Acute Coagulopathy of Trauma in the Rat. Shock 39 (2013)

To the Editor Darlington and colleagues (1) at the US Army Institute of Surgical Research are to be congratulated in attempting to develop a rat model of acute coagulopathy resulting from polytrauma and hemorrhage. As the authors point out, coagulopathy occurs early in hemorrhagic trauma and is a major contributor to mortality and morbidity. Coagulopathic bleeding was first reported in the Vietnam War (2) and rediscovered some 40 years later by Brohi (3). Several large trials have shown that 24% to 36% of severely injured patients have acute traumatic coagulopathy on admission to the emergency department (mean arrival time, 75 min), and it was associated with a 4-fold increase in mortality (3–5). In 2011, and 2012, we reported profound hypocoagulability in nonheparinized, mild accidental hypothermic (~34°C), male Sprague-Dawley rats during 20-min pressure-controlled bleeding (∼40% blood loss) and 60-min shock (6, 7). We further showed that 0.3 mL intravenous bolus of 7.5% NaCl adenosine-lidocaine/Mg2+ (ALM) raised mean arterial pressure into the hypotensive range, and it fully corrected PT and aPTT to baseline levels at 60-min resuscitation (7). Darlington and colleagues also showed increases in PT and aPTT in their rat model, although these were markedly reduced in comparison to our study. With the exception of minor surgery for ventilation tube insertion, the 10-fold increases in PT and aPTT we argued in our study were related to (1) 40% blood loss and (2) the emergent shock state and tissue hypoperfusion (7). A surprising result from the Darlington study was that while increases in PT and aPTT indicate hypocoagulopathy (Fig. 2), they report rotational thromboelastometry (ROTEM) shortening of ExTEM clotting time (CT) indicating hypercoagulability. Although there was a dip in aPTT at 120 min (Fig. 2), this fall was a return to baseline, not below baseline to support a hypercoagulable state. Was this shortening in ExTEM CT found in InTEM CT, because aPTT is equivalent to InTEM, not ExTEM? Were there differences in InTEM and ExTEM mean clot firmness? What was the core temperature in their rat model of coagulopathy over the 300 min, as this was not specified, and changes in body temperature have a profound effect on coagulation. In 2013, Park and colleagues (8) demonstrated in rats exposed to uncontrolled blood loss that their blood clotted less firmly during traumatic hemorrhage, and hypothermia prolonged CTs. Another concern with the study of Darlington and colleagues is the complexity of their results, which they acknowledge, and this may be reflected in the complexity of their model, which involved hemorrhage after crush injuries to the small intestine and right and left liver lobes, right leg skeletal muscle, and a right femur fracture. Animal models to test novel resuscitation strategies must be clinically and battlefield relevant (9); however, perhaps we should all take heed of Ockham’s razor principle of economy, “Plurality should not be posited without necessity,” when attempting to unravel the underlying mechanisms of acute coagulopathy of trauma. Hayley L. Letson Geoffrey P. Dobson Heart and Trauma Research Laboratory Department of Physiology and Pharmacology School of Biomedical Sciences James Cook University Townsville, Queensland Australia