Extracorporeal Applications of Active Carbons

Hemoadsorption, or hemoperfusion (HP) was introduced by H. Yatzidis in early 1960s [1]. It is an extracorporeal technique that cleanses blood by passing it through an adsorbent column. Active carbon (AC) was the first choice due to its undisputable superiority as an adsorbent over other materials. Although the initial results were very successful, this procedure induced a series of complications, the most severe being the release of fine particles from the carbon granules causing blockage of blood microvessels [2]. The solution was found in coating of adsorbent granules with a haemocompatible semi-permeable membrane [3]. Required biocompatibility thus was achieved, but at the cost of the adsorbent performance. Adsorption of high molecular weight solutes is particularly affected. A 3-5 μ thick membrane virtually cuts off HMW molecules and significantly reduces adsorption of "middle molecules" with MW between 300 and 15,000 [4]. Initially this was not recognized as the major drawback as the main application of HP remained in the treatment of acute poisoning, usually with low MW substances. Commercial haemoperfusion columns contain charcoal produced from peat or pitch and coated with cellulose (Adsorba 300 C and Adsorba 150C, Gambro), polyHEMA (Hemosorba, Asahi Medical and Nextron Medical Technologies), or heparin hydrogel (Clark R&D) [5-7]. As many small molecules are strongly protein-bound in the blood, usually with serum albumin, MW 67 kDa, they cannot cross the coating membrane; hence, haemoperfusion over coated adsorbents would be efficient in removing only protein-free solutes of low MW.