Technical aspects of extracorporeal ultrafiltration: mechanisms, monitoring and dedicated technology.

Fluid overload may occur in patients with heart failure. Further complications may arise when cardiorenal syndromes develop and the kidneys are unable to eliminate the accumulated fluid. Diuretics represent the fist line of treatment, although in some case they may be ineffective or even dangerous for the patient. In these conditions, extracorporeal ultrafiltration may be required. Extracorporeal ultrafiltration can be performed continuously or intermittently, using dedicated machines. The goal is to remove the right amount of fluid without causing hemodynamic instability or further ischemia to the kidneys. For this purpose, special technologies are available and they can be utilized in combination to prevent iatrogenic complications. First of all, a complete analysis of heart and kidney function should be carried out. Then, an evaluation of biomarkers of heart failure and a careful analysis of body fluid composition by bioimpedance vector analysis should be carried out to establish the level of hydration and to guide fluid removal strategies. Last but not least, an adequate extracorporeal technique should be employed to remove excess fluid. Preference should be given to continuous forms of ultrafiltration (slow continuous ultrafiltration, continuous venovenous hemofiltration); these techniques guided by a continuous monitoring of circulating blood volume allow for an adequate restoration of body fluid composition minimizing hemodynamic complications and worsening of renal function especially during episodes of acute decompensated heart failure.