Total haemoglobin mass, but not haemoglobin concentration, is associated with preoperative cardiopulmonary exercise testing-derived oxygen-consumption variables.

Background: Cardiopulmonary exercise testing (CPET) measures peak exertional oxygen consumption ( V˙O2peak ) and that at the anaerobic threshold ( V˙O2 at AT, i.e. the point at which anaerobic metabolism contributes substantially to overall metabolism). Lower values are associated with excess postoperative morbidity and mortality. A reduced haemoglobin concentration ([Hb]) results from a reduction in total haemoglobin mass (tHb-mass) or an increase in plasma volume. Thus, tHb-mass might be a more useful measure of oxygen-carrying capacity and might correlate better with CPET-derived fitness measures in preoperative patients than does circulating [Hb]. Methods: Before major elective surgery, CPET was performed, and both tHb-mass (optimized carbon monoxide rebreathing method) and circulating [Hb] were determined. Results: In 42 patients (83% male), [Hb] was unrelated to V˙O2 at AT and V˙O2peak ( r =0.02, P =0.89 and r =0.04, P =0.80, respectively) and explained none of the variance in either measure. In contrast, tHb-mass was related to both ( r =0.661, P <0.0001 and r =0.483, P =0.001 for V˙O2 at AT and V˙O2peak , respectively). The tHb-mass explained 44% of variance in V˙O2 at AT ( P <0.0001) and 23% in V˙O2peak ( P =0.001). Conclusions: In contrast to [Hb], tHb-mass is an important determinant of physical fitness before major elective surgery. Further studies should determine whether low tHb-mass is predictive of poor outcome and whether targeted increases in tHb-mass might thus improve outcome.

Transfusion in critical care - a UK regional audit of current practice.

A consistent message within critical care publications has been that a restrictive transfusion strategy is non-inferior, and possibly superior, to a liberal strategy for stable, non-bleeding critically ill patients. Translation into clinical practice has, however, been slow. Here, we describe the degree of adherence to UK best practice guidelines in a regional network of nine intensive care units within Wessex. All transfusions given during a 2-month period were included (n = 444). Those given for active bleeding or within 24 h of major surgery, trauma or gastrointestinal bleeding were excluded (n = 148). The median (IQR [range]) haemoglobin concentration before transfusion was 73 (68-77 [53-106]) g.l-1 , with only 34% of transfusion episodes using a transfusion threshold of < 70 g.l-1 . In a subgroup analysis that did not study patients with a history of cardiac disease (n = 42), haemoglobin concentration before transfusion was 72 (68-77 [50-98]) g.l-1 , with only 36% of transfusion episodes using a threshold of < 70 g.l-1 (see Fig. 3). Most blood transfusions given to critically ill patients who were not bleeding in this audit used a haemoglobin threshold > 70 g.l-1 . The reason why recommendations on transfusion triggers have not translated into clinical practice is unclear. With a clear national drive to decrease usage of blood products and clear evidence that a threshold of 70 g.l-1 is non-inferior, it is surprising that a scarce and potentially dangerous resource is still being overused within critical care. Simple solutions such as electronic patient records that force pause for thought before blood transfusion, or prescriptions that only allow administration of a single unit in non-emergency circumstances may help to reduce the incidence of unnecessary blood transfusions.