Biofilm Assessment and Metagenomic Analysis of Venoarterial Extracorporeal Membrane Oxygenation Cannulas and Membrane Oxygenators

Venoarterial extracorporeal membrane oxygenation (VA-ECMO) exposes the patient to infectious complications related to the cannulas or the site of insertion. The aim of the current study was to investigate and compare the prevalence of cannula and membrane oxygenators colonization using three different methods: microbiological culture, scanning electron microscopy, and metagenomic (rRNA 16S analysis). A monocentric prospective study was conducted between December 2017 and June 2018. Consecutive patients undergoing VA-ECMO support for refractory cardiac arrest or cardiogenic shock were included. Ten patients were included with a median age of 64 (52-62) years. Venoarterial extracorporeal membrane oxygenation was inserted for refractory cardiac arrest in five (50%), cardiogenic shock in four (40%), and self-poisoning in one (10%) cases. Microbiological culture of all (8/8, 100%) membrane oxygenators was negative, whereas all (10/10, 100%) were colonized by biofilm, and eight (8/9, 89%) presented bacterial DNA. Three (3/9, 33%) arterial and venous cannulas were positive in culture and seven (7/9, 78%) were colonized by biofilm, respectively. Seven (7/9, 78%) arterial and four (4/9, 44%) venous cannulas presented bacterial DNA. Colonization of cannulas and membranes is more frequent when assessed by electron microscopy or metagenomic analysis than with culture. Membrane oxygenators are more often colonized than cannulas.

Early Blood Clot Detection Using Forward Scattering Light Measurements Is Not Superior to Delta Pressure Measurements

The occurrence of thrombus formation within an extracorporeal membrane oxygenator is a common complication during extracorporeal membrane oxygenation therapy and can rapidly result in a life-threatening situation due to arterial thromboembolism, causing stroke, pulmonary embolism, and limb ischemia in the patient. The standard clinical practice is to monitor the pressure at the inlet and outlet of oxygenators, indicating fulminant, obstructive clot formation indicated by an increasing pressure difference (ΔP). However, smaller blood clots at early stages are not detectable. Therefore, there is an unmet need for sensors that can detect blood clots at an early stage to minimize the associated thromboembolic risks for patients. This study aimed to evaluate if forward scattered light (FSL) measurements can be used for early blood clot detection and if it is superior to the current clinical gold standard (pressure measurements). A miniaturized in vitro test circuit, including a custom-made test chamber, was used. Heparinized human whole blood was circulated through the test circuit until clot formation occurred. Four LEDs and four photodiodes were placed along the sidewall of the test chamber in different positions for FSL measurements. The pressure monitor was connected to the inlet and the outlet to detect changes in ΔP across the test chamber. Despite several modifications in the LED positions on the test chamber, the FSL measurements could not reliably detect a blood clot within the in vitro test circuit, although the pressure measurements used as the current clinical gold standard detected fulminant clot formation in 11 independent experiments.

The Hematological Effects of Extracorporeal Membrane Oxygenator Exchange

Membrane oxygenator failure during venovenous (V-V) extracorporeal membrane oxygenation (ECMO) can lead to life-threatening hypoxia, high replacement costs, and may be associated with a hyperfibrinolytic state and bleeding. The current understanding of the underlying mechanisms that drive this is limited. The primary aim of this study therefore is to investigate the hematological changes that occur before and after membrane oxygenator and circuit exchanges (ECMO circuit exchange) in patients with severe respiratory failure managed on V-V ECMO. We analyzed 100 consecutive V-V ECMO patients using linear mixed-effects modeling to evaluate hematological markers in the 72 hours before and 72 hours after ECMO circuit exchange. A total of 44 ECMO circuit exchanges occurred in 31 of 100 patients. The greatest change from baseline to peak were seen in plasma-free hemoglobin (42-fold increase p < 0.01) and the D-dimer:fibrinogen ratio (1.6-fold increase p = 0.03). Bilirubin, carboxyhemoglobin, D-dimer, fibrinogen, and platelets also showed statistically significant changes ( p < 0.01), whereas lactate dehydrogenase did not ( p = 0.93). Progressively deranged hematological markers normalize more than 72 hours after ECMO circuit exchange, with an associated reduction in membrane oxygenator resistance. This supports the biologic plausibility that ECMO circuit exchange may prevent further complications such as hyperfibrinolysis, membrane failure, and clinical bleeding.

Hemostatic Complications During Neonatal Extracorporeal Membrane Oxygenation: Roller Pump and Centrifugal Pump Driven Circuits

Recently three different neonatal extracorporeal membrane oxygenation (ECMO) circuits have been employed in our clinic. These circuits were compared for clotting and bleeding complications. Initially, we used an ECMO circuit containing a roller pump and venous bladder without severe complications. Manufacturing of circuit components was discontinued, necessitating the replacement of this circuit by a circuit with a centrifugal pump with 3/8 inch inlet and outlet. Acute increase of oxygenator resistance requiring emergency changeout became unexpectedly a regularly occurring complication. The increase in resistance was suspected to be caused by oxygenator clotting, although oxygenator function was preserved. To prevent this complication, we changed to a levitating centrifugal pump with 1/4 inch inlet and outlet, after which no oxygenator malfunction has been observed. Macroscopic and electron microscopic analysis demonstrates that small clots are formed within the circuit, presumably in or near the centrifugal pump, which are transported to the oxygenator and clog up the hollow fiber layer at the inlet side, barely penetrating the oxygenator beyond this first layer. Our results suggest that low blood velocities accompanied with recirculation of blood within or near the centrifugal pump and/or heat generation within the pump could contribute to the formation of these clots.

Comparison of hemodynamic features and thrombosis risk of membrane oxygenators with different structures: A numerical study

PURPOSE

The geometric structure of the membrane oxygenator can exert an impact on its hemodynamic features, which contribute to the development of thrombosis, thereby affecting the clinical efficacy of ECMO treatment. The purpose of this study is to investigate the impact of varying geometric structures on hemodynamic features and thrombosis risk of membrane oxygenators with different designs.

METHODS

Five oxygenator models with different structures, including different number and location of blood inlet and outlet, as well as variations in blood flow path, were established for investigation. These models are referred to as Model 1 (Quadrox-i Adult Oxygenator), Model 2 (HLS Module Advanced 7.0 Oxygenator), Model 3 (Nautilus ECMO Oxygenator), Model 4 (OxiaACF Oxygenator) and Model 5 (New design oxygenator). The hemodynamic features of these models were numerically analyzed using the Euler method combined with computational fluid dynamics (CFD). The accumulated residence time (ART) and coagulation factor concentrations (C[i], where i represents different coagulation factors) were calculated by solving the convection diffusion equation. The resulting relationships between these factors and the development of thrombosis in the oxygenator were then investigated.

RESULTS

Our results show that the geometric structure of the membrane oxygenator, including the location of the blood inlet and outlet as well as the design of the flow path, has a significant impact on the hemodynamic surroundings within the oxygenator. In comparison to Model 4, which had the inlet and outlet located in the center position, Model 1 and Model 3, which had the inlet and outlet at the edge of the blood flow field, exhibited a more uneven distribution of blood flow within the oxygenator, particularly in areas distant from the inlet and outlet, which was accompanied with lower flow velocity and higher values of ART and C[i], leading to the formation of flow dead zones and an elevated risk of thrombosis. The oxygenator of Model 5 is designed with a structure that features multiple inlets and outlets, which greatly improves the hemodynamic environment inside the oxygenator. This results in a more even distribution of blood flow within the oxygenator, reducing areas with high values of ART and C[i], and ultimately lowering the risk of thrombosis. The oxygenator of Model 3 with circular flow path section shows better hemodynamic performance compared to the oxygenator of Model 1 with square circular flow path. The overall ranking of hemodynamic performance for all five oxygenators is as follows: Model 5 > Model 4 > Model 2 > Model 3 > Model 1, indicating that Model 1 has the highest thrombosis risk while Model 5 has the lowest.

