Comparison of Rapid-, Kaolin-, and Native-TEG Parameters in Burn Patient Cohorts With Acute Burn-induced Coagulopathy and Abnormal Fibrinolytic Function

Although use of thromboelastography (TEG) to diagnose coagulopathy and guide clinical decision-making is increasing, relative performance of different TEG methods has not been well-defined. Rapid-TEG (rTEG), kaolin-TEG (kTEG), and native-TEG (nTEG) were performed on blood samples from burn patients presenting to a regional center from admission to 21 days. Patients were categorized by burn severity, mortality, and fibrinolytic phenotypes (Shutdown [SD], Physiologic [PHYS], and Hyperfibrinolytic [HF]). Manufacturer ranges and published TEG cutoffs were examined. Concordance correlations (Rc) of TEG parameters (R, α-angle, maximum amplitude [MA], LY30) measured agreement and Cohen's Kappa (κ) determined interclass reliability. Patients (n = 121) were mostly male (n = 84; 69.4%), with median age 40 years, median TBSA burn 13%, and mortality 17% (n = 21). Severe burns (≥40% TBSA) were associated with lower admission α-angle for rTEG (P = .03) and lower MA for rTEG (P = .02) and kTEG (P = .01). MA was lower in patients who died (nTEG, P = .04; kTEG, P = .02; rTEG, P = .003). Admission HF was associated with increased mortality (OR, 10.45; 95% CI, 2.54-43.31, P = .001) on rTEG only. Delayed SD was associated with mortality using rTEG and nTEG (OR 9.46; 95% CI, 1.96-45.73; P = .005 and OR, 6.91; 95% CI, 1.35-35.48; P = .02). Admission TEGs showed poor agreement on R-time (Rc, 0.00-0.56) and α-angle (0.40 to 0.55), and moderate agreement on MA (0.67-0.81) and LY30 (0.72-0.93). Interclass reliability was lowest for R-time (κ, -0.07 to 0.01) and α-angle (-0.06 to 0.17) and highest for MA (0.22-0.51) and LY30 (0.29-0.49). Choice of TEG method may impact clinical decision-making. rTEG appeared most sensitive in parameter-specific associations with injury severity, abnormal fibrinolysis, and mortality.

Safety of Bioplasma FDP and Hemopure in rhesus macaques after 30% hemorrhage

Objectives

Prehospital transfusion can be life-saving when transport is delayed but conventional plasma, red cells, and whole blood are often unavailable out of hospital. Shelf-stable products are needed as a temporary bridge to in-hospital transfusion. Bioplasma FDP (freeze-dried plasma) and Hemopure (hemoglobin-based oxygen carrier; HBOC) are products with potential for prehospital use. In vivo use of these products together has not been reported. This study assessed the safety of intravenous administration of HBOC+FDP, relative to normal saline (NS), in rhesus macaques (RM).

Methods

After 30% blood volume removal and 30 minutes in shock, animals were resuscitated with either NS or two units (RM size adjusted) each of HBOC+FDP during 60 minutes. Sequential blood samples were collected. After neurological assessment, animals were killed at 24 hours and tissues collected for histopathology.

Results

Due to a shortage of RM during the COVID-19 pandemic, the study was stopped after nine animals (HBOC+FDP, seven; NS, two). All animals displayed physiologic and tissue changes consistent with hemorrhagic shock and recovered normally. There was no pattern of cardiovascular, blood gas, metabolic, coagulation, histologic, or neurological changes suggestive of risk associated with HBOC+FDP.

Conclusion

There was no evidence of harm associated with the combined use of Hemopure and Bioplasma FDP. No differences were noted between groups in safety-related cardiovascular, pulmonary, renal or other organ or metabolic parameters. Hemostasis and thrombosis-related parameters were consistent with expected responses to hemorrhagic shock and did not differ between groups. All animals survived normally with intact neurological function.

Level of evidence

Not applicable.

The Effect of Prehospital Clinical Trial-Related Procedures on Scene Interval, Cognitive Load, and Error: A Randomized Simulation Study

INTRODUCTION

Globally, very few settings have undertaken prehospital randomized controlled trials. Given this lack of experience, there is a risk that such trials in these settings may result in protocol deviations, increased prehospital intervals, and increased cognitive load, leading to error. Ultimately, this may affect patient safety and mortality. The aim of this study was to assess the effect of trial-related procedures on simulated scene interval, self-reported cognitive load, medical errors, and time to action.

METHODS

This was a prospective simulation study. Using a cross-over design, ten teams of prehospital clinicians were allocated to three separate simulation arms in a random order. Simulations were: (1) Eligibility assessment and administration of freeze-dried plasma (FDP) and a hemoglobin-based oxygen carrier (HBOC), (2) Eligibility assessment and administration of HBOC, (3) Eligibility assessment and standard care. All simulations also required clinical management of hemorrhagic shock. Simulated scene interval, error rates, cognitive load (measured by NASA Task Load Index), and competency in clinical care (assessed using the Simulation Assessment Tool Limiting Assessment Bias (SATLAB)) were measured. Mean differences between simulations with and without trial-related procedures were sought using one-way ANOVA or Kruskal-Wallis test. A p-value of <0.05 within the 95% confidence interval was considered significant.

RESULTS

Thirty simulations were undertaken, representing our powered sample size. The mean scene intervals were 00:16:56 for Simulation 1 (FDP and HBOC), 00:17:22 for Simulation 2 (HBOC only), and 00:14:24 for Simulation 3 (standard care). Scene interval did not differ between the groups (p = 0.27). There were also no significant differences in error rates (p = 0.28) or cognitive load (p = 0.67) between the simulation groups. There was no correlation between cognitive load and error rates (r = 0.15, p = 0.42). Competency was achieved in all the assessment criteria for all simulation groups.

CONCLUSION

In a simulated environment, eligibility screening, performance of trial-related procedures, and clinical management of patients with hemorrhagic shock can be completed competently by prehospital advanced life support clinicians without delaying transport or emergency care. Future prehospital clinical trials may use a similar approach to help ensure graded and cautious implementation of clinical trial procedures into prehospital emergency care systems.

Trends in Traumatic Brain Injury Among U.S. Service Members Deployed in Iraq and Afghanistan, 2002-2016

INTRODUCTION

Traumatic brain injury (TBI) is a major health issue for service members deployed and is more common in recent conflicts; however, a thorough understanding of risk factors and trends is not well described. This study aims to characterize the epidemiology of TBI in U.S. service members and the potential impacts of changes in policy, care, equipment, and tactics over the 15 years studied.

METHODS

Retrospective analysis of U.S. Department of Defense Trauma Registry data (2002-2016) was performed on service members treated for TBI at Role 3 medical treatment facilities in Iraq and Afghanistan. Risk factors and trends in TBI were examined in 2021 using Joinpoint regression and logistic regression.

RESULTS

Nearly one third of 29,735 injured service members (32.4%) reaching Role 3 medical treatment facilities had TBI. The majority sustained mild (75.8%), followed by moderate (11.6%) and severe (10.6%) TBI. TBI proportion was higher in males than in females (32.6% vs 25.3%; p<0.001), in Afghanistan than in Iraq (43.8% vs 25.5%; p<0.001), and in battle than in nonbattle (38.6% vs 21.9%; p<0.001). Patients with moderate or severe TBI were more likely to have polytrauma (p<0.001). TBI proportion increased over time, primarily in mild TBI (p=0.02), slightly in moderate TBI (p=0.04), and most rapidly between 2005 and 2011, with a 2.48% annual increase.

CONCLUSIONS

One third of injured service members at Role 3 medical treatment facilities experienced TBI. Findings suggest that additional preventive measures may decrease TBI frequency and severity. Clinical guidelines for field management of mild TBI may reduce the burden on evacuation and hospital systems. Additional capabilities may be needed for military field hospitals.

Pre-Hospital Plasma is Non-Inferior to Whole Blood for Restoration of Cerebral Oxygenation in a Rhesus Macaque Model of Traumatic Shock and Hemorrhage

INTRODUCTION

Traumatic shock and hemorrhage (TSH) is a leading cause of preventable death in military and civilian populations. Utilizing a TSH model, we compared Plasma with whole blood (WB) as pre-hospital interventions, evaluating restoration of cerebral tissue oxygen saturation (CrSO2), systemic hemodynamics, colloid osmotic pressure (COP) and arterial lactate, hypothesizing plasma would function in a non-inferior capacity to WB, despite dilution of hemoglobin (Hgb).

METHODS

Ten anesthetized male rhesus macaques underwent TSH before randomization to receive a bolus of O(-) WB or AB(+) Plasma at T0. At T60, injury repair and shed blood (SB) to maintain mean arterial pressure (MAP) > 65 mmHg began, simulating hospital arrival. Hematologic data and vital signs were analyzed via t-test and two-way repeated measures ANOVA, data presented as mean ± standard deviation, significance = P < 0.05.

RESULTS

There were no significant group differences for shock time, SB volume or hospital SB. At T0, MAP and CrSO2 significantly declined from baseline, though not between groups, normalizing to baseline by T10. COP declined significantly in each group from baseline at T0 but restored by T30, despite significant differences in Hgb (WB 11.7 ± 1.5 v Plasma 6.2 ± 0.8 g/dL). Peak lactate at T30 was significantly higher than baseline in both groups (WB 6.6 ± 4.9 v Plasma 5.7 ± 1.6 mmol/L) declining equivalently by T60.

