Earlier debridement and antibiotic administration decrease infection.

Timing of debridement and local antibiotic administration on infection has not been clearly defined. A contaminated critical size rat femur defect model was used to determine if earlier debridement with local antibiotics decreased infection. Defects were inoculated with Staphylococcus aureus. At 2, 6, or 24 hours following contamination, defects were irrigated and debrided then directly closed or treated with antibiotic-impregnated PMMA beads and then closed. Two weeks later, defects were examined for evidence of infection. There was a significant increase in evidence of infection between 2 and 6 hours and a further increase between 6 and 24 hours with debridement alone as well as with debridement plus local antibiotics. Treatment with antibiotics resulted in significantly less evidence of infection at 2 and 6 hours compared to debridement alone. It was concluded that early debridement in combination with local delivery of antibiotics of contaminated defects may reduce infections.

Is survival time after hemorrhage a heritable, quantitative trait?: an initial assessment.

Enhancing survival to hemorrhage of both civilian and military patients is a major emphasis for trauma research. Previous observations in humans and outbred rats show differential survival to similar levels of hemorrhage. In an initial attempt to determine potential genetic components of such differential outcomes, survival time after a controlled hemorrhage was measured in 15 inbred strains of rats. Anesthetized rats were catheterized, and approximately 24 h later, 55% of the calculated blood volume was removed during a 26-min period from conscious unrestrained animals. Rats were observed for a maximum of 6 h. Survival time was 7.7-fold longer in the longest-lived strain (Brown Norway/Medical College of Wisconsin; 306 +/- 36 min; mean +/- SEM) than in the shortest-lived strain (DA; 40 +/- 5 min; P < or = 0.01). Mean survival times for the remaining inbred strains ranged from 273 +/- 44 to 49 +/- 4 min (Dahl-Salt Sensitive > Brown Norway > Munich Wistar Fromter> Dahl-Salt Resistant > Copenhagen > Noble > Spontaneous-hypertensive > Lewis > BDIX > Fawn Hooded Hypertensive > FISCHER 344 > Black agouti > PVG). The variance in the hazard of death attributable to different strains was estimated to be 1.22 log-hazard units, corresponding to a heritability of approximately 48%. Graded and divergent survival times to hemorrhage in inbred rat strains are remarkable and suggest multiple genetic components for this characteristic. However, this interpretation of differential responses to hemorrhage may be confounded by potential strain-associated differences related to the surgical preparation. Identification of inbred strains divergent in survival time to hemorrhage provides the opportunity for future use of these strains to identify genes associated with this complex response.

Thrombelastography is better than PT, aPTT, and activated clotting time in detecting clinically relevant clotting abnormalities after hypothermia, hemorrhagic shock and resuscitation in pigs.

BACKGROUND: Hypothermia and hemorrhagic shock contribute to coagulopathy after trauma. In this study, we investigated the independent and combined effects of hypothermia and hemorrhage with resuscitation on coagulation in swine and evaluated clinically relevant tests of coagulation. METHODS: Pigs (n = 24) were randomized into four groups of six animals each: sham control, hypothermia, hemorrhage with resuscitation, and hypothermia, hemorrhage with resuscitation combined. Hypothermia to 32 degrees C was induced with a cold blanket. Hemorrhage was induced by bleeding 35% of total blood volume followed by resuscitation with lactated Ringer's solution. Coagulation was assessed by thrombin generation, prothrombin time (PT), activated partial thromboplastin time (aPTT), activated clotting time (ACT), and thrombelastography (TEG) from blood samples taken at baseline and 4 hour after hypothermia and/or hemorrhage with resuscitation. Data were compared with analysis of variance. RESULTS: Baseline values were similar among groups. There were no changes in any measurements in the control group. Compared with baseline values, hemorrhage with resuscitation increased lactate to 140% +/- 15% (p < 0.05). Hypothermia decreased platelets to 73% +/- 3% (p < 0.05) with no effect on fibrinogen. Hemorrhage with resuscitation reduced platelets to 72% +/- 4% and fibrinogen to 71% +/- 3% (both p < 0.05), with similar decreases in platelets and fibrinogen observed in the combined group. Thrombin generation was decreased to 75% +/- 4% in hypothermia, 67% +/- 6% in hemorrhage with resuscitation, and 75% +/- 10% in the combined group (all p < 0.05). There were no significant changes in PT or aPTT by hemorrhage or hypothermia. ACT was prolonged to 122% +/- 1% in hypothermia, 111% +/- 4% in hemorrhage with resuscitation, and 127% +/- 3% in the combined group (all p < 0.05). Hypothermia prolonged the initial clotting time (R) and clot formation time (K), and decreased clotting rapidity (alpha) (all p < 0.05). Hemorrhage with resuscitation only decreased clot strength (maximum amplitude [MA], p < 0.05). TEG parameters in the combined group reflected the abnormal R, K, MA, and alpha observed in the other groups. CONCLUSION: Hypothermia inhibited clotting times and clotting rate, whereas hemorrhage impaired clot strength. Combining hypothermia with hemorrhage impaired all these clotting parameters. PT, aPTT were not sensitive whereas ACT was not specific in detecting these coagulation defects. Only TEG differentiated mechanism related to clotting abnormalities, and thus may allow focused treatment of clotting alterations associated with hypothermia and hemorrhagic shock.

