Hemoglobin‐Based Oxygen Carriers in Trauma Care: Scientific Rationale for the US Multicenter Prehosptial Trial

Abstract

The greatest need for blood substitutes worldwide is in patients with unanticipated acute blood loss, and trauma is the most likely scenario. The blood substitutes reaching advanced clinical trials today are red blood cell (RBC) substitutes derived from hemoglobin. The hemoglobin-based oxygen carriers (HBOCs) tested currently in advanced clinical trials are polymerized hemoglobin solutions. In the USA, the standard approach to restoring oxygen delivery for hemorrhagic shock has been crystalloid administration to expand intravascular volume, followed by stored RBCs for critical anemia. Allogeneic RBCs, however, may have adverse immunoinflammatory effects that increase the risk of postinjury multiple organ failure (MOF). Phase II in hospital clinical trials, as well as in vitro and in vivo work, suggest that resuscitation with an HBOC--in lieu of stored RBCs--attenuates the systemic inflammatory response invoked in the pathogenesis of MOF. Specifically, an HBOC has been shown to obviate stored RBC-provoked polymorphonuclear neutrophil (PMN) priming, endothelial activation, and systemic release of interleukins (IL) 6, 8, and 10. In a 2-event rodent study of shock-induced PMN-mediated acute respiratory distress syndrome (ARDS), the simulated prehospital administration of an HBOC markedly attenuated lung injury. Based on this background and work by others, we have initiated a US multicenter prehospital trial in which severely injured patients with major blood loss [systolic blood pressure (SBP)<or=90 mmHg] are randomized to initial field resuscitation with crystalloid versus HBOC. During the hospital phase, the control group is further resuscitated with stored RBCs whereas the study group receives HBOC (up to 6 units) in the first 12 hours. The primary study endpoint is decreased 30-day mortality, and secondary endpoints include reductions in administration of allogeneic RBCs and uncrossmatched RBCs; avoiding circulating hemoglobin levels<5 g/dl; and decreased ARDS and MOF. To date, >500 injured patients have been enrolled in this multicenter trial, and the final interim analyses support the original target of 720.