The Evolution of Biocompatibility: From Microinflammation to Microvesiscles

Haemodialysis (HD) is a life-saving treatment for patients with chronic kidney disease (CKD) stage 5. CKD persists as a chronic worldwide epidemic and HD is the more frequently (70%) adopted treatment modality. Exponential growth trend continues on a global scale. The HD population becomes every year increasingly older (average age: 75 yrs) and sicker due to the associated co-morbidities such as cardiovascular disease (heart failure, coronary heart disease, and peripheral vascular disease), diabetes, hypertension, and peripheral vascular disease. Most of the complications associated with HD involve the cardiovascular system (Go et al., 2004; Culleton et al., 1999, Goodkin et al., 2003, Foley 2004; Barret, 2002). The evolution in the history of HD technology has greatly helped to make the HD procedure a safe and more biocompatible extracorporeal therapy. However, it must be admitted that despite significant improvements in HD technology and in the management of patients due to a better understanding of uremia toxicity, improvements in dialysis technology, better correction of anaemia and metabolic abnormalities, implementation of best practice guidelines, no significant improvement has been achieved in patient survival over the last decade (Rayner et al., 2004). The extracorporeal circuit offers a large surface of contact of the blood with foreign materials, namely the dialysis membrane, the tubings and the large volumes of the dialysate. The concept of biocompatibility has greatly evolved in the last two decades. Initially, numerous studies focused on the blood-dialyzer membrane interaction, leading to the activation of plasma systems (complement, coagulation, fibrinolysis). These studies helped in the understanding of some unknown effects occurring in the early stages of the HD session leading to pulmonary sequestration of leukocytes (mainly neutrophils) that explained the profound neutropenia associated with the cuproammonium membranes. The availability of reliable testing of complement-activated