CONCLUSIONS

Plasma restored hemodynamic support and CrSO2, in a capacity not inferior to WB, despite absence of additional Hgb supplementation. This was substantiated via return of physiologic COP levels, restoring oxygen delivery to microcirculation, demonstrating the complexity of restoring oxygenation from TSH beyond simply increasing oxygen carrying capacity.

Immunopathology of terminal complement activation and complement C5 blockade creating a pro-survival and organ-protective phenotype in trauma

BACKGROUND AND PURPOSE

Traumatic haemorrhage (TH) is the leading cause of potentially preventable deaths that occur during the prehospital phase of care. No effective pharmacological therapeutics are available for critical TH patients yet. Here, we identify terminal complement activation (TCA) as a therapeutic target in combat casualties and evaluate the efficacy of a TCA inhibitor (nomacopan) on organ damage and survival in vivo.

EXPERIMENTAL APPROACH

Complement activation products and cytokines were analysed in plasma from 54 combat casualties. The correlations between activated complement pathway(s) and the clinical outcomes in trauma patients were assessed. Nomacopan was administered to rats subjected to lethal TH (blast injury and haemorrhagic shock). Effects of nomacopan on TH were determined using survival rate, organ damage, physiological parameters, and laboratory profiles.

KEY RESULTS

Early TCA was associated with systemic inflammatory responses and clinical outcomes in this trauma cohort. Lethal TH in the untreated rats induced early TCA that correlated with the severity of tissue damage and mortality. The addition of nomacopan to a damage-control resuscitation (DCR) protocol significantly inhibited TCA, decreased local and systemic inflammatory responses, improved haemodynamics and metabolism, attenuated tissue and organ damage, and increased survival.

CONCLUSION AND IMPLICATIONS

Previous findings of our and other groups revealed that early TCA represents a rational therapeutic target for trauma patients. Nomacopan as a pro-survival and organ-protective drug, could emerge as a promising adjunct to DCR that may significantly reduce the morbidity and mortality in severe TH patients while awaiting transport to critical care facilities.

Trends in Traumatic Brain Injury Related to Consumer Products Among U.S. School-aged Children Between 2000 and 2019

INTRODUCTION

Consumer product‒related traumatic brain injury in children is common, but long-term trends have not been well characterized. Understanding the long-term trends in consumer product‒related traumatic brain injury may inform prevention efforts. The study objective is to examine the trends in consumer product‒related traumatic brain injury in school-aged children.

METHODS

Data were extracted from the National Electronic Injury Surveillance System-All Injury Program for initial emergency department visits for consumer product‒related traumatic brain injury (2000-2019) in school-aged children and analyzed in 2021.

RESULTS

Approximately 6.2 million children presented to emergency department with consumer product‒related traumatic brain injury during 2000-2019. Consumer product‒related traumatic brain injury increased from 4.5% of overall consumer product‒emergency department visits in 2000 to 12.3% in 2019, and its incidence rate (cases per 100,000 population) was higher in males (681.2; 95% CI=611.2, 751.2) than in females (375.8; 95% CI=324.1, 427.6). The annual percentage change in consumer product‒related traumatic brain injury was 3.6% from 2000 to 2008, 13.3% from 2008 to 2012, and ‒2.0% through 2019. Average annual percentage change was higher in females (5.1%; 95% CI=3.4, 6.8) than in males (2.8%; 95% CI=1.6, 3.9). Consumer product‒related traumatic brain injury increased from 2000 to 2012 in females and then remained stable. In males, annual percentage change increased from 2008 to 2012 and then declined through 2019.

CONCLUSIONS

Traumatic brain injury incidence rate in school-aged children increased from 2000 to 2019, peaked in 2012, and then declined in males but not in females. Percentage increases were highest in females. Prevention strategies should continue, with a specific focus on reducing consumer product‒related traumatic brain injury in female children.

The risk of thromboembolic events with early intravenous 2- and 4-g bolus dosing of tranexamic acid compared to placebo in patients with severe traumatic bleeding: A secondary analysis of a randomized, double-blind, placebo-controlled, single-center trial

BACKGROUND

Screening for the risk of thromboembolism (TE) due to tranexamic acid (TXA) in patients with severe traumatic injury has not been performed in randomized clinical trials. Our objective was to determine if TXA dose was independently-associated with thromboembolism.

STUDY DESIGN AND METHODS

This is a secondary analysis of a single-center, double-blinded, randomized controlled trial comparing placebo to a 2-g or 4-g intravenous TXA bolus dose in trauma patients with severe injury. We used multivariable discrete-time Cox regression models to identify associations with risk for thromboembolic events within 30 days post-enrollment. Event curves were created using discrete-time Cox regression.

RESULTS

There were 50 patients in the placebo group, 49 in the 2-g, and 50 in the 4-g TXA group. In adjusted analyses for thromboembolism, a 2-g dose of TXA had an hazard ratio (HR, 95% confidence interval [CI]) of 3.20 (1.12-9.11) (p = .029), and a 4-g dose of TXA had an HR (95% CI) of 5.33 (1.94-14.63) (p = .001). Event curves demonstrated a higher probability of thromboembolism for both doses of TXA compared to placebo. Other parameters independently associated with thromboembolism include time from injury to TXA administration, body mass index, and total blood products transfused.

DISCUSSION

In patients with severe traumatic injury, there was a dose-dependent increase in the risk of at least one thromboembolic event with TXA. TXA should not be withheld, but thromboembolism screening should be considered for patients receiving a dose of at least 2-g TXA intravenously for traumatic hemorrhage.

Analysis of Nonbattle Deaths Among U.S. Service Members in the Deployed Environment

OBJECTIVE

Describe etiologies and trends in non-battle deaths (NBD) among deployed U.S. service members to identify areas for prevention.

BACKGROUND

Injuries in combat are categorized as battle (result of hostile action) or nonbattle related. Previous work found that one-third of injured US military personnel in Iraq and Afghanistan had nonbattle injuries and emphasized prevention. NBD have not yet been characterized.

METHODS

U.S. military casualty data for Iraq and Afghanistan from 2001 to 2014 were obtained from the Defense Casualty Analysis System (DCAS) and the Department of Defense Trauma Registry (DoDTR). Two databases were used because DoDTR does not capture prehospital deaths, while DCAS does not contain clinical details. Nonbattle injuries and NBD were identified, etiologies classified, and NBD trends were assessed using a weighted moving average and time-series analysis with autoregressive integrated moving average. Future NBD rates were forecast.

RESULTS

DCAS recorded 59,799 casualties; 21.0% (n = 1431) of all deaths (n = 6745) were NBD. DoDTR recorded 29,958 casualties; 11.5% (n = 206) of all deaths (n = 1788) were NBD. After early fluctuations, NBD rates for both Iraq and Afghanistan stabilized at approximately 21%. Leading causes of NBD were gunshot wounds and vehicle accidents, accounting for 66%. Approximately 25% was self-inflicted. A 24% NBD rate was forecasted from 2015 through 2025.

CONCLUSIONS

Approximately 1 in 5 deaths were NBD. The majority were potentially preventable, including a significant proportion of self-inflicted injuries. A single comprehensive data repository would facilitate future mortality monitoring and performance improvement. These data may assist military leaders with implementing targeted safety strategies.

Hemorrhagic shock and hemostatic resuscitation in canine trauma

Hemorrhage is a significant cause of death among military working dogs and in civilian canine trauma. While research specifically aimed at canine trauma is limited, many principles from human trauma resuscitation apply. Trauma with significant hemorrhage results in shock and inadequate oxygen delivery to tissues. This leads to aberrations in cellular metabolism, including anaerobic metabolism, decreased energy production, acidosis, cell swelling, and eventual cell death. Considering blood and endothelium as a single organ system, blood failure is a syndrome of endotheliopathy, coagulopathy, and platelet dysfunction. In severe cases following injury, blood failure develops and is induced by inadequate oxygen delivery in the presence of hemorrhage, tissue injury, and acute stress from trauma. Severe hemorrhagic shock is best treated with hemostatic resuscitation, wherein blood products are used to restore effective circulating volume and increase oxygen delivery to tissues without exacerbating blood failure. The principles of hemostatic resuscitation have been demonstrated in severely injured people and the authors propose an algorithm for applying this to canine patients. The use of plasma and whole blood to resuscitate severely injured canines while minimizing the use of crystalloids and colloids could prove instrumental in improving both mortality and morbidity. More work is needed to understand the canine patient that would benefit from hemostatic resuscitation, as well as to determine the optimal resuscitation strategy for these patients.

Circulating Syndecan-1 and Tissue Factor Pathway Inhibitor, Biomarkers of Endothelial Dysfunction, Predict Mortality in Burn Patients

OBJECTIVE

The aim of this study is to evaluate the association between burn injury and admission plasma levels of Syndecan-1 (SDC-1) and Tissue Factor Pathway Inhibitor (TFPI), and their ability to predict 30-day mortality.