CONCLUSION

The study reveals that the different structures can affect the hemodynamic characteristics inside membrane oxygenators. The design of multiple inlets and outlets can improve the hemodynamic performance and reduce the thrombosis risk in membrane oxygenators. These findings of this study can be used to guide the optimization design of membrane oxygenators for improving hemodynamic surroundings and reducing thrombosis risk.

Exposure to Arterial Hyperoxia During Extracorporeal Membrane Oxygenator Support and Mortality in Patients With Cardiogenic Shock

BACKGROUND

Exposure to hyperoxia, a high arterial partial pressure of oxygen (PaO2), may be associated with worse outcomes in patients receiving extracorporeal membrane oxygenator (ECMO) support. We examined hyperoxia in the Extracorporeal Life Support Organization Registry among patients receiving venoarterial ECMO for cardiogenic shock.

METHODS

We included Extracorporeal Life Support Organization Registry patients from 2010 to 2020 who received venoarterial ECMO for cardiogenic shock, excluding extracorporeal CPR. Patients were grouped based on PaO2 after 24 hours of ECMO: normoxia (PaO2 60-150 mmHg), mild hyperoxia (PaO2 151-300 mmHg), and severe hyperoxia (PaO2 >300 mmHg). In-hospital mortality was evaluated using multivariable logistic regression.

RESULTS

Among 9959 patients, 3005 (30.2%) patients had mild hyperoxia and 1972 (19.8%) had severe hyperoxia. In-hospital mortality increased across groups: normoxia, 47.8%; mild hyperoxia, 55.6% (adjusted odds ratio, 1.37 [95% CI, 1.23-1.53]; P<0.001); severe hyperoxia, 65.4% (adjusted odds ratio, 2.20 [95% CI, 1.92-2.52]; P<0.001). A higher PaO2 was incrementally associated with increased in-hospital mortality (adjusted odds ratio, 1.14 per 50 mmHg higher [95% CI, 1.12-1.16]; P<0.001). Patients with a higher PaO2 had increased in-hospital mortality in each subgroup and when stratified by ventilator settings, airway pressures, acid-base status, and other clinical variables. In the random forest model, PaO2 was the second strongest predictor of in-hospital mortality, after older age.

CONCLUSIONS

Exposure to hyperoxia during venoarterial ECMO support for cardiogenic shock is strongly associated with increased in-hospital mortality, independent from hemodynamic and ventilatory status. Until clinical trial data are available, we suggest targeting a normal PaO2 and avoiding hyperoxia in CS patients receiving venoarterial ECMO.

Bioimpedance Analysis as Early Predictor for Clot Formation Inside a Blood-Perfused Test Chamber: Proof of Concept Using an In Vitro Test-Circuit

Clot formation inside a membrane oxygenator (MO) due to blood-to-foreign surface interaction represents a frequent complication during extracorporeal membrane oxygenation. Since current standard monitoring methods of coagulation status inside the MO fail to detect clot formation at an early stage, reliable sensors for early clot detection are in demand to reduce associated complications and adverse events. Bioimpedance analysis offers a monitoring concept by integrating sensor fibers into the MO. Herein, the feasibility of clot detection via bioimpedance analysis is evaluated. A custom-made test chamber with integrated titanium fibers acting as sensors was perfused with heparinized human whole blood in an in vitro test circuit until clot formation occurred. The clot detection capability of bioimpedance analysis was directly compared to the pressure difference across the test chamber (ΔP-TC), analogous to the measurement across MOs (ΔP-MO), the clinical gold standard for clot detection. We found that bioimpedance measurement increased significantly 8 min prior to a significant increase in ΔP-TC, indicating fulminant clot formation. Experiments without clot formation resulted in a lack of increase in bioimpedance or ΔP-TC. This study shows that clot detection via bioimpedance analysis under flow conditions in a blood-perfused test chamber is generally feasible, thus paving the way for further investigation.

Different mechanisms of oxygenator failure and high plasma von Willebrand factor antigen influence success and survival of venovenous extracorporeal membrane oxygenation

OBJECTIVE

Failure of membrane oxygenator (MO) function of venovenous extracorporeal membrane oxygenators (VV ECMO) remains problematic. The development of device-induced coagulation disorder (COD) or worsened gas transfer (WGT) necessitates a system exchange. The aim was to correlate von Willebrand factor antigen (vWF:Ag) with the predisposition to MO failure and mortality.

METHODS

Laboratory parameters (inflammation, coagulation) and ECMO-related data from 31 VV ECMO patients were analyzed before and after the first MO exchange. Study groups were identified according to the exchange reasons (COD, WGT) and the extent of vWF:Ag (low, ≤425%; high, >425%).

RESULTS

vWF:Ag remained unchanged after system exchange. High vWF:Ag was associated with systemic endothelial activation of older and obese patients with elevated SOFA score, increased norepinephrine and higher requirement of continuous renal replacement therapy without an effect on MO runtime and mortality. Including the mechanism of MO failure (COD, WGT), various patient group emerged. COD/low vWF:Ag summarized younger and less critically ill patients that benefit mainly from ECMO by a significant improvement of their inflammatory and coagulation status (CRP, D-dimers, fibrinogen) and highest survival rate (91%). Instead, WGT/high vWF:Ag presented older and more obese patients with a two-digit SOFA score, highest norepinephrine, and aggravated gas transfer. They benefited temporarily from system exchange but with worst survival (33%).

CONCLUSIONS

vWF:Ag levels alone cannot predict early MO failure and outcome in VV ECMO patients. Probably, the mechanism of clotting disorder in combination with the vWF:Ag level seems to be essential for clot formation within the MO. In addition, vWF:Ag levels allows the identification different patient populations In particular, WGT/high vWF:Ag represented a critically ill population with higher ECMO-associated mortality.

Analysis of Thrombotic Deposits in Extracorporeal Membrane Oxygenators by High-resolution Microcomputed Tomography: A Feasibility Study

Coagulative disorders, especially clotting during extracorporeal membrane oxygenation, are frequent complications. Direct visualization and analysis of deposits in membrane oxygenators using computed tomography (CT) may provide an insight into the underlying mechanisms causing thrombotic events. However, the already established multidetector CT (MDCT) method shows major limitations. Here, we demonstrate the feasibility of applying industrial micro-CT (µCT) to circumvent these restrictions. Three clinically used membrane oxygenators were investigated applying both MDCT and µCT. The scans were analyzed in terms of clot volume and local clot distribution. As validation, the clot volume was also determined from the fluid volume, which could be filled into the respective used oxygenator compared to a new device. In addition, cross-sectional CT images were compared with crosscut oxygenators. Based on the µCT findings, a morphological measure (sphericity) for assessing clot structures in membrane oxygenators is introduced. Furthermore, by comparing MDCT and µCT results, an augmentation of the MDCT method is proposed, which allows for improved clot volume determination in a clinical setting.

Oxygenator Impact on Ceftaroline in Extracorporeal Membrane Oxygenation Circuits

OBJECTIVES

To determine the oxygenator impact on alterations of ceftaroline in a contemporary neonatal/pediatric (1/4-inch) and adolescent/adult (3/8-inch) extracorporeal membrane oxygenation circuit including the Quadrox-i oxygenator (Maquet, Wayne, NJ).

DESIGN

Quarter-inch and 3/8-inch, simulated closed-loop extracorporeal membrane oxygenation circuits were prepared with a Quadrox-i pediatric and Quadrox-i adult oxygenator and blood primed. Additionally, 1/4-inch and 3/8-inch circuits were also prepared without an oxygenator in series. An one-time dose of ceftaroline was administered into the circuits, and serial pre- and postoxygenator concentrations were obtained at 5 minutes, 1-, 2-, 3-, 4-, 5-, 6-, and 24-hour time points. Ceftaroline was also maintained in a glass vial, and samples were taken from the vial at the same time periods for control purposes to assess for spontaneous drug degradation.

