The effect of flow and pressure on the intraoxygenator flow path of different contemporary oxygenators: an in vitro trial.

INTRODUCTION: This study analyzed the effect of different flows and pressures on the intraoxygenator flow path in three contemporary oxygenators and its consequences for oxygen transfer efficiency. METHODS: In an experimental setup, intraoxygenator flow path parameters were analyzed at post-oxygenator pressures of 150, 200, and 250 mm Hg and at flows ranging from 2 L/min to the oxygenators' maximum permitted flow, with and without pulsatility. The oxygen gradient and the oxygen transfer per minute and per 100 mL blood were calculated using previously collected clinical data and compared with the flow path parameters. RESULTS: Increasing pressure did not affect the flow path parameters, whereas pulsatile flow led to significantly increased dynamic oxygenator blood volumes. Increased flow resulted in decreased values of the flow path parameters in all oxygenators, indicating increased flow through short pathways in the oxygenator. In parallel, oxygen transfer/100 mL blood decreased in all oxygenators (average 2.5 ± 0.4 to 2.4 ± 0.3 mL/dL, p > 0.001) and the oxygen gradient increased from 229 ± 45 to 287 ± 29 mm Hg, p > 0.001, indicating decreased oxygen transfer efficiency. Oxygen transfer/min increased (101 ± 15 to 143 ± 20 mL/min/m2, p > 0.001), however, due to the increased flow through the oxygenator. CONCLUSION: Varying trans-membrane oxygenator pressures did not lead to changes in the intraoxygenator flow path, while an increased flow exhibited lower flow path parameters resulting in less efficient use of the gas exchange compartment. The latter was confirmed by a decrease in O2 transfer efficiency during higher blood flows.

Extracorporeal membrane oxygenation-induced fibrinolysis detected by rotational thromboelastometry and treated by oxygenator exchange.

Coagulopathy and bleeding is a frequent phenomenon in patients on extracorporeal membrane oxygenation. The cause may be multifactorial and it may change over time. We present a case when bleeding was caused by hyperfibrinolysis induced by oxygenator. The diagnosis was established by comparing thromboelastometry result from blood obtained before and after oxygenator. Hyperfibrinolysis and bleeding could be successfully treated merely by oxygenator exchange.

Use of a Modified Cardiopulmonary Bypass Circuit for Suction Embolectomy with the AngioVac Device.

The AngioVac suction cannula and circuit were designed for the percutaneous removal of soft thrombus and emboli in procedures requiring extracorporeal circulatory support. We describe a modification of the AngioVac suction catheter and cardiopulmonary bypass (CPB) circuit to effectively remove thrombus while maintaining the ability to rapidly initiate full CPBs during a medical crisis. This article will discuss the design concepts of the modified circuit as well as procedural protocols and considerations. The design modifications of incorporating an oxygenator, reservoir, and bridge allow for an increased flexibility that allows adaption to veno-venous extracorporeal membrane oxygenation or full CPB support when required for oxygenation or hemodynamic support.

Functional Performance of Different Venous Limb Options in Simulated Neonatal/Pediatric Cardiopulmonary Bypass Circuits.

OBJECTIVE: Hemodilution is a concern in cardiopulmonary bypass (CPB). Using a smaller dual tubing rather than a single larger inner diameter (ID) tubing in the venous limb to decrease prime volume has been a standard practice. The purpose of this study is to evaluate these tubing options. METHODS: Four different CPB circuits primed with blood (hematocrit 30%) were investigated. Two setups were used with two circuits for each one. In Setup I, a neonatal oxygenator was connected to dual 3/16" ID venous limbs (Circuit A) or to a single 1/4" ID venous limb (Circuit B); and in Setup II, a pediatric oxygenator was connected to dual 1/4" ID venous limbs (Circuit C) or a single 3/8" ID venous limb (Circuit D). Trials were conducted at arterial flow rates of 500 ml/min up to 1500 ml/min (Setup I) and up to 3000 ml/min (Setup II), at 36°C and 28°C. RESULTS: Circuit B exhibited a higher venous flow rate than Circuit A, and Circuit D exhibited a higher venous flow rate than Circuit C, at both temperatures. Flow resistance was significantly higher in Circuits A and C than in Circuits B (P<0.001) and D (P<0.001), respectively. CONCLUSION: A single 1/4" venous limb is better than dual 3/16" venous limbs at all flow rates, up to 1500 ml/min. Moreover, a single 3/8" venous limb is better than dual 1/4" venous limbs, up to 3000 ml/min. Our findings strongly suggest a revision of perfusion practice to include single venous limb circuits for CPB.

