A critical step in the successful management of heart failure is the recognition and control of fluid retention. Disease progression is often associated with a decline in renal perfusion, and hence a decline in the response to diuretic therapy. The decrease in effective circulatory blood volume lowers the glomerular filtration rate, neurohumoral factor release increases, and the kidneys avidly reabsorb sodium and water, causing fluid retention and systemic congestion. In particular, angiotensin II, which controls glomerular and proximal tubule function, plays a central role in both the physiology of sodium reabsorption and the pathophysiology of fluid retention. Retention impairs the mechanics and function of liver, gut, and lungs, decreases exercise capacity, and worsens symptoms. The vicious circle can be broken by the use of angiotensin-converting enzyme inhibitors and loop diuretics, which delay progression and improve prognosis. However, some patients fail to improve, or suffer rapid recurrence despite optimal medical therapy, requiring repeated or prolonged hospitalization. Mechanical renal replacement therapies, such as hemodialysis, ultrafiltration, and hemofiltration, have recently been proposed to control fluid retention in the presence of progressive drug resistance.
Hemodialysis is used in severe renal impairment and is based on a diffusion mechanism that draws off large amounts of hypertonic fluid and catabolites, restoring blood volume with a “physiologic” isotonic solution. Ultrafiltration employs a convection mechanism that slowly removes isotonic fluid from circulating blood; the hydrostatic and oncotic pressure gradient determined by the plasma protein concentration increases between the intravascular and interstitial compartments, resulting in the reabsorption of interstitial fluid (refilling). Hemofiltration combines hemodialysis and ultrafiltration, removing both electrolytes (dialysis) and water (ultrafiltration). The choice of technique is dictated by clinical parameters, including the amount of fluid that needs to be removed (Table).
management; ultrafiltration; fluid retention; diuretic; hemodialysis; hemofiltration; refractory heart failure