BACKGROUND

SDC-1 and TFPI are expressed by vascular endothelium and shed into the plasma as biomarkers of endothelial damage. Admission plasma biomarker levels have been associated with morbidity and mortality in trauma patients, but this has not been well characterized in burn patients.Methods: This cohort study enrolled burn patients admitted to a regional burn center between 2013 and 2017. Blood samples were collected within 4 h of admission and plasma SDC-1 and TFPI were quantified by ELISA. Demographics and injury characteristics were collected prospectively. The primary outcome was 30-day in-hospital mortality.

RESULTS

Of 158 patients, 74 met inclusion criteria. Most patients were male with median age of 41.5 years and burn TBSA of 20.5%. The overall mortality rate was 20.3%. Admission SDC-1 and TFPI were significantly higher among deceased patients. Plasma SDC-1 >34 ng/mL was associated with a 32-times higher likelihood of mortality [OR: 32.65 (95% CI, 2.67-399.78); P = 0.006] and a strong predictor of mortality (area under the ROC [AUROC] 0.92). TFPI was associated with a nine-times higher likelihood of mortality [OR: 9.59 (95% CI, 1.02-89.75); P = 0.002] and a fair predictor of mortality (AUROC 0.68).

CONCLUSIONS

SDC-1 and TFPI are associated with a higher risk of 30-day mortality. We propose the measurement of SDC-1 on admission to identify burn patients at high risk of mortality. However, further investigation with a larger sample size is warranted.

Inhalation Injury is Associated with Endotheliopathy and Abnormal Fibrinolytic Phenotypes in Burn Patients: A Cohort Study

Burn injury is associated with endothelial dysfunction and coagulopathy and concomitant inhalation injury increases morbidity and mortality. The aim of this work is to identify associations between inhalation injury (IHI), coagulation homeostasis, vascular endothelium, and clinical outcomes in burn patients. One-hundred and twelve patients presenting to a regional burn center were included in this retrospective cohort study. Whole blood was collected at set intervals from admission through 24 hours and underwent viscoelastic assay with rapid TEG (rTEG). Syndecan-1 (SDC-1) on admission was quantified by ELISA. Patients were grouped by the presence (n=28) or absence (n=84) of concomitant IHI and rTEG parameters, fibrinolytic phenotypes, SDC-1, and clinical outcomes were compared. Of the 112 thermally injured patients, 28 (25%) had IHI. Most patients were male (68.8%) with a median age of 40 (IQR, 29-57) years. Patients with IHI had higher overall mortality (42.68% vs. 8.3%; p<0.0001). rTEG LY30 was lower in patients with IHI at hours 4 and 12 (p<0.05). There was a pattern of increased abnormal fibrinolytic phenotypes among IHI patients. There was a greater proportion of IHI patients with endotheliopathy (SDC-1 > 34 ng/mL) (64.7% vs. 26.4%; p=0.008). There was a pattern of increased mortality among patients with inhalation injury and endotheliopathy (0% vs. 72.7%; p=0.004). Significant differences between patients with and without IHI were found in measures assessing fibrinolytic potential and endotheliopathy. Mortality was associated with abnormal fibrinolysis, endotheliopathy, and inhalation injury. However, the extent to which IHI associated dysfunction is independent of TBSA burn size remains to be elucidated.

Lessons Learned From the Battlefield and Applicability to Veterinary Medicine - Part 2: Transfusion Advances

Since the inception of recent conflicts in Afghanistan and Iraq, transfusion practices in human military medicine have advanced considerably. Today, US military physicians recognize the need to replace the functionality of lost blood in traumatic hemorrhagic shock and whole blood is now the trauma resuscitation product of choice on the battlefield. Building on wartime experiences, military medicine is now one of the country's strongest advocates for the principle of hemostatic resuscitation using whole blood or balanced blood components as the primary means of resuscitation as early as possibly following severe trauma. Based on strong evidence to support this practice in human combat casualties and in civilian trauma care, military veterinarians strive to practice similar hemostatic resuscitation for injured Military Working Dogs. To this end, canine whole blood has become increasingly available in forward environments, and non-traditional storage options for canine blood and blood components are being explored for use in canine trauma. Blood products with improved shelf-life and ease of use are not only useful for military applications, but may also enable civilian general and specialty practices to more easily incorporate hemostatic resuscitation approaches to canine trauma care.

Early abnormal fibrinolysis and mortality in patients with thermal injury: a prospective cohort study

INTRODUCTION

Abnormal fibrinolysis early after injury has been associated with increased mortality in trauma patients, but no studies have addressed patients with burn injury. This prospective cohort study aimed to characterize fibrinolytic phenotypes in burn patients and to see if they were associated with mortality.

METHODS

Patients presenting to a regional burn centre within 4 h of thermal injury were included. Blood was collected for sequential viscoelastic measurements using thromboelastography (RapidTEG™) over 12 h. The percentage decrease in clot strength 30 min after the time of maximal clot strength (LY30) was used to categorize patients into hypofibrinolytic/fibrinolytic shutdown (SD), physiological (PHYS) and hyperfibrinolytic (HF) phenotypes. Injury characteristics, demographics and outcomes were compared.

RESULTS

Of 115 included patients, just over two thirds were male. Overall median age was 40 (i.q.r. 28-57) years and median total body surface area (TBSA) burn was 13 (i.q.r. 6-30) per cent. Some 42 (36.5 per cent) patients had severe burns affecting over 20 per cent TBSA. Overall mortality was 18.3 per cent. At admission 60.0 per cent were PHYS, 30.4 per cent were SD and 9.6 per cent HF. HF was associated with increased risk of mortality on admission (odds ratio 12.61 (95 per cent c.i. 1.12 to 142.57); P = 0.041) but not later during the admission when its incidence also decreased. Admission SD was not associated with mortality, but incidence increased and by 4 h and beyond, SD was associated with increased mortality, compared with PHYS (odds ratio 8.27 (95 per cent c.i. 1.16 to 58.95); P = 0.034).

DISCUSSION

Early abnormal fibrinolytic function is associated with mortality in burn patients.

Hemostatic capacity of canine chilled whole blood over time

OBJECTIVE

To determine the hemostatic potential of canine chilled whole blood maintained at clinically relevant storage conditions.

DESIGN

In vitro experimental study.

SETTING

Government blood and coagulation research laboratory and government referral veterinary hospital.

ANIMALS

Ten healthy Department of Defense military working dogs.

INTERVENTIONS

One unit of fresh whole blood was collected from each of 10 military working dogs using aseptic technique. Blood was maintained in a medical-grade refrigerator for 28 days at 4°C (39°F) and analyzed before refrigeration (day 0) and after (days 2, 4, 7, 9, 11, 14, 21, and 28).

MEASUREMENTS AND MAIN RESULTS

Ten units of canine blood were analyzed with whole blood platelet aggregation, thromboelastography, CBC, biochemical analysis, blood gas, and prothrombin/activated partial thromboplastin/fibrinogen assay. Clotting strength of chilled blood was maintained up to 21 days despite significant decreases in platelet aggregation to ADP, collagen, or γ-thrombin, significant prolongation of prothrombin and activated partial thromboplastin times, and reduced speed of clot formation (K time, alpha angle). Fibrinogen concentration, WBC, RBC, and platelet counts did not change over time.

CONCLUSIONS

Chilled canine whole blood loses a small percentage of clot strength through 21 days of refrigerated storage. Further research is needed to determine if this hemostatic potential is clinically relevant in hemorrhaging dogs who require surgical intervention or are exposed to traumatic events.

Evidence-Based and Clinically Relevant Outcomes for Hemorrhage Control Trauma Trials

OBJECTIVE

To address the clinical and regulatory challenges of optimal primary endpoints for bleeding patients by developing consensus-based recommendations for primary clinical outcomes for pivotal trials in patients within 6 categories of significant bleeding, (1) traumatic injury, (2) intracranial hemorrhage, (3) cardiac surgery, (4) gastrointestinal hemorrhage, (5) inherited bleeding disorders, and (6) hypoproliferative thrombocytopenia.

BACKGROUND

A standardized primary outcome in clinical trials evaluating hemostatic products and strategies for the treatment of clinically significant bleeding will facilitate the conduct, interpretation, and translation into clinical practice of hemostasis research and support alignment among funders, investigators, clinicians, and regulators.

METHODS

An international panel of experts was convened by the National Heart Lung and Blood Institute and the United States Department of Defense on September 23 and 24, 2019. For patients suffering hemorrhagic shock, the 26 trauma working-group members met for almost a year, utilizing biweekly phone conferences and then an in-person meeting, evaluating the strengths and weaknesses of previous high quality studies. The selection of the recommended primary outcome was guided by goals of patient-centeredness, expected or demonstrated sensitivity to beneficial treatment effects, biologic plausibility, clinical and logistical feasibility, and broad applicability.

CONCLUSIONS

For patients suffering hemorrhagic shock, and especially from truncal hemorrhage, the recommended primary outcome was 3 to 6-hour all-cause mortality, chosen to coincide with the physiology of hemorrhagic death and to avoid bias from competing risks. Particular attention was recommended to injury and treatment time, as well as robust assessments of multiple safety related outcomes.