SETTING

A free-standing extracorporeal membrane oxygenation circuit.

PATIENTS

None.

INTERVENTION

Single dose administration of ceftaroline into closed-loop extracorporeal membrane oxygenation circuits prepared with and without an oxygenator in series with serial preoxygenator, postoxygenator, and reference samples obtained for concentration determination over a 24-hour study period.

MEASUREMENTS AND MAIN RESULTS

For the 1/4-inch circuit with an oxygenator, there was 79.8% drug loss preoxygenator and 82.5% drug loss postoxygenator at 24 hours. There was a statistically significant difference (p < 0.01) in the amount of ceftaroline remaining at 24 hours when compared with each prior time point for the 1/4-inch circuit. For the 1/4-inch circuit without an oxygenator, there was no significant drug loss at any study time point. For the 3/8-inch circuit with an oxygenator, there was 76.2% drug loss preoxygenator and 77.6% drug loss postoxygenator at 24 hours. There was a statistically significant difference (p < 0.01) in the amount of ceftaroline remaining at 24 hours when compared with each prior time point for the 3/8-inch circuit. For the 3/8-inch circuit without an oxygenator, there was no significant drug loss at any study time point. The reference ceftaroline concentrations remained relatively constant during the entire study period demonstrating the ceftaroline loss in each size of the extracorporeal membrane oxygenation circuit with or without an oxygenator was not a result of spontaneous drug degradation and primarily the result of the oxygenator.

CONCLUSIONS

This ex vivo investigation demonstrated significant ceftaroline loss within an extracorporeal membrane oxygenation circuit with an oxygenator in series with both sizes of the Quadrox-i oxygenator at 24 hours. Therapeutic concentrations of ceftaroline in the setting of extracorporeal membrane oxygenation may not be achieved with current U.S. Food and Drug Administration-recommended doses, and further evaluation is needed before specific drug dosing recommendations can be made for clinical application with extracorporeal membrane oxygenation.

An In-Vitro Study Comparing the GME Handling of Two Contemporary Oxygenators

Gaseous microemboli (GME) are a potential complication of cardiopulmonary bypass (CPB). Though it is difficult to prove that GME is the only major cause of neurological deficits, it may increase the chance of post-operative cognitive dysfunction if not removed. The objectives of this research were to compare LivaNova-Sorin Inspire (Inspire) oxygenator with a Medtronic arterial filter to the Medtronic Fusion (Fusion) oxygenator with and without a Medtronic arterial filter based on each system's ability to handle GME. The Inspire and Fusion systems were evaluated in vitro. GME handling was observed by introducing air in the sampling manifold connected to the venous return at a 60 mL bolus or 1 liter per minute (LPM). The emboli detection and classification (EDAC) system measured GME preand post-oxygenator/arterial filter. The Inspire with a filter was able to remove a statistically significant greater amount of total emboli per second during the 60 mL bolus and 1 LPM tests than the Fusion with and without an arterial filter. The Inspire with an arterial filter was more efficient in removing GME during a 60 mL bolus and 1 LPM than the Fusion and Fusion with an arterial filter. However, the Fusion with an arterial filtered performed better than the Fusion system without the arterial filter.

Use of Volatile Anesthetic Agent in Extracorporeal Circuit as a Cause of Break in Polycarbonate Connector-Lessons Learnt

Mishaps, near misses, and lethal incidents are known to occur during cardiopulmonary bypass. We share one such rare case of break in polycarbonate connector because of the use of isoflurane in extracorporeal circuit and its successful management.

A potential propensity for failure secondary to clot embolism in neonatal ECMO

Objective: To report a single case of oxygenator failure caused by clot embolism originating from the bladder; and to discuss some preventative options.

Case report: A 2.5 kg neonate with a diagnosis of influenza A received veno-arterial (V / A) extracorporeal membrane oxygenation (ECMO) for cardiorespiratory support. Halfway through treatment, she underwent an elective circuit change for numerous clots in her circuit. The patient continued to consume vast quantities of platelets and developed a fatal oxygenator failure after 18 days.

Discussion: Amongst the factors influencing the outcome in events of a sudden unexpected oxygenator failure are the severity of patient illness, the size of the clot relative to the size of the oxygenator, the availability of a previously primed circuit and the ease and speed of priming a new oxygenator.

Conclusion: There is a need for improvement in the design of small oxygenators and ECMO circuits. Adjustment of the coagulation parameters and lowering the tolerance towards clots in the circuit by electively changing them may reduce the incidence of sudden unexpected oxygenator failure. However, using a slightly larger Medos oxygenator may gain valuable time needed to arrange an oxygenator/circuit change.

Comparison of hollow-fiber membrane oxygenators in terms of pressure drop of the membranes during normothermic and hypothermic cardiopulmonary bypass in neonates

The objective of this study was to investigate the effects of two hollow-fiber membrane oxygenators, the Capiox SX10 and the Lilliput 901, on pressure drop of the membranes during normothermic and hypothermic cardiopulmonary bypass (CPB) in neonates.

Methods: Twenty-six congenital heart surgery patients (n=13 in each group) with a mean weight of 3 kg were included in this study. Pressure drops of the membranes, pre- and post-oxygenator extracorporeal circuit pressures (ECC) were recorded during normothermic CPB, hypothermic CPB (208C) and after rewarming. There were no differences between the groups in mean arterial pressure, pump flow rate, temperature, duration of CPB, cross- clamp time or the severity of the surgical repairs.

Results: Pressure drop of the Capiox SX10 oxygenator was significantly lower during normothermic (329/10 versus 559/16 mmHg, p B/0.001), hypothermic (389/15 versus 729/18 mmHg, p B/0.001) and post-rewarming (429/13 versus 729/21 mmHg, p B/0.001) periods compared to the Lilliput oxygenator. In the Capiox group, the pre-oxygenator ECC pressure was also significantly lower during normothermic CPB (1429/27 versus 1849/43 mmHg, p B/0.01), hypothermic CPB (1629/30 versus 1999/38 mmHg, p B/0.01) and after rewarming periods (1729/32 versus 2129/42 mmHg, p B/0.01). Post-oxygenator pressures in the Capiox group were also lower than in the Lilliput group, but results were not statistically significant.

Conclusions: These results suggest that the Capiox SX10 hollow-fiber membrane oxygenator produced significantly lower membrane pressure drops and pre- and post-oxygenator ECC during normothermic and hypothermic CPB. Thus, blood trauma with the Capiox during extracorporeal circulation may be significantly lower compared to the Lilliput. Further studies, including the level of complements, platelets, neutrophils and cytokines, with these oxygenators are warranted.

Performance of polymethyl pentene oxygenators for neonatal extracorporeal membrane oxygenation: a comparison with silicone membrane oxygenators

Objective: To review the performance of polymethyl pentene versus silicone oxygenators in terms of efficiency in priming and oxygenation, oxygenator resistance, requirements for coagulation proteins and consumption of blood products, for neonatal extracorporeal membrane oxygenation (ECMO) patients.

Study design: Forty consecutive neonates were selected retrospectively pre- and post-introduction of the new polymethyl pentene (PMP) oxygenators. They formed two equal groups. After calculation of the sample size, data were collected from ELSO registry forms and patient records. Results were analysed using parametric and non-parametric tests.

Results: Neonatal PMP (N-PMP) oxygenators were smaller, faster and easier to prime. They were less efficient than silicone oxygenators, especially in carbon dioxide elimination, and, therefore, required higher sweeps. The preservation of coagulation proteins was significantly better, but there was no reduction in the consumption of blood products, despite having less than half the surface area and significantly lower blood path resistance.

