Selective Fibrinogen Apheresis for Improvement in Microvascular Hemodynamics

vascular stores with the intravascular compartment, followed by a slower rate of resynthesis. Twenty-four hours after treatment, fibrinogen levels are 50% of initial levels, while it may require 72 h or more to attain levels which are 75% of pretreatment values [5] . When multiple treatments are performed over a short period (i.e. three or more treatments per week), the depletion is more pronounced and may require several days for spontaneous recovery [2–5] . Thus, given the relatively short half-life of fibrinogen (approximately 4 days), it would appear that maintaining a time-averaged reduction in the plasma fibrinogen level, and, in so doing, maintaining the beneficial effects on the microvascular circulation, one would have to perform repetitive treatments over a prolonged period of time. Such an experience was documented in a previous report on this selective apheresis technique. In that publication, Koll et al. [6] demonstrated that repeated fibrinogen apheresis could maintain a time averaged fibrinogen level at about 200 mg/dl in patients whose pretreatment values were approximately 325 mg/dl. This time-averaged reduction was maintained over the course of 12 consecutive treatments. Unfortunately, the publication did not report on the scheduling of the 12 treatments (i.e. daily, weekly, or some other schedule). Thus, given the available evidence, one must conclude that in order to maintain the improved microvascular hemodynamics brought about by this procedure one would require repetitive treatments performed on a continuous basis. In this issue of Blood Purification , Ramunni’s group [1] reports on the short-term effects of fibrinogen apheresis in patients with peripheral arterial disease. Their study was designed to elucidate the immediate post-treatment effect of an abrupt reduction in fibrinogen on the hemodynamics of the lower extremities. The basic concept of the procedure is that fibrinogen is a major determinant of whole blood viscosity and that an apheresis procedure designed to rapidly lower the fibrinogen concentration would improve the flow dynamics of the microcirculation. The symptomatic improvement was impressive, with both total and pain-free walking distance increasing significantly (pain-free WD 60 8 52 vs. 173 8 76 m, p ! 0.003; total WD 79 8 60 vs. 194 8 80 m, p ! 0.006). These results are certainly noteworthy, but how long would these effects last? The data presented in this paper do not answer that question, but several previously reported data would allow one to make a reasonable prediction. When albumin is used as the replacement fluid during standard, nonselective plasma exchange there is a depletion of fibrinogen [2–5] . Immediately after a single plasma exchange, fibrinogen will be decreased by approximately 60%. Rebound of the fibrinogen level is biphasic, characterized by a rapid initial increase in the first 4 h after treatment, followed by a slower increase over the next few days [2] . This dual rate of recovery probably represents a relatively rapid initial re-equilibration of extraPublished online: September 28, 2007