Evaluation of a range of extracorporeal membrane oxygenators

Design Optimization of a Phototherapy Extracorporeal Membrane Oxygenator for Treating Carbon Monoxide Poisoning

We designed a photo-ECMO device to speed up the rate of carbon monoxide (CO) removal by using visible light to dissociate CO from hemoglobin (Hb). Using computational fluid dynamics, fillets of different radii (5 cm and 10 cm) were applied to the square shape of a photo-ECMO device to reduce stagnant blood flow regions and increase the treated blood volume while being constrained by full light penetration. The blood flow at different flow rates and the thermal load imposed by forty external light sources at 623 nm were modeled using the Navier-Stokes and convection-diffusion equations. The particle residence times were also analyzed to determine the time the blood remained in the device. There was a reduction in the blood flow stagnation as the fillet radii increased. The maximum temperature change for all the geometries was below 4 °C. The optimized device with a fillet radius of 5 cm and a blood priming volume of up to 208 cm3 should decrease the time needed to treat CO poisoning without exceeding the critical threshold for protein denaturation. This technology has the potential to decrease the time for CO removal when treating patients with CO poisoning and pulmonary gas exchange inhibition.

Oxygen transfer performance of a new Sarns membrane oxygenator

Oxygen transfer performance of the SMO 2, a new hollow-fibre membrane oxygenator from Sarns/3M, was evaluated. The maximum oxygen transfer of the SMO 2 (504 ml 0 2/min) was 57% higher than that for the SMO. This was true even though the membrane surface area increased by only 11% (1.8 m 2 to 2.0 m 2). The average gas phase-arterial oxygen gradient and the average shunt fraction was decreased by 35% and 30% respectively. The diffusing capacity of the SMO 2 was increased by 74% over the SMO. The oxygen transfer performance compared favourably, not only to the SMO, but to five other previously evaluated membrane oxygenators. It performed better in each category regardless of whether the result was expressed in absolute terms or relative to membrane surface area.

Can an oxygenator design potentially contribute to air embolism in cardiopulmonary bypass? A novel method for the determination of the air removal capabilities of neonatal membrane oxygenators

At present, air handling of a membrane oxygenator is generally studied by using an ultrasonic sound bubble counter. However, this is not a quantitative method and it does not give any information on where air was entrapped in the oxygenator and if it eventually was removed through the membrane for gas exchange. The study presented here gives a novel technique for the determination of the air-handling characteristics of a membrane oxygenator. The study aimed at defining not only the amount of air released by the oxygenator, but also the amount of air trapped within the oxygenator and/or removed through the gas exchange membrane. Two neonatal membrane oxygenators without the use of an arterial filter were investigated: the Polystan Microsafe and the Dideco Lilliput. Although the air trap function of both oxygenators when challenged with a bolus of air was similar, the Microsafe obtained this effect mainly by capturing the air in the heat exchanger compartment while the Lilliput did remove a large amount of air through the membrane. In conclusion, the difference in trap function was most striking during continuous infusion of air. Immediate contact with a microporous membrane, avoidance of high velocities within the oxygenator, pressure drop, transit time and construction of the fibre mat all contribute to the air-handling characteristics of a membrane oxygenator.

Clinical evaluation of a new generation membrane oxygenator: a prospective randomized study

