Editorial II

Blood transfusion in surgical practice—matching supply to demand

J. C. Howie1 and P. J. Tansey1

1 Victoria Infirmary Glasgow G12 9TY UK

The paper by van Klei and colleagues,1 in this issue, demonstrates the ability of a simple algorithm to identify surgical patients, in whom it may be unnecessary to take blood for group and screen preoperatively. Any such predictive rule inevitably requires a trade off between sensitivity and specificity. The authors have identified a score, modified by preoperative haemoglobin, which allows a reduction of 35% in group and screen procedures.

Adoption of this approach has the capacity to reduce workload in transfusion laboratories. However, it does so at the expense of requiring, in this study, emergency crossmatching to be performed in 13% of patients. More significantly we may presume this to have been urgent in the 6% of patients in whom more than 2 units of blood were required. It follows that the extent to which a hospital could follow such a policy would depend on the totality of local factors, which determine the time from blood being drawn to delivery of blood to the operating theatre.

Transfusion laboratories, over the last 25 yr, have seen technical advances such as low ionic strength solutions (LISS) and column agglutination technology (CAT). These have allowed crossmatch incubation times to fall in routine crossmatching practice from 90 min to an optimum of 20 min, while still retaining the sensitivity to detect clinically significant antigen/antibody reactions. It follows that blood should be available for transfusion within 40 min of a specimen reaching the laboratory when using current crossmatch techniques. Thus, crossmatching blood in an emergency setting can provide blood with comparable serological safety to that provided electively. The major difference resides in the extent of recommended laboratory checking procedures, which does represent a reduction in safety margins.

It is important that, when confronted with the requirement to provide emergency transfusion, the anaesthetist understands the range of options available, in terms of both rapidity of supply and relative safety of the available blood products. If a 40–60 min time frame does not meet the patient’s clinical requirements, then these options involve the use of a rapid-spin restricted crossmatch (effectively confirms ABO compatibility), group-specific blood, or screened group O –ve cells.

Rapid-spin crossmatch methods have the capacity to reduce the overall time to approximately 20 min. If the patient has had a routine group and screen, with no antibodies found, dropping the crossmatch altogether and using group-specific blood will also take approximately 20 min. A retrospective review of screening results on blood taken from approximately 40 000 patients indicates that this would carry the risk of missing clinically significant irregular erythrocyte antibodies, only once in 2900 units.2 This risk increases where the patient’s blood group is known but no previous antibody screen of their blood has been undertaken. It is important to appreciate that the use of group-specific blood, in this situation, rather than screened O –ve blood, has no additional safety. In reality there is a small increase in the safety margin associated with O –ve blood, as blood supplied for this purpose has already been screened for the presence of the most significant non-ABO antibodies. The benefit of using group-specific blood relates exclusively to the limited availability of screened O –ve blood.

Where the blood group is not known, unmatched screened O –ve may be used. Constraints on the use of O –ve blood relate to the residual risk of irregular erythrocyte antibodies. If supplies of O –ve blood are exhausted, it may be necessary to use O +ve blood. The most significant additional risk is in women of child-bearing age who will, if rhesus –ve, develop rhesus antibodies. If time allows, rapid blood grouping can be performed in a few minutes to exclude this concern. As with group-specific blood, O +ve blood is not supplied pre-screened. Where the transfusion laboratory is a significant distance from the theatre, ‘snatch boxes’ can be provided in the theatre blood fridge, giving immediate access to screened O –ve blood.

Whenever emergency transfusion is required for major haemorrhage, the anaesthetist is required to make a judgement on the value of achieving and maintaining critical red cell mass, and weighing this against the relatively low risk of using uncrossmatched blood. Reluctance to use anything other than crossmatched blood in the acutely bleeding patient may lead to critical delay in life-saving transfusion. A few minutes spent discussing the options with the laboratory allows coordination of the activities of the resuscitation team and transfusion laboratory. This is a dynamic process. Grouping and crossmatching is being undertaken while the most appropriate emergency blood supply is being transfused. In the context of massive transfusion, there is a point at which ongoing crossmatching is unnecessary, and group-specific blood will be supplied.

While crossmatched blood is at present viewed as a gold standard in terms of quality and current guideline compliance,3 it is quite likely that there will be a departure from this practice, with a move towards more rigorous screening of both donor and recipient blood. This would avoid the current requirement to allocate a specific number of units to a given patient, so reducing wastage. At present, the only way to minimize this wastage is by more precisely estimating an individual patient’s likely transfusion requirement. This can be done using an approach similar to that used by van Klei and colleagues.1 A number of models have been described. At its simplest, a Maximum Surgical Blood Ordering Schedule is established locally, following discussions between clinicians and the transfusion service. Ideally, this is informed by data on average transfusion requirements for common procedures. A tariff is allocated for each procedure, with group and screen reserved for those with a predicted risk of transfusion of less than 30%. The local Hospital Transfusion Committee should monitor the effectiveness of the blood ordering policy using the crossmatch:transfusion ratio. Greater precision can be attempted by incorporating factors reflecting the capacity of a given patient to tolerate red cell loss. This is dependent on preoperative red cell volume and the transfusion threshold appropriate for a given category of patient. The former is a function of haematocrit, sex, weight, and height; the latter may be modified by factors such as age, and cardiovascular comorbidity.4

Blood ordering strategies should be part of an overall perioperative strategy which seeks to avoid wastage of a scarce resource, and limits transfusion to those patients who have a realistic expectation of benefit. The latter objective, while relevant to addressing issues of supply and demand, is particularly important given the current uncertainty surrounding safety of the product. While no transmission of variant Creutzfeld Jacob disease by transfusion has thus far been documented, concern has been sufficient to exclude UK donor plasma from fractionation and to institute universal leucodepletion of blood. In spite of this, no absolute guarantee of safety can be given.

Transfusion issues specifically relevant to anaesthetists have been the subject of a working party report from the Association of Anaesthetists of Great Britain and Ireland,5 while more wide-ranging recommendations are available in a recently published guideline from the Scottish Inter collegiate Guidelines Network (SIGN).6 It is expected that all hospitals in Scotland will formally implement this guideline. However, we believe UK wide adoption of these evidence-based recommendations would represent a significant step forward. In particular, they would assist the surgical team to offer patients informed choices on the risks and benefits of strategies which seek to reduce exposure to allogeneic transfusion. All SIGN guidelines can be accessed at www.sign.ac.uk.

References

1 vanKlei WA, Moons KGM, Rheineck-Leyssius AT, Kalkman CJ, Rutten CLG, Knape JTA, Grobbee DE. Validation of a clinical prediction rule to reduce preoperative type and screen procedures. Br J Anaesth 2002; 89: 221–5[Abstract/Free Full Text]

2 Blood Transfusion Task Force. Guidelines for pretransfusion compatibility procedures in blood transfusion laboratories. Transfusion Med 1996; 6: 273–83[ISI][Medline]

3 Mercuriali F, Inghilleri G. Proposal of an algorithm to help the choice of the best transfusion strategy. Curr Med Res Opin 1996; 8: 465–78

4 Lown JA, Barr AL, Jackson JM. A reappraisal of pre-transfusion testing procedures in a hospital blood bank. Pathology 1985; 17: 489–92[ISI][Medline]

5 Association of Anaesthesists of Great Britain and Ireland. Blood Transfusion and the Anaesthesist. Red Cell Transfusion. Association of Anaesthesists of Great Britain and Ireland, 2001

6 Scottish Intercollegiate Guidelines Network. Perioperative Blood Transfusion for Elective Surgery. A National Clinical Guideline. SIGN 54, Edinburgh, 2001





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