Hollow-fiber Oxygenator Research Articles

Spontaneous gas bubbling in microporous oxygenators.

During operation of the microporous membrane oxygenators at some conditions, gas microbubbles penetrate into the blood. This effect, so-called spontaneous bubbling, takes place even when the blood pressure is higher than the gas pressure. This phenomenon was confirmed experimentally both in a model cell with hydrophobic microporous hollow fibers being used in the oxygenators and in in vitro tests on the actual microporous hollow fiber oxygenator. We proposed a mechanism of spontaneous gas bubbling into liquid that contains dissolved gases. Because of a partial pressure gradient, the dissolved gases and water vapors are transported from blood into the gas pore. This causes Stefans gas flow directed from the liquid-gas interface. Because of the high hydraulic resistance of the micropores, gas pressure at the meniscus increases up to gas bubbling. A mishandled priming of the oxygenator as well as the blood pressure pulsation caused by the roller pump operation contribute to spontaneous gas bubbling in the microporous oxygenators. The flow and pressure in the hydrophobic pores were calculated for various gases.

Percutaneous extracorporeal arteriovenous CO2 removal for severe respiratory failure

Background. In previous animal studies, arteriovenous CO2 removal (AVCO2R) achieved significant reduction in ventilator pressures and improvement in the Pao2 to fraction of inspired oxygen ratio during severe respiratory failure. For our initial clinical experience, 5 patients were approved for treatment of severe respiratory failure and CO2 retention to evaluate the feasibility and safety of percutaneous AVCO2R.Methods. Patients were anticoagulated with heparin (activated clotting time, 260 to 300 seconds), underwent percutaneous femoral cannulation (10F to 12F arterial and 12F to 15F venous catheters), and then were connected to a low-resistance, 2.5-m2 hollow-fiber oxygenator for 72 hours.Results. Mean AVCO2R flow at 24, 48, and 72 hours was 837.4 ± 73.9, 873 ± 83.6, and 750 ± 104.5 mL/min, respectively, with no vascular complications and no significant change in heart rate or mean arterial pressure. Removal of CO2 plateaued at an AVCO2R flow of 1086 mL/min with 208 mL/min CO2 removed. Average CO2 transfer at 24 and 48 hours was 142 ± 17 and 129 ± 16 mL/min. Use of AVCO2R allowed a significant decrease in minute ventilation from 7.2 ± 2.3 L/min at baseline to 3.4 ± 0.8 L/min at 24 hours.Conclusions. All patients survived the experimental period without adverse sequelae. Percutaneous AVCO2R can achieve approximately 70% CO2 removal in adults with severe respiratory failure and CO2 retention without hemodynamic compromise or instability.

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.

Uncoated and coated blood contact surfaces of a hollow-fiber oxygenator: an in-vitro comparison

Uncoated and coated blood contact surfaces of a hollow-fiber oxygenator: an in-vitro comparison

Cardiac bypass haemostasis: putting blood through the mill.

Cardiac bypass haemostasis: putting blood through the mill.

Ultrastructural lung injury in patients undergoing open-heart surgery with cardiopulmonary bypass

O-14 Introduction: Pulmonary injury is a recognized complication after cardiopulmonary bypass (CPB) with bubble, and disc [1] oxygenators. We investigated ultrastructural changes in the lung following the use of hollow-fibre oxygenator. Methods: Lung biopsies were taken from the left upper lobe of 20 patients without pre-existing lung pathology (age 40-72 yr) 20 min after cardiopulmonary bypass. Pre-CPB biopsies served as controls. Tissue specimens were placed in cacodylate-buffered glutaraldehyde, postfixed in s-collidine-buffered osmium tetroxide and embedded in epon 812. For light microscopy fragments were stained with haematoxylin-eosin. Results: Light microscopic observations revealed few pathological changes, e.g. the presence of some extravasated erythrocytes as well as oedematous fluid in the lumen of alveoli. The ultrastructural observations after CPB showed many morphological alterations in the gas exchange unit structure. Several type I pneumocytes had oedematous or even necrotic appearances, many endothelial cells of alveolar capillaries were swollen, and several were apparently leaky. Type II pneumocytes exhibited swelling of the cytoplasm and endoplasmic reticulum. Oedema and extravasated erythrocytes were present in many alveoli. Structures of pulmonary surfactant were seen in the lumen of alveolar capillaries which are likely due to disruption of the air-blood barrier. No patient exhibited significant postoperative complications. Conclusion: The results of this investigation suggest that cardiopulmonary bypass with the use of hollow-fibre oxygenator and subsequent reperfusion influences the morphology of the gas exchange unit. Our results suggest that ultrastructural changes do not correlate with clinical outcome, at least not in a healthy lung.