Conclusion: Small PMP oxygenators (Medos Hilite 800 LT) provide adequate gas exchange and offer technical advantages in terms of more efficient priming, reduced haemodynamic resistance and better control and preservation of coagulation proteins than silicone oxygenators.

Evaluation of coated oxygenators in cardiopulmonary bypass systems and their impact on neurocognitive function

Introduction: Coronary artery bypass graft surgery (CABG) using cardiopulmonary bypass (CPB) is assumed to be associated with a decline of neurocognitive functions. This study was designed to analyse the neurocognitive function of patients with coronary heart disease before and after CABG and to determine possible protective effects of oxygenator surface coating on neurological outcome.

Methods: Forty patients scheduled for selective CABG were prospectively randomized into two groups of 20 patients each according to the type of hollow-fibre membrane oxygenator used. Non-coated oxygenators (Group A) were compared to phosphorylcholine (PC)- coated oxygenators (Group B). A battery of six neurological tests was administered preoperatively, 7 - 10 days and 4 - 6 months after surgery.

Results: One patient of Group A suffered from a perioperative stroke and died on postoperative day 3, presumably because of sudden heart failure. Two patients of Group A (10%) developed a symptomatic transitory delirious psychotic syndrome (STPT) on postoperative days 3 and 5. None of the patients of Group B had perioperative complications. The test analysis revealed a trend of declined neurocognitive function early after CABG, but did not show any difference in neurocognitive outcome between the two groups.

Discussion: PC coating of the oxygenators did not show any significant benefit on neurocognitive function after CABG using CPB.

Doppler microembolic signals during cardiopulmonary bypass: Comparison of two membrane oxygenators

We undertook this study to evaluate the dependence of Doppler microembolic signal (MES) counts, detected during cardiopulmonary bypass, on the type of oxygenator used. A total of 90 patients, 71 men and 19 women, aged 60 +/- 10 years (mean +/- SD), undergoing elective cardiac surgery for coronary artery bypass grafting (one vessel, n = 6; two vessels, n = 24; three vessels, n = 33; four vessels, n = 9) or valve replacement (mitral valve, n = 2, aortic valve, n = 15, both valves, n = 1) were monitored with transcranial Doppler sonography during the complete surgical procedure. The surgical and anesthetic techniques were standardized in all patients, except for the type of membrane oxygenator used (COBE CML Duo, n = 55 or DIDECO D 703, n = 35). MES count was expressed as total number of MES detected in both middle cerebral arteries during cardiopulmonary bypass (CPB) and also as total MES number divided by the CPB duration in minutes (MES min(-1)). No significant differences in patients' age or sex and type and duration of operation were noted between the two groups. MES incidence while the patients were on cardiopulmonary bypass was 100%. MES counts during CPB were 309 (236-502) and 143 (86-233) for DIDECO and COBE oxygenators, respectively (p < 0.00001). MES min(-1) were also significantly higher in patients operated with DIDECO, as compared to COBE oxygenators (3.7 (2.4-5.6) versus 1.5 (1-2.4), respectively, p < 0.0001). Inter-observer variability was satisfactory (k = 0.72). Use of a DIDECO D 703 oxygenator resulted in significantly higher MES counts as compared to the COBE CML Duo oxygenator. The clinical relevance of this finding remains to be determined.

[Factors of intravascular hemolysis in cardiosurgical patients after cardiopulmonary bypass procedures]

The study included patients with ischemic heart disease with moderate (52 patients) and apparent (23 patients) hemolysis after coronary bypass surgery in cardiopulmonary bypass (CB). The concentration of free hemoglobin in blood plasma, mechanical resistance and sorption capacity of red cells as well as the content of TBA-active products, cholesterol and phospholipids in red cells and reticulocytes levels in blood were studied before and after operation. It was shown that among patients with apparent post-perfusion hemolysis (in contrast to the patients with a moderate hemolysis) the sorption capacity of red cells and amount of reticulocytes in blood are increased before operation; level of TBA-active products in erythrocytes is increasing after operation. Development of moderate hemolysis is associated with the decreased mechanical resistance of erythrocytes and increased cholesterol/phospholipid-ratio in membranes before operation. Thus, individually-specified apparent post-perfusion hemolysis is based on free-radical mechanism of erythrocytes damage and moderate hemoglobin level is referred to mechanical trauma of blood cells during CB.

A comparison of radiographic signs of pulmonary inflammation during ECMO between silicon and poly-methyl pentene oxygenators

INTRODUCTION

The inflammatory response caused by extracorporeal membrane oxygenation (ECMO) is clearly visible within the first 24 h of cannulation. The inflammatory process affects all areas of the lung, even areas previously spared by the primary disease.

OBJECTIVE

To compare the change in the radiographic signs of inflammatory response to ECMO between poly-methyl pentene and silicon oxygenators.

STUDY DESIGN

Retrospective review of neonates and adults pre- and post-replacement of silicon oxygenators with poly-methyl pentene devices. Data were collected from Extracorporeal Life Support Organisation (ELSO) registry forms and patient records. Results were analysed by quantitative and semi-quantitative methods.

RESULTS

There was a significant reduction in the radiographic signs of inflammatory response to ECMO, and a reduction in the time taken to revert to pre-ECMO state in the neonatal poly-methyl pentene group compared to silicon. However, there was no significant reduction in the duration of ECMO runs and the percentage survival between these groups in the neonates. In adults, there was no difference in severity of radiographic signs between groups. However, the inflammatory changes were relatively delayed in the adult poly-methyl pentene group.

CONCLUSION

Polymethyl pentene (Medos) oxygenators have reduced the host's response phenomenon 'white out' in neonates, and caused a delayed response in adults. This is most likely a consequence of smaller blood contact surface area combined with the effect of heparin coating of the oxygenator membrane. However, recovery was not a function of the type of gas exchange device used.

Effect of biopassive and bioactive surface-coatings on the hemocompatibility of membrane oxygenators

Postoperative complications associated with cardiopulmonary bypass (CPB) surgery and extracorporeal circulation (ECC) procedures are still a major clinical issue. Improving the hemocompatibility of blood contacting devices used for ECC procedures may ameliorate various postpump syndromes. In a simulated CPB model using human blood, we investigated the hemocompatibility, fibrinogen adsorption, and platelet receptor (GPIIb-IIIa) binding capacity of surface-modified membrane oxygenators (Jostra Quadrox). Three groups were compared: (i) biopassive protein coatings (SafeLine), (ii) bioactive heparin coatings (BioLine), and (iii) noncoated controls. During the 2 h recirculation period, plasma concentrations of activation markers for platelets (beta-thromboglobulin), inflammation (elastase), complement (C5a), and coagulation (prothrombin fragment 1+2, thrombin-antithrombin III) were lower in the groups with biopassive and bioactive coatings compared to the noncoated group (p < 0.01). These parameters did not significantly differ between the two surface-coated groups, except for complement activation: C5a levels were higher in the biopassive group compared to the bioactive group (p < 0.01). Moreover, surface-coated oxygenators showed less fibrinogen adsorption, GPIIb-IIIa binding, and platelet/leukocyte adhesion (p < 0.01). We assume that fewer fibrinogen and platelet receptor molecules bound to the surface-coated oxygenator surfaces results in fewer platelet adhesion and activation, which will significantly contribute to the improved hemocompatibility of the biopassive and bioactive oxygenators. Our results suggest that the application of bioactive oxygenators (BioLine) during CPB surgery may reduce postoperative complications for the patient more effectively than biopassive oxygenators (SafeLine).

