Mechanism of action for the Hemosep device
The Hemosep device relies upon two main elements for its primary function of concentrating blood cells from haemodiluted media. These components are the control membrane and the superabsorber, the other elements of the device are designed to simply contain the blood prior to and during processing and to contain plasma removed from the blood product. In use haemodiluted blood is transferred via the suction tool into the blood reservoir and then pumped into the Hemosep device.
The blood is separated from a superabsorber pad by a control membrane with a pore size which prevents the migration of cellular species from the blood into the superabsorber section of the device. Free passage of the plasma however is not restricted and as this fluid passes from the blood through the membrane into the superabsorber, it results in a concentration of the cellular components of the blood held within the bag. Once the appropriate level of haemoconcentration is achieved (normally a packed cell volume in excess of 33%), the concentrated blood held in the bag is transferred into a transfer bag for subsequent transfusion to the patient.
The Hemosep bag
The Hemosep bag element of the system is the active processing section of the device. It consists of a blood bag with a filter membrane bag suspended within it, within which is a sheet of superabsorbent material. The filter membrane material employed in the device has a unique pore structure.
The filter membrane is the control membrane of the system and the unique pore size for this important element of the device has been selected to ensure that no cellular components of the blood product can pass into the superabsorber during use. The unique pore size is small enough to permit efficient fluid transport into the superabsorber but is too restrictively small to permit the passage of cells, even the smallest intact cells, the platelets.
The Hemosep shaker
Although the Hemosep device is capable of concentrating blood cells passively, the time taken to achieve the desired concentration is considerably shortened by employing some agitation of the device. The reason for this is that as plasma is drawn across the wetted control membrane by the superabsorber, cells can be deposited in the pores reducing the number of pores available for fluid transport.
The blood collection bag is a simple blood bag which is connected to the outlet of the Hemosep bag after blood processing and into which the concentrated blood is drained.
Intended clinical performance
The Hemosep device is intended to concentrate the residual blood during and after the operative procedure. This blood is highly haemodiluted and if returned to the patient in its raw state, may lead to excessive bleeding and patient haemodilution in the critical post surgical recovery phase. Concentration of this blood product to near-normal cell concentrations (PCV level 33 – 45%) renders it suitable for re-transfusion and diminishes the bleeding risk of unprocessed blood. The transfusion of the processed autologous blood reduces the need for donor blood products and their associated transfusion reactions. The Hemosep device, under normal clinical conditions, is intended to concentrate residual blood from low PCV’s (20% or less) to near-normal levels (at least 33%) without the need for centrifuge technology.