Effects of Blood Flow Pulse Frequency on Mass Transfer Efficiency of a Commercial Hollow Fibre Oxygenator

The clinical advantages achievable through pulsatile blood perfusion during cardio-pulmonary bypass have recently suggested the design of new pulsatile systems for extracorporeal circulation. Still it is not clear whether current commercial membrane oxygenators could be adopted with such systems, since their behaviour with pulsatile perfusion has not been satisfactorily documented yet. In a previous paper, we assessed that pulsatile perfusion of a widely used hollow fibre oxygenator (Sorin Monolyth) at 60 bpm provides more time-consistent oxygen transfer than steady perfusion. The present work is aimed to evaluate how the pulse frequency influences the gas transfer performance of the same device. The oxygenator was subjected to in vitro trials using a roller pump with pulsatile module (Stockert Instrumente) to generate pulsed flow. Four different pulse frequencies (45, 60, 75 and 90 bpm) were investigated at a fixed blood flow rate (4.0 l/min). The experiments lasting six hours were carried out using bovine blood with inlet conditions according to AAMI standards requirements. Blood samples were withdrawn every hour and O2 and CO2 transfer rates were evaluated. The experimental findings confirm that with pulsatile blood flow no time decay take place during prolonged perfusion. Moreover, when pulse frequency increases, transition levels occur for both O2 and CO2. Over these thresholds gas transfer rates display significant increases (p < 0.05), though of little magnitude (up to 2.5% for oxygen over 60 bpm; up to 3.7% for carbon dioxide over 75 bpm).

Mass transfer efficiency of a commercial hollow fibre oxygenator during six-hour in vitro perfusion with steady and with pulsatile blood flow

Detailed data about the behaviour of commercial membrane oxygenators with pulsatile blood flow are rarely available. This work deals with an experimental evaluation of the effects induced on gas transfer efficiency by pulsatile perfusion of a hollow fibre oxygenator (Monolyth Sorin Biomedica). The oxygenator was subjected to two in vitro trials both carried out with identical experimental protocols except for the flow type, steady and pulsatile. A roller pump with pulsatile module (Stockert Instrument) was used to generate both flow types. Three different mean blood flow rates (3.2, 4.0 and 4.8 Umin) were tested. The experiments lasting six hours were carried out using bovine blood with inlet conditions according to AAMI standard requirements. Blood samples were withdrawn every hour and the calculated gas transfer obtained in the two sessions were compared. The device proved to be well-designed for steady flow and to be liable to similar gas transfer performance when used in pulsatile conditions. Furthermore, the use of pulsatile flow rather than steady flow provided more consistent conditions and resulted in a higher eventual oxygen transfer efficiency (final mean difference = 6.2%, p &lt; 0.05), proving to be able to avoid any performance decays. (Int J Artif Organs 1998; 21:97–106)

Evaluation of the bio-compatablity and clinical usefulness of an ultra-thin silicone-coated polypropylene hollow-fiber oxygenator.

Evaluation of the bio-compatablity and clinical usefulness of an ultra-thin silicone-coated polypropylene hollow-fiber oxygenator.

Clinical Evaluation of a Silicone Coated Hollow Fiber Oxygenator

Clinical Evaluation of a Silicone Coated Hollow Fiber Oxygenator

Silicone-Coated Polypropylene Hollow-Fiber Oxygenator: Experimental Evaluation and Preliminary Clinical Use

