The Effects of Temperature on Clot Microstructure and Strength in Healthy Volunteers

The effect of diabetic ketoacidosis (DKA) and its treatment on clot microstructure: Are they thrombogenic?

BACKGROUND

Diabetic ketoacidosis (DKA) is a medical emergency with a high mortality rate and is associated with severe metabolic acidosis and dehydration. DKA patients have an increased risk of arterial and venous thromboembolism, however little is known about this metabolic derangement in the first 24 hours of admission and to assess its effect on coagulation. We therefore utilised a novel functional marker of clot microstructure (fractal dimension - df) to assess these changes within the first 24 hours.

METHODS

Prospective single centre observational study to demonstrate whether the tendency of blood clot formation differs in DKA patients.

RESULTS

15 DKA patients and 15 healthy matched controls were recruited. Mean df in the healthy control group was 1.74±0.03. An elevated df of 1.78±0.07 was observed in patients with DKA on admission. The mean pH on admission was 7.14±0.13 and the lactate was 3.6±2.0. df changed significantly in response to standard treatment and was significantly reduced to 1.68±0.09 (2-6& h) and to 1.66±0.08 at 24& h (p < 0.01 One-way ANOVA). df also correlated significantly with lactate and pH (Pearson correlation coefficient 0.479 and -0.675 respectively, p < 0.05).

CONCLUSIONS

DKA patients at presentation have a densely organising less permeable thrombogenic clot microstructure as evidenced by high df. These structural changes are due to a combination of dehydration and a profound metabolic acidosis, which was reversed with treatment. These changes were not mirrored in standard clinical markers of thromboge-nicity.

Does Exercise Influence the Susceptibility to Arterial Thrombosis? An Integrative Perspective

Arterial thrombosis is the primary cause of death worldwide, with the most important risk factors being smoking, unhealthy diet, and physical inactivity. However, although there are clear indications in the literature of beneficial effects of physical activity in lowering the risk of cardiovascular events, exercise can be considered a double-edged sword in that physical exertion can induce an immediate pro-thrombotic environment. Epidemiological studies show an increased risk of cardiovascular events after acute exercise, a risk, which appear to be particularly apparent in individuals with lifestyle-related disease. Factors that cause the increased susceptibility to arterial thrombosis with exercise are both chemical and mechanical in nature and include circulating catecholamines and vascular shear stress. Exercise intensity plays a marked role on such parameters, and evidence in the literature accordingly points at a greater susceptibility to thrombus formation at high compared to light and moderate intensity exercise. Of importance is, however, that the susceptibility to arterial thrombosis appears to be lower in exercise-conditioned individuals compared to sedentary individuals. There is currently limited data on the role of acute and chronic exercise on the susceptibility to arterial thrombosis, and many studies include incomplete assessments of thrombogenic clotting profile. Thus, further studies on the role of exercise, involving valid biomarkers, are clearly warranted.

The effect of the acute inflammatory response of burns and its treatment on clot characteristics and quality: A prospective case controlled study

INTRODUCTION

Burns are known to have an effect on coagulation in the early period after burn. Current coagulation tests have been criticised in acute burns due to their inherent limitations. This study aims to investigate the potential for a new quantitative functional biomarker of clot quality, fractal dimension, to identify changes in clot microstructure as a result of the burn inflammatory response and its treatment.

METHODS

A total of fifty-eight burn patients were included in this prospective case-controlled study. The control group (29 patients mean TBSA 1%), and case group (29 patients mean TBSA 30%) were compared at baseline and the case group investigated further over four time points (baseline, 12h, 24h and 5-7 days). Fractal analysis was performed, as well as current markers of coagulation, inflammatory markers and point-of-care tests, Thromboelastography and Multiplate analysis.

RESULTS

Fractal dimension did not differ between groups at admission (1.73±0.06 and 1.72±0.1), and fell within the healthy index normal range (1.74±0.7), suggesting a normal clot microstructure in the early period after burn. Fractal dimension significantly reduced from baseline over the first 24h following injury (1.59±0.03 p<0.005), indicating a significant reduction in mechanical clot strength and functionality consistent with a hypocoagulable state, not identified with other markers.

CONCLUSIONS

This is the first study to quantify the changes in clot microstructure following burn injury. This study confirms clot microstructure is significantly altered during the first 24h after burn, with the production of a weaker, more porous fibrin clot, consistent with a hypocoagulable state.

Hemostatic responses to exercise, dehydration, and simulated bleeding in heat-stressed humans

Heat stress followed by an accompanying hemorrhagic challenge may influence hemostasis. We tested the hypothesis that hemostatic responses would be increased by passive heat stress, as well as exercise-induced heat stress, each with accompanying central hypovolemia to simulate a hemorrhagic insult. In aim 1, subjects were exposed to passive heating or normothermic time control, each followed by progressive lower-body negative pressure (LBNP) to presyncope. In aim 2 subjects exercised in hyperthermic environmental conditions, with and without accompanying dehydration, each also followed by progressive LBNP to presyncope. At baseline, pre-LBNP, and post-LBNP (<1, 30, and 60 min), hemostatic activity of venous blood was evaluated by plasma markers of hemostasis and thrombelastography. For aim 1, both hyperthermic and normothermic LBNP (H-LBNP and N-LBNP, respectively) resulted in higher levels of factor V, factor VIII, and von Willebrand factor antigen compared with the time control trial (all P < 0.05), but these responses were temperature independent. Hyperthermia increased fibrinolysis [clot lysis 30 min after the maximal amplitude reflecting clot strength (LY₃₀)] to 5.1% post-LBNP compared with 1.5% (time control) and 2.7% in N-LBNP ( P = 0.05 for main effect). Hyperthermia also potentiated increased platelet counts post-LBNP as follows: 274 K/µl for H-LBNP, 246 K/µl for N-LBNP, and 196 K/µl for time control ( P < 0.05 for the interaction). For aim 2, hydration status associated with exercise in the heat did not affect the hemostatic activity, but fibrinolysis (LY₃₀) was increased to 6-10% when subjects were dehydrated compared with an increase to 2-4% when hydrated ( P = 0.05 for treatment). Central hypovolemia via LBNP is a primary driver of hemostasis compared with hyperthermia and dehydration effects. However, hyperthermia does induce significant thrombocytosis and by itself causes an increase in clot lysis. Dehydration associated with exercise-induced heat stress increases clot lysis but does not affect exercise-activated or subsequent hypovolemia-activated hemostasis in hyperthermic humans. Clinical implications of these findings are that quickly restoring a hemorrhaging hypovolemic trauma patient with cold noncoagulant fluids (crystalloids) can have serious deleterious effects on the body's innate ability to form essential clots, and several factors can increase clot lysis, which should therefore be closely monitored.

