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PubMed1992

Assessment of oxygen transfer in membrane oxygenators during clinical cardiopulmonary bypass.

Although functional replacement of the heart and lungs by a pump and oxygenator is a widespread surgical procedure, no widely accepted technique for describing gas exchange in oxygenators exists. In this study, 8 types of commercially available membrane oxygenator (2 flat sheet membrane, 4 gas in hollow fibre membrane and 2 blood in hollow fibre membrane) have been studied during clinical cardiopulmonary bypass. O2 transfer increased with blood flow rate but the O2 transfer at a given blood flow was lower than that obtained by the manufacturers in laboratory studies. Overall O2 transfer coefficients were calculated from the ratio of O2 transfer rate to an O2 difference expressed either as an O2 partial pressure or an O2 concentration. Specific O2 transfer coefficients (overall coefficient divided by membrane area) were similar for oxygenators with a flat sheet or gas in hollow fibre membrane configuration. The two types of oxygenator with blood in hollow fibre membranes had significantly lower (P less than 0.01) specific O2 transfer coefficients. This study shows that oxygenator gas transfer characteristics can be studied in the clinical environment and that O2 transfer coefficients can be related to oxygenator design features.

Aged↗
PubMedDate not supplied

[Oxygen transport in membrane oxygenators].

Mass transfer properties of the Soviet membrane oxygenator, MOCT, are tested. The liquid chambers of the oxygenator are made of disk membranes separating the moving blood from gas chambers. Processes of transportation and saturation of the blood film with oxygen are described by the simultaneous solution of the hydrodynamic and diffusion problem that is complicated by the chemical reaction. To derive approximate analytical solution the concept of a spreading front separating the area of the saturated blood layer from the venous area is applied. The expression for the thickness of the saturated layer and the oxygen flow to the blood is deduced as a function of the following parameters: membrane permeability, blood output, hemoglobin concentration, etc. The analytical solution is found to be satisfactory in describing experimental data obtained in the course of laboratory, clinical and biomedical tests.

Humans↗
PubMed2003

Development of disposable self-regulating blood pumps and automatically-controlled portable extracorporeal membrane oxygenation systems for neonatal extracorporeal membrane oxygenation.

For safer and simpler neonatal ECMO management, the authors have been developing an innovative, automatically-controlled ECMO machine using self-regulating blood pumps. The newest model is an air-driven, tube-type blood pump. A pair of blood pumps are placed in parallel and actuated alternately with compressed air. The pump flow is automatically regulated in accordance with hemodynamic changes of the body. The need for a venous reservoir is eliminated because the circuit does not generate excessive negative pressure when there are shortages of draining blood. Therefore, the priming volume of the circuit is only 85 ml. This ECMO apparatus has three driving modes, one of which is a "delay" mode. This enables the pump flow to easily be varied from 10 to 500 ml/min under automatic control, and it can be used when the pump flow is decreased for weaning. This newest ECMO apparatus was clinically used in 3 neonates with severe lung hypoplasia and persistent fetal circulation. The ECMO duration was 139 h to 168 h, and the maximum ECMO flow 71.3 to 109.0 ml/min/kg. Thanks to the self-regulation, intensive observation of the circuit was not necessary during ECMO. Damage to blood cells was less significant, and the use of blood products was only minimal (15.7 ml/kg/day) because a large volume of blood to stabilize the pump performance was not necessary. In conclusion, the automatically-controlled ECMO apparatus worked well without complications by changing the ECMO flow automatically in accordance with hemodynamic changes. This automatic ECMO system required fewer personnel expenditures and was also favorable in terms of hematological findings.

Acute Disease↗
PubMedDate not supplied

Neonatal and pediatric extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation provides an external circulation for the critically ill patient with components capable of supporting the cardiorespiratory system while the patient's innate organs recover from the primary insult. This therapy is often used in children with relatively well-elucidated indications. Although initially used in the setting of neonatal respiratory failure, the use of extracorporeal membrane oxygenation for pediatric respiratory and cardiac indications is not uncommon. The complications and the outcomes of extracorporeal membrane oxygenation compare favorably with other forms of conventional therapy.

Critical Illness↗
PubMed1999

The effect of left-to-right shunting on coronary oxygenation during extracorporeal membrane oxygenation.

