Vascular Access in Continous Renal Replacement therapy Essay

Vascular Access in Continous Renal Replacement therapy - Essay Example 24). CRRT uses diffusion (haemodialysis), convection (haemofiltration) or combines these two methods (heamodiafiltration) in order to achieve solute removal from the blood. Small molecular weight substances like potassium, urea and creatinine are efficiently removed through haemodialysis (Kellum, Mehta, Angus, Palevsky and Ronco, 2002, p.1858). For larger solute molecules, heamofiltration is the most efficient method of their removal in comparison with dialysis. In haemofiltration, filtration of plasma through the semi-permeable membrane is caused by hydrostatic pressure. In addition, solutes cross the membrane alongside the plasma which results in convective solute transport flowing in the same direction as water (Medve, Preda and Gondos, 2010, p. 104). Therefore, haemofiltration needs the use of replacement fluid to avert excessive removal of fluid, electrolyte depletion as well as iatrogenic acidosis. Since the plasma solute concentration is the same as that of the removed filtrat e, concentration of the solutes in the blood plasma remaining need to be diluted using substitution fluid. The use of combined convective and diffusive clearance as well as haemofiltration is effective for removal of large and small molecular weight solutes (Joannidis and Oudemans-van Straaten, 2007, p. 219). Modalities The several modalities of CRRT available are continuous veno-venous haemodiafiltration (CVVHDF), continuous veno-venous haemofiltration (CVVH) and continuous veno-venous haemofiltration (CVVHD). In terms of solute clearance rate, CRRT is lower in comparison with IHD (Intermittent haemodialysis treatments). However, balance clearance within the 24 hr period that CRRT is undertaken is much higher. Moreover, fluid elimination during CRRT is much slower and requires continuous use of anticoagulants which risks bleeding (Uchino, Bellomo, Morimatsu, Morgera, et al. 2007, p. 1567). Continuous veno-venous haemodiafiltration (CVVHDF) There is counter-flow of blood and dialysi s solution within the dialysis filter Blood flows at a speed of between 100 and 200ml/min Dialysis solution speed is between 1 and 2 l/h Optimisation of the ultrafiltration speed is dictated by convective transport of dissolved substances and volume loss. The removal of solutes is done simultaneously by both diffusion and convection Substitution fluid is used to replace lost fluid Continuous veno-venous haemofiltration (CVVH) Removal of solutes occurs via convective transport Ultrafiltrate which is produced must be replaced using a substitution solution Removal of ultrafiltrate may cause patient’s volume loss Continuous veno-venous haemofiltration (CVVHD) There is counter-flow of blood and dialysis solution within the dialysis filter Blood flows at a speed of between 100 and 200ml/min Dialysis solution speed is between 1 and 2 l/h The administration of fluid is not routine Solute removal occurs through diffusion Principles and Indications Membrane characteristics must be cons idered when choosing treatment modalities of CRRT. These characteristics include; biocompatibility, solute removal and water permeability (Fall and Szerlip, 2010, p. 583). In general, efficiency of small molecules in CRRT is largely depended on