Gaseous microemboli and the influence of microporous membrane oxygenators

Gaseous microemboli (GME) are still an unsolved problem of extracorporeal circuits. They are associated with organ injury during cardiopulmonary bypass. Microbubbles of different sizes and number are generated in the blood as the result of different components of the extracorporeal circuit as well as surgical maneuvers. The aim of our study was to observe the behavior of microporous membrane oxygenators to GME in the daily use and in an in vitro model. For the detection of microbubbles, we used a two-channel ultrasonic bubble counter based on 2-MHz Doppler-System with special ultrasound probes. The amount and size of GME were monitored before and after membrane. In 28 scheduled cases with 3 different oxygenators and variability of surgical procedures, we observed the bubble activity in the extracorporeal circuit. In addition, we used an in-vitro model to study the ability of six different oxygenators by removing air in various tests. The oxygenators tested were manufactured with different membrane technologies. The results of our investigations showed varying membrane design lead to a partial removal of GME as well as a change in size and numbers of microbubbles.

[Oxygenator thrombosis without heparin resistance]

A 55-year-old male with a history of positive HIV serology and Polycytemia vera underwent coronary artery bypass graft surgery with normothermic extracorporeal circulation. Following heparin administration the activated clotting time (ACT) was 633 seconds (Hemocron) with kaolin). Lower than expected arterial and venous oxygen partial pressures together with high pressure (350 mmHg) in the arterial line upstream of the oxygenator were observed. Because of these signs the oxygenator was changed during the procedure. The outcome was uneventful. Electronic microscopic examination of the oxygenator membrane and thermic exchanger revealed fibrin and platelet deposits.

A multicenter investigation into the occurrence of high-pressure excursions

The occurrence of sudden increases in premembrane pressures and membrane pressure differentials has drawn considerable attention and debate in the perfusion community. Several terms have been applied to this phenomenon, but the term that best describes this event is "high-pressure excursion" (HPE). The exact causes of HPE are still uncertain, but nonetheless widely speculated. However, their increased appearance seems to be very closely related to the removal/absence of human serum albumin from priming solutions. To investigate the reasons why HPE occur in some cardiopulmonary bypass cases, we present our findings in a multicenter, retrospective analysis of 2696 cardiopulmonary bypass cases. Of the 31 cases of HPE that were documented from the analysis, 60 preoperative and perioperative variables were gathered from the participating tertiary care centers. Our findings indicate that these pressure excursions had an occurrence of 1.14% in the three centers involved with this analysis. The largest occurrence of HPE tended to be in male (87.1%) coronary artery disease patients (96.8%) during the presence of the IV anesthetic Diprivan (74.2%). In conclusions, HPE are not perfusate related because it occurred in the presence of three perfusate combinations. They also do not seem to be oxygenator related or exclusive to hypothermic temperatures or heat exchangers.

Does priming implementation with low-dose albumin reduce postoperative bleeding following cardiopulmonary bypass?

This study aimed to assess whether low doses of albumin in the priming solution for cardiopulmonary bypass (CPB) reduce postoperative bleeding. Three-hundred and seventy-seven patients undergoing CPB were retrospectively assigned to group A (154 patients, CPB primed with 20 ml/kg Ringer Lactate solution + 0.75 mg/kg albumin 20%) and group B (223 patients with 20 ml/kg Ringer Lactate). A significant difference was found in terms of reoperations for bleeding (group A 0/154 versus group B 9/223; P=0.033). The mean number of blood derivatives transfused per patient was higher in group B than in group A (P<0.001). Platelet count after CPB was higher in group A than in group B (175 +/- 52x10(3)/microl versus 131 +/- 70x10(3)/microl; P=0.045). The amount of postoperative bleeding was 525 ml versus 680 ml at 24 hrs (P<0.001), 819 ml versus 1102 ml at 48 hrs, (P<0.001), 963 ml versus 1294 ml at 72 hrs, (P<0.045) (group A versus group B respectively). Crystalloid priming with low-dose albumin reduces postoperative bleeding.

High risk of intraoperative awareness during cardiopulmonary bypass with isoflurane administration via diffusion membrane oxygenators

In cardiac surgery with the aid of extracorporeal circulation (ECC), inhalation anaesthetics can be administered via the oxygenator. Until the recent advent of a new type of diffusion membrane oxygenator, we routinely added the inhalation agent, isoflurane, to the gas flow of a microporous capillary membrane-type oxygenator. Applying this procedure to the diffusion-type oxygenators, the depth of anaesthesia appeared to be affected, which manifested itself through unusually high intraoperative perfusion pressures. This observation led to a prospective randomized study comprising 60 patients and two models of a microporous capillary membrane oxygenator, as well as two models of a diffusion membrane oxygenator. Simultaneous isoflurane concentration measurements at both the gas inlet and outlet ports of the oxygenators showed that, whereas in the microporous capillary-type oxygenators the isoflurane administered was reduced by about 50% during the passage of gas through the device, there was only a minimal transfer of isoflurane in the diffusion-type membrane oxygenators.

Oxygenator thrombosis: worst case after development of an abnormal pressure gradient--incidence and pathway

The development of an abnormally high pressure gradient (APG) before the membrane oxygenator (MO) is a complication that occurs during some extracorporeal circulation (ECC) procedures. The present study deals with the incidence of an APG and discusses a probable causative pathway by comparing surface-coated and uncoated oxygenation systems. Five thousand six hundred and seventeen adult ECCs were carried out (2,581 without and 3,036 with surface coatings). The incidence of an APG, therefore, amounted to 0.03% in the group with coated systems and 4.3% in the uncoated group. In addition, an in vitro study demonstrated significantly reduced adhesion and activation of platelets and leucocytes when the surfaces of the MOs were coated with heparin or polypeptides. The advantages of coating surfaces of ECC devices possibly depend on the selective adsorption of particular plasma proteins. These will presumably form a biocompatible membrane on the surface, and minimize pathological deposit of fibrin, platelets and other blood cells, and, therefore, implicate the prevention of an oxygenator failure.

A clinical evaluation of platelet function, haemolysis and oxygen transfer during cardiopulmonary bypass comparing the Quantum HF-6700 to the HF-5700 hollow fibre membrane oxygenator

The continued improvement of oxygenators is an important aspect of patient safety during cardiopulmonary bypass (CPB). The purpose of this study was to compare the Bard William Harvey HF-5700 oxygenator to the upgraded Bard Quantum HF-6700, which has recently been introduced into clinical practice. No clinical evaluation of this device has been published to date. The two oxygenators differ principally in that the Quantum has a smaller priming volume, achieved at the expense of a smaller membrane surface area which could result in sub-optimal gas exchange characteristics, increased haemolysis and increased platelet dysfunction during CPB. Twenty adult patients undergoing elective, first time coronary artery bypass grafting (CABG) were randomly assigned either to the HF-5700 (n=10) or to the HF-6700 (n=10) group. One patient underwent mitral valve repair in addition to CABG and was excluded from further study. There were no statistically significant differences in either preoperative or operative parameters between the two groups. Samples were obtained at the start of CPB, at 30 min, 60 min, at the end of CPB and at 1 h following termination of CPB. No significant differences between the two groups were found in oxygen transfer, haemolysis (plasma haptoglobin levels) or platelet function (a novel platelet activating factor (PAF)-induced platelet activation test) at any of the time points during CPB. It was concluded that the Quantum HF-6700 matches the HF-5700 for the parameters studied, whilst having the advantage of requiring a smaller priming volume.

