Has Extracorporeal Gas Exchange Performance Reached Its Peak?

Extracorporeal gas exchange therapies evolved considerably within the first three-four decades of their appearance, and have since reached a mature stage, where minor alterations and discrete fine-tuning might offer some incremental improvement. A different approach is introduced here, making use of modern, purely diffusive membrane materials, and taking advantage of the elevated concentration gradient ensuing from gas pressure buildup in the gas chamber of the oxygenator. An assortment of silicone membrane gas exchangers were tested in vitro as per a modified protocol in pursuance of assessing their gas exchange efficiency under both regular and high-pressure aeration conditions. The findings point to a stark performance gain when pressurization of the gas compartment is involved; a 40% rise above atmospheric pressure elevates oxygen transfer rate (OTR) by nearly 30%. Carbon dioxide transfer rate (CTR) does not benefit as much from this principle, yet it retains a competitive edge when higher gas flow/blood flow ratios are employed. Moreover, implementation of purely diffusive membranes warrants a bubble-free circulation. Further optimization of the introduced method ought to pave the way for in vivo animal trials, which in turn may potentially unveil new realms of gas exchange performance for therapies associated with extracorporeal circulation.

A new approach towards extracorporeal gas exchange and first in vitro results.

OBJECTIVES: Extracorporeal life support (ECLS) pertains to therapeutic and prophylactic techniques utilized in a wide range of medical applications, with severe pulmonary diseases being the most prominent cases. Over the past decades, little progress has been made in advancing the basic principles and properties of gas exchangers. Here, in an unconventional approach, dialysis hollow fibers are handled with silicone to create a purely diffusive coating that prevents plasma leakage and promotes gas exchange. METHODS: Commercial dialyzers of varying surface area and fiber diameter have been coated with silicone, to determine the impact of each parameter on performance. The impermeability of the silicone layer has been validated by pressurization and imaging methods. SEM images have revealed a homogeneous silicone film coating the lumen of the capillaries, while fluid dynamic investigations have confirmed its purely diffusive nature. RESULTS: The hemodynamic behavior and the gas exchange efficiency of the silicone-coated prototypes have been investigated in vitro with porcine blood under various operating conditions. Their performance has been found to be similar to that of a commercial PMP oxygenator. CONCLUSIONS: This novel class of gas exchangers is characterized by high versatility and expeditious manufacturing. Intraoperability between conventional ECLS systems and dialysis machines broadens the range of application infinitely. Ultimately, long-term clinical applicability ought to be determined over in vivo animal investigations.

In vitro evaluation of the performance of an oxygenator depending on the non-standard gas content of the inlet blood with special regard on CO2 elimination.

INTRODUCTION: The performance of an oxygenator, as found in literature, is evaluated according to protocols that define standard values of the gas content in the inlet blood. However, when dealing with simulations of lung insufficiency, a more extensive evaluation is needed. This work aims to investigate and assess the gas exchange performance of an oxygenator for different input values of gas content in blood. METHODS: Three commercially available oxygenators with different membrane surfaces were investigated in a mock loop for three blood flow rates (0.5l/min, 1l/min, and 5l/min) and two gas-to-blood ratios (1:1, and 15:1). The initial CO2 and O2 partial pressures (pCO2 and pO2) in blood were set to ≥ 100 mmHg and ≤10 mmHg, respectively. For each ratio, the efficiency, defined as the ratio between the difference of pressure inlet and outlet and the inlet pCO2 (pCO2(i)), was calculated. RESULTS: The CO2 elimination in an oxygenator was higher for higher pCO2(i). While for a pCO2(i) of 100 mmHg, an oxygenator eliminated 80 mmHg, the same oxygenator at the same conditions eliminated 5 mmHg CO2 when pCO2(i) was 10 mmHg. The efficiency of the oxygenator decreased from 76,9% to 49,5%. For simulation reasons, the relation between the pCO2(i) and outlet (pCO2(o)) for each oxygenator at different blood and gas flows, was described as an exponential formula. CONCLUSION: The performance of an oxygenator in terms of CO2 elimination depends not only on the blood and gas flow, but also on the initial pCO2 value. This dependence is crucial for simulation studies in the future.

Oxygenation performance assessment of an artificial lung in different central anatomic configurations.

