since continuous haemofiltration ( hf ) was first described by kramer as a new form of renal replacement therapy , it has undergone many changes , making it a widely accepted treatment modality for acute renal failure in critically ill patients . concomitantly , new insights into the pathogenesis of severe sepsis and septic shock recently led to new forms of immunomodulatory therapy for septic shock . a number of clinical trials investigating the effect of antiendotoxin or anticytokine interventions were unable to demonstrate a consistent improvement in survival of patients with sepsis or septic shock . another possible immunotherapy is removal of various inflammatory substances , including endotoxin , cytokines , oxygen - free radicals and arachidonic acid metabolites , by hf . in this issue of critical care ratanarat and coworkers report the results of an observational study in patients with septic shock who were treated with ' pulse high volume hemofiltration ' . ratanarat and colleagues utilized a hf rate of 85 ml / kg per hour for 68 hours , followed by a more conventional rate of 35 ml / kg per hour . it is indeed now accepted that 35 ml / kg per hour should be used in patients with acute renal failure who are treated with hf . bearing in mind that removal of the so - called ' middle molecules ' is a convective process , grootendorst opted to apply much higher volumes of ultrafiltration ( uf ) . grooten - dorst and coworkers   introduced the concept of high - volume haemofiltration ( hvhf ) in a pig endotoxin model , in which they demonstrated improvement in haemodynamics in the study animals as compared with controls . moreover , infusion of the ultrafiltrate from the endotoxic animals into healthy ones induced the same symptoms as in the endotoxic group . in another study hvhf started before the mesenteric artery was clamped significantly diminished bowel damage and prevented haemodynamic deterioration . these studies established that convective removal of septic mediators can be performed when sufficiently high uf rates are applied . a similar improvement in haemodynamics was found , and some even reported an increase in survival [ 7 - 9 ] . in one study , different uf rates were compared in a clinically representative model of severe pancreatitis in pigs . hvhf at a rate of 100 ml / kg per hour was better than low - volume hf . frequent filter change , allowing more adsorption of cytokines , was also better than no change . several studies have examined the effects of hvhf in patients . in one study   hvhf was performed during cardiopulmonary bypass in children undergoing cardiac surgery , which resulted in a blunted inflammatory response , reduction in postoperative blood loss and improved oxygenation . in a prospective cohort analysis , in which 306 critically ill patients with acute renal failure were treated with an uf rate of 3.8 l / hour , the observed survival rates were significantly better than predicted . in a small trial of 11 patients with shock and multiple organ dysfunction syndrome the authors compared an uf rate of 1 l / hour with 6 l / hour using a crossover design . hvhf resulted in a significant reduction in vasopressor requirements and a greater reduction in levels of complement 3 and 5 . in another study conducted in 20 patients with refractory septic shock , honor and coworkers   gave a 4-hour treatment with hvhf , followed by conventional continuous venovenous haemofiltration . eleven patients responded to the treatment with increases in cardiac index , venous oxygen saturation and arterial ph , and a decrease in norepinephrine requirement . of these responders , nine out of eleven survived to 28 days ; all of the nonresponders died . ratanarat and coworkers   show that hvhf , following its birth as a theoretical concept and subsequent experimental research in animals , is progressing toward the bedside of our critically ill patients . this modality is feasible with modern hf machines and the available fluids , and can be performed without major side effects . it is increasingly accepted that the ' renal dose ' of hf is not the same as the ' septic dose ' . we must define those patient populations that may require this form of treatment and those that can be treated with more conventional renal replacement therapy . despite initial scepticism , we are beginning to learn that hf for severe sepsis and septic shock is more than bloodletting , 21st century style .
in the past decade we have learned a lot about the pathophysiology of septic shock . 
 a lot of experimental research has been performed in vitro and in vivo , showing that hemofiltration can improve hemodynamics and survival . with modern machines 
 , hemofiltration is becoming a sepsis treatment in patients .