Trends, Advantages and Disadvantages in Combined Extracorporeal Lung and Kidney Support From a Technical Point of View

Abstract

Extracorporeal membrane oxygenation (ECMO) provides pulmonary and/or cardiac support for critically ill patients. Due to their diseases, they are at high risk of developing acute kidney injury. In that case, continuous renal replacement therapy (CRRT) is applied to provide renal support and fluid management. The ECMO and CRRT circuits can be combined by an integrated or parallel approach. So far, all methods used for combined extracorporeal lung and kidney support present serious drawbacks. This includes not only high risks of circuit related complications such as bleeding, thrombus formation, and hemolysis, but also increase in technical workload and health care costs. In this sense, the development of a novel optimized artificial lung device with integrated renal support could offer important treatment benefits. Therefore, we conducted a review to provide technical background on existing techniques for extracorporeal lung and kidney support and give insight on important aspects to be addressed in the development of this novel highly integrated artificial lung device.

Keywords: artificial kidney; artificial lung; artificial organ; continuous RRT; extracorporeal life support; kidney insufficiency; veno-venous ECMO.

Figure 1

The lungs and the kidneys cross-talk mechanism of renal compensation to pulmonary acidosis and pulmonary compensation to metabolic acidosis as explained by Sorino et al. (20).

Figure 2

Scheme representing a simplified VV-ECMO circuit, providing partial to complete pulmonary support in severe respiratory failure. On the right side, a diagram represents the main components of the circuit (light blue boxes) connected to the patient (dark blue box). The flow of oxygenated blood is represented by a red line and deoxygenated blood by a blue line.

Figure 3

Typical partial pressures of oxygen (pO₂) and carbon dioxide (pCO₂) in the lung's alveoli, in deoxygenated blood and oxygenated blood. In addition, typical operating conditions and partial pressure of gases as driving force for gas exchange in the core of oxygenators (55, 56).

Figure 4

The renal replacement therapy circuit while providing continuous hemodialysis, continuous hemofiltration, and continuous hemodiafiltration. Replacement fluid can be delivered before or after the hemofilter.

Figure 5

Solute clearance in renal replacement therapy can be achieved by diffusion or convection. In diffusion-based methods (hemodialysis), solutes move down their concentration gradient from the bloodstream to a dialysate solution. Methods based on convection (hemofiltration) apply a pressure gradient (ΔP) to force solutes and fluid flow across the filter.

Figure 6

CRRT and extracorporeal membrane oxygenation ECMO connected to the patient by two independent circuits. The ECMO and CRRT machines are connected to the patient via separate vascular accesses.

Figure 7

(Top left) (A) In-line connection of a hemofilter to the ECMO circuit. The hemofilter is connected to the high-pressure part of the ECMO circuit after the blood pump or post oxygenator. (Top right) (B) Connection of a CRRT machine to the ECMO circuit with a roller pump. The inlet of the CRRT circuit is connected to the ECMO circuit before the pump and CRRT outlet is returned before the pump and ECMO bladder or directly to the bladder. (Bottom left) (C) Connection of a CRRT machine to the ECMO circuit with a centrifugal pump. The inlet access of the CRRT machine is connected to the high-pressure line of the ECMO circuit and the CRRT outlet is returned before the pump. (Bottom right) (D) Connecting the CRRT machine to the ECMO circuit via existing access points pre-oxygenator and post-oxygenator.

Figure 8

The iLA oxygenator (Xenios) offers CRRT connectors for simultaneous lungs and extracorporeal renal replacement therapy without the need of additional vascular access. The CRRT circuit is connected to the iLA system by the use of a inlet and outlet CRRT connector with the assistance of blood clamps. Modified from the ILA membrane ventilator (Xenios) procedure description (59).

Figure 9

Lung and kidney support provided by parallel CRRT and ECMO circuits. Scheme represents possible circuit derived complications including risks of hemolysis, bleeding, and thrombus formation.

Figure 10

Possible challenges related to the development of an extracorporeal lung and kidney support device may include the configuration which oxygenation and hemofiltration fiber will be combined, the filtration mode, and future device miniaturization.

Figure 11

Design of the modified iLA membrane oxygenator combining 50% of oxygenation and 50% of hemofiltration fiber (112).