New horizons (Baltimore, Md.)
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The evolution of renal replacement therapy has permitted the treatment of critically ill patients with acute renal failure. In intensive care settings, continuous renal replacement therapies have been shown to be better tolerated and clinically useful. Continuous hemofiltration is now performed with blood pumps and double-lumen venous catheters, thus avoiding the complications found in previous arteriovenous treatments. ⋯ Continuous therapies are today moving toward newer indications and applications. The ability to remove proinflammatory substances by filtration and/or adsorption has opened a series of potential indications. The concept that renal support and protection take place during hemofiltration suggests that very early use of this technique is desirable, even before the onset of oliguria or azotemia.
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Despite the often multifactorial nature of renal insults in critically ill patients, inadequate renal blood flow (RBF) is common and frequently causes a reduction in the glomerular filtration rate (GFR). Renal autoregulation acts to maintain both the RBF and GFR constant across a broad range of renal perfusion pressure (RPP) levels; however, the lower limit of this range (approximately 80 mm Hg for RBF, and 10-15 mm Hg higher for GFR) is often above the RPP achieved in critically ill patients. Furthermore, renal autoregulation is often lost, resulting in a linear pressure-flow relationship in the "at-risk" kidney. ⋯ Preliminary data, using nitric oxide (NO.) synthase inhibitors to augment blood pressure, showed a detrimental effect on renal perfusion, perhaps due to the central role of NO. in the normal vasoregulation of the kidney. Dopaminergic agonists have been commonly used as renal vasodilators; however, their actions are complex and include a proximal tubular diuretic effect, renal vasodilation, and systemic hemodynamic effects. Their specific action to increase RBF and GFR has not been demonstrated in clinically relevant studies and no prospective randomized study has shown a reduction in the incidence of renal impairment or acute renal failure.
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Continuous hemofiltration was first described as a new form of renal replacement for critically ill patients in the late 1970s. Since then, it has undergone remarkable technical and conceptual modifications and has become a widely used form of dialytic therapy in the ICU. More recent insights into the pathogenesis of sepsis and the role of soluble molecules in the mediation of organ injury during septic shock have led to a resurgence of the concept of blood purification during life-threatening infection. ⋯ Experimental studies have shown that continuous hemofiltration has beneficial hemodynamic effects in septic animals and that such effects may correlate with the intensity of ultrafiltration. Cardiac function also appears to improve and myocardial depressant factors are removed from the circulation. Continuous hemofiltration offers some promise as an adjunctive form of treatment in severe sepsis.