A new generation hollow-fibre membrane oxygenator (Spiral Gold) has been introduced by Baxter Healthcare (Irvine, CA, USA). The purpose of this study was to evaluate the operational performance of this device under clinical conditions and to compare it to the Univox Gold membrane oxygenator. Following institutional review board approval, and the obtainment of informed consent, 26 patients undergoing coronary artery bypass grafting were randomly assigned to either a Spiral Gold (Spiral) (n = 13) or Univox Gold (Univox) (n = 13) group. Study parameters were grouped into the following categories: haematological, haemodynamic, oxygenator performance and perioperative outcomes. All patients received identical surgical, anaesthesia and postoperative care. There were no statistically significant differences in either preoperative or operative parameters between groups. During cardiopulmonary bypass, the Spiral group had a significantly lower pressure drop (26.9 +/- 8.2 vs 46.7 +/- 16.2 mmHg, p < 0.001). The Spiral group had significantly lower plasma free haemoglobin levels during all time periods of CPB compared to the Univox group. Heat exchange coefficients were higher during the rewarming period in the Spiral patients (0.59 +/- 0.28) compared to the Univox group (0.36 +/- 0.19), p = 0.06. There were no differences in oxygen transfer between groups, but ventilation gas sweep rates and FiO2 levels were statistically lower in the Spiral group at two of the three sampling time periods. The ratio of ventilating gas sweep rate to blood flow rate was lower in the Spiral group (0.56 +/- 0.12) compared to the Univox group (0.74 +/- 0.23), p < 0.03. The Spiral Gold oxygenator had superior oxygen transfer efficiency and lower haemolysis rates than the Univox Gold oxygenator.

Air trapping ability of the Spiral Gold membrane oxygenator: an ex vivo study

Despite an overall improvement in cardiopulmonary bypass (CPB) technology and materials, air emboli still occur. The latest generation membrane oxygenator from Bentley Laboratories, the SpiralGold, was tested ex vivo for its air handling ability. The study was conducted on four calves. Bolus amounts of air of 10, 15 and 20 cm3 were each injected three times, upstream of the oxygenator and a bubble detector located directly downstream. The amount of bubbles was measured semiquantitatively on a 10 unit scale (U one semiquantitative unit). The animals were killed 10 days after the CPB. When 10 cm3 of air was injected, no bubbles were detected. With 15 and 20 cm3, respectively, 1 +/- 1.5 and 5 +/- 3.3 U of bubbles were detected. Despite a total of 135 cm3 of air injected as large bolus amounts, all the animals survived without any obvious neurological deficit secondary to air bubble manipulation. In conclusion, the SpiralGold oxygenator per se can reliably trap an air bolus of up to 10 cm3. This feature should be taken into account when choosing an oxygenator, as it offers an additional barrier to air bubbles in the CPB circuit.

Clinical evaluation of the oxygenation capacity and controllability of 15 commercially available membrane oxygenators during alpha-stat regulated hypothermic cardiopulmonary bypass

Oxygenation performance was tested in 15 membrane oxygenators by calculating the resistance for oxygenation (R) and the calculation of oxygen transferred versus FiO2. The clinical data reveal that the SARNS Turbo 440 (36.7-51.9%), the AFFINITY (37.2-50.1%) and the HF 5400 (37.5-52.3%) are the oxygenators with the lowest FiO2 settings for comparable amounts of oxygen transferred during hypothermia and during normothermia followed by MAXIMA Plus (39.1-55.8%), MAXIMA Plus PRF (39.1-56.2%), CAPIOX SX 18 (39.7-61.2%), MONOLYTH (43.0-61.3%), OXIM 11-34 (44.1-63.9%), COBE Duo (44.7-64.9%), COBE Optima (47.4-66.4%), COMPACTFLO (48.3-65.3%), SAFE II (49.0-67.6%), UNIVOX (49.8-71.3%), MAXIMA (50.2-70.1%) and the CM 50 (58.6-77.0%). Similar results were found by calculation of R. HF 5400 (2.41-1.87 mmHg/min/ml O2), AFFINITY (2.63-1.87 mmHg/min/ml O2). OXIM II-34 (2.72-2.45 mmHg/min/ml O2), MAXIMA Plus PRF (2.75-2.07 mmHg/min/ ml O2), COBE Optima (2.83-2.13 mmHg/min/ml O2), UNIVOX (2.84-2.17 mmHg/min/ml O2), MONOLYTH (2.89-2.24 mmHg/min/ml O2), SARNS Turbo 440 (3.03-2.12 mmHg/min/ml O2), MAXIMA Plus (3.09-2.28 mmHg/min/ml O2), SAFE 11 (3.19-2.50 mmHg/min/ml O2), CAPIOX SX 18 (3.27-2.44 mmHg/ min/ml O2), COMPACTFLO (3.41-2.50 mmHg/min/ml O2), MAXIMA (3.53-2.72 mmHg/min/ml O2), COBE Duo (3.57-2.71 mmHg/min/ml O2) and the CM 50 (3.53-2.72 mmHg/min/ml O2). As a measure of controllability of oxygenation, the coefficient of variation on the FiO2 ordered on the normothermic blood samples was used, giving as a result CAPIOX SX 18 (2.9-2.5%), AFFINITY (3.6-3.5%), COBE Duo (4.3-2.9%), HF 5400 (5.7-4.7%), MAXIMA Plus (8.1-5.4%), COMPACTFLO (8.2-5.0%), MONOLYTH (8.3-4.0%), MAXIMA (8.7-3.4%), COBE Optima (9.6-6.8%), SARNS Turbo 440 (10.1-7.3%), MAXIMA Plus PRF (10.9-8.7%), CM 50 (11.9-2.4%), UNIVOX (13.3-8.9%), OXIM 11-34 (15.5-17.3%) and the SAFE II (16.1-9.8%). The low FiO2 settings and the lower resistance for oxygenation are an indication of the reserve capacity of the oxygenators whose importance is proven by clinical data of emergency perfusions on patients under full resuscitation.