[Evaluation of bubble oxygen inhalators' performances and an investigation on their solutions for improvement].

This paper analyses the defects of bubble oxygen inhalators currently used, and investigates into their solutions for improvement.

Erythrocyte survival following extracorporeal circulation. A question of membrane versus bubble oxygenator.

Five groups of seven dogs were studied. Each animal had 250 ml of blood withdrawn and tagged with Cr51. Group I (control) samples were combined with 500 ml of lactated Ringer's solution and reinfused into the respective animals after 3 hours of incubation at 37 degrees C. Group II samples were pumped in a closed-circuit bubble oxygenator with 500 ml of lactated Ringer's prime for 2 hours before reinfusion into the animals. Group III samples were pumped in a bubble oxygenator for 3 hours before reinfusion. Group IV samples were pumped in a closed-circuit membrane oxygenator for 2 hours, and Group V samples were pumped in a membrane circuit for 3 hours. All extracorporeal pump runs were performed at 37 degrees C. Blood samples were drawn from the dogs at regular intervals after bypass for 30 days. Erythrocyte survival was determined by Cr51 activity recorded by a gamma counter. The red cell half-life was determined for each dog. The control half-life was 24.1 +/- 2.03 days; Group II, 19.88 +/- 1.69 (p < 0.05); Group III, 9.63 +/- 1.4 (p < 0.001); Group IV, 19.4 +/- 1.65 (p < 0.05); and Group V, 9.13 +/- 1.45 (p < 0.001). These data indicate that serious red cell injury does occur with extracorporeal circulation but that the injury is a function of pump time, rather than of the type of oxygenator.

Fate of indium 111-labeled platelets during cardiopulmonary bypass performed with membrane and bubble oxygenators.

To elucidate the effects of bubble and membrane oxygenators on platelet integrity, we developed a quantitative method of determining platelet lysis during cardiopulmonary bypass. Two groups of dogs whose platelets had been labeled with indium 111 were subjected to 1 hour of cardiopulmonary bypass. In Group A (bubble oxygenator), platelet lysis as measured by free plasma 111In levels increased from 6% +/- 1% to 33% +/- 7% during bypass. In Group B (membrane oxygenator), plasma 111In levels increased from 5% +/- 2% to 10% +/- 6% during bypass (p less than 0.01). After 1 hour of bypass, the ratio of 111In-labeled platelets to prebypass levels was 36% +/- 8% in Group A and 67% +/- 9% in Group B. Platelet deposition on the oxygenator was greater in bubble oxygenators (19% +/- 4% of total injected 111In) than in membrane oxygenators (12% +/- 3% of total injected 111In). These data indicated that membrane oxygenators maintain a higher circulating platelet count both intraoperatively and postoperatively and result in less platelet destruction than bubble oxygenators following 1 hour of cardiopulmonary bypass in dogs.

A comparison of membrane and bubble oxygenation as used in cardiopulmonary bypass in patients. The importance of pericardial blood as a source of hemolysis.

A prospective clinical study involving more than 500 patients was designed to compare the Landé-Edwards membrane oxygenator and the Bentley bubble oxygenator. First, the importance of exposure of blood to the pericardium as the major source of hemolysis during open-heart surgery was confirmed. Because of this finding, we included in this study only those patients in whom the blood spilled into the pericardium was not returned to the pump. Under these circumstances, we found that hemolysis was relatively low in patients oxygenated with the membrane oxygenator.

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

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

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.

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

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

Clinical comparison between membrane and bubble oxygenators in cardiopulmonary bypass.

The clinical course of two similar patient groups was compared in whom, during cardiopulmonary bypass, a membrane or bubble oxygenator was employed. According to our results there is no significant functional difference between the two types of oxygenators as long as the perfusion time does not exceed 90 minutes. Beyond this time limit, the membrane oxygenator has distinct advantages, particularly with regard to hemolysis. We presently prefer the bubble oxygenator. The use of a membrane oxygenator is restricted to complex open heart procedures with suspected technical problems.

Membrane and bubble oxygenators compared by preservation of myocardial function.

