John T. Owings

Platelet Activation and Function after Trauma

BACKGROUND Abnormal hemostasis is associated with many of the complications of trauma-associated morbidity and mortality. Platelets are integral in the maintenance of hemostasis. METHODS Samples were obtained from 100 trauma patients on arrival at the emergency room (initial time) and at 24, 48, and 72 hours later. Samples were also obtained from 10 healthy controls at the same time intervals. Using flow cytometry, three parameters were used to measure platelet activation: platelet microparticles, expression of P-selectin (CD62P), and expression of the activated conformation of glycoprotein IIb-IIIa (PAC-1 binding). Platelet function was measured using a platelet function analyzer (PFA-100, Dade International Inc., Miami, FL). RESULTS One hundred trauma patients were enrolled. The average age was 40 years, 75% were men, and 84% had blunt injuries. The mean Injury Severity Score was 22.3 +/- 10.9 (mean +/- SD) and the average Glasgow Coma Scale score was 11 +/- 4. All three platelet activation parameters were increased in trauma patients versus controls for all time periods (p < 0.001). Trauma patients had a trend toward a shorter initial collagen/epinephrine closure time versus controls (p = 0.096). Compared with the 24-, 48-, and 72-hour time intervals, initial collagen/epinephrine closure times were shortened (p < 0.001, p < 0.001, and p < 0.001). Platelet function returned to normal reference ranges within 24 hours but platelet activation parameters remained elevated at least 72 hours after initial trauma. In contrast, when trauma patients with and without brain injury were compared, brain injury patients had increased platelet activation but decreased platelet function (increased collagen/epinephrine closure times). In addition, there was a significant prolongation in collagen/epinephrine closure times for the 24-, 48-, and 72-hour time points in nonsurviving patients versus survivors. There was no association between platelet activation and function and other adverse outcomes including pulmonary embolism, deep venous thrombosis, and disseminated intravascular coagulation. CONCLUSION Severe injury usually results in increased platelet activation and function. However, the combination of increased platelet activation with decreased function was associated with increased mortality.

Hypercoagulability is most prevalent early after injury and in female patients

BACKGROUND Hypercoagulability after injury is a major source of morbidity and mortality. Recent studies indicate that there is a gender-specific risk in trauma patients. This study was performed to determine the course of coagulation after injury and to determine whether there is a gender difference. We hypothesized that hypercoagulability would occur early after injury and that there would be no difference between men and women. METHODS This was a prospective cohort study. Inclusion criteria were admission to the intensive care unit, Injury Severity Score > 4, and the ability to obtain consent from the patient or a relative. A Thrombelastograph (TEG) analysis was performed and routine coagulation parameters and thrombin-antithrombin complexes were measured within 24 hours of injury and then daily for 4 days. RESULTS Sixty-five patients met criteria for entry into the study. Their mean age was 42 +/- 17 years and their mean Injury Severity Score was 23 +/- 12. Forty patients (62%) were men. The prevalence of a hypercoagulable state by TEG was 62% on day 1 and 26% on day 4 (p < 0.01). Women were significantly more hypercoagulable on day 1 than men as measured by the time to onset of clotting (women, 2.9 +/- 0.7 minutes; men, 3.9 +/- 1.5 minutes; p < 0.01; normal, 3.7-8.3 minutes). Mean platelet counts, international normalized ratios, and partial thromboplastin times were within normal limits throughout the study. Thrombin activation as measured by thrombin-antithrombin complexes decreased from 34 +/- 15 microg/L on day 1 to 18 +/- 8 microg/L (p < 0.01) on day 4, consistent with the prevalence of hypercoagulability by TEG. CONCLUSION Hypercoagulability after injury is most prevalent during the first 24 hours. Women are more hypercoagulable than men early after injury. The TEG is more sensitive than routine coagulation assays for the detection of a hypercoagulable state.

Increased use of prophylactic vena cava filters in trauma patients failed to decrease overall incidence of pulmonary embolism.

BACKGROUND Recent studies have reported that placement of vena cava filters (VCFs) early after injury may decrease the incidence of pulmonary embolism (PE) in high-risk trauma patients. STUDY DESIGN This was a retrospective review of all trauma patients with placement of VCFs admitted to a single level-1 trauma center between 1989 and 1997. Two cohorts corresponding to years of high or low prophylactic VCF use (PVCF) were compared. RESULTS Records were reviewed for 299 trauma patients identified as having had placement of a VCE Two hundred forty-eight filters were placed before the diagnosis of PE. During years of low PVCF use, the overall PE incidence was 0.31%; during years of high PVCF use, the incidence of PE was higher at 0.48% (p = 0.045, chi-square). CONCLUSIONS Increased use of PVCFs failed to decrease the overall rate of PE in our trauma patient population.