Background. A membrane oxygenator consisting of a microporous polypropylene hollow fiber with a 0.2-μm ultrathin silicone layer (cyclosiloxane) was developed. Animal experimental and preliminary clinical studies evaluated its reliability in bypass procedures.Methods. Five 24-hour venoarterial bypass periods were conducted on dogs using the oxygenator (group A). In 5 controls, bypass periods were conducted using the same oxygenator without silicone coating (group B). As a preliminary clinical study, 14 patients underwent cardiopulmonary bypass with the silicone-coated oxygenator.Results. Eight to 16 hours (mean, 12.2 hours) after initiation of bypass, plasma leakage occurred in all group B animals, but none in group A. The O2 and CO2 transfer rates after 24 hours in group A were significantly higher than at termination of bypass in group B (p < 0.005 and p < 0.03, respectively). Scanning electron microscopy of silicone-coated fibers after 24 hours of bypass revealed no damage to the silicone coating of the polypropylene hollow fibers. In the clinical study, the oxygenator showed good gas transfer, acceptable pressure loss, low hemolysis, and good durability.Conclusions. This oxygenator is more durable and offers greater gas transfer capabilities than the previous generation of oxygenators.(Ann Thorac Surg 1997;63:1730–6)

CLINICAL EVALUATION OF SILICONE-COATED HOLLOW FIBER OXYGENATOR

In this article, the clinical experience with a cardiopulmonary bypass (CPB) using a newly developed hollow fiber oxygenator with an ultra-thin layer of silicone is reported. A comparative study of biocompatibility between the new oxygenator and a heparin coated oxygenator is also described. The CPB was performed with a silicone coated oxygenator, Mera Excelung Binding Prim HPO 15 H-C (Group I, n = 6) or Binding Prim HPO 25 H-C (Group II, n = 10) (Senko Medical Instrument Mfg., Tokyo, Japan). Air could be vented through the silicone coated hollow fibers, and it was easy to prime the circuits. The CPB duration was 101 +/- 37 min and 170 +/- 64 min for Groups I and II, respectively. There were no deaths and no complications from CPB. Partial arterial pressure of O2 levels 60 minutes after the start of CPB were 529 +/- 28 mm Hg and 529 +/- 28 mmHg for Group I and II, respectively. Partial arterial pressure of CO2 levels 60 min after the start of CPB were 36.4 +/- 4.6 mmHg and 39.4 +/- 4.4 mmHg, respectively. Plasma free hemoglobin at 60 min was 33.5 +/- 17.2 mg/ dL and 46.7 +/- 26.1 mg/dL for Groups I and II, respectively. As an evaluation of biocompatibility, the effects of the new oxygenator on platelet activation (GP Ib, IIb/IIIa), coagulation (TAT), fibrinolysis (PIC), and inflammatory response (C3a, granulocyte elastase) were investigated during CPB and comparing to those of the heparin coated oxygenator. There were no significant differences in GP Ib, GP IIb/IIa, TAT, PIC, and granulocyte elastase between the two oxygenators. However, 60 min after the start of CPB, the C3a was significantly lower for the new oxygenator group than for the heparin coated oxygenator group (p < 0.03). The new oxygenator showed good gas transfer, low hemolysis, and good biocompatibility. Because of its durability and good biocompatibility, the new oxygenator was determined to be suitable for prolonged extra corporeal circulation.

Analysis of Clinical Trends in a Program of Emergent ECLS for Cardiovascular Collapse

Between June 1986 and October 1995, 81 patients were emergently resuscitated with a portable extracorporeal life support (ECLS) system. Venoarterial perfusion was achieved using a centrifugal pump (BioMedicus; Medtronic, Anaheim, CA) and a hollow fiber oxygenator (BARD in 56 patients; Medtronic heparin-bonded MAXIMA, [MAXIMA, Medtronic, Minneapolis, MN] in the last 25 patients. The ECLS system was used at various locations in the hospital with the setup, priming, and initiation of perfusion done by ECLS trained intensive care unit nurses. Clinical data in these patients were reviewed to analyze variables influencing survival and trends that develop as the authors' experience accumulated and the technology evolved. The indication for ECLS was cardiac arrest in 68 patients and refractory cardiogenic shock in 13 patients. Thirty-five patients (43.2%) survived > 24 hrs after termination of ECLS, whereas 20 patients (24.7%) are long-term survivors (> 30 days). The ECLS system permitted an additional therapeutic surgical intervention in 45 cases. Patients who had a surgically remediable problem were more likely to survive. Prolongation of cardiopulmonary resuscitation beyond 30 mins before initiation of ECLS correlated with a decreased likelihood of survival.

