Bailliere's clinical anaesthesiology最新文献

Burns injuries affect 10 000 people annually in the UK and of these 650–700 die. Many who would have previously died now survive as the treatment of burns patients improves. Ethical dilemmas may occur when decisions need to be made about the treatment of incompetent patients. These decision may concern the initiation, continuation or termination of treatment. The ethical principles of autonomy, beneficence, non-maleficence and justice are described and how their application allows, both morally and legally, the initiation and termination of treatment, even when the patient cannot be involved in the decision. The debate surrounding advance directives which would give the patient some control over what was done to him when incompetent to make decisions and euthanasia are reviewed.

Because of the potential risks of transmission of viral diseases by homologous blood, the so-far unsolved relevance of immunomodulation-suppression by homologous blood and the seasonal shortage of homologous blood, autologous transfusion techniques have gained importance over the last decade. As each single autologous transfusion measure has limitations of its own, these techniques should most effectively be combined into what has been called the ‘concept of autologous transfusion’ (CAT). This concept consists of the technical measures of autologous transfusion, for example acute normovolaemic haemodilution with intra- and post-operatively salvaged blood being either mechanically processed or unprocessed and directly retransfused, the autologous pre-deposit being separated into autologous blood donation with or without haemoseparation and into autologous pre-operative plasmapheresis. Establishing and routinely applying CAT resulted in a decrease of homologous blood by approximately 90% in major bone and joint surgery; on differentiating between aseptic and infectious orthopaedic surgery, more than 90% of the former were supplied with autologous blood while the latter was supplied by approximately 20% of autologous blood. The incidence of adverse events occurring in an autologous pre-deposit programme in more than 28 000 patients with more than 130 000 autologous units was 2.08% with respect to the number of patients taking part in this programme or 0.44% with respect to the number of autologous units harvested. Among this total number of 588 adverse events there were three severe ones (two male patients with myocardial infarction and one female patient with an apoplexy) and two fatal adverse events (one patient dying of massive pulmonary embolism and one female patient dying of an acute severe asthmatic attack). While CAT has been proven to reduce effectively the need for homologous blood it has also been shown that the appropriate selection of the patients as well as close and experienced monitoring and management of adverse events are necessary to make CAT not only an effective but also a safe alternative to homologous blood transfusion.

Intravenous (i.v.) artificial oxygen carriers are intended to ensure adequate tissue oxygenation in critical anaemia (haemorrhagic shock, profound normovolaemic haemodilution). As regards their efficacy, both synthetic haemoglobin solutions and perfluorocarbon (PFC) emulsions, are suited to preserve tissue oxygenation after nearly complete blood exchange in various experimental models. Safety aspects, however, have so far limited the administration of artificial oxygen carriers. While pharmacological properties of synthetic haemoglobin solutions facilitate their administration as ‘resuscitation fluids’ in haemorrhagic shock (possible 1:1 replacement of shed blood), PFC emulsions can only be infused in low doses to avoid overload of the reticuloendothelial system. Therefore PFC are unsuitable for volume resuscitation in shock. Low-dose i.v. PFC can be used to increase the margin of safety for tissue oxygenation in haemodiluted patients, experiencing intraoperative blood loss. ‘Bridging’ the bleeding period by allowing severe normovolaemic haemodilution in the presence of i.v. PFC, together with the possibility of replacing the temporarily restricted oxygen transport capacity of i.v. PFC emulsions with autologous red blood cells, might become part of an allogeneic blood transfusion sparing concept in elective surgery.

The risks of cancer recurrence and post-operative bacterial infection which are attributed by some authors to an immunomodulatory effect of allogeneic transfusion have remained controversial for 15 years, as many observational studies and four randomized controlled trials have produced contradictory results. A review of these discrepant findings suggests that a deleterious immunomodulatory transfusion effect might exist, but it might operate only in specific surgical settings. The challenge is to identify those settings and to determine the magnitude of the adverse effect if it exists. This will require further randomized controlled trials designed to establish causal relationships and new observational studies designed to explain disagreements between published investigations. Lessons learned from the methodological limitations of the earlier reports can guide the design of future studies. It is hoped that the new studies will permit the formulation of rational guidelines for peri-operative transfusion practice which will prevent any deleterious effect(s) of transfusion-induced immunomodulation.