High-level long-term white blood cell microchimerism after transfusion of leukoreduced blood components to patients resuscitated after severe traumatic injury

BACKGROUND: Long‐term white blood cell (WBC) microchimerism (MC), of at least 2 years, has been reported in trauma patients receiving fresh nonleukoreduced (non‐LR) blood. It is unknown, however, whether this occurs with LR blood products that are nearly devoid of WBCs. Twenty‐seven patients transfused with LR and non‐LR blood products were studied after severe traumatic injury. A secondary aim was to explore donor‐recipient mixed lymphocyte reactivity in vitro.

Effect of critical injury on plasma antithrombin activity: Low antithrombin levels are associated with thromboembolic complications

OBJECTIVE Determine whether severe injury results in decreased plasma antithrombin (AT) activity and whether this decreased AT activity is associated with thromboembolic complications. DESIGN Prospective observational. SUBJECTS A total of 157 critically injured trauma patients. METHODS Each patient underwent laboratory analysis on arrival to the emergency room at hours 8, 16, 24, and 48, and days 3, 4, 5, and 6. Laboratory analyses included AT, tissue factor pathway inhibitor, protein C, prothrombin fragment 1.2, thrombin-antithrombin complex, and D-dimer. Patients were followed for thromboembolic complications including: deep venous thrombosis (DVT), pulmonary embolus, disseminated intravascular coagulation (DIC) and adult respiratory distress syndrome (ARDS). RESULTS Mean Injury Severity Score was 23 (+/-11). AT activity fell below normal in 95 (61%) patients; AT activity rose to greater than normal in 51 (32%) patients. Nine (6%) patients developed DVT, two (1%) pulmonary embolus, 13 (8%) DIC and 26 (17%) ARDS. Using logistic regression analysis, low AT levels were a significant predictor of DVT, DIC, and ARDS (p < 0.05). Supranormal At levels were associated with closed head injury (p < 0.05). D-dimer levels were inversely correlated with AT (p < 0.05). CONCLUSIONS AT activity was depressed in critically injured patients. Patients with head injury developed supranormal AT activity. The risk factors for AT deficiency mimicked those for thromboembolism. Patients with decreased AT activity were at increased risk for thromboembolic complications. Given heparins dependence on AT, these data call into question the use of unmonitored heparin thromboembolism prophylaxis.

Blood transfusion is associated with donor leukocyte microchimerism in trauma patients.

INTRODUCTION Blood transfusion can result in survival of donor leukocyte subpopulations in the recipient. Persistence of donor leukocytes in the transfusion recipient is termed microchimerism. Microchimerism likely reflects engraftment of the recipient with donor hematopoietic stem cells and is very uncommon with transfusion for elective surgery, sickle cell anemia, thalassemia, and HIV. We have found, however, that microchimerism may be more common in trauma patients. OBJECTIVE To determine how frequently transfusion after trauma is associated with microchimerism. METHODS We prospectively enrolled 45 trauma patients who were transfused > or =2 units of PRBCs. We sampled blood before hospital discharge and determined microchimerism by polymerase chain reaction (PCR) analysis of specimens using quantitative allele-specific HLA DR assays to detect non-recipient alleles. Data are expressed as median with interquartile range. RESULTS Patients had a median age of 38 (interquartile range 25, 58) years, ISS of 19 (13, 29), and mortality of 7%. Seventy-eight percent were men, and 84% had blunt trauma. Patients received a median of 6 (4, 16) (range 2, 87) units of PRBCs. Of the 45 patients, 24 (53%) had evidence of microchimerism. Compared with patients without evidence of microchimerism, these patients had no difference in mean age, gender, ISS, units of PRBCs transfused, time from transfusion to blood sampling, or proportion that underwent splenectomy. Twenty-one of the 24 patients with microchimerism had only 1 or 2 non-recipient DR alleles identified by PCR. CONCLUSIONS Transfusion after trauma is associated with over half of recipients having evidence of microchimerism. Age, sex, ISS, and splenectomy of the recipient and the number of transfused units did not correlate with microchimerism. Because the median time from transfusion to sampling for PCR analysis was not longer in the group without microchimerism, it is unlikely microchimerism is due merely to failure of the recipient to clear transfused donor leukocytes.

Enhanced ascertainment of microchimerism with real-time quantitative polymerase chain reaction amplification of insertion-deletion polymorphisms

BACKGROUND: The characterization of microchimerism (MC) by gene amplification has been limited by few allogeneic markers, ascertainment bias, and assay analytic performance. To address this, a panel of 12 MC assays based on insertion‐deletion (InDel) polymorphisms had been optimized.