Lessons Learned From the Battlefield and Applicability to Veterinary Medicine-Part 1: Hemorrhage Control

In humans, the leading cause of potentially preventable death on the modern battlefield is undoubtedly exsanguination from massive hemorrhage. The US military and allied nations have devoted enormous effort to combat hemorrhagic shock and massive hemorrhage. This has yielded numerous advances designed to stop bleeding and save lives. The development of extremity, junctional and truncal tourniquets applied by first responders have saved countless lives both on the battlefield and in civilian settings. Additional devices such as resuscitative endovascular balloon occlusion of the aorta (REBOA) and intraperitoneal hemostatic foams show great promise to address control the most difficult forms (non-compressible) of hemorrhage. The development of next generation hemostatic dressings has reduced bleeding both in the prehospital setting as well as in the operating room. Furthermore, the research and fielding of antifibrinolytics such as tranexamic acid have shown incredible promise to ameliorate the effects of acute traumatic coagulopathy which has led to significant morbidity and mortality in service members. Advances from lessons learned on the battlefield have numerous potential parallels in veterinary medicine and these lessons are ripe for translation to veterinary medicine.

Effects of refrigerated storage on hemostatic stability of four canine plasma products

OBJECTIVE

To assess clotting times, coagulation factor activities, sterility, and thromboelastographic parameters of liquid plasma (LP), thawed fresh frozen plasma (FFP-T), and 2 novel formulations of freeze-dried plasma (FDP) stored refrigerated over 35 days.

SAMPLE

6 units of canine LP and FFP-T from a commercial animal blood bank and 5 units each of 2 formulations of canine FDP.

PROCEDURES

Prothrombin time; activated partial thromboplastin time; activities of coagulation factors II, V, VII, VIII, IX, X, XI, and XII; and thromboelastographic parameters were determined for each product on days 0 (baseline), 3, 7, 14, 21, 28, and 35. For each day, a sample of each product was also submitted for aerobic bacterial culture.

RESULTS

Small changes in coagulation factor activities and mild increased time to initial clot formation in LP and FFP-T were noted over the 35-day storage period. Activities of factor VIII in FDP1 and factor XII in FDP2 were < 50% at baseline but varied throughout. Compared with FFP-T, time to initial clot formation was increased and clot strength was preserved or increased for the FDPs throughout the study. One FDP had decreased pH, compared with other products. No plasma product yielded bacterial growth.

CONCLUSIONS AND CLINICAL RELEVANCE

Liquid plasma and FFP-T would be reasonable to use when stored refrigerated for up to 35 days. Both FDP products showed variability in coagulation factor activities. Studies investigating the usefulness of these plasma products (FDPs) in dogs and the variable days of refrigerated storage (all products) are warranted. (Am J Vet Res 2020;81:964-972).

The Immunologic Effect of Early Intravenous Two and Four Gram Bolus Dosing of Tranexamic Acid Compared to Placebo in Patients With Severe Traumatic Bleeding (TAMPITI): A Randomized, Double-Blind, Placebo-Controlled, Single-Center Trial

Background

The hemostatic properties of tranexamic acid (TXA) are well described, but the immunological effects of TXA administration after traumatic injury have not been thoroughly examined. We hypothesized TXA would reduce monocyte activation in bleeding trauma patients with severe injury.

Methods

This was a single center, double-blinded, randomized controlled trial (RCT) comparing placebo to a 2 g or 4 g intravenous TXA bolus dose in trauma patients with severe injury. Fifty patients were randomized into each study group. The primary outcome was a reduction in monocyte activation as measured by human leukocyte antigen-DR isotype (HLA-DR) expression on monocytes 72 h after TXA administration. Secondary outcomes included kinetic assessment of immune and hemostatic phenotypes within the 72 h window post-TXA administration.

Results

The trial occurred between March 2016 and September 2017, when data collection ended. 149 patients were analyzed (placebo, n = 50; 2 g TXA, n = 49; 4 g TXA, n = 50). The fold change in HLA-DR expression on monocytes [reported as median (Q1–Q3)] from pre-TXA to 72 h post-TXA was similar between placebo [0.61 (0.51–0.82)], 2 g TXA [0.57 (0.47–0.75)], and 4 g TXA [0.57 (0.44–0.89)] study groups (p = 0.82). Neutrophil CD62L expression was reduced in the 4 g TXA group [fold change: 0.73 (0.63–0.97)] compared to the placebo group [0.97 (0.78–1.10)] at 24 h post-TXA (p = 0.034). The fold decrease in plasma IL-6 was significantly less in the 4 g TXA group [1.36 (0.87–2.42)] compared to the placebo group [0.46 (0.19–1.69)] at 72 h post-TXA (p = 0.028). There were no differences in frequencies of myeloid or lymphoid populations or in classical complement activation at any of the study time points.

Conclusion

In trauma patients with severe injury, 4 g intravenous bolus dosing of TXA has minimal immunomodulatory effects with respect to leukocyte phenotypes and circulating cytokine levels.

Clinical Trial Registration

www.ClinicalTrials.gov, identifier NCT02535949.

Forgot calcium? Admission ionized-calcium in two civilian randomized controlled trials of prehospital plasma for traumatic hemorrhagic shock

BACKGROUND

Randomized clinical trials (RCTs) support the use of prehospital plasma in traumatic hemorrhagic shock, especially in long transports. The citrate added to plasma binds with calcium, yet most prehospital trauma protocols have no guidelines for calcium replacement. We reviewed the experience of two recent prehospital plasma RCTs regarding admission ionized-calcium (i-Ca) blood levels and its impact on survival. We hypothesized that prehospital plasma is associated with hypocalcemia, which in turn is associated with lower survival.

METHODS

We studied patients enrolled in two institutions participating in prehospital plasma RCTs (control, standard of care; experimental, plasma), with i-Ca collected before calcium supplementation. Adults with traumatic hemorrhagic shock (systolic blood pressure ≤70 mm Hg or 71-90 mm Hg + heart rate ≥108 bpm) were eligible. We use generalized linear mixed models with random intercepts and Cox proportional hazards models with robust standard errors to account for clustered data by institution. Hypocalcemia was defined as i-Ca of 1.0 mmol/L or less.

RESULTS

Of 160 subjects (76% men), 48% received prehospital plasma (median age, 40 years [interquartile range, 28-53 years]) and 71% suffered blunt trauma (median Injury Severity Score [ISS], 22 [interquartile range, 17-34]). Prehospital plasma and control patients were similar regarding age, sex, ISS, blunt mechanism, and brain injury. Prehospital plasma recipients had significantly higher rates of hypocalcemia compared with controls (53% vs. 36%; adjusted relative risk, 1.48; 95% confidence interval [CI], 1.03-2.12; p = 0.03). Severe hypocalcemia was significantly associated with decreased survival (adjusted hazard ratio, 1.07; 95% CI, 1.02-1.13; p = 0.01) and massive transfusion (adjusted relative risk, 2.70; 95% CI, 1.13-6.46; p = 0.03), after adjustment for confounders (randomization group, age, ISS, and shock index).

CONCLUSION

Prehospital plasma in civilian trauma is associated with hypocalcemia, which in turn predicts lower survival and massive transfusion. These data underscore the need for explicit calcium supplementation guidelines in prehospital hemotherapy.

LEVEL OF EVIDENCE

Therapeutic, level II.

Association of Prehospital Plasma Transfusion With Survival in Trauma Patients With Hemorrhagic Shock When Transport Times Are Longer Than 20 Minutes: A Post Hoc Analysis of the PAMPer and COMBAT Clinical Trials

Importance

Both military and civilian clinical practice guidelines include early plasma transfusion to achieve a plasma to red cell ratio approaching 1:1 to 1:2. However, it was not known how early plasma should be given for optimal benefit. Two recent randomized clinical trials were published, with apparently contradictory results. The Prehospital Air Medical Plasma (PAMPer) clinical trial showed a nearly 30% reduction in mortality with plasma transfusion in the prehospital environment, while the Control of Major Bleeding After Trauma (COMBAT) clinical trial showed no survival improvement.

Objective

To facilitate a post hoc combined analysis of the COMBAT and PAMPer trials to examine questions that could not be answered by either clinical trial alone. We hypothesized that prehospital transport time influenced the effects of prehospital plasma on 28-day mortality.

Design, Setting, and Participants

A total of 626 patients in the 2 clinical trials were included. Patients with trauma and hemorrhagic shock were randomly assigned to receive either standard care or 2 U of thawed plasma followed by standard care in the prehospital environment. Data analysis was performed between September 2018 and January 2019.

Interventions

Prehospital transfusion of 2 U of plasma compared with crystalloid-based resuscitation.

Main Outcomes and Measures

The main outcome was 28-day mortality.

Results

In this post hoc analysis of 626 patients (467 men [74.6%] and 159 women [25.4%]; median [interquartile range] age, 42 [27-57] years) who had trauma with hemorrhagic shock, a Cox regression analysis showed a significant overall survival benefit for plasma (hazard ratio [HR], 0.65; 95% CI, 0.47-0.90; P = .01) after adjustment for injury severity, age, and clinical trial cohort (COMBAT or PAMPer). A significant association with prehospital transport time was detected (from arrival on scene to arrival at the trauma center). Increased mortality was observed in patients in the standard care group when prehospital transport was longer than 20 minutes (HR, 2.12; 95% CI, 1.05-4.30; P = .04), while increased mortality was not observed in patients in the prehospital plasma group (HR, 0.78; 95% CI, 0.40-1.51; P = .46). No serious adverse events were associated with prehospital plasma transfusion.