Experimental evaluation of a newly developed ultra-thin silicone layer coated hollow fiber oxygenator

Experimental evaluation of a newly developed ultra-thin silicone layer coated hollow fiber oxygenator

Development of an intravascular pumping oxygenator using a new silicone membrane.

A new intravascular pumping oxygenator (IVPO) was developed for intravascular gas exchange and circulatory assistance in critically ill patients with respiratory and circulatory failure. The IVPO utilizes new silicone hollow fibers (diameter, 1 mm; membrane width, 50 microns) and consists of two driving tubes for the oxygenation and pumping of circulating blood. The performance characteristics of the IVPO were studied using an experiment ex vivo model. With a mean hemoglobin concentration of 10.5 +/- 2.3 g/dl, total oxygen transfer was 5.6 +/- 1.5 ml/min at a blood flow of 200 ml/min and 6.3 +/- 2.2 ml/min at a blood flow of 250 ml/min. Total CO2 transfer was 3.8 +/- 1.4 ml/min at a blood flow of 200 ml/min and 4.2 +/- 1.6 ml/min at a blood flow of 250 ml/min. Blood flow increased to a maximum of 250 ml/min during IVPO pumping. This preliminary experiment demonstrated that the IVPO has the capacity to function both as circulatory assist pump and as an intravascular hollow fiber oxygenator.

Contribution of hyperoxia to lipid peroxidation in coronary artery operations: Should we keep a low oxygen tension?

Oxygen free radicals are known to play a significant role in the morbidity associated with cardiac operations. They seem to be produced through two major pathways, heart ischemia-reperfusion I and leukocyte aetivation. 2 Another possible pathway might be the hyperoxia that occurs during cardiopulmonary bypass (CPB) and within a short period during which the patient is still supported by mechanical ventilation. The contribution of hyperoxia to oxygen free radical generation and consequent lipid peroxidation in cardiac operations has to date not been addressed. The purpose of the present study was to elucidate the role of hyperoxia in lipid peroxidation during cardiac operations. Patients and methods. After obtaining informed consent, we entered 24 conseeutive patients scheduled for routine coronary artery operation into the study. Patients in cardiogenic shock were excluded from the study. The mean age was 63.2 _+ 2.1 years (range 44 to 83) and there were 17 men and 7 women. Ischemic time was 46.8 + 3.2 minutes (range 24 to 92) CPB time 98.7 _+ 5.4 minutes (range 67 to 174), and blood partial 02 tension (Po2) during CPB 45.4 -+ 1.2 kPa (range 29 to 57). Anesthesia was instituted with fentanyl, pancuronium, and isoflurane. A membrane oxygenator (CML membrane hollow-fiber oxygenator, Cobe Inc., Lakewood, Colo.) was used for extracorporeal circulation and pH management was done with the pH-stat method. Myocardial protection was achieved with the use of intermittent fibrillation. The nasopharyngeal temperature was maintained at approximately 32 ° C during the CPB period. No patient received drugs known specifically to scavenge free radicals (allopurinol, mannitol, captopril, and desferrioxamine). Anesthetists and perfusionists responsible for controlling the degree of oxygenation were blind to the study. Peripheral venous blood samples for determination of whole plasma hydroperoxide concentrations (WPHC) were obtained before the operation and 1, 6, 24, and 72 hours after CPB was discontinued. The venous blood

Non-Destructive Evaluation of Membrane Lung Gas Exchange Performance

This paper describes a method of evaluating the gas exchange effectiveness of hollow fiber oxygenators utilizing gas on both sides of the membrane. The goal of the study was to develop an evaluation technique which was accurate, reliable, and did not harm or contaminate a new. sterile oxygenator. Three pediatric oxygenators were tested and compared: the Medtronic Minimax Plus, the Terumo Capiox 320, and the Sorin Masterflo 34 (all with rated blood flows of 2-2.5 L/min). Gas entering the "blood" side was a mixture of CO2, O2, and N2 in a mixture matching typical venous blood partial pressures. The "blood" flows used were 0.5, 1, 1.5, or 2 L/min. Gas entering the gas port had an FiO2 of 0.4 flowing at 0.5, 1, 1.5, 2, 2.5, 3, or 3.5 L/min. Fractional contents of CO2 and O2 at all inlets and outlets were determined using a gas analyzer and converted to partial pressures. Efficacy indices and gas transfer rates were calculated and compared. Of the devices studied, the Masterflo 34 had the highest gas transport rates and effectiveness followed by the Minimax-Plus and the Capiox 320. Reversing the direction of the flow through the "blood" phase of the Minimax-Plus greatly changed its gas exchange effectiveness. The techniques described in this study should allow for a more uniform and consistent evaluation of gas exchange by membrane lungs which can be made inexpensively and relatively quickly. In addition, these methods should allow manufactures to evaluate gas exchange effectiveness and transfer rates of individual units during production as well as reduce the complexity involved when evaluating newly developed oxygenators.

