2.5 and 5.0 liters per minute with gas flow : blood flow ratios of 1:1 and 2:1 at both blood flows. All testing was performed under normothermic conditions. The data shows that oxygen transfer increases as blood flow is increased in both oxygenators. Similarly, carbon dioxide transfer is increased by both increased blood and gas flows. Finally, the pressure drop was dependent on blood flow rate alone. This study demonstrated these two oxygenators to be comparable in both oxygen and carbon dioxide transfer and also in transoxygenator pressure drop.

Clinical evaluation of six hollow-fibre membrane oxygenators.

In a clinical evaluation to study the performance of hollow-fibre membrane oxygenators, we compared the gas exchange characteristics and the production of plasma free haemoglobin for different oxygenators. In this study, the data of the Univox, Cobe-Optima, Capiox-SX, Affinity, Safe II and Sarns Turbo 440 oxygenators were evaluated during cardiac surgery in comparable patient groups. Thirteen patients scheduled for elective surgery were enrolled in each group. In all groups, cardiopulmonary bypass (CPB) was conducted using pulsatile blood flow during fibrillation and the period in which the aorta was crossclamped. Arterial and venous blood gases were determined from which oxygen transfer, carbon dioxide transfer, oxygen gradient, shunt fraction and diffusing capacity were calculated. Blood samples were taken 5, 30, 60 and 90 min after beginning CPB. As a result of our measurements we found that the gas exchange capacities of all six oxygenators are within clinically acceptable limits, although the data considering oxygen and carbon dioxide transfer showed a significantly higher capacity for the Sarns Turbo 440 oxygenator (p < 0.05) in comparison with the other oxygenators. Plasma free haemoglobin was, however, significantly higher in the Univox and Sarns Turbo 440 groups (p < 0.005). This difference was already present after 30 min of bypass and increased with time, and is considered as a negative aspect, in relation to optimal patient care.

The isolated perfused porcine liver: assessment of viability during and after six hours of perfusion.

Isolated liver perfusion was developed for the study of liver physiology and preservation. The recent development of new perfusion devices and appropriate liver preservation solutions prompted us to reconsider liver perfusion for the specific purpose of evaluating viability in terms of biochemical changes, paying special attention to modifications in the histological ultrastructure. Twenty-two isolated pig livers were perfused with autologous blood. Arterio-portal perfusions were carried out using an extracorporeal perfusion circuit with a hollow fibre membrane oxygenator. Four groups of pig livers were studied using three different liver flushing solutions [Ringer's lactate, ELOHES, and University of Wisconsin (UW)] and two different oxygenation modalities. Liver function tests and histological studies were done. Our results revealed that a high partial oxygen pressure (PO2) level was deleterious to the ultrastructural elements of hepatocytes, in particular to the mitochondria. It was also associated with deficient metabolic performance, i.e., poor bile production and lack of aerobic metabolism. Normal blood gas values could be obtained with the use of air for liver oxygenation. Flushing of the liver with Ringer's lactate or a macromolecular solution such as ELOHES was associated with severe liver cell injuries, as reflected by a marked rise in liver enzymes and histological lesions. Satisfactory results were obtained when UW solution was used for liver harvesting. We conclude that an appropriate liver preservation solution, normal blood gas values, and normal physiological arterio-portal pressure and blood flow are essential for appropriate liver function with preservation of liver architecture and of hepatocyte ultrastructures. Total bilirubin in bile and Factor V are sensitive indicators of good liver function.

Surgical Repair of Ventricular Septal Defect in 2085 Pediatric Patients

Of 5587 operations for congenital heart disease that we performed between January 1976 and December 1993, 2085 were for correction of ventricular septal defects. Paramembranous, muscular, and atrioventricular canal types were repaired through a right atrial incision, whereas subpulmonary and conus type defects were repaired through a pulmonary artery incision. Circulatory arrest under deep hypothermia was used for patients under 2 years of age or with body weight of less than 10 kg. There were 48 postoperative deaths. The overall mortality was 2.3% and it was related to the age and weight of the patients. The age at which surgical repair was undertaken depended on the position and size of the defect and the degree of intracardiac shunt. Patients with associated pulmonary hypertension underwent surgery before 2 years of age. Early repair of subpulmonary ventricular defects is recommended to prevent aortic insufficiency resulting from valve prolapse. The keys to successful repair were avoidance of a right ventricular incision, improvement of right ventricular function, and postoperative management of pulmonary hypertension. The operative mortality was reduced from 10.14% in the 1970s to 6.43% in the early 1980s by improvements in surgical procedure and postoperative management with a further reduction to 1.25% in recent years, which we attribute partly to the use of a hollow fiber membrane oxygenator.