Conclusions and Relevance

These data suggest that prehospital plasma is associated with a survival benefit when transport times are longer than 20 minutes and that the benefit-risk ratio is favorable for use of prehospital plasma.

Trial Registration

ClinicalTrials.gov identifiers: NCT01838863 (COMBAT) and NCT01818427 (PAMPer).

Hypercoagulation and Hypermetabolism of Fibrinogen in Severely Burned Adults

This study investigated changes in plasma fibrinogen metabolism and changes in coagulation in severely burned adults. Ten patients (27 ± 3 years; 91 ± 6 kg) with 51 ± 3% TBSA were consented and enrolled into an institutional review board-approved prospective study. On the study day, stable isotope infusion of 1-13C-phenylalanine and d5-phenylalanine was performed to quantify fibrinogen production and consumption. During the infusion, vital signs were recorded and blood samples were drawn every hour. Coagulation was measured by thromboelastograph (TEG). Ten normal healthy volunteers (37 ± 7 years; 74 ± 4 kg) were included as the control group. Burned adults had elevated heart rates (120 ± 2 vs 73 ± 5 [control] beats/minute), respiration rates (23 ± 2 vs 15 ± 1 breaths/minute), plasma glucose (127 ± 10 vs 89 ± 2 mg/dl), and fibrinogen levels (613 ± 35 vs 239 ± 17 mg/dl); and decreased albumin (1.3 ± 0.2 vs 3.7 ± 0.1 g/dl) and total protein (4.4 ± 0.2 vs 6.8 ± 0.1 g/dl, all P < .05). Fibrinogen breakdown was elevated in the burn group (2.3 ± 0.4 vs. 1.0 ± 0.3 µmol/kg/minute); and fibrinogen synthesis was further enhanced in the burn group (4.4 ± 0.7 vs 0.7 ± 0.2 µmol/kg/minute, both P < .05). Clotting speed (TEG-alpha) and clot strength (TEG-MA) were increased in the burn group (62 ± 4 vs 50 ± 4°, and 76 ± 2 vs 56 ± 2 mm, respectively, both P < .05). Fibrinolysis of TEG-LY60 was accelerated in the burn group (16 ± 6 vs 3 ± 1) and so was the increase in D-dimer level in the burn group (4.5 ± 0.4 vs 1.9 ± 0.3 mg/l, both P < .05). The hypercoagulable state postburn is in part a result of increased fibrinogen synthesis, over and above increased fibrinogen breakdown.

A 12-Year Analysis of Nonbattle Injury Among US Service Members Deployed to Iraq and Afghanistan

Importance

Nonbattle injury (NBI) among deployed US service members increases the burden on medical systems and results in high rates of attrition, affecting the available force. The possible causes and trends of NBI in the Iraq and Afghanistan wars have, to date, not been comprehensively described.

Objectives

To describe NBI among service members deployed to Iraq and Afghanistan, quantify absolute numbers of NBIs and proportion of NBIs within the Department of Defense Trauma Registry, and document the characteristics of this injury category.

Design, Setting, and Participants

In this retrospective cohort study, data from the Department of Defense Trauma Registry on 29 958 service members injured in Iraq and Afghanistan from January 1, 2003, through December 31, 2014, were obtained. Injury incidence, patterns, and severity were characterized by battle injury and NBI. Trends in NBI were modeled using time series analysis with autoregressive integrated moving average and the weighted moving average method. Statistical analysis was performed from January 1, 2003, to December 31, 2014.

Main Outcomes and Measures

Primary outcomes were proportion of NBIs and the changes in NBI over time.

Results

Among 29 958 casualties (battle injury and NBI) analyzed, 29 003 were in men and 955 were in women; the median age at injury was 24 years (interquartile range, 21-29 years). Nonbattle injury caused 34.1% of total casualties (n = 10 203) and 11.5% of all deaths (206 of 1788). Rates of NBI were higher among women than among men (63.2% [604 of 955] vs 33.1% [9599 of 29 003]; P < .001) and in Operation New Dawn (71.0% [298 of 420]) and Operation Iraqi Freedom (36.3% [6655 of 18 334]) compared with Operation Enduring Freedom (29.0% [3250 of 11 204]) (P < .001). A higher proportion of NBIs occurred in members of the Air Force (66.3% [539 of 810]) and Navy (48.3% [394 of 815]) than in members of the Army (34.7% [7680 of 22 154]) and Marine Corps (25.7% [1584 of 6169]) (P < .001). Leading mechanisms of NBI included falls (2178 [21.3%]), motor vehicle crashes (1921 [18.8%]), machinery or equipment accidents (1283 [12.6%]), blunt objects (1107 [10.8%]), gunshot wounds (728 [7.1%]), and sports (697 [6.8%]), causing predominantly blunt trauma (7080 [69.4%]). The trend in proportion of NBIs did not decrease over time, remaining at approximately 35% (by weighted moving average) after 2006 and approximately 39% by autoregressive integrated moving average. Assuming stable battlefield conditions, the autoregressive integrated moving average model estimated that the proportion of NBIs from 2015 to 2022 would be approximately 41.0% (95% CI, 37.8%-44.3%).

Conclusions and Relevance

In this study, approximately one-third of injuries during the Iraq and Afghanistan wars resulted from NBI, and the proportion of NBIs was steady for 12 years. Understanding the possible causes of NBI during military operations may be useful to target protective measures and safety interventions, thereby conserving fighting strength on the battlefield.

The need for dried plasma - a national issue

Recent studies have demonstrated that early transfusion of plasma or RBCs improves survival in patients with severe trauma and hemorrhagic shock. Time to initiate transfusion is the critical factor. It is essential that transfusion begin in the prehospital environment when transport times are longer than approximately 15 to 20 minutes. Unfortunately, logistic constraints severely limit the use of blood products in the prehospital setting, especially in military, remote civilian, and mass disaster circumstances, where the need can be most acute. US military requirements for logistically supportable blood products are projected to increase dramatically in future conflicts. Although dried plasma products have been available and safely used in a number of countries for over 20 years, there is no dried plasma product commercially available in the United States. A US Food and Drug Administration-approved dried plasma is urgently needed. Considering the US military, disaster preparedness, and remote civilian trauma perspectives, this is an urgent national health care issue.

Utilizing Plasma Composition Data to Help Determine Procoagulant Dynamics in Patients with Thermal Injury: A Computational Assessment

INTRODUCTION

The development of methods that generate individualized assessments of the procoagulant potential of burn patients could improve their treatment. Beyond its role as an essential intermediate in the formation of thrombin, factor (F)Xa has systemic effects as an agonist to inflammatory processes. In this study, we use a computational model to study the FXa dynamics underlying tissue factor-initiated thrombin generation in a small cohort of burn patients.

MATERIALS AND METHODS

Plasma samples were collected upon admission (Hour 0) from nine subjects (five non-survivors) with major burn injuries and then at 48 hours. Coagulation factor concentrations (II, V, VII, VIII, IX, X, TFPI, antithrombin (AT), protein C (PC)) were measured and used in a computational model to generate time course profiles for thrombin (IIa), FXa, extrinsic tenase, intrinsic tenase and prothrombinase complexes upon a 5 pM tissue factor stimulus in the presence of 1 nM thrombomodulin. Parameters were extracted from the thrombin and FXa profiles (including max rate (MaxRIIa and MaxRFXa) and peak level (MaxLIIa and MaxLFXa)). Procoagulant potential was also evaluated by determining the concentration of the complexes at select times. Parameter values were compared between survivors and non-survivors in the burn cohort and between the burn cohort and a simulation based on the mean physiological (100%) concentration for all factor levels.

RESULTS

Burn patients differed at Hour 0 (p < 0.05) from 100% mean physiological levels for all coagulation factor levels except FV and FVII. The concentration of FX, FII, TFPI, AT and PC was lower; FIX and FVIII were increased. The composition differences resulted in all nine burn patients at Hour 0 displaying a procoagulant phenotype relative to 100% mean physiological simulation (MaxLIIa (306 ± 90 nM vs. 52 nM), MaxRIIa (2.9 ± 1.1 nM/s vs. 0.3 nM/s), respectively p < 0.001); MaxRFXa and MaxLFXa were also an order of magnitude greater than 100% mean physiological simulation (p < 0.001). When grouped by survival status and compared at the time of admission, non-survivors had lower PC levels (56 ± 18% vs. 82 ± 9%, p < 0.05), and faster MaxRFXa (29 ± 6 pM/s vs. 18 ± 6 pM/s, p < 0.05) than those that survived; similar trends were observed for all other procoagulant parameters. At 48 hours when comparing non-survivors to survivors, TFPI levels were higher (108 ± 18% vs. 59 ± 18%, p < 0.05), and MaxRIIa (1.5 ± 1.4 nM/s vs. 3.6 ± 0.7 nM/s, p < 0.05) and MaxRFXa (13 ± 12 pM/s vs. 35 ± 4 pM/s, p < 0.05) were lower; similar trends were observed with all other procoagulant parameters. Overall, between admission and 48 hours, procoagulant potential, as represented by MaxR and MaxL parameters for thrombin and FXa, in non-survivors decreased while in survivors they increased (p < 0.05). In patients that survived, there was a positive correlation between FX levels and MaxLFXa (r = 0.96) and reversed in mortality (r= -0.91).

