Effect of haemodilution with diaspirin cross-linked haemoglobin on the oxygen reserve in a rodent model of surgical blood loss

The efficacy of pre-operative haemodilution is limited by the reduction in haemoglobin concentration. Acellular haemoglobin-based oxygen carriers provide an alternative to colloid as a haemodiluent, potentially extending the safe limits of this procedure. The aim of this investigation was to determine whether haemodilution with a cross-linked haemoglobin solution, diaspirin cross-linked haemoglobin solution (DCLHb), would enhance the oxygen reserve compared to pentastarch. Sprague Dawley rats were placed in a metabolic box to directly measure systemic oxygen consumption (VO2). Rats were randomized to be haemodiluted to a cellular haemoglobin of 80 g L-1 with either DCLHb or pentastarch. Oxygen reserve was assessed during isovolemic haemorrhage by determining the critical oxygen delivery (DO(2)crit) and haemoglobin concentration at the point of oxygen supply dependency (OSD). Following haemodilution and for the duration of the experiment, cardiac index (CI) was significantly lower and systemic vascular resistance was significantly higher in the DCLHb than the pentastarch group. The DO(2)crit (3.2+/-0.4 mL minAg(-1) and 3.4+/-0.5 mL minAg(-1), DCLHb versus pentastarch) and cellular haemoglobin concentration (51+/-9 g L-1 and 48+/-9 g L-1), at which rats entered OSD were similar in both groups. Total haemoglobin concentration (cellular and plasma DCLHb) and arterial oxygen content were significantly higher in the DCLHb group (total haemoglobin, 66+/-8 g L-1 and arterial content, 9.2+/-1.4 mL dL(-1)) compared to the pentastarch group (total haemoglobin, 48+/-9 g L-1 and arterial content, 7.3+/-1.4 mL dL(-1)). Oxygen extraction ratios increased from baseline levels to 0.53+/-0.07 and 0.56+/-0.1, for the DCLHb and pentastarch groups, respectively, and were not significantly different. The increase in arterial oxygen content from DCLHb in plasma was offset by the decrease in CI observed in this group. Plasma DCLHb did not extend the limits of haemodilution beyond the capacity of the cellular haemoglobin concentration.