A novel swine model for evaluation of potential intravascular hemostatic agents.

Because uncontrolled hemorrhage is a leading cause of battlefield mortality, finding an intravenous treatment that could assist endogenous clotting mechanisms is a major mission for military researchers. Evaluation of potential intravenous hemostatic agents requires both in vitro and in vivo tests. For in vivo evaluation, we have developed a novel swine model in which 1) bleeding times (BT) and coagulation function could be ascertained after multiple doses of hemostatic drug administration and 2) a subsequent exsanguinating injury could be performed in the same animal, yielding screening information regarding the effects of drug pretreatment on blood loss and survival. Transection of small mesenteric arteries and veins allowed for multiple and reproducible BT measures that correlated with coagulation function. Subsequent excision of defined areas of the liver produced bleeding predominantly from small vessels (diameter, less than 2 mm) and parenchyma while resulting in 62% mortality without the use of either heparinization or aggressive fluid infusion. This swine model allows for multiple, repeatable BT measures in the same animal in experiments already involving laparotomy. Such a model is well suited for terminal studies to test effects of multiple doses of the same drug or multiple drugs on BT and allows for multiple, easily visualized measures that permit enhanced repeatability. The liver injury provides for numerous small vessel lesions that could be amenable to closure by coagulation. Therefore, drugs or mechanisms that enhance coagulation and concomitantly decrease blood loss and increase survival time may be accurately evaluated in this new model.

Efficacy of FDA-approved hemostatic drugs to improve survival and reduce bleeding in rat models of uncontrolled hemorrhage.

Several FDA-approved intravenous drugs are used to reduce surgical bleeding. This series of studies tested whether these drugs (aprotinin, desmopressin, tranexamic acid, epsilon-aminocaproic acid) could reduce bleeding due to traumatic injuries in two models of uncontrolled hemorrhage in rats. In the first phase of each study, a nonlethal tail bleeding model was used that incorporated limited fluid resuscitation (lactate Ringer's solution). Four doses of vehicle or the test substance were given successively with bleeding time and blood loss measured after each dose. In the second phase of each study, a lethal liver injury was produced by excising a section of the median lobe (approximately 0.8% of body weight) and an infusion of either vehicle or the test substance was immediately begun. This model included aggressive fluid resuscitation and a severe dilutional coagulopathy. Blood loss, survival time and mortality rate were recorded. Three studies were performed, testing each of the drugs singly and in combination. None of the drugs significantly reduced either bleeding time or blood loss in the tail bleeding model, nor were blood loss, survival time or mortality rate altered in the liver injury model. Taken together, these results suggest that these FDA-approved drugs, when used either singly or in combination, are not efficacious in these models of traumatic uncontrolled hemorrhage.

Effects of increasing doses of activated recombinant factor VII on haemostatic parameters in swine.