The effect of tyramine infusion and exercise on blood flow, coagulation and clot microstructure in healthy individuals

BACKGROUND

The long term benefits of exercise on the cardiovascular status of a patient have been proven, however, their benefit/risk relationship with exercise intensity is unclear. Furthermore, many thromboembolic diseases such as myocardial infarction and ischaemic stroke are associated with profound catecholamine release. In this study we explore the relationship between catecholamine release and hemodynamic changes and their effect on coagulation.

MATERIALS AND METHODS

Twelve healthy recreationally active males were recruited. Local anesthesia was given and catheters were placed under aseptic conditions, in the femoral artery and vein of the experimental leg. The first experiment involved tyramine infusion into the femoral artery at a dose of 1.0 μmol·min^-1·L leg volume^-1. The second experiment involved single leg knee-extensor exercise performed at 30 W for 15 min. Venous blood was collected at each time point to assess clot microstructure using the d_f biomarker.

RESULTS AND CONCLUSIONS

Tyramine infusion causes a local noradrenaline release in the leg. The increase in noradrenaline was associated with a significant increase in clot microstructure formation (d_f increased from 1.692 ± 0.029 to 1.722 ± 0.047, p = 0.016). Additionally moderate intensity single leg knee extensor exercise, which minimally alters sympathetic activity, also induced an increases in d_f (from 1.688 ± 0.025 to 1.723 ± 0.023, p = 0.001). This suggests that exercise can alter clot microstructure formation both via an increase in catecholeamine levels and by factors related to muscle activity per se, such as increased blood flow and consequent shear. These findings have implications for recommendations of exercise in patients at risk of cardiovascular events.

Measuring coagulation in burns: an evidence-based systematic review

Introduction

Dynamic monitoring of coagulation is important to predict both haemorrhagic and thrombotic complications and to guide blood product administration. Reducing blood loss and tailoring blood product administration may improve patient outcome and reduce mortality associated with transfusion. The current literature lacks a systematic, critical appraisal of current best evidence on which clinical decisions may be based.

Objectives

Establishing the role of different coagulation markers in burn patients, diagnosing coagulopathy, tailoring blood product administration and indicating prognosis.

Methods

Literature during 2004-2017 from the Cochrane Library, PubMed, Scopus, Medline and Embase was reviewed. Eligibility criteria included randomised controlled trials, systematic reviews, multi-/single-centre study and meta-analyses. Keywords searched were 'burns', 'blood coagulation disorders', 'rotem', 'blood coagulation' and 'thromboelastography'. The PRISMA flow system was used for stratification and the CASP framework for appraisal of the studies retrieved.

Results

In total, 13 articles were included after inclusion/exclusion criteria had been applied to the initial 79 studies retrieved. Hypercoagulation increases in proportion to the severity of thermal injury. Whole blood testing, using thrombelastography (TEG) and rotation thromboelastometry (ROTEM), was superior to standard plasma based tests, including prothrombin time (PT) and activated partial thromboplastin time (APTT) at detecting burn-related coagulopathies.

Conclusions

Routine laboratory markers such as PT/APTT are poor indicators of coagulation status in burns patients. Viscoelastic tests, such as TEG and ROTEM, are efficient, fast and have a potential use in the management of burn patients; however, strong evidence is lacking. This review highlights the need for more randomised controlled trials, to guide future practice.

Comparison of forced-air and water-circulating warming for prevention of hypothermia during transcatheter aortic valve replacement

Introduction

Transcatheter Aortic Valve Replacement (TAVR) procedures at our institution were complicated by perioperative hypothermia despite use of the standard of care forced-air convective warming device (the BairHugger, Augustine Medical Inc, Eden Prairie, MN, USA). To remedy this problem, we initiated a quality improvement process that investigated the use of a conductive warm water-circulating device (the Allon ThermoWrap, Menen Medical Corporation, Trevose, PA, USA), and hypothesized that it would decrease the incidence of perioperative hypothermia.

Methods

We compared two different intraoperative warming devices using a historic control. We retrospectively reviewed intraoperative records of 80 TAVRs between 6/2013 and 6/2015, 46 and 34 of which were done with the forced-air and water-circulating devices, respectively. Continuous temperature data obtained from pulmonary artery catheter, temperature upon arrival to cardiothoracic ICU (CTU), age, BSA, height, and BMI were compared.

Results

Patients warmed with both devices were similar in terms of demographic characteristics. First recorded intraoperative temperature (mean 36.26 ± SD 0.61 vs. 35.95 ± 0.46°C, p = 0.02), lowest intraoperative temperature (36.01 ± 0.58 vs