Membrane oxygenators reputedly preserve erythrocytes, platelets, kidneys, brain and lungs better than bubble oxygenators; preservation of ventricular function by the two types of oxygenator is compared in isolated hearts, extremely sensitive to imperfections of perfusion, by isovolumic tests which are simple and accurate, especially for evaluating compliance. Canine hearts were perfused for three hours with either disposable bubble (Temptrol) or membrane (Lande-Edwards) oxygenators. Values at a standard point on regression slopes os isovolumic contractile force, velocity and compliance (volume) against end-diastolic pressure were used to express final functions as percentages of initial ones. Terminal proportional ventricular weight was an index of oedema. The final mean percentages with standard error measurements of initial values for the 12 hearts perfused on buble oxygenators and the 10 on membrane oxygenators were, respectively: 97 +/- 11.5% and 87 +/- 10.7% for contractile force, 117 +/- 23.1% and 88 +/- 10.44% for contractile velocity, and 97.2 +/- 8.48% and 117.3 +/- 12.5% for ventricular compliance, which was the function nearest to showing a significant difference with P less than 0.1. There was no significant difference in weights. This membrane oxygenator, as cheap and simple as conventional ones, probably has similar advantages for the myocardium as for other tissues.

Clinical and laboratory evaluation of the Shiley S-100-A oxygenator-heat exchanger.

A new oxygenator the Shiley S-100-A has been evaluated. It incorporates a heat exchanger based on an anodised aluminium tube which replaces the polyurethane coated tube of the previous S-100 model. Data from 46 patients perfused with the Shiley S-100-A were reviewed and compared with figures derived from a previous group of 225 patients in whom the S-100 model was used. The gas transfer capacity of the S-100-A model is very good and comparable to that of the S-100 oxygenator at a low gas flow/blood flow ratio. However both "in vitro" and "in vivo" studies confirmed the superiority of the heat exchange capacity of the S-100-A model. The times required for cooling (from 36.5 to 29.6 degrees C) and rewarming (from 29.6 to 37 degrees C) for an adult patient of average build were 9.1 and 26 minutes for the S-100 model and 6.7 and 15 minutes for the S-100-A model respectively. In a separate group of patients cooled to and rewarmed from 26 degrees C the cooling and rewarming times were 12.4 and 23 minutes respectively.

Emboli from an extraluminal blood flow hollow fiber oxygenator with and without an arterial filter during cardiopulmonary bypass in a pig model.

The effect of an arterial filter on visceral emboli was quantified with autologous indium-111 labeled platelets (INPLT) during cardiopulmonary bypass (CPB) in Yorkshire pigs. Biodistribution of INPLT was determined in 12 control pigs (30-35 kg, unoperated control [n = 6] and sham operated control [n = 6]). CPB was carried out with (n = 6) and without (n = 6) an arterial filter in 12 pigs at a flow rate of 2.5-3.5 L/min. Platelets labeled with In-111 tropolone (650-780 microCi) were injected intravenously 24 hr before CPB. All pigs were systemically heparinized (activated coagulation time > 400 sec); CPB was instituted with a roller pump, an extraluminal blood flow oxygenator (Bentley Univox, 1.8 m2), and an arterial filter (0.25 m2) and continued for 3 hr. Platelet kinetics, pooling, and counts were monitored by a Geiger probe and a Coulter counter. The thrombi in the oxygenator and arterial filter and emboli in viscera and brain were imaged with a gamma camera and measured with an ion chamber and gamma counter. Percentage of INPLT (mean +/- SD) in organs, tissues, and components of the circuit in four groups of pigs was calculated. Flow cytometry with antibodies to CD61 (GPIIIa) and CD62P (GMP-140: control) of porcine platelets was carried out with blood samples taken before, during, and after CPB for estimation of circulating platelet aggregates and platelet microparticles. Pulmonary, renal, cardiac, and cerebral emboli in pigs undergoing CPB with and without a filter were similar (p < 0.1). The amount of filter adherent thrombi was small (0.04 +/- 0.01%); oxygenator adherent thrombus in both groups was similar (p < 0.1). Emboli were found in the cerebral medulla, hippocampus, and posterior cerebral cortex in both groups. During CPB, the arterial filter functioned minimally as a trap for platelet thrombi detached from the oxygenator and circulating emboli. Flow cytometry of blood demonstrated the shift of equilibria from single platelets to platelet aggregates and microparticles during CPB and their gradual reversal to single platelets after CPB; the loosely adherent emboli disaggregated and further shifted these equilibria to single platelets and smaller aggregates, probably through the action of endogenous nitric oxide and prostacyclin. The emboli were trapped in organs and tissues and microparticles were sequestered by the reticuloendothelial system.

Blood--artificial surface interactions during cardiopulmonary bypass. A comparative study of four oxygenators.

