Membranas en el fracaso renal agudo / Membranes in acute renal failure

RESUMEN

Las membranas de diálisis con las mejores propiedades biológicas deben ser biocompatibles, capaces de excluir las impurezas del baño de diálisis y tener grandes poros que permitan la eliminación de sustancias lo más parecido al riñón nativo sano, con pérdida casi nula de albúmina o moléculas de mayor tamaño. Los dializadores que mejor se ajustan a estas características son los dializadores de alto flujo o de alta permeabilidad. En la elección de la membrana de diálisis para el tratamiento del FRA se deben tener en cuenta la biocompatibilidad y la permeabilidad a pequeños solutos y a solutos de tamaño mediano-grande

ABSTRACT

When choosing the appropriate dialysis membrane in the acute setting, both biocompatibility and permeability should be considered. The parameters used when selecting a filter for acute dialysis are small solute removal, middle/large solute removal, and biocompatibility. With respect to small solute removal, membrane pore characteristics (pore size distribution and density) and surface area are important membrane-related determinants. Membrane characteristics define biocompatibility, although other factors, such as disinfectants may influence. Unlike in chronic hemodialysis, in which leukopenia and complement activation are well-accepted indicators of poor biocompatibility (i.e. bioincompatibility), the markers of inflammation in critically ill patients with acute renal failure are less clearly defined. In critical patients with acute renal failure activation of several inflammatory pathways preclude clear evaluation of the independent contribution of membrane biocompatibility. However, it has been demonstrated that in patients with acute renal failure, the use of cuprophan membranes can lead to complement activation and lipoxygenase stimulation. Despite initial studies demonstrated lower mortality with the use of biocompatible membranes in acute renal failure, subsequent studies casted doubts on these earlier findings. Most studies were undepowered and had randomization problems. Current evidence does not allow to recommend the unrestricted use of biocompatible membranes. However, bioincompatible membranes (grade B) and unsubstituted cellulose membranes (grade A) should be avoided. With respect to permeability, each membrane has intrinsic permeability characteristic that allow their classification according to their water and solute permeability. With respect to water permeability, membranes are classified according the ultrafiltration coefficient (CUF) expressed as mL/h/mmHg (ultrafiltered mL per hour per each mmHg of transmembrane pressure). Low permeability membranes are those with a CUF lower than 12 mL/h/mm Hg and high permeability membranes those with a CUF higher than 20 mL/h/mm Hg. With respect to solute permeability, membranes should resemble the native kidney, with a cut-off for albumin. Solute permeability is expressed by the sieving coefficient. Currently, it is not possible to recommend permeability characteristics for dislyzer membranes in the treatment of acute renal failure. However, it is plausible to recommend medium-high permeability membranes (grade C). The decision will be influenced by the dialysis modality in each particular patient