Platelet activation and degradation in an experimental extracorporeal system. A comparison between a silicone membrane and a hollow-fibre oxygenator

Blood platelets are rapidly activated in contact with biomaterials and, therefore, can be used as markers of the biocompatibility of various components in an extracorporeal system. In the present work two different oxygenators, one membrane oxygenator (Avecor) and one hollow-fibre oxygenator ("Lilliput', Dideco) were compared. Complete in vitro extracorporeal membrane oxygenation circuits were perfused with fresh, heparinized human blood for 24 h. Eight experiments were performed with the hollow-fibre oxygenator and five experiments with the membrane oxygenator. Blood gases, electrolytes, glucose and haematocrit were kept within physiological limits. Platelet count, plasma concentration of beta-thromboglobulin, platelet serotonin content, platelet membrane glycoprotein lb and its degradation product glycocalicin, as well as plasma haemoglobin concentration were assayed. As regards most of these variables, significant differences in favour of the hollow-fibre oxygenator were observed.

Experimental evaluation of a newly developed ultrathin silicone layer coated hollow fiber oxygenator.

The authors developed a new membrane oxygenator that consists of microporous polypropylene hollow fibers coated with a 0.2 micron ultrathin silicone layer. Five venoarterial bypasses were conducted on mongrel dogs for 24 hr using these new oxygenators. The blood flow rate was maintained at 750 ml/min, and the V/Q ratio was maintained at 1:1. As a control, three venoarterial bypasses were conducted under the same conditions using an oxygenator with the same design but without the silicone coating. Eight to 16 hr after the initiation of bypass, severe plasma leakage occurred in all control experiments, so the bypasses were terminated. However, plasma leakage did not occur throughout the 24 hr of any of the experiments using the new oxygenator. The O2 transfer rate of the new oxygenators after 24 hr of perfusion was 59.7 +/- 6.6 ml/min/m2, and the plasma free hemoglobin level 8 hr after the initiation of bypass was 41.4 +/- 40.2 mg/dl, compared with 145.3 +/- 189.6 mg/dl in the control group. Scanning electron microscopic examination of the silicone coated fibers after 24 hr of bypass revealed a few scattered platelet adherents and no damage to the silicone coated surface. These results suggest that this new oxygenator has satisfactory gas transfer and good durability.

Development of a membrane oxygenator for ECMO using a novel fine silicone hollow fiber.

One of the limitations of conventional silicone hollow fiber oxygenators compared with microporous membrane oxygenators is poor gas permeability. However, the silicone hollow fiber is free from plasma leakage, which is the major life limiting factor of the microporous membrane oxygenator. It has been difficult to fabricate a fine, thin hollow fiber for reduction of resistance to gas permeability because of the poor mechanical strength of conventional silicone materials. The authors developed a novel silicone material with sufficient mechanical strength, and a fine silicone hollow fiber with a diameter of 30 microns and wall thickness of 50 microns, which is approximately half that of a conventional silicone hollow fiber. Using this newly developed silicone hollow fiber, the authors developed a compact extracapillary flow membrane oxygenator. The oxygenator consists of fine silicone hollow fibers inserted in a housing made of polycarbonate. The housing is a cylindrical case, 20 cm long and 55 mm in inside diameter. The hollow fibers are cross-wound. The surface area of the membrane is 2.0 m2, and priming volume is 230 ml. Gas transfer performance of the newly developed oxygenator was evaluated by in vitro experiments. Oxygen and carbon dioxide transfer rates were 195 ml/min and 165 ml/min, at a blood flow rate 3 L/min. The novel silicone membrane oxygenator developed in this study can be used for extended duration in such applications as extracorporeal membrane oxygenation.