CONCLUSIONS

Thrombin and FXa generation are increased in burn patients at admission compared to mean physiological simulations. Over the first 48 hours, burn survivors became more procoagulant while non-survivors became less procoagulant. Differences between survivors and non-survivors appear to be present in the underlying dynamics that contribute to FXa dynamics. Understanding how the individual specific balance of procoagulant and anticoagulant proteins contributes to thrombin and FXa generation could ultimately guide therapy and potentially reduce burn injury-related morbidity and mortality.

The interagency strategic plan for research and development of blood products and related technologies for trauma care and emergency preparedness 2015-2020

Intensive blood use is expected to occur at levels, which will overwhelm blood supplies as they exist with current capabilities and technologies, both in civilian mass casualty events and military battlefield trauma. New technologies are needed for trauma care, and specifically to provide safer, more effective, and more logistically supportable blood products to treat patients with, or at risk of developing, acquired bleeding disorders resulting from trauma, acute radiation exposure, or other causes. Three of the primary agencies with major research and development programs related to blood products, the Biomedical Advanced Research and Development Authority (BARDA), the Department of Defense (DoD), and the National Heart, Lung, and Blood Institute are uniquely positioned to partner in addressing these issues, which have significant implications for each respective agency, as well as for the US population. Providing leadership, coordination, and oversight for the Food and Drug Administration's national and global health security, counterterrorism, and emerging threats portfolios, the US Food and Drug Administration Office of Counterterrorism and Emerging Threats serves in a critical advisory and facilitative role regarding development and availability of blood products. This plan is informed by the 2012 PHEMCE Strategy (US Department of Health and Human Services, 2012), the 2007 "Shaping the Future of Research" Strategic Plan for the National Heart, Lung, and Blood Institute, the 2011 BARDA Strategic Plan, the DoD Combat Casualty Care Research Program: Policy Review, the 2015 DoD Hemorrhage and Resuscitation Research and Development Strategic Plan, and more than 30 participants from other agencies who participated in planning.

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

This study examined dose-response relationships between activated recombinant factorVII (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 μg/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 α -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 μg/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.

Effects of an acidic environment on coagulation dynamics

Essentials Acidosis, an outcome of traumatic injury, has been linked to impaired procoagulant efficiency. In vitro model systems were used to assess coagulation dynamics at pH 7.4 and 7.0. Clot formation dynamics are slightly enhanced at pH 7.0 in blood ex vivo. Acidosis induced decreases in antithrombin efficacy offset impairments in procoagulant activity.

SUMMARY

Background Disruption of hydrogen ion homeostasis is a consequence of traumatic injury often associated with clinical coagulopathy. Mechanisms by which acidification of the blood leads to aberrant coagulation require further elucidation. Objective To examine the effects of acidified conditions on coagulation dynamics using in vitro models of increasing complexity. Methods Coagulation dynamics were assessed at pH 7.4 and 7.0 as follows: (i) tissue factor (TF)-initiated coagulation proteome mixtures (±factor [F]XI, ±fibrinogen/FXIII), with reaction progress monitored as thrombin generation or fibrin formation; (ii) enzyme/inhibitor reactions; and (iii) TF-dependent or independent clot dynamics in contact pathway-inhibited blood via viscoelastometry. Results Rate constants for antithrombin inhibition of FXa and thrombin were reduced by ~ 25-30% at pH 7.0. At pH 7.0 (+FXI), TF-initiated thrombin generation showed a 20% increase in maximum thrombin levels and diminished thrombin clearance rates. Viscoelastic analyses showed a 25% increase in clot time and a 25% reduction in maximum clot firmness (MCF). A similar MCF reduction was observed at pH 7.0 when fibrinogen/FXIII were reacted with thrombin. In contrast, in contact pathway-inhibited blood (n = 6) at pH 7.0, MCF values were elevated 6% (95% confidence interval [CI]: 1%-11%) in TF-initiated blood and 15% (95% CI: 1%- 29%) in the absence of TF. Clot times at pH 7.0 decreased 32% (95% CI: 15%-49%) in TF-initiated blood and 51% (95% CI: 35%-68%) in the absence of TF. Conclusions Despite reported decreased procoagulant catalysis at pH 7.0, clot formation dynamics are slightly enhanced in blood ex vivo and suppression of thrombin generation is not observed. A decrease in antithrombin reactivity is one potential mechanism contributing to these outcomes.

Comprehensive US government program for dried plasma development

Transfusion of plasma early after severe injury has been associated with improved survival. There are significant logistic factors that limit the ability to deliver plasma where needed in austere environments, such as the battlefield or during a significant civilian emergency. While some countries have access to more logistically supportable dried plasma, there is no such product approved for use in the United States. There is a clear need for a Food and Drug Administration (FDA)‐approved dried plasma for military and emergency‐preparedness uses, as well as for civilian use in remote or austere settings. The Department of Defense (DoD) and Biomedical Advanced Research and Development Authority are sponsoring development of three dried plasma products, incorporating different technologic approaches and business models. At the same time, the DoD is sponsoring prospective, randomized clinical studies on the prehospital use of plasma. These efforts are part of a coordinated program to provide a dried plasma for military and civilian applications and to produce additional information on plasma use so that, by the time we have an FDA‐approved dried plasma, we will better understand how to use it.

Dose Responses of Ibuprofen In Vitro on Platelet Aggregation and Coagulation in Human and Pig Blood Samples

INTRODUCTION

Ibuprofen is commonly used by warfighters in the deployed environment. This study investigated its dose effects on in vitro coagulation in human and pig blood.

METHODS

Blood samples were collected from 6 normal volunteers and 6 healthy pigs and processed to make platelet-adjusted samples (100 × 10(3)/μL, common transfusion trigger in trauma). Ibuprofen was added to the samples at concentrations of 0 μg/mL (control), the concentration from the highest recommended oral dose (163 μg/mL, 1×), and 2×, 4×, 8×, 10×, 12×, 16×, and 20×. Platelet aggregation by Chrono-Log aggregometer and coagulation by rotational thrombelastogram (Rotem) were assessed at 15 minutes after the addition of ibuprofen.

RESULTS

A robust inhibition of ibuprofen on arachidonic acid-induced platelet aggregation was observed at all doses tested in human or pig blood. Collagen-stimulated platelet aggregation was inhibited starting at 1× in human blood and 4× in pig blood. Rotem measurements were similarly compromised in pig and human blood starting at 16×, except clot formation time was prolonged at 1× in human blood (all p < 0.05).

CONCLUSION

Ibuprofen inhibited platelet aggregation at recommended doses, and compromised coagulation at higher doses. Human blood was more sensitive to ibuprofen inhibition. Further effort is needed to investigate ibuprofen dose responses on coagulation in vivo.

Rapid Detection of Neutrophil Oxidative Burst Capacity is Predictive of Whole Blood Cytokine Responses

BACKGROUND

Maladaptive immune responses, particularly cytokine and chemokine-driven, are a significant contributor to the deleterious inflammation present in many types of injury and infection. Widely available applications to rapidly assess individual inflammatory capacity could permit identification of patients at risk for exacerbated immune responses and guide therapy. Here we evaluate neutrophil oxidative burst (NOX) capacity measured by plate reader to immuno-type Rhesus Macaques as an acute strategy to rapidly detect inflammatory capacity and predict maladaptive immune responses as assayed by cytokine array.

METHODS

Whole blood was collected from anesthetized Rhesus Macaques (n = 25) and analyzed for plasma cytokine secretion (23-plex Luminex assay) and NOX capacity. For cytokine secretion, paired samples were either unstimulated or ex-vivo lipopolysaccharide (LPS)-stimulated (100μg/mL/24h). NOX capacity was measured in dihydrorhodamine-123 loaded samples following phorbol 12-myristate 13-acetate (PMA)/ionomycin treatment. Pearson's test was utilized to correlate NOX capacity with cytokine secretion, p<0.05 considered significant.

RESULTS

LPS stimulation induced secretion of the inflammatory molecules G-CSF, IL-1β, IL-1RA, IL-6, IL-10, IL-12/23(p40), IL-18, MIP-1α, MIP-1β, and TNFα. Although values were variable, several cytokines correlated with NOX capacity, p-values≤0.0001. Specifically, IL-1β (r = 0.66), IL-6 (r = 0.74), the Th1-polarizing cytokine IL-12/23(p40) (r = 0.78), and TNFα (r = 0.76) were strongly associated with NOX.

CONCLUSION

NOX capacity correlated with Th1-polarizing cytokine secretion, indicating its ability to rapidly predict inflammatory responses. These data suggest that NOX capacity may quickly identify patients at risk for maladaptive immune responses and who may benefit from immuno-modulatory therapies. Future studies will assess the in-vivo predictive value of NOX in animal models of immune-mediated pathologies.

Early hemostatic responses to trauma identified with hierarchical clustering analysis

BACKGROUND

Trauma-induced coagulopathy is a complex multifactorial hemostatic response that is poorly understood.

