Background: Providing safe blood for transfusion remains a challenge despite advances in preventing transmission of hepatitis B, hepatitis C, AIDS/HIV, West Nile virus(WNV), and transfusion-transmitted bacterial infection. Human errors such as misidentifying patients and drawing blood samples from the wrong person present much more of a risk than transmissible diseases. Additional risks include transfusion related acute lung injury (TRALI), a potentially life-threatening condition with symptoms such as dyspnea, fever, and hypotension occurring within hours of transfusion, and also transfusion-associated immunomodulation, which may suppress the immune response and cause adverse effects such a small increase in the risk of postoperative infection. Other risks such as variant Creutzfeldt-Jakob disease (vCJD), an invariably fatal disease, remain worrisome. Blood centers worldwide have instituted criteria to reject donors who may have been exposed to vCJD. Screening for transmissible diseases and deferral policies for vCJD designed to improve safety have contributed to shrinking the donor pool. Blood shortages exist in the United States and worldwide. In many industrialized countries 5% or less of the eligible population are blood donors.
Red blood cells processed by cell salvage and stored at room temperature can be safely transfused up to 6 hours following collection. As a result, the global medical community has increasingly moved from allogenic blood (blood collected from another person) towards autologous infusion, in which patients receive their own blood. Another impetus for autologous transfusion is the position of Jehovah's Witnesses on blood transfusions. For religious reasons, Jehovah's Witnesses will not accept any allogeneic transfusions from a volunteer's blood donation, but may accept the use of autologous blood salvaged during surgery to restore their blood volume and homeostasis during the course of an operation, although not autologous blood donated beforehand.
During the surgical procedure, wall suction is not utilized to clear the operative field; the cell salvage suction pressure can be regulated if the field needs to be cleared quickly. Heparinised normal saline or citrate anticoagulant is added as the shed blood is collected. Filtering and washing remove contaminants such as cell fragments, fat globules, bone chips, and potassium leaked from haemolysis (Haemolysis is a condition that occurs when haemoglobin is released from red blood cells when the cell membranes are damaged.). The final washing steps utilize only normal saline to produce red blood cells (no functional platelets or clotting factors) suspended in saline for transfusion to the patient.
The technology of cell salvage has evolved since its initial implementation in the 1970's. In the early days, cell salvage was limited to simply filtering by gravity. Subsequently, washing techniques involved "bowl technology", centrifugation within a constrained bowl, with a full bowl mandatory for effective, efficient washing. The most advanced technology utilizes "coil technology", with the shed blood directed into a continuous washing chamber, allowing for continuous processing.
This technology avoids wasting partially filled bowls of shed blood and allows for a readily available product to be transfused to the patient. The computerised process of the cell salvage equipment facilitates the role of the perfusionist in balancing the suction pressure, the washing chamber fill rate, and the wash cycle flow rate to the priority of the patient's physiological need for red blood cell transfusion.
As with all health care technology, the relative advantages and limitations of intra-operative cell salvage must be weighed up in the clinical setting. Intra-operative cell salvage is most effective in major surgical blood loss (1000 ml or greater) procedures and especially effective for patients with adequate pre-operative haemoglobin.
Contamination of the surgical site, ongoing infectious processes, use of topical antibiotics or anticoagulants, potential presence of amniotic fluid or cancer cells in the surgical field is controversial when considering intra-operative cell salvage. If 1 to 1 ½ times the patient's blood volume is shed, close monitoring for signs of coagulopathy (a disease or condition affecting the blood's ability to coagulate) becomes essential. Financial aspects to bear in mind include the cell salvage device itself, the disposables required for each patient, the availability of skilled operators (perfusionists), and the frequency of surgical cases where cell salvage is applicable.
Theatre activity data must be analysed to estimate the number of suitable cases and the pattern of the demand. Intra-operative cell salvage is indicated during "clean" surgery where the anticipated blood loss is >20% of the patient's blood volume, that is one litre for a 70kg man. Cell salvage will not always replace the need for donor blood, particularly with large volume losses, but may make a contribution to the transfusion requirements.
The hospital case mix is important. Some types of elective surgery will guarantee a supply of suitable cases. Examples of these include:
- Open cardiac surgery
- Vascular surgery
- Major orthopaedic surgery
Having established an estimate of case numbers, the pattern of the demand should be examined. For hospitals with a significant emergency workload 24-hour availability must be the gold standard. At present there are probably only a handful of hospitals in the UK that are able to guarantee this. Even if this standard cannot be met at the outset, it is worth building towards it.
Edited by John Sandham IEng MIET MIHEEM