The viral safety of virus-inactivated plasma products has been markedly enhanced by the improvement in tests for screening donations and by the improvement in techniques for manufacture of plasma derivatives including methods for virus inactivation. Nevertheless, there remains a weakness in removing inactivating heat-resistant non-enveloped viruses, such as parvovirus B19. Manufacturers' efforts should continue to be concentrated on this challenge.

The vast majority of blood transfusions are uneventful and the desired result is achieved safely. Nevertheless, about 10% of transfusion recipients may suffer some form of untoward effect, yet severe morbidity and mortality are relatively rare. Febrile non-haemolytic transfusion reactions due to the presence of white cell antibodies in the recipient are the commonest type of reaction; although these cause great discomfort to the patient, they are not life-threatening. Although a minority of severe transfusions reactions, such as transfusion related lung injury (TRALI) cannot be prevented, the vast majority of serious reactions are preventable. ABO incompatibility is the most common cause of immediate deaths following transfusion reactions and invariably occurs as a result of procedural errors resulting in mis-identification of the recipient. Appropriate monitoring of patients during blood transfusion will enable prompt remedial action. Serious reactions due to bacterial contamination of blood products are becoming increasingly common and meticulous cleansing of the donor's arm, storage of blood and blood components compliant with recommended standards and guidelines and examination of the unit before transfusion will prevent most of these reactions. Other preventable serious hazards are caused by accidental injection of water into the circulation, administering red cells through a small gauge cannula, inappropriate heating of blood prior to administration or accidental freezing.

While every endeavour should be made to eliminate preventable hazards of transfusion, over-transfusion is unfortunately still a problem in many countries. In order to present serious adverse effects, clinicians should be mindful that blood transfusions should only be prescribed when the benefits clearly outweigh the risks.

Blood components have replaced whole-blood transfusion because they allow better maintenance of quality, more effective use of the donor's blood and more appropriate dosage to the patients. The techniques for the preparation and storage of components, both from whole blood and via apheresis, have developed gradually. The oxygen-releasing capacity of the erythrocytes is still influenced negatively even after short storage with currently used systems, but better methods have been described. Leukocyte removal from red cell and platelet preparations results in different degrees of purity. Filtration as well as some apheresis techniques have improved in recent years so that the aim, <5 × 10⁶ leukocytes per transfusion, can be achieved confidently. Transfusion-associated graft-versushost disease requires attention. Collection of haematopoietic stem cells from peripheral blood for transplantation has become an important new task. Bacterial contamination, being a greater problem in platelet concentrates than earlier believed, can be detected by testing and probably soon counteracted by decontamination.

Pre-donation of blood in cancer patients is effective and recommendable, but is limited by tumour anaemia, urgent scheduling of surgery and variable blood loss resulting in discarded autologous blood or homologous transfusions. Intra-operative autotransfusion is considered to be contraindicated in cancer surgery. This was confirmed by the recent demonstration of the frequent existence of vital, proliferating, invasive and tumorigenic tumour cells in high numbers in the blood shed during surgery of various cancers. Leukocyte depletion filters are unable to guarantee complete elimination of contaminating tumour cells because of the limited reduction rates. The radiosensitivity of the nucleated tumour cells, in contrast to the radioresistance of the unnucleated red blood cells, can be used for efficient elimination. For 50 Gy a 12 decade reduction can be calculated from radiosensitivity data, and experimentally a 10 decade reduction has been demonstrated, sufficient to eliminate any supposed tumour cell contamination. This combination of two well-established methods, intra-operative blood salvage and blood irradiation, in clinical practice proved to be an effective, practical and safe procedure for using autologous blood in cancer patients.

Pre-operative autologous blood donation (PAD) has become a widely distributed practice in many countries pushed forward by the fear of acquired immunodeficiency syndrome transmission by transfusion of allogenous blood. With the declining risk of transfusion-transmitted infection as a result of improved testing and the increasing limitation of health care resources the cost-effectiveness of PAD has become of great interest. This article describes the most widely used procedures of PAD and discusses the topics that the recent debate has been focused on. It is demonstrated that a clear medical indication for PAD is indispensable and that the inherent risk of PAD has to be balanced against the alleged benefit. We provide a mathematical approach to tackle this problem. Furthermore, we suggest measures able to reduce the costs of PAD without neglecting the medicolegal aspects and the legitimate claim of the patient in order to reach an acceptable cost: benefit ratio of PAD.