Nitric oxide added to the sweep gas infusion reduces local clotting formation in adult blood oxygenators

Nitric oxide (NO) is an inhibitor of platelet aggregation. We analyzed the effect of direct infusion of NO into adult blood oxygenators on local clot formation. Nonheparinized calves in a control group (n = 3) and NO group (n = 4) were connected to a jugulocarotid cardiopulmonary bypass (CPB; centrifugal pump) for 6 hours. The venous line and pumphead were heparin coated, whereas the oxygenator, the heat exchanger, and the arterial line were not. A total of 80 ppm of NO was mixed with the sweep gas infusion in the NO group. The pressure gradient through the oxygenator (delta<gd>P.Ox.) was monitored, and its evolution was compared between groups. Oxygenators membranes were analyzed and photographed, allowing for calculation of the percentage of surface area covered with clots by using a computer image analysis program. The delta<gd>P.Ox. reached a plateau of 193 +/- 26% of the basal value in the NO group after 120 minutes, whereas a similar plateau of 202 +/- 22% was reached after only 20 minutes in the control group (p < 0.05). The surface area of the oxygenator covered with clots was significantly reduced in the NO group (0.54 +/- 0.41%) compared with the control group (5.78 +/- 3.80%, p < 0.05). However, general coagulation parameters were not modified by local NO administration. The activated coagulation time remained stable between 110 and 150 seconds in both groups (p = not significant [ns]), and there were no differences in hematocrit, thrombin time, partial thromboplastin time, or fibrinogen between groups during the 6 hours of CPB. Thus, the mixed infusion of a continuous low dose of NO into adult oxygenators during prolonged CPB prevented local clot formation, whereas the general coagulation pattern remained unchanged.

Nitric oxide donors attenuate increase in pressure drop across membrane oxygenators

We have evaluated the effect of nitric oxide (NO) on the pressure drop across a membrane oxygenator in one in vitro model and two in vivo models (using four dogs and five pigs). In all the experiments sodium nitroprusside (SNP) was used as a NO source, whereas gaseous NO was only used in the in vitro model. The drugs were given when the pressure drop or resistance across the device increased to at least twice the baseline values. In the in vitro model, both SNP and gaseous NO decreased the pressure drop to 75% of its peak value after 10 min and to 67% after 20 min. In the dog model, resistance decreased from 390 to 153 mmHg/l/min after 5 min and to 85 mmHg/l/min after 20 min for a baseline value of 75 mmHg/l/min. The initial resistance across the membrane oxygenator in the pig model increased from 6.6+/-1.3 to 74+/-38 mmHg/l/min. An infusion of 10 microg/kg/min SNP reduced the resistance to 16+/-5 mmHg/l/min.

Effect of surface coating on platelet count drop during cardiopulmonary bypass

This study was designed to investigate the effect of surface coating on platelet count drop during cardiopulmonary bypass (CPB). Sixty patients undergoing open-heart surgery were randomly divided into three groups each receiving a different type of coated hollow-fiber membrane oxygenator. The patients were given either an uncoated oxygenator (noncoated group), an oxygenator coated with Carmeda (Carmeda group) or an uncoated oxygenator with albumin in the priming solution (albumin group). Comparisons were made in platelet count pre-CPB, on bypass (15-25 min) and during the warming period. Calculations were used to account for the effect of hemodilution. The albumin group had significantly lower platelet count drops (-4.8+/-7.1%) than the Carmeda group (11.0+/-8.3%) and the noncoated group (20.3+/-14.5%). Carmeda surface coating demonstrated some beneficial effects, but to a lesser degree than the albumin.

The proposed use of a 'screening test' to assess oxygenator performance

This study aimed to assess whether the use of the physiological shunt equation could (within the first five minutes of initiating CPB) serve as a 'screen' to differentiate normal and dysfunctional oxygenator performance. If dysfunction severe enough to require replacement was necessary, the normothermic patient could be weaned from CPB and replacement would be carried out under safe, controlled conditions. This technique would require postponing the induction of hypothermia (if used), aortic cross-clamping, and arresting the heart until after this screen was completed. This study demonstrates that a strong negative correlation exists between the degree of blood shunting and the membrane's 0 2 transfer performance (r = -0.874). This relation enables us to predict 0 2 transfer performance when only the shunt fraction is known. Of the 41 oxygenators used in this study, 40 demonstrated normal, or below-normal, shunt fractions. Oxygen transfer performance at or above predicted levels would be anticipated for these oxygenators. One of the 41 oxygenators had mildly elevated shunt fractions, which we predicted would be associated with mild 0 2 transfer dysfunction. Based on the performance screen worksheet we created, replacement was not necessary since the oxygenator maintained high levels of 0 2 transfer in reserve despite its marginal performance dysfunction. Assessment of oxygenator performance dysfunction in this earliest phase of CPB would greatly reduce the incidence of emergency oxygenator replacement secondary to actual or perceived oxygenator failure later in the course of the procedure.

A new heparin-bonded dense membrane lung combined with minimal systemic heparinization prolonged extracorporeal lung assist in goats

Heparin was covalently bonded to a new hollow-fiber dense membrane artificial lung and extracorporeal circuit using a silane coupling agent and polyethyleneimine. This study investigated whether prolonged, venoarterial bypass extracorporeal lung assist (V-A bypass ECLA) could be sustained in a goat by the combination of the new membrane lung and minimal systemic heparinization. We maintained ECLA with the hollow-fiber lungs (surface area, 0.8 m2) and circuits by titrating the activated clotting time (ACT) to below 150 s with minimal systemic heparinization in 5 goats. The outcome was assessed from the function of the artificial lung via macro and microscopic examinations after the experiments and the incidence of systemic complications. The 5 goats were maintained on ECLA for 6 to 27 days. The bypass flow rate, blood gases at the return and drainage sites, platelet counts, and platelet aggregation activity were well maintained. Although the hemoglobin concentration, hematocrit, and plasma protein at the start of the ECLA were significantly lower than the pre-ECLA values due to hemodilution, the values remained stable during ECLA. A cerebral infarction occurred in 1 goat. However, in the other 4 goats, no complications such as bleeding, thrombosis, or plasma leakage from the artificial lung were observed. Although several thrombi were observed in the stagnant area of the artificial lung, these local thrombi did not cause the function of the artificial lung to deteriorate. We found that this new type of highly biocompatible, dense membrane artificial lung, when combined with minimal systemic heparinization, prolonged ECLA without the deterioration of the artificial lung function and was suitable for prolonged ECLA.

Protein adsorption and platelet adhesion on the surface of an oxygenator membrane

Platelet adhesion on an oxygenator membrane is associated with thrombocytopenia or thrombus formation during extracorporeal circulation. The authors evaluated protein adsorption and platelet adhesion on three oxygenator hollow fiber membranes fabricated with polypropylene, silicone, and double layer polyolefin. Adsorbed proteins were analyzed by bicinchoninic acid protein assay, sodium dodecyl sulfate polyacrylamide gel electrophoresis, and Western blot. Platelet adhesion was assessed with enzyme immunoassays using monoclonal antibodies directed against CD42b and CD61. After 3 hr of incubation at 37 degrees C in whole blood, the amount of adsorbed protein was the least on silicone and increased from silicone < double polyolefin < polypropylene. The adsorbed protein pattern was similar; however, silicone showed less adsorption for all protein bands, and the gamma chain of fibrinogen was not detected. In contrast, double polyolefin showed the highest fibrinogen adsorption. The optical density at a wavelength of 450 nm for CD42b was 1.47 +/- 0.35 in polypropylene, 1.16 +/- 0.38 in silicone, and 1.85 +/- 0.19 in double polyolefin (p < 0.01 vs silicone) and for CD61 0.98 +/- 0.39 in polypropylene, 0.91 +/- 0.22 in silicone, and 1.69 +/- 0.25 in double polyolefin (p < 0.01 vs silicone and polypropylene). These data suggest that silicone is advantageous for long term extracorporeal respiratory support in terms of less platelet adhesion and no plasma leakage through the pores.

A newly developed silicone-coated membrane oxygenator for long-term cardiopulmonary bypass and cardiac support

The surface of polypropylene hollow fiber was successfully coated with a very thin (0.2 micron) silicone layer. Experimental studies were performed in long-term (6 h) normothermic cardiopulmonary bypass (CPB) using 10 goats. A conventional membrane oxygenator (Mera Excelung HPO-15H, MERA, Tokyo, Japan) was used for 5 goats as a control (Group C) and a new silicone-coated membrane oxygenator, which is of the same construction as that of the one used for Group C, for 5 (Group S). The O2 transfer and CO2 removal functions showed the same ranges. In the other parameters, there were no differences between the 2 groups. As for hemolysis, however, the plasma free hemoglobin of Group S was lower than that of Group C. Currently, 3 chronic percutaneous cardiopulmonary support (PCPS) experimental models have been conducted, and there has been no evidence of thromboembolism or deterioration of the oxygenator. In conclusion, this new oxygenator is suitable not only for CPB, but also for long-term cardiac support.