BACKGROUND/PURPOSE: Blood perfusion to the coronary artery (CA) during venoarterial (VA) extracorporeal membrane oxygenation (ECMO) was examined to determine whether it was receiving highly oxygenated ECMO blood or desaturated blood from the pulmonary circulation of diseased lungs. METHODS: In the first experiment, left ventricle output and oxygen saturation in the left ventricle (LV) and CA were measured in dogs placed on VA ECMO. In the second experiment, dogs with an artificial subclavian-pulmonary artery shunt were placed on VA ECMO at 100 mL/kg/min, and oxygen saturation was measured as the shunt flow increased. RESULTS: Without an artificial shunt, a substantial portion of coronary perfusion was found to be supplied by the left ventricle (54 + 30%), even at a high ECMO flow rate of 100 mL/kg/min and low LV output (22+/-17%) relative to ECMO flow. With a shunt, oxygen saturation in the CA was more than 95%, even when shunt flow was only 7.5% of ECMO flow and output from the left ventricle was less than 25% of the ECMO flow rate. CONCLUSIONS: These results suggest that an excessive "lung rest" strategy during VA ECMO may produce suboptimal coronary oxygenation possibly leading to myocardial damage. The presence of a small left-to-right shunt may prevent coronary hypoxia.

Animals↗
PubMed2001

Neonatal electroencephalogram does not predict cognitive and academic achievement scores at early school age in survivors of neonatal extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation is an effective rescue treatment for severe cardiorespiratory failure in term or near-term neonates, although a wide range of neurologic sequelae have been noted in a substantial minority of survivors. The objective of the present study was to determine the value of the neonatal electroencephalogram (EEG) for predicting Wechler Preschool and Primary Scale of Intelligence-Revised (WPPSI-R), Wide Range Achievement Test, and Wide Range Assessment of Memory and Language scores at early school age in 66 testable survivors of extracorporeal membrane oxygenation who were not severely brain damaged. Technically satisfactory EEG recordings were obtained at least twice following admission to our nursery and prior to discharge. The EEGs were classified and graded according to standard criteria. The developmental test results of those who had only normal or mildly abnormal neonatal EEGs (group 1, n = 9) were compared with those who had at least one moderately or markedly abnormal recording (group 2, n = 57). School-age test and subtest scores were not statistically significantly worse in group 2 versus group 1 infants. No child in group 1 and five children in group 2 had WPPSI-R Full-Scale IQ scores of less than 70. Of the nine children in group 2 who had at least one markedly abnormal neonatal EEG recording (graded as burst suppression or as electrographic seizure), only two had abnormally low WPPSI-R Full-Scale IQ scores. We conclude that EEG recordings obtained during the neonatal course of neonates treated with extracorporeal membrane oxygenation do not predict cognitive and academic achievement test results in survivors at early school age who were testable and not severely brain damaged.

Brain Damage, Chronic↗
PubMedDate not supplied

A siliconized hollow fiber membrane oxygenator.

Most membrane oxygenators are built with microporous fibers known for plasma leakage in long-term use such as extracorporeal life support or extracorporeal membrane oxygenation. The current study was designed to evaluate the Quadrox oxygenator in which the fibers have been coated with silicone (Jostra). Six calves (mean weight, 62 +/- 4 kg) were connected to cardiopulmonary bypass (CPB) by jugular venous and carotid arterial cannulation, with a mean flow rate of 3 L/min for 6 hours. They were randomly assigned to a standard Quadrox oxygenator (standard group, n = 3) or a siliconized Quadrox oxygenator (silicone group, n = 3). After 7 days, the animals were sacrificed. A standard battery of blood samples was taken before bypass, after mixing for 10 minutes, and after 1, 2, 5, and 6 hours of perfusion. Analysis of variance was used for repeated measurements. Total oxygen transfer and carbon dioxide transfer did not differ between groups (p = 0.5 for comparison). Blood trauma, evaluated by plasma hemoglobin (Hb), did not detect any significant hemolysis in either group. Thrombocyte and white blood cell count profiles in both groups were parallel and without significant differences (p = 0.1 and 0.6, respectively). At the end of testing no clot deposition was found in the oxygenator. At postmortem, there were no signs of peripheral emboli. The results of this study suggest that this silicone coating of hollow fibers allows for good gas transfer, while preserving all the mechanical advantages of a conventional hollow fiber oxygenator.

