Efficient CO2 removal using extracorporeal lung and renal assist device

Dialoxygenation: A Preclinical Trial for Transforming the Artificial Kidney Into an Oxygenator

Critically ill patients sometimes require tandem application of extracorporeal membrane oxygenation (ECMO) and continuous renal replacement therapy (CRRT) which is easier and cheaper. We aimed to transform the kidney membrane into a lung membrane by adding hydrogen peroxide (H 2 O 2 ) to the dialysate as the oxygen source. A solution containing H 2 O 2 and a dialysate fluid mixture was used as the final dialysate. Starting with 100% H 2 O 2 solution and gradually reducing the volume of H 2 O 2 , respectively: 50%, 10%, 5%, 4%, 3%, 2%, and 1%. PRISMAFLEX system, Prismaflex M60 set and a bag of packed red blood cells (pRBCs) were the prototype. blood flow rate was about 40 ml/minute and the dialysis rate was about 200 ml/m 2 /minute/1.73 m 2 . blood sampling times were; at the beginning ( T0 ), at 15th ( T1 ), 30th ( T2 ), 60th ( T3 ) minutes. Amongst eight attempts H 2 O 2 concentration that increased the partial oxygen pressure (pO 2 ) level significantly in a reasonable period, without any bubbles, was 3%. Methemoglobinemia was not observed in any trial. After the test with 3%, H 2 O 2 in the dialysate fluid decreased progressively without any H 2 O 2 detection at post-membrane blood. Three percent H 2 O 2 solution is sufficient and safe for oxygenation in CRRT systems. With this new oxy-dialysate solution, both pulmonary and renal replacement can be possible viaa single membrane in a simpler manner.

A mock circulation loop to test extracorporeal CO2 elimination setups

Background

Extracorporeal carbon dioxide removal (ECCO₂R) is a promising yet limited researched therapy for hypercapnic respiratory failure in acute respiratory distress syndrome and exacerbated chronic obstructive pulmonary disease. Herein, we describe a new mock circuit that enables experimental ECCO₂R research without animal models. In a second step, we use this model to investigate three experimental scenarios of ECCO₂R: (I) the influence of hemoglobin concentration on CO₂ removal. (II) a potentially portable ECCO₂R that uses air instead of oxygen, (III) a low-flow ECCO₂R that achieves effective CO₂ clearance by recirculation and acidification of the limited blood volume of a small dual lumen cannula (such as a dialysis catheter).

Results

With the presented ECCO₂R mock, CO₂ removal rates comparable to previous studies were obtained. The mock works with either fresh porcine blood or diluted expired human packed red blood cells. However, fresh porcine blood was preferred because of better handling and availability. In the second step of this work, hemoglobin concentration was identified as an important factor for CO₂ removal. In the second scenario, an air-driven ECCO₂R setup showed only a slightly lower CO₂ wash-out than the same setup with pure oxygen as sweep gas. In the last scenario, the low-flow ECCO₂R, the blood flow at the test membrane lung was successfully raised with a recirculation channel without the need to increase cannula flow. Low recirculation ratios resulted in increased efficiency, while high recirculation ratios caused slightly reduced CO₂ removal rates. Acidification of the CO₂ depleted blood in the recirculation channel caused an increase in CO₂ removal rate.

Conclusions

We demonstrate a simple and cost effective, yet powerful, “in-vitro” ECCO₂R model that can be used as an alternative to animal experiments for many research scenarios. Moreover, in our approach parameters such as hemoglobin level can be modified more easily than in animal models.

Oxygen delivery to the blood stream by the dialysis fluid during continuous renal replacement therapy ex vivo

Continuous renal replacement therapy (CRRT) maintains a balance in body water and electrolytes. CRRT supplies a higher quantity of fluid than intravenous fluid therapy along with simultaneous fluid withdrawal. We hypothesized that use of a high-oxygen-containing solution for high-volume fluid exchange would improve oxygenation in the blood during CRRT. To start with, we prepared a solution containing high oxygen. The objective of this study was to determine if this solution would increase the partial pressure of oxygen (pO₂) in the blood more than that using a conventional solution during CRRT. We compared the gas profile of the experimental fluid ex vivo in a simulated CRRT for 24 h, using 2-L batches of bovine blood. A significant increase in the pO₂, pH, and total oxygen delivery, and a significant decrease in the partial pressure of carbon dioxide (pCO₂) were estimated in the bovine blood using the experimental solution during the simulated CRRT. This method is simpler to apply for oxygenation than the conventional method, and will be beneficial to hypoxic patients in terms of improving their blood oxygenation during CRRT.