Impact of oxygenator design on hemolysis, shear stress, and white blood cell and platelet counts

To determine whether relative pressure drop, shear stress, hemolysis, and white blood cell and platelet counts are influenced by different oxygenator designs. To compare the oxygenator results with the average shear stress over an arterial cannula. Prospective; patients enrolled consecutively. University hospital. Three groups of 12 adults patients, scheduled for routine cardiac surgery. Each group was submitted to a different oxygenator design: group 1 to a high-pressure hollow-fiber membrane oxygenator (Sarns Turbo); group 2 to a medium-pressure hollow-fiber membrane oxygenator (Cobe optima); and group 3 to a flat-sheet membrane oxygenator (Cobe Duo). Although the investigated oxygenators have important differences in pressure drop and shear stress, no statistical differences were found in hemolysis generation or blood handling among the different groups. Actually, the study shows much higher shear stress levels over an average arterial cannula than over any of the evaluated oxygenators. The pressure drop over an oxygenator does not correlate well with shear stress and hemolysis because the dimensions of the system (radius and length) must be included in the calculation of shear stress from pressure drop.

Leakage across hollow-fibre membranes in oxygenators: a pilot study.

The purpose of this study was to create an in vitro system to quantify the fluid loss over two different types of hollow-fibre membrane oxygenators. In the first stage of the study, the circuit was primed with 0.9% NaCl and the line pressure was 200 mmHg; in the second stage, the line pressure was 400 mmHg. The experiment was repeated using bovine blood. A clear difference (p < 0.005) was found in the first stage, accumulating to 47.46 ml (SD 0.41) in the Capiox-SX group and 72.33 ml (SD 3.77) in the Univox group after 4 h. This difference persisted when using bovine blood. Surprisingly, no differences in volume loss occurred when the line pressure was increased to 400 mmHg. In conclusion, leakage in hollow-fibre microporous polypropylene membrane oxygenators can be quantified and the amount of leakage appears to be dependent on the type of membrane and the manufacturing process.

Reduction in Homologous Blood Transfusions Using a Low Prime Circuit

Due to a low estimated blood volume, small adults (weight less than 70 kg) undergoing cardiopulmonary bypass (CPB) are at highest risk for low hematocrit and homologous blood transfusion (HBT). To determine whether reductions in HBT could be achieved we compared the use of a low prime circuit (1400 ml) with our standard (2200 ml) cardiopulmonary bypass (CPB) circuit. Eighty consecutive adult patients (&gt;age 18, &lt;70 kg) undergoing non-emergent CPB were randomly divided into two groups. Group LP (n=40) was the low prime group and group SP (n=40) was the standard prime group. In Group LP, either of two “low prime” hollow fiber membrane oxygenators with a 3/8 X 3/8 inch A-V loop were utilized. Alternately, in Group SP, a larger membrane oxygenator with a 3/8 X 1/2 A-V loop was utilized. Circuits and CPB management were otherwise identical. Excluded from the study were those patients who had bleeding disorders, reoperations, ejection fractions of less than 30% and history of cerebral vascular insufficiency. Patients were closely matched for age, BSA, gender, preoperative risk and procedure. Mean weight (kg) was less in Group LP (59.2 vs 62.2, P&lt;0.02). Pre-CPB hematocrits (HCT) were similar in both groups. Initial on CPB HCT was higher in Group LP (19.8 vs 18.4, P&lt;0.04). Group LP had a higher frequency of initial on CPB HCTs of 20% or greater (55% vs 33% , P&lt;0.04). Group LP had a lower packed red blood cell (PRBC) transfusion rate on CPB (0.4 vs 0.9 units, P&lt;0.03). Group LP had higher percentage of patients that did not require transfusion on CPB (78% vs 55%, P&lt;0.03). Despite fewer transfusions, Group LP had a higher post CPB HCT (20.6 vs 19.3, P&lt;0.04). A trend was noted with a lower total PRBC transfusion rate in Group LP (1.9 vs 2.4, P=.10). During the entire length of stay, fewer Group LP patients required any homologous transfusion (26/40 versus 34/40, P &lt;0.04). Chest drainage, 24 hour HCT and discharge HCT were similar in both groups. Transfusion of platelets, fresh frozen plasma and cryoprecipitate was similar in both groups. There were no deaths in either group. Patients with low blood volume are at high risk of homologous transfusion when undergoing CPB. A significant reduction in prime volume appears to be safe, simple and reduces HBTs in these individuals. Prime reduction should be part of a comprehensive multi-modality blood conservation program.

Reduction of Platelet Trapping in Membrane Oxygenators by Transmembraneous Application of Gaseous Nitric Oxide

Bleeding during extracorporeal circulation (ECC) is often induced and/or aggravated by thrombocytopenia due to platelet-trapping in hollow fiber membrane oxygenators (HFMO). Nitric oxide (NO) has platelet anti-aggregating and dis-aggregating properties. In a paired system we tested whether gaseous NO, added to the gas compartment of one of two parallel running heparin-bonded HFMO attenuated platelet-trapping. Platelet consumption was markedly reduced in the NO-treated HFMO. These data strongly indicate that the application of gaseous NO could prove a new therapeutical approach to reduce bleeding during ECC, serving as a new way of preventing platelet loss, thus reducing the need for high systemic heparinization.