Animals↗
PubMed2000

The effects of nitric oxide on coagulation during simulated extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation (ECMO) is associated with profound alterations in hemostasis, with platelet dysfunction often being implicated as a causative factor for transfusion. Nitric oxide (NO) has shown to be a rapid yet temporary inhibitor of platelet function. The purpose of this study was to evaluate the effects of NO on platelet number and function in an in vitro ECMO model. Eight silicone membrane oxygenators were primed with fresh, heparinized, bovine blood and allowed to circulate for 48 hours. The treatment group (NO) consisted of four oxygenators that had an end concentration of 20 ppm NO applied to the sweep gas. Platelet counts, methemoglobin levels, plasma-free hemoglobin levels, activated clotting times, and thromboelastographic (TEG) studies were performed at baseline, 1, 6, 12, and 24 h. Scanning electron microscopy (SEM) was performed on sample areas from each oxygenator. The treatment group maintained an average of 25% higher platelet counts than the control group (85.1 +/- 32.0, x 10(3) versus 66.5 +/- 30.9 x 10(3)) although statistical significance was not achieved. Methemoglobin levels were significantly elevated in the treatment circuit at hours 12 and 24 (p < .05). This could be attributed to the lack of a biological interaction that would break down this toxic by-product. TEG indices steadily declined in both groups from baseline (-0.4 +/- 3.6) to (-17.2 +/- 3.3 p < .0007) treatment and (-20 +/- 4.5, p < .0001) control, with the treatment circuit maintaining only slightly improved indices over the most of the study. SEM data showed increased fibrin and cellular deposits in the control group (p = .05) when compared with the treatment group. NO added to the sweep gas of a simulated ECMO circuit at 20 ppm had little effect on the maintenance of platelet number and function.

Blood Coagulation↗
PubMed1988

Life-threatening intrathoracic complications during treatment with extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation (ECMO) has been successful (greater than 80% survival) in 35 centers in greater than 900 newborns with severe respiratory failure having an estimated mortality of greater than 80% on conventional management. During the last 3 years we have treated 79 newborns with 74 survivors (94%). Their diagnoses included meconium aspiration, persistent fetal circulation, respiratory distress syndrome, congenital diaphragmatic hernia, and sepsis. Seven patients (9%) had life-threatening intrathoracic complications requiring emergent intervention while on ECMO: tension hemothorax (3), tension pneumothorax (2), and pericardial tamponade (2). Pericardial tamponade and tension hemothorax and pneumothorax show a similar pathophysiology of increasing intrapericardial pressure and decreasing venous return. Perfusion is initially maintained by the nonpulsatile flow of the ECMO circuit before further decrease in venous return results in decreasing ECMO flow and progressive hemodynamic deterioration. Each of the seven patients demonstrated a clinical triad that includes increasing PaO2 and decreasing peripheral perfusion (as evidenced by decreasing pulse pressure and decreasing SvO2) followed by decreasing ECMO flow with progressive deterioration. The diagnoses were confirmed by transillumination, chest x-ray, or cardiac echocardiogram. Initial emergent placement of a percutaneous drainage catheter was temporizing in all seven cases. However, four patients required emergent thoracotomy for definitive treatment while still on ECMO. All seven patients were weaned from ECMO and are short-term survivors (6 months to 3.5 years). As use of ECMO for newborn severe respiratory failure increases, responsible physicians must be familiar with life-threatening intrathoracic complications and appropriate treatment strategies.

Cardiac Tamponade↗
PubMed1987

Lung compliance as a measure of lung function in newborns with respiratory failure requiring extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation (ECMO) can now be used as an alternative mode of therapy for infants 2.0 kg or more with life-threatening respiratory failure. Current criteria for removal from ECMO are limited. We attempted to determine whether lung compliance (CL) could be used as a sensitive indicator of the neonates' lung improvement while they are on ECMO, as well as a predictor of their ability to tolerate removal from bypass. We obtained serial CL measurements in 13 infants, all of whom weaned successfully from ECMO. All had an initial CL on ECMO of 0.5 ml/cm H2O X kg or less (mean = 0.3), with a final CL of 0.8 ml/cm H2O X kg or more (mean = 1.7). The average change in CL from the initial to the final measurement was 0.6 ml/cm H2O X kg or more (mean = 1.5). CL findings correlated well with estimated bypass, expressed as a percent of cardiac output, and a radiographic score of pulmonary abnormality (r = -.66, p less than .0001, and r = -.52, p less than .0001, respectively). We conclude that CL measurements can be used to monitor clinical improvement in infants on ECMO, to predict their successful removal from bypass, and ultimately to shorten their total time spent on bypass.