A comparison of gaseous emboli release in five membrane oxygenators

The purpose of this study was to compare the air handling capability of five currently used membrane oxygenators: the Avecor Affinity, the Bentley SpiralGold, the Medtronic Maxima Plus, the Sarns Turbo and the Sorin Monolyth M. A circuit was constructed to include a hardshell venous reservoir and roller pump. Pressure monitoring sites and ultrasonic microbubble detection probes were located proximal and distal to the oxygenator. An air injection/infusion site was provided proximal to the roller pump inlet. Each circuit was primed with fresh anticoagulated bovine blood, adjusted to a haematocrit of 25% and maintained at 38 +/- 1 degree C. Three different bolus amounts of air (10, 20 and 40 cm3) were injected at three blood flow rates (3, 4.5 and 6 l/min). A 1-min infusion of air delivered at 1 ml/s was also administered at three blood flow rates (3, 4.5 and 6 l/min). The hardshell reservoir was also completely emptied at each flow rate to simulate a massive air infusion. At any given blood flow, outlet microbubble counts were usually higher with greater bolus amounts of air. When indexed to the inlet bubble counts, the following average percent microbubbles were released from the outlet: Turbo 25%, Affinity 7%, Monolyth 5%, Maxima 3% and SpiralGold 1%. With a constant air infusion of 1 ml/s, greater outlet microbubble counts were associated with higher blood flow rates. Again, when indexed to the inlet bubble counts, the following average percent microbubbles were released from the outlet: Turbo 44%, Affinity 25%, Maxima 19%, Monolyth 16% and SpiralGold 0%. All oxygenators deprimed when the hardshell reservoir was emptied and all shed microbubbles into the outlet blood except the SpiralGold. The results of this study indicate that air handling is not a simple function of blood flow pattern (i.e. top to bottom versus bottom to top), but also includes dynamics associated with oxygenator design, fibre arrangement and flow resistance.

Potential problem when using the new lower-prime hollow-fibre membrane oxygenators with uncoated stainless steel heat exchangers

A prospective study was conducted to evaluate the trans-oxygenator pressure gradient across three different hollow-fibre membrane oxygenators during routine cardiopulmonary bypass (CPB). Sixty consecutive open-heart surgery patients were randomly divided into three groups each receiving a different model of membrane oxygenator. Inlet and outlet pressures, as well as patients' pressures, blood flow, revolutions per minute and tympanic membrane temperature were recorded every 15 min during CPB. Within the study groups, there were subsets of patients who exhibited high trans-oxygenator pressures. Although most of these episodes were transient and resolved over a period of time, there were several cases during which the high trans-membrane pressures persisted, resulting in decreasing oxygenator performance. In one such case, oxygenator change-out was required. After extensive analysis and review, the only similarities or correlation that could be made were with the marriage of the newer lower-prime hollow-fibre membrane oxygenators (with corresponding narrow blood path) and the integral uncoated stainless steel heat exchangers. Further study needs to be performed to pinpoint the mechanism and pathophysiology that are involved in this phenomenon.

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.

Platelet and neutrophil distributions in pump oxygenator circuits. III. Influence of nitric oxide gas infusion

The authors used quantitative gamma scintigraphy to evaluate the influence of nitric oxide gas on platelet and neutrophil deposition in Cobe Duo microporous oxygenators during cardiopulmonary bypass (CPB). The effects of nitric oxide gas on circulating platelet and neutrophil counts and platelet function also were assessed. Animals were prepared by standard methods. Cells were harvested, labeled (111 In platelet and 99mTc neutrophil), infused, and recirculated. Nitric oxide gas, a guanylate cyclase pathway promoter, was infused int he Duo gas port at 500 ppm (t = 0-60 min), increased to 1,000 (t = 60-80 min), and stopped (final, 10 min). Images were taken at 10-15 min intervals during CPB. Standard isotope image corrections were made. No differences between nitric oxide gas and control experiments were observed for flow, pressure, hematocrit, or replacement volume. Nitric oxide gas infusion significantly (p < 0.05) reduced both platelet adherence to the oxygenator and in vitro platelet aggregation. Neutrophil adhesion tended to be lower, and circulating platelet and neutrophil counts tended to be higher with nitric oxide gas infusion. Results of in vitro aggregometry studies using rabbit platelets indicate that the class V phosphodiesterase inhibitor zaprinast can strongly enhance the inhibitory effects of nitric oxide. The authors conclude nitric oxide gas is a promising platelet sparing agent in the setting of CPB.

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.

Inhibition of surface-induced platelet activation by nitric oxide

This study was undertaken to determine whether the nitric oxide/platelet cyclic guanosine monophosphate (NO/cGMP) pathway might be used to reduce platelet activation by artificial surfaces. Because serotonin release (SR) is a platelet activation indicator, rabbit platelets in their own plasma (PRP) were labeled with 3H-serotonin. Labeled PRP was incubated with glass beads for 5-10 min, at 37 degrees C with gentle agitation, and SR was measured. PRP pretreatment with NO gas or nitroprusside + N-acetylcysteine inhibited SR 50%. Dose response studies indicate the existence of an optimal NO concentration above which its inhibitory effect is diminished. The guanylate cyclase inhibitor methylene blue attenuates the NO effect, implicating cGMP in NO mediated inhibition of surface induced platelet activation. Adult pigs were supported on a membrane oxygenator in an in vitro model of cardiopulmonary bypass (CPB). Introduction of NO gas into the oxygenator sweep gas at 500 ppm reduced platelet adherence to the oxygenator surfaces, increased circulating platelet counts, and decreased the rate of platelet aggregation (whole blood impedance platelet aggregometry) compared with the results of the control animals. Indications of NO toxicity were seen when the NO flow rate was increased to 1,000 ppm. These studies support the hypothesis that NO reduces platelet activation by artificial surfaces in clinical devices.

Intravenacaval membrane oxygenation and carbon dioxide removal in severe acute respiratory failure

STUDY OBJECTIVE

To characterize the physiologic response to, and safety of, intravenacaval membrane oxygenation and carbon dioxide removal.

DESIGN

Interventional before-after study.

SETTING

University teaching hospital ICU.

PATIENTS

Twenty-two patients with severe acute respiratory distress syndrome (ARDS).

INTERVENTIONS

Implantation of a hollow-fiber membrane oxygenator (IVOX; CardioPulmonics; Salt Lake City, Utah) into the superior and inferior venae cavae by venotomy of the right femoral or right internal jugular vein for a duration of up to 20 days.

MEASUREMENTS

Hemodynamic measurements using pulmonary artery and systemic artery catheters, ventilator settings (FIO2, minute ventilation, peak inspiratory pressure, and positive end-expiratory pressure), arterial and mixed venous blood gases (pH, PCO2, PO2, and measured saturation), and clinical laboratory determinations (CBC, fibrinogen, plasma hemoglobin, complement C3 and C5) were obtained. Calculations of PaO2/FIO2 ratio and PaCO2-VE product were used to assess gas exchange efficacy. Microbiologic cultures were obtained from the device and wound following explantation. Survival to ICU discharge and hospital discharge were recorded.