OBJECTIVES: Aim of this work was to characterize possible central anatomical configurations in which a future artificial lung (AL) could be connected, in terms of oxygenation performance. METHODS: Pulmonary and systemic circulations were simulated using a numerical and an in vitro approach. The in vitro simulation was carried out in a mock loop in three phases: (1) normal lung, (2) pulmonary shunt (50% and 100%), and (3) oxygenator support in three anatomical configurations: right atrium-pulmonary artery (RA-PA), pulmonary artery-left atrium (PA-LA), and aorta-left atrium (Ao-LA). The numerical simulation was performed for the oxygenator support phase. The oxygen saturation (SO2) of the arterial blood was plotted over time for two percentages of pulmonary shunt and three blood flow rates through the oxygenator. RESULTS: During the pulmonary shunt phase, SO2 reached a steady state value (of 68% for a 50% shunt and of nearly 0% for a 100% shunt) 20 min after the shunt was set. During the oxygenator support phase, physiological values of SO2 were reached for RA-PA and PA-LA, in case of a 50% pulmonary shunt. For the same conditions, Ao-LA could reach a maximum SO2 of nearly 60%. Numerical results were congruous to the in vitro simulation ones. CONCLUSIONS: Both in vitro and numerical simulations were able to properly characterize oxygenation properties of a future AL depending on its placement. Different anatomical configurations perform differently in terms of oxygenation. Right to right and right to left connections perform better than left to left ones.

Quantification of dissolved H2 and continuous monitoring of hydrogen-rich water for haemodialysis applications: An experimental study.

The prevalence of oxidative and inflammatory stress in end-stage renal disease (ESRD) patients has often been associated with chronic haemodialysis therapies. Over the past decades, several reports have shown the potential of hydrogen molecule as an antioxidant in the treatment of various medical conditions in animal models, as well as in pilot studies with human patients. Recently, a hydrogen-enriched dialysate solution has been introduced, holding promise in reducing the oxidative and/or inflammatory complications arising during haemodialysis. To this end, a standardised measuring method to determine the levels of hydrogen in dialysate and subsequently in blood is required. This study explores the possibility of quantifying hydrogen concentration using a novel contactless sensor that detects dissolved hydrogen in liquids. An experimental circuit is assembled to validate the sensitivity and accuracy of the hydrogen monitoring system (Pureron Japan Co., Ltd) through in vitro investigations with physiological solutions. Measurements of dissolved molecular hydrogen concentration are corroborated by an established oxygen sensor providing continuous partial pressure readings. The relationship between the applied H2 content in the gaseous mixture and the H2 concentration value at equilibrium is linear. At the same time, the hydrogen monitoring system has a rather long response time, and its readings seem to slightly diverge from sensor to sensor as well as at different temperatures. For this reason, a sensor recalibration might be necessary, which could become part of the product's ongoing development. Nevertheless, the aforementioned minor deficiencies can be mostly considered negligible in applications such as haemodialysis.

The course of hematocrit value along the length of a dialyzer's fiber: Hemoconcentration modeling and validation methods.

OBJECTIVES: Contemporary therapies for chronic kidney disease patients encompass a wide range of hemodialysis treatments, most of which rely greatly on dialyzers and hemofilters. The filtration process taking place in these devices with respect to the hemodynamic characteristics of the flow, has not yet been fully investigated. This study aims at improving the understanding of hemodynamics in a dialyzer by employing experimental methods and mathematical models. METHODS: A semiempirical model has been formulated based on the principles of hemodynamics, considering the dominant phenomena of filtration-backfiltration and the corresponding driving forces. An in vitro hemodialysis circuit was accordingly assembled for experimental data acquisition, and subsequently for model validation. The circuit consisted of two dialyzers arranged in sequential order, in pursuance of increasing the number of sampling points. Fresh, heparinized porcine blood was used throughout the course of this study. Pressure and flow data obtained from in vitro investigations with the hemodialysis circuit were used as an input for the semiempirical model. FINDINGS: The model predicted a substantial divergence in the course of hematocrit value along the length of the hollow fibers, which is corroborated by the experimental data. Particularly in certain operational conditions, hematocrit rose from 25% at the inlet to 65% halfway along the dialyzers' length, to end at 30% at the outlet. CONCLUSION: Validation of the model's predictions with experimental data demonstrated a very good agreement, confirming the model's accuracy. Potential implementation of the model in clinical practice in the future might contribute greatly to an improved hemodialysis experience.