Cardiac Output↗
PubMed1988

Neonatal brain: color Doppler imaging. Part II. Altered flow patterns from extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation (ECMO), a lifesaving procedure in neonates with severely impaired lung function, requires ligation of the right common carotid artery. In an investigation of the collateral pathways that maintain perfusion of the brain after right common carotid artery ligation, ten infants were studied with color Doppler imaging during and after ECMO. The circle of Willis was seen in all infants, and in every case there was retrograde flow in the distal internal carotid artery and the proximal (A1) segment of the anterior cerebral artery. Bilateral flow in the middle cerebral arteries and in distal branches of the anterior cerebral arteries was also seen, documenting flow to both cerebral hemispheres.

Carotid Arteries↗
PubMed1992

Gentamicin pharmacokinetics in term neonates receiving extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation (ECMO) may affect the pharmacokinetics of certain drugs. The objectives of this study were to determine (1) the pharmacokinetics of gentamicin in neonates on ECMO and compare them to reported values for a similar patient population not on ECMO, (2) if the pharmacokinetics of gentamicin differ between venous-venous and venous-arterial bypass, and (3) if the pharmacokinetics of gentamicin are affected by oxygenator surface area (0.6 m2 vs 0.8 m2 oxygenators). The medical records of 29 term neonates who received gentamicin while on ECMO were reviewed. Data collected included gentamicin dosage, peak and trough serum concentrations determined at steady state, duration of treatment, time on ECMO, daily weights, and pertinent laboratory values. An initial dosage of gentamicin 2.5 mg/kg every 18 hours is suggested for term neonates on ECMO. Dosage adjustments should be based on gentamicin serum concentrations, and modifications may also be required after ECMO.

Bacterial Infections↗
PubMedDate not supplied

Scanning-electron-microscopic and functional studies of oxygenator-membranes during long-term-perfusion.

Various types and amount of deposits were noted on the surface of different membrane oxygenators during experimental long-term perfusion in sheep studied by SEM. They were present in spite of adequate heparinization. The deposition of blood material suggests, that the imperfection of the membranes by fabrication must be controlled and improved by oneself for use in long-term perfusion.

Animals↗
PubMed1994

Gas exchange across native lungs and extracorporeal membrane in neonates and pigs during extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation (ECMO) is a commonly used treatment modality for severe neonatal respiratory failure. The aim of the present study was to evaluate the relationship between ECMO blood flow and gas exchange across the native lungs and the extracorporeal membrane. In three healthy pigs, the ECMO flow correlated significantly with oxygen transfer (VO2) across the membrane (n = 12, r = .90, P < .001) and inversely with VO2 across the lungs (n = 12, r = -.75, p < .005). In three pigs with acute respiratory distress syndrome induced by repeated bronchoalveolar lavage, flow also significantly correlated with VO2 across the membrane (n = 9, r = .93, P < .001) and inversely with VO2 across the lungs (n = 9, r = -.97, P < .001). Eight neonates had measurements taken at different time intervals and different flow rates during ECMO. The ECMO flow correlated significantly with VO2 across the membrane (n = 45, r = .61, P < .001) and inversely with VO2 across the lungs (n = 15, r = -.54, P < .05). The relationship between carbon dioxide transfer (VCO2) and ECMO flow rates had the same trend as VO2 on all occasions. It is concluded that the ECMO flow rate is one of the main determinants of gas exchange across the lungs and the membrane.

Animals↗
PubMedDate not supplied

Neonatal extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation is an effective life support technique that has had most success in the treatment of neonatal cardiopulmonary failure. We review the technique and its potential indications and present the latest UK and worldwide survival data.

Extracorporeal Membrane Oxygenation↗