RESULTS

Implantation was successful in 20 of 22 patients. Gas exchange rates averaged 50.4 +/- 15.8 mL.min-1 for carbon dioxide and 71.1 +/- 20.2 mL.min-1 for oxygen. A reduction in FIO2 from 0.78 +/- 0.16 to 0.63 +/- 0.21 and in VE from 177 +/- 94 mL.kg-1.min-1 to 127 +/- 58 mL.kg-1.min-1 was possible within 4 h post-implantation. By 12 h, FIO2 was reduced to 0.57 +/- 0.18. Indices of gas exchange improved significantly after implantation, with PaO2/FIO2 ratio increasing from 79 +/- 20 to 112 +/- 47 and PaCO2-VE product decreasing from 7.6 +/- 4.2 to 4.9 +/- 2.5 within 4 h. A significant reduction in peak inspiratory pressure was achieved (45 +/- 10 to 38 +/- 9 cm H2O). Major complications were blood loss during implantation requiring transfusion in 11 patients, a retroperitoneal bleed in 1 patient, and femoral deep venous thrombosis in 4 patients, but there were no long-term sequelae or IVOX-related deaths. The ICU and hospital survival were 10/20 (50%) and 8/20 (40%), respectively.

CONCLUSIONS

Intravenacaval membrane oxygen and carbon dioxide removal can provide partial respiratory support during severe respiratory failure and permit reductions in the level of mechanical ventilator support, with an acceptable safety profile.

Clinical comparison of blood oxygenators: a retrospective study

The results for platelet count (PC), activated clotting time (ACT), postoperative bleeding, and hemoderivatives usage in cardiac surgeries were crossed against the type of oxygenator used. These were two bubble and one membrane type. A sample of the surgery population for each type was selected at random. Thus, the patients in this study were divided into 3 groups: BA: 87 patients, bubble oxygenator; BB: 87 patients, bubble oxygenator; M: 73 patients, membrane oxygenator. The groups were statistically similar (p > 0.05) for age, body surface area, cardiopulmonary bypass (CPB) time, and prevalence of cardiac disease. The rate of PC 15 min after CPB end and before its beginning was BA, 0.48 +/- 0.02; BB, 0.49 +/- 0.02; M, 0.55 +/- 0.03. The rate of ACT after protamine administration and before CPB was BA, 1.22 +/- 0.03; BB, 1.16 +/- 0.03; M, 1.16 +/- 0.03. Volume (ml) of total postoperative bleeding (POB) was BA, 904 +/- 72; BB, 963 +/- 73; M, 867 +/- 83. Patient percentage that used hemoderivatives (HD) was BA, 86.3%; BB, 88.5%; M, 90.0%. No statistical difference was found between groups (p > 0.05). This study indicates that although membrane oxygenators have better theoretic and experimental biocompatibility, no significant difference in PC, ACT, POB, and HD usage was observed in the clinical setting. All values are expressed as the mean +/- standard error of the mean.

Development of an intra blood circuit membrane oxygenator

This paper deals with development of a prototype intra blood circuit membrane oxygenator. The shell of the oxygenator is made of a flexible polyvinyl chloride tube. The membrane surface area of the oxygenator is 0.3 m2. The total blood priming volume, including the oxygenator, was only 400-600 ml, which allows for extracorporeal circulation with no additional blood. Its potential was evaluated in in vitro experiments. The oxygen transfer rate was 140 ml/min, and the carbon dioxide transfer rate was 85 ml/min at a blood flow rate of 3 l/min. The device could make blood circuits simpler and more compact, with lower priming volumes. This indicates that it may prove useful for extracorporeal circulation.

Membrane versus bubble oxygenator in hyperthermic regional perfusion: a prospective randomized clinical study

In a prospective randomized clinical study a routinely used bubble oxygenator (Bentley-5) was compared with a hollow fiber membrane oxygenator (D 701 Masterflo 34) during hyperthermic isolated extremity perfusion. This was done to find out whether there were differences between the two oxygenators in hemolysis, cellular damage, oxygenation and temperature achieved during extremity perfusion. In 30 perfusions blood samples were obtained at defined times: plasma hemoglobin (Hb), serum lactate dehydrogenase (s-LDH), number of erythrocytes, mean corpuscular volume (MCV), hemoglobin and bilirubin were determined for hemolysis, leukocyte count (neutrophils, lymphocytes, monocytes) and platelets as a check for cellular damage, and PO2, PCO2, O2 saturation and pH to define blood oxygenation and CO2 elimination. Maximal increase in temperature after 30 min and perfusion time until maximum tissue temperature were also recorded. The membrane oxygenator yielded better results from the aspect of hemolysis: s-LDH and plasma Hb were significantly different (p < 0.001). Cellular damage was less with the membrane oxygenator: platelet differences were significant (p < 0.01). Oxygenation and hyperthermia were obtained more quickly and were better controllable in membrane oxygenator. Further advantages for the patient were the smaller volume of blood needed for priming in a membrane oxygenator (750 vs. 1,200 ml) and improved safety resulting from a 'closed' perfusion system. On the basis of the clinical prospective randomized trial conducted, we conclude that membrane oxygenators must be adopted as the new standard in isolated hyperthermic extremity perfusion.

Comparison of gaseous microemboli counts in arterial, simultaneous and venous heat exchange with a hollow fiber membrane oxygenator

Potential sources of gaseous microemboli during cardiopulmonary bypass are varied. However, it is known that membrane oxygenators generate fewer gaseous microemboli than bubble oxygenators and that bubblers cannot utilize arterial heat exchange without generating significant gaseous microemboli during rewarming. A membrane oxygenator utilizing simultaneous gas and heat exchange raises the concern that concurrent gas and heat exchange would result in a higher production of gaseous microemboli compared to conventional venous heat exchange devices. This in vitro study compared venous, simultaneous, arterial and control (venous) heat exchanger gaseous microemboli counts during rewarming. No significant difference was found between the four heat exchangers when comparing inlet and outlet gaseous microemboli counts. This in vitro study suggests that there is no difference in gaseous microemboli generation when varying the position of the heat exchanger in the extracorporeal circuit incorporating a microporous membrane oxygenator.

Time-course of free radical activity during coronary artery operations with cardiopulmonary bypass

Myocardial and pulmonary impairment after cardiopulmonary bypass may be caused by oxygen free radicals produced by reperfusion and by activated neutrophils. Free radical activity was assessed by assays for lipid peroxidation (thiobarbituric acid-reactive material) and phospholipid-esterified diene conjugation (18:2[9,11]/18:2[9,12] molar ratio) in 25 patients during coronary artery operations. Arterial blood samples were obtained before, during the ischemic period, and for 24 hours thereafter. There were no significant changes in free radical indices during the ischemic periods, but after cessation of bypass they increased significantly. Ten minutes after bypass thiobarbituric acid-reactive material rose from 96 (median; range 65 to 145) nmol/gm albumin to 138 (85 to 200) nmol/gm albumin (p < 0.001), and molar ratio rose from 2.23% (0.45% to 7.70%) to 2.51% (0.39% to 7.93%) (p < 0.02). Values of thiobarbituric acid-reactive material subsequently decreased, but molar ratio reached a peak at 4 hours after bypass, 2.64% (0.55% to 10.08%) (p < 0.001), thereafter returning to baseline. The postoperative increases in thiobarbituric acid-reactive material and in molar ratio were correlated (r = +0.53; p = 0.006). These increases in thiobarbituric acid-reactive material and in molar ratio were not related to age, preoperative left ventricular function, or the number of grafts performed. Increase in thiobarbituric acid-reactive material correlated with the duration of cardiopulmonary bypass (r = +0.43; p = 0.03). In 10 patients in whom cardiopulmonary bypass was performed using a bubble oxygenator, the increases in thiobarbituric acid-reactive material were significantly greater than in the 15 in whom a membrane oxygenator was used (p < 0.02). These data show that after apparently uncomplicated coronary operations with bypass there is an increase in lipid peroxidation and diene conjugation, indicating increased free radical activity. This increase varies between patients and does not relate to patient or surgical factors but may depend on the type of oxygenator employed during bypass.