Air handling characteristics of five membrane oxygenators

This project looked at the potential of five different membrane oxygenators to allow passage of catastrophic quantities of air in a clinically simulated environment. All the oxygenators were set up in an identical circuit using heparinized human blood as the perfusate. The study was carried out at flow rates ranging from 1.0 to 6.0 l/min. The clinical situation of obstructed venous drainage was simulated by clamping the venous return line at each respective flow rate, while the initial level of blood in the open system hard shell venous reservoir was maintained at 600 ml. The time interval between the application of the clamp on the venous line and the first appearance of macroscopic air in the arterial line was recorded at each level of flow rate. A graph of time versus flow rate was plotted for each oxygenator type. At a flow rate of 6 l/min, the Safe II oxygenator took 20 seconds to allow passage of air after the venous line was clamped, while it took the Bentley Univox Oxygenator only 10 seconds. The Dideco oxygenator, which has a valve incorporated in its reservoir, did not, however, allow any air to be pumped forward at all. At low rates, some of the oxygenators offered protection against passage of air into the arterial line. Thus the Cobe oxygenator offered protection at flow rates of less than 2 l/min, the Safe II oxygenator at flow rates of up to 2.5 l/min and the Bard oxygenator at flow rates up to 3 l/min.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical evaluation of a new hollow fibre membrane oxygenator

Twelve consecutive patients undergoing elective cardiac surgery were perfused with the Cobe Optima hollow fibre oxygenator. Gas transfer characteristics and blood handling were studied. The device had a maximum oxygen transfer of 315 ml/minute. The average shunt fraction was 4.5%, and was not influenced by blood-flow rate. Mean platelet count declined slightly to 91% of the baseline at the end of the study period. Haemolysis was evaluated by monitoring serum-free haemoglobin, serum haptoglobin and serum haemopexin. The evolution was as follows: free haemoglobin increased from 14 +/- 5 mg/100 ml to 85 +/- 0.8/100 ml (p = 0.01) at the end of bypass; haptoglobin decreased from 1.33 +/- 0.90 g/l to 0.89 +/- 0.15 g/l (p = 0.01); and haemopexin decreased from 0.84 +/- 0.13 g/l to 0.74 +/- 0.15 g/l (p = nonsignificant). In all patients the residual capacity of serum haptoglobin to protect against haemolysis was satisfactory. All patients had an uneventful postoperative course.