This study examined dose-response relationships between activated recombinant factor VII (rFVIIa) and (1) in vivo haemostasis and (2) in vitro measures of coagulation and platelet function. Anesthetized swine were used. Ear bleeding time (BT) was measured and blood was sampled following increasing doses of rFVIIa (0, 90, 180, 360 and 720 microg/kg; n=6) or saline (n=6). BT was not altered by rFVIIa. Prothrombin time (PT) using standard or pig-specific methods was decreased by rFVIIa. Activated clotting time (ACT) was decreased by rFVIIa. Thromboelastography using collagen (COLL) or pig thromboplastin (p-ThP) as agonist demonstrated shorter reaction times, shortened time to reach maximum velocity of clot formation, and increased alpha-angle in the presence of rFVIIa. rFVIIa dosing increased maximum velocity of clot formation when p-ThP was used to initiate the reaction but not when COLL was used. rFVIIa at the highest concentration increased maximum amplitude when COLL was used to initiate the reaction. Platelet aggregation was not altered by rFVIIa. Following completion of the dose escalation phase, a severe liver injury was produced. rFVIIa altered neither blood loss nor survival time following injury but improved mean arterial pressure. A small increase in systemic thrombin-antithrombin III complex occurred after administration of rFVIIa at doses of 180 microg/kg and above. However, there was no histological evidence of intravascular coagulation after rFVIIa administration. In summary, rFVIIa activity was detectable in vitro but did not change haemostasis in normal swine.

Comparisons of normal saline and lactated Ringer's resuscitation on hemodynamics, metabolic responses, and coagulation in pigs after severe hemorrhagic shock.

BACKGROUND: Ongoing improvements in trauma care now recommend earlier use of blood products as part of damage control resuscitation, but generally these products are not available at far forward battlefield locations. For the military, questions continue to arise regarding efficacy of normal saline (NS) vs. lactated Ringer's (LR). Thus, this study compared the effects of LR and NS after severe hemorrhage in pigs. METHODS: 20 anesthetized pigs were randomized into control (n = 6), LR (n = 7), and NS (n = 7) groups. Hemorrhage of 60% estimated total blood volume was induced in LR and NS groups by removing blood from the left femoral artery using a computer-controlled pump. Afterwards, the pigs were resuscitated with either LR at 3 times the bled volume or the volume of NS to reach the same mean arterial pressure (MAP) as in LR group. Hemodynamics were measured hourly and blood samples were taken at baseline (BL), 15 min, 3 h and 6 h after resuscitation to measure changes in coagulation using thrombelastograph®. RESULTS: MAP was decreased by hemorrhage but returned to BL within 1 h after resuscitation with LR (119 ± 7 ml/kg) or NS (183 ± 9 ml/kg, p < 0.05). Base excess (BE) was decreased by hemorrhage; resuscitation with LR recovered BE but not with NS. Total peripheral resistance was decreased with NS and LR, with a larger drop shown in NS. Serum potassium was increased with NS, but not affected with LR. Coagulation changes were similar between LR and NS. CONCLUSIONS: NS may be inferior to LR in resuscitation due to its vasodilator effects and the risks of metabolic acidosis and hyperkalemia.

Different recovery profiles of coagulation factors, thrombin generation, and coagulation function after hemorrhagic shock in pigs.

BACKGROUND: Hemorrhagic shock contributes to coagulopathy after trauma. We investigated daily changes of coagulation components and coagulation function for 5 days in hemorrhaged and resuscitated pigs. METHODS: Fourteen pigs were randomized into the sham control (C) and the hemorrhage and lactated Ringer's resuscitation (H-LR) groups. On day 1, hemorrhage was induced in the H-LR group by bleeding 35% of the total blood volume, followed by LR resuscitation at three times the bled volume. Pigs in the C group were not hemorrhaged or resuscitated. Hemodynamics and coagulation were measured daily after H-LR on day 1 to day 5. RESULTS: No changes in hemodynamics and coagulation function occurred in C. Hemorrhage decreased mean arterial pressure and increased heart rate. LR resuscitation corrected these changes within 2 hours. Compared with the baseline values (BL) on day 1, fibrinogen levels were decreased to 76% ± 6% by H-LR on day 1, increased to 217% ± 16% on day 2, and remained increased thereafter; platelet counts were decreased to 63% ± 5% by H-LR on day 1 and remained lower on days 2 and 3 but returned to BL by days 4 and 5 (all p < 0.05). Thrombin generation was decreased by H-LR on days 1 and 2 but then increased to above BL on days 4 and 5. Coagulation factor levels were decreased by H-LR on day 1 but returned to BL on day 3 except for factor XIII. Clot strength was decreased by H-LR on day 1 and returned to BL by day 2. Clot rapidity did not change on day 1 but was decreased on days 2 and 3 and returned to BL on days 4 and 5. CONCLUSION: Hemorrhage and resuscitation reduced coagulation components and compromised coagulation function, which showed different recovery profiles over the 5-day study period.