OBJECTIVES

To identify distinct hemostatic responses to trauma and identify key components of the hemostatic system that vary between responses.

PATIENTS/METHODS

A cross-sectional observational study of adult trauma patients at an urban level I trauma center emergency department was performed. Hierarchical clustering analysis was used to identify distinct clusters of similar subjects according to vital signs, injury/shock severity, and comprehensive assessment of coagulation, clot formation, platelet function, and thrombin generation.

RESULTS

Among 84 total trauma patients included in the model, three distinct trauma clusters were identified. Cluster 1 (N = 57) showed platelet activation, preserved peak thrombin generation, plasma coagulation dysfunction, a moderately decreased fibrinogen concentration and normal clot formation relative to healthy controls. Cluster 2 (N = 18) showed platelet activation, preserved peak thrombin generation, and a preserved fibrinogen concentration with normal clot formation. Cluster 3 (N = 9) was the most severely injured and shocked, and showed a strong inflammatory and bleeding phenotype. Platelet dysfunction, thrombin inhibition, plasma coagulation dysfunction and a decreased fibrinogen concentration were present in this cluster. Fibrinolytic activation was present in all clusters, but was particularly increased in cluster 3. Trauma clusters were most noticeably different in their relative fibrinogen concentration, peak thrombin generation, and platelet-induced clot contraction.

CONCLUSIONS

Hierarchical clustering analysis identified three distinct hemostatic responses to trauma. Further insights into the underlying hemostatic mechanisms responsible for these responses are needed.

Effect of Ibuprofen dose on platelet aggregation and coagulation in blood samples from pigs

INTRODUCTION

Ibuprofen is commonly used by Soldiers in the deployed environment. This study investigated its dose-effects on in vitro coagulation.

METHODS

Blood samples were collected from 4 normal healthy pigs and were processed to make platelet-adjusted (100×10(3)/μL) blood samples. Ibuprofen was added to the samples at doses of 0 μg/mL (control), recommended oral dose (163 μg/mL, 1×), 2×, 4×, 8×, 10×, 12×, 16×, and 20×. Arachidonic acid or collagen-stimulated platelet aggregation was assessed at 15 minutes after the addition of ibuprofen. Coagulation was assessed with measurements of prothrombin time (PT) and activated partial thromboplastin time (aPTT), and thrombelastography by Rotem.

RESULTS

A robust inhibition of ibuprofen on arachidonic acid-induced platelet aggregation was observed at all doses tested. Collagen-stimulated platelet aggregation was inhibited to 71%±5% and 10%±5% of the control values at ibuprofen doses of 4× and 20×, respectively (both p<0.05). No changes were observed in PT at any dose, but aPTT was prolonged at dose of 16× and 20×. Rotem measurements of coagulation time, clot formation time, maximum clot firmness, and A10 were compromised at dose 16× and 20× (all p<0.05).

CONCLUSION

Ibuprofen inhibited platelet aggregation at recommended doses, but did not compromise aPTT or coagulation profile until at 16 times the recommended doses and higher. Further effort is needed to clarify whether there are different dose-responses between human and pig blood samples in trauma situations.

Tranexamic acid in remote damage control resuscitation

With the advent of remote damage control resuscitation and far-forward surgery, a renewed emphasis has been placed on examining a variety of pharmacologic adjuncts to controlling blood loss before definitive operative intervention. In this paper, the authors review the current state of the art for tranexamic acid (TXA) and its potential benefits to those patients who are in need of a massive transfusion. Specifically addressed are its biologic and pharmacologic properties, as well the results of a number of recent studies. The 2010 CRASH-2 trial randomized in excess of 20,000 patients and demonstrated a reduction in all-cause mortality from 16.0 to 14.5% and death due to bleeding from 5.7 to 4.9%. The 2012 Military Application of Tranexamic Acid in Trauma Emergency Resuscitation study provided a retrospective analysis of 896 wounded cared for at a military hospital in Afghanistan. This study demonstrated a 23.9%-17.4% reduction in all-cause mortality. Finally, they discuss the potential complications associated with TXA use as well as areas of future research, which are needed to solidify our knowledge of TXA and its potential beneficial effects on controlling bleeding.

Effects of In vitro hemodilution, hypothermia and rFVIIa addition on coagulation in human blood

INTRODUCTION

Coagulopathy can occur after hemorrhage, trauma and resuscitation, and has been associated with dilution of coagulation factors and hypothermia. Recombinant activated Factor VII (rFVIIa) has been used, often as a last resort, to improve hemostasis in trauma/hemorrhage patients with coagulopathy. The aim of this study was to further characterize the effects of rFVIIa on various coagulation parameters and the influence of temperature and hemodilution.

METHODS

WHOLE BLOOD FROM HEALTHY HUMAN VOLUNTEERS WAS INCUBATED IN A COMBINATION OF THREE CONDITIONS: undiluted or diluted 40% with either lactated Ringer's solution or Hextend, at 37°C or 34°C, and with and without rFVIIa (1.26 μg/ml, final concentration). Blood or plasma, as appropriate, was measured for coagulation by thrombin generation, thromboelastography (TEG), prothrombin Time (PT) and activated partial thromboplastin (aPTT).

RESULTS

Incubation of plasma at 34°C significantly elevated thrombin generation, and prolonged PT and aPTT. Dilution of blood or plasma with 40% Hextend, but not lactated Ringer's, had a significant effect on TEG parameters, and prolonged PT and aPTT. In control conditions (37°C, 0 dilution), the addition of rFVIIa to human plasma or whole blood led to a significant change in all TEG parameters, and Lagtime for thrombin generation, but not to PT or aPTT.

CONCLUSION

Theses data show that thrombin generation is affected by hypothermia, but not 40% dilution. TEG is affected by 40% dilution with Hextend, but not by hypothermia. PT and aPTT are significantly affected by both hypothermia and dilution. Recombinant FVIIa caused a greater change in thrombin generation at 34°C as compared to 37°C, and a greater change in PT at 40% dilution, suggesting that the effect of rFVIIa on coagulation is both temperature and dilution dependant.

Effect of haemodilution, acidosis, and hypothermia on the activity of recombinant factor VIIa (NovoSeven)

Background

A range of plasma volume expanders is used clinically, often in settings where haemostasis may already be impaired. The haemostatic agent, recombinant activated factor VII (rFVIIa, NovoSeven^®), may be used to improve haemostasis but potential interactions with different volume expanders are poorly understood.

Methods

Clot formation was measured by thromboelastography (TEG) using blood from healthy volunteers. In vitro effects of rFVIIa with haemodilution, acidosis, and hypothermia were examined. Conditions were induced by dilution with NaCl (0.9%), lactated Ringer's solution, albumin 5%, or hydroxyethyl starch (HES) solutions [MW (molecular weight) 130–670 kDa]; by adjusting pH to 6.8 with 1 M HEPES (N-2-hydroxyethylpiperazine-N′-2-ethanesulphonic acid) buffer; or by reducing temperature to 32°C. We also studied the effect of low vs high MW HES (MW 200 vs 600 kDa) and rFVIIa on in vivo bleeding time (BT) in rabbits.

Results

Haemodilution progressively altered TEG parameters. rFVIIa improved TEG parameters in the presence of acidosis, hypothermia or 20% haemodilution (P<0.05). At 40% haemodilution, the rFVIIa effect was diminished particularly with high MW HES. In vivo, rFVIIa shortened the BT (P<0.05) with low but not high MW HES.

Conclusions

Efficacy of rFVIIa was affected by the degree of haemodilution and type of volume expander, but not by acidosis or hypothermia.

The Clinical and Laboratory Response to Recombinant Factor VIIa in Trauma and Surgical Patients with Acquired Coagulopathy

OBJECTIVE

In bleeding patients who are coagulopathic, the clinical response to administration of recombinant factor VIIa (rFVIIa) relates to the changes in prothrombin time (PT).

DESIGN

Retrospective review of all surgical and trauma patients who were coagulopathic and received factor VIIa at the authors' institution over the past 27 months.

SETTING

Academic tertiary referral facility and level I trauma center.

PARTICIPANTS

Eighteen patients met inclusion criteria, 10 trauma and 8 surgical. Mean age 50 years (range, 17-84).

RESULTS

Overall mortality was 39%. All but 1 patient (17/18) had resolution of coagulopathic bleeding with rFVIIa, and all clinical responders (n = 17) (defined as clinical cessation of bleeding within 24 hours determined by either attending surgeon or chief resident progress note) had a decrease in PT to normal range. In contrast, the single clinical nonresponder had an insignificant PT decrease (19 to 18 seconds). Prothrombin time decreased from 20 +/- 4 seconds to 12 +/- 2 seconds, p < 0.05 (n = 17). International Normalized Ratio (INR) decreased from 1.59 to 0.86, p < 0.05 (n = 17). Fibrinogen before administration was 299.73 (range, 105-564) (n = 15). pH before administration was 7.25 (+/-0.18) (n = 10). Patient temperature was 98.64 (+/-2.06). Effect in partial thromboplastin time (PTT) was inconsistent (50 +/- 49 seconds to 34 +/- 6 seconds, p > 0.05). Transfusion requirements for red blood cells (14 to 3 units) and plasma (12 to 3 units) were significantly reduced after rFVIIa. There were no significant differences in percentage PT decrease between dose > or =100 mcg/kg vs <100 mcg/kg, surgical vs trauma patients, survivors vs nonsurvivors, and those with pretreatment platelet count > or =100 K vs <100 K.

