Recently published papers: What not to do and how not to do it?

The delivery of oxygen to tissues remains a central tenet of intensive care medicine. Much of the attention has focused on optimizing cardiac output and perfusion pressure, not least because we possess therapeutic tools that affect these parameters. The second element in the equation is oxygen carrying capacity, which is primarily determined by haemoglobin concentration and hence red cell mass. Transfusion of stored red blood cells is used to maintain oxygen carrying capacity, although the optimal use of this therapy remains an area of considerable controversy. It is well established that transfused red blood cells carry but do not efficiently release oxygen for at least 24 hours, because of 2,3-diphospho-glycerate depletion. In addition, they do not deform to facilitate transit through the microcirculation. Use of a low transfusion threshold has been shown to be of benefit [1], as has a more permissive approach [2]. Habib and colleagues [3] have added to this controversy in their detailed study of the effects of anaemia and red blood cell transfusion in patients undergoing cardiopulmonary bypass. They measured changes in renal function as an index of end-organ damage due to impaired tissue oxygen delivery. The results, which are eloquently discussed in an accompanying editorial [4], demonstrate renal injury caused both by anaemia and transfusion. In the words of the editorialist, 'damned if you do/damned if you don't!'However, a recent animal study may yet offer us some salvation. Young and colleagues have been developing a substitute for red blood cell transfusion by conjugating haemoglobin tetramers with polyethylene glycol (PEG). In their most recent paper [5] they resuscitated a pig model of intraoperative haemorrhagic shock with a single, small volume bolus of Ringer's acetate, 10% pentastarch, 4 g/dl stroma-free haemoglobin, or their PEG-conjugated human haemoglobin. The animals then received an autologous blood transfusion, the blood having been removed as t