Evaluation of the biocompatibility of four different types of oxygenator (bubble, membrane, hollow fibre and 'hybrid') was performed on 26 patients undergoing cardiopulmonary bypass during elective coronary surgery. More platelet derangement and an increased degree of hemolysis, revealed by higher plasmatic concentration of beta-thromboglobulin, platelet factor 4 and plasmatic free hemoglobin (p less than 0.05), was seen when using the bubble oxygenator. Damage to blood cells was minimal with the membrane oxygenator while the 'hybrid' and the hollow fibre oxygenators proved to rank at an intermediate level. Complement activation at the beginning of the cardiopulmonary bypass occurred via the alternative pathway as demonstrated by C3ades arg increase (up to nine times) without a concomitant elevation of C4ades arg. Cardiopulmonary bypass complement activation was quantitatively similar with all the oxygenators. A further activation via the classical pathway occurred in all the patients after protamine injection. Consistent differences as far as clinical and biological effects exist among the various commercially available cardiopulmonary bypass apparatus; our study provides guidelines for the evaluation and selection of devices which might reduce postoperative sequelae.

Blood compatibility of two different types of membrane oxygenator during cardiopulmonary bypass in infants.

The contact of blood with the artificial extracorporeal circuit causes a systemic inflammatory response due to blood activation. In this study, we compared two different paediatric membrane oxygenators used for extracorporeal circulation: a hollow fibre membrane oxygenator (Dideco Masterflo D-701, n = 10), and a flat sheet silicone membrane oxygenator (Avecor Kolobow 800-2A, n = 10). Blood compatibility was indicated by measuring complement activation as well as leukocyte and platelet activation. In patients perfused with a flat sheet membrane oxygenator, concentrations of complement split products C3a were significantly increased 30 minutes after the start of bypass (p < 0.01), whereas only a mild increase of C3a was found in patients perfused with a hollow fibre membrane oxygenator. Leukocyte and platelet counts dropped uniformly in both groups after the start of bypass mainly due to hemodilution. Activation of leukocytes and platelets identified by both plasma beta-glucuronidase and beta-thromboglobulin was similar in both groups. Infants perfused with a flat sheet membrane oxygenator received significantly more donor blood than those perfused with a hollow fibre oxygenator (p < 0.05). These results indicate that when used during paediatric cardiopulmonary bypass, a flat sheet membrane oxygenator has a higher complement activity than a hollow fibre membrane oxygenator, which is probably due to the relatively larger blood-surface contacting area of the oxygenator.

Limitations using the vacuum-assist venous drainage technique during cardiopulmonary bypass procedures.

Vacuum-assist venous drainage (VAVD) can increase venous blood return during cardiopulmonary bypass (CPB) procedures. However, the negative pressure created in the closed cardiotomy reservoir can be transmitted to the oxygenator if a nonocclusive or centrifugal arterial pump is used, resulting in bubble transgression (BT) from the gas to blood compartment of the oxygenator. We analyzed the vacuum pressure required to produce BT using an in vitro circuit including successively a closed reservoir, a pump (centrifugal or roller), and an oxygenator. A constant hydrostatic pressure was maintained onto the oxygenator. Vacuum was applied on the cardiotomy reservoir, progressively increasing negative pressure from 0 to -80 mmHg and monitoring BT with a bubble detector. Six different oxygenators were compared. A partially occlusive roller pump and a centrifugal pump were compared to a control, which was without any pump. A mean negative pressure of -53 +/- 7 mmHg was necessary to produce BT in all the oxygenators in the absence of a pump. The presence of a centrifugal pump between the reservoir and the oxygenator significantly increased the negative pressure required to produce BT compared to the control (-67 +/- 7 mmHg, p < .05). No bubbles were detected using the roller pump (> -80 mmHg needed for BT), thus statistically significant when compared to the centrifugal pump (p < .05). The centrifugal pump offers significant resistance to BT but not as much compared to the roller pump, though BT cannot be prevented if the pump is turned off while the vacuum remains on the reservoir. Therefore, VAVD is a safe technique as long as the perfusionist stops the vacuum when the arterial pump is no longer in use.

Current developments in oxygen concentrator technology.

Oxygen concentrators are electrically powered devices which are designed to provide oxygen for patients who require long-term domiciliary oxygen. The machines have been available for the last 10 to 15 years, but it is only recently that improvements in design have led to them being generally accepted as a reliable and economical means of supplying long-term oxygen therapy. There are two basic types of concentrator currently available: the molecular sieve (MS) concentrator, and the membrane oxygen enricher. In this article the characteristics and principles of operation of these machines are reviewed, together with the development and present state of MS concentrator technology. A summary of a comparative evaluation of seven MS concentrators is presented and the results discussed. Relevant safety standards and current trends in concentrator design are then reviewed.