CONCLUSIONS

The administration of rFVIIa caused a decrease in the PT in nearly all patients. There were an insufficient number of patients to support the use of PT as a clinical predictor of response; however, the data are suggestive of such utility. If the PT does not correct, then it is likely that there is a deficiency of other factors of the coagulation cascade.

Does Bicarbonate Correct Coagulation Function Impaired by Acidosis in Swine?

BACKGROUND

Coagulopathy is an important contributor to morbidity and mortality in trauma patients. Acidosis contributes to coagulopathy. Acidosis can be neutralized with intravascular bicarbonate, but it is unclear if the coagulation defect is rapidly reversed. The effects of acidosis and bicarbonate neutralization on coagulation function were investigated in vivo.

METHODS

Acidosis was induced in 12 pigs by infusing 0.2 mol/L HCl to pH 7.1. Pigs were then infused with either LR to maintain a pH of 7.1 (A-LR, n = 6) or 0.3 mol/L bicarbonate to a pH of 7.4 (A-Bi, n = 6). Blood samples were taken at baseline, 15 minutes after acidosis induction, and 15 minutes after bicarbonate neutralization. Coagulation function was assessed by prothrombin time (PT), partial thromboplastin time (PTT), thrombin generation, initial clot formation time (R), clotting rapidity (alpha), and clot strength (MA).

RESULTS

Compared with baseline values, acidosis reduced fibrinogen concentration to 66% +/- 2% in A-LR and to 71% +/- 3% in A-Bi, and decreased platelet counts to 49% +/- 4% in A-LR and to 53% +/- 4% in A-Bi. Thrombin generation decreased to 60% +/- 4% in A-LR and to 53% +/- 7% in A-Bi. Acidosis prolonged PT and PTT about 20% and decreased alpha and MA. After pH neutralization, fibrinogen and platelet levels remained depleted and no reversal of acidosis-induced changes in thrombin generation, PT, PTT, alpha, and MA were observed.

CONCLUSION

Acidosis impaired coagulation by depleting fibrinogen and platelets and by inhibiting clotting kinetics. The deficit associated with acidosis was not reversed with bicarbonate pH neutralization.

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.

A special report on the chitosan-based hemostatic dressing: experience in current combat operations

BACKGROUND

Hemorrhage remains a leading cause of death in both civilian and military trauma patients. The HemCon chitosan-based hemostatic dressing is approved by the US Food and Drug Administration (FDA) for hemorrhage control. Animal data have shown the HemCon dressing to reduce hemorrhage and improve survival. The purpose of this article is to report preliminary results of the hemostatic efficacy of the HemCon dressing used in the prehospital setting on combat casualties.

METHODS

A request for case information on use of HemCon dressings in Operation Iraqi Freedom and Operation Enduring Freedom was sent to deployed Special Forces combat medics, physicians, and physician assistants.

RESULTS

Sixty-eight uses of the HemCon dressing were reported and reviewed by two US Army physicians. Four of the 68 cases were determined duplicative resulting in a total of 64 combat uses. Dressings were utilized externally on the chest, groin, buttock, and abdomen in 25 cases; on extremities in 35 cases; and on neck or facial wounds in 4 cases. In 66% of cases, dressings were utilized following gauze failure and were 100% successful. In 62 (97%) of the cases, the use of the HemCon dressing resulted in cessation of bleeding or improvement in hemostasis. There were two reported dressing failures that occurred with blind application of bandages up into large cavitational injuries. Dressings were reported to be most useful on areas where tourniquets could not be applied to control bleeding. The dressings were reported to be most difficult to use in extremity injuries where they could not be placed easily onto or into the wounds. No complications or adverse events were reported.

CONCLUSION

This report on the field use of the HemCon dressing by medics suggests that it is a useful hemostatic dressing for prehospital combat casualties and supports further study to confirm efficacy.

Making Sense of the Preclinical Literature on Advanced Hemostatic Products

A number of new hemostatic products have been developed recently for use in trauma settings of severe uncontrolled bleeding. Currently, the literature on these products is controversial, with efficacy demonstrated under some circumstances but not others. In this review, we analyze the current literature pertaining to four of the most promising products (dry fibrin sealant dressing, Rapid Deployment Hemostat, HemCon chitosan dressing, and QuikClot) that have been suggested for use in combat casualty care applications. In particular, this analysis takes into account the characteristics of the animal models used for efficacy testing of these products, the desired characteristics of hemostatic dressings, and specific safety considerations. Animal models ranged from those featuring low-pressure/low-flow bleeding to those featuring high-pressure/high-flow bleeding. When data are viewed in the context of the specific characteristics of the differing animal models used, seemingly disparate experimental results related to efficacy and safety become quite complementary and lead to recommendations for the use of different products in different injury scenarios. Mission and training requirements will dictate the use of these products by military and civilian prehospital care providers.

Acute changes in fibrinogen metabolism and coagulation after hemorrhage in pigs

Hemorrhagic coagulopathy is involved in the morbidity and mortality of trauma patients. Nonetheless, many aspects of the mechanisms underlying this disorder are poorly understood. We have therefore investigated changes in fibrinogen metabolism and coagulation function after a moderate hemorrhagic shock, using a new stable isotope approach. Twelve pigs were randomly divided into the control (C) and hemorrhage (H) groups. Hemorrhage was induced by bleeding 35% total blood volume over a 30-min period. A primed constant infusion of [1-(13)C]phenylalanine (Phe), d5-phenylalanine, and alpha-[1-(13)C]-ketoisocaproate (KIC) was given to quantify fibrinogen synthesis and breakdown, together with measurements of circulating liver enzyme activities and coagulation function. Mean arterial pressure was decreased by hemorrhage from 89 +/- 4 mmHg in C to 47 +/- 4 mmHg in H (P < 0.05), followed by a rebound to 68 +/- 5 mmHg afterward. Fibrinogen fractional synthesis rate increased from 2.7 +/- 0.2%/h in C to 4.2 +/- 0.4%/h in H by Phe (P < 0.05) and from 3.1 +/- 0.4%/h in C to 4.4 +/- 0.5%/h in H by KIC (P < 0.05). Fibrinogen fractional breakdown rate increased from 3.6 +/- 1.0%/h in C to 12.9 +/- 1.8%/h in H (P < 0.05). The absolute breakdown rate accelerated from 3.0 +/- 0.4 mg x kg(-1) x h(-1) in C to 5.4 +/- 0.6 mg x kg(-1) x h(-1) in H (P < 0.05), but the absolute synthesis rate remained unchanged. These metabolic changes were accompanied by a reduction in blood clotting time to 92.7 +/- 1.6% of the baseline value by hemorrhage (P < 0.05). No changes were found in liver enzyme activities. We conclude that the observed changes in coagulation after hemorrhagic shock are mechanistically related to the acute acceleration of fibrinogen degradation.

Mechanistic implications for the use and monitoring of recombinant activated factor VII in trauma

As interest in the use of activated recombinant factor VII (rFVIIa) in trauma grows, questions arise regarding how best to monitor rFVIIa therapy and when rFVIIa may be expected to improve hemostasis. Knowledge of the mechanisms of action may be combined with available data on laboratory monitoring and efficacy in various coagulopathic states in coming to clinically relevant conclusions. This review addresses the physiology of hemostasis, placing emphasis on how rFVIIa influences the process by both tissue factor dependent and tissue factor independent mechanisms. This is extended to a mechanistic consideration of how rFVIIa may function under acidotic, hypothermic, and hemodilutional and/or consumptive conditions of trauma related coagulopathy. When these considerations are viewed alongside the available clinical data, it becomes apparent that rFVIIa has potential to improve hemostasis during trauma coagulopathy, within limitations. Common laboratory procedures are discussed with reference to mechanisms of action of rFVIIa and the available clinical data. Although there is no single assay that can predict rFVIIa efficacy in trauma, the prothrombin time (PT) is recommended as a minimum. Although a shortened PT does not predict success, correction of PT into the normal range may be a better indicator. A nonresponding PT appears to indicate that rFVIIa alone will not lead to hemostasis, and that additional blood products and other measures must be applied. Once the patient is more stable, PT and thromboelastography are recommended.

Physiological Evaluation of the U.S. Army One-Handed Tourniquet

OBJECTIVE

To provide a physiological assessment of the U.S. Army one-handed tourniquet (OHT).

METHODS

An OHT was self-applied by 26 subjects, to maximal tolerable tightness, to the proximal arm or thigh under different conditions and positions, and the presence of blood flow was assessed using Doppler ultrasonography or occlusion plethysmography.

RESULTS

Doppler sound was eliminated at the radial artery for all subjects with OHT application but was not stopped at the popliteal or dorsalis pedis artery for any subjects. The OHT reduced forearm blood flow by 79% but decreased leg blood flow by only approximately 50%, regardless of condition and position of application to the thigh.

CONCLUSIONS

The OHT appears to effectively minimize blood flow in the arm but not in the lower extremities, and clinical assessment of blood flow disappearance by Doppler ultrasonography may underestimate the magnitude of actual blood flow to the limb.