Leukoreduction of blood transfusions does not diminish transfusion‐associated microchimerism in trauma patients

BACKGROUND: Transfusion of trauma patients can result in long‐term survival of donor white blood cells (WBCs) or “transfusion‐associated microchimerism” (TA‐MC). The aim was to determine whether leukoreduction of blood transfusions, advocated to reduce the immunomodulatory effect of transfusion, decreases the likelihood of developing TA‐MC.

Comparing Direct Thrombin Inhibitors Using aPTT, Ecarin Clotting Times, and Thrombin Inhibitor Management Testing

BACKGROUND: Patients with heparin-induced thrombocytopenia and thrombosis may be acutely anticoagulated with direct thrombin inhibitors (DTIs). The anticoagulation is typically monitored using the activated partial thromboplastin time (aPTT) or ecarin clotting time (ECT). OBJECTIVE: To compare 14 methods for measuring aPTT, as well as ECT and thrombin inhibitor management test (TIM), in samples containing DTIs. METHODS: DTIs were added to pooled normal plasma to achieve low (0.1–1.2 μg/mL) and high (1.5–8.0 μg/mL) drug concentrations. Each low-concentration DTI sample was tested using all aPTT reagents, while each low- and high-concentration DTI was tested using the ECT and TIM. RESULTS: All aPTT reagents had a significant dose-dependent correlation with drug concentration. Only Actin FSL and APTT-S demonstrated equivalent aPTT ratios obtained from any DTI. The TAS-aPTT was the most sensitive aPTT reagent to argatroban, with the aPTT ranging from 52.7 to 121.2 seconds corresponding to 0.1 to 1.2 μg/mL of drug concentration. The TAS-aPTT and Pathromtin were the most sensitive aPTT reagents to bivalirudin, with aPTTs of 87.4 seconds and 101.5 seconds, respectively, at 1.2 μg/mL of drug. Pathromtin was the most sensitive aPTT reagent to lepirudin, with a maximum aPTT of 108.9 seconds at 1.2 μg/mL of drug. There was no statistically significant difference between the TIM and ECT clotting times for each DTI. Lepirudin and bivalirudin ECT and TIM clotting times were equivalent. CONCLUSIONS: There are unique differences between reagent manufacturers in the monitoring of DTIs. Acceptable alternatives to aPTT monitoring of DTI anticoagulation include the ECT and TIM.

Practical utility of the D-dimer assay for excluding thromboembolism in severely injured trauma patients.

BACKGROUND We have advocated the use of a D-dimer assay to exclude the diagnosis of pulmonary embolism (PE) and deep venous thrombosis (DVT) in surgical and trauma patients suspected of having these diagnoses. Injury is known to increase D-dimer levels independent of thromboembolism. The purpose of this study was to assess the period after injury over which the D-dimer assay remains positive because of injury exclusive of thromboembolism. METHODS We prospectively sampled the plasma of severely injured patients for D-dimer using an enzyme-linked immunosorbent assay method at admission; at hours 8, 16, 24, and 48; and at days 3, 4, 5, and 6. Patients were then screened for DVT with a routine duplex Doppler at day 7. Patients were followed for PE, adult respiratory distress syndrome, and disseminated intravascular coagulation. RESULTS One hundred fifty-four patients (mean Injury Severity Score of 23) underwent a total of 1,230 D-dimer assays. Twenty-six (17%) had thromboembolism. Nine (6%) patients developed DVT, 2 (1%) developed PE, 13 (8%) developed disseminated intravascular coagulation, and 11 (7%) developed severe adult respiratory distress syndrome. None of the trauma patients with thromboembolism had a (false) negative D-dimer at or after the time of their thromboembolic complication. True-negative D-dimer results as a function of time from injury are: 0 hours, 18%; 8 hours, 16%; 16 hours, 17%; 24 hours, 22%; 48 hours, 37%; day 3, 34%; day 4, 32%; day 5, 30%; and day 6, 30%. The negative predictive value of the assay was 100%. D-dimer levels were significantly higher in those who developed a thromboembolic complication than in those who did not (independent of Injury Severity Score). CONCLUSION These data serve to validate D-dimer as a means of excluding thromboembolism, specifically in patients with severe injury (100% negative predictive value). Before 48 hours after injury, however, the vast majority of these patients without thromboembolism had positive D-dimer assays. Because of the high false-positive rate early after severe injury, the D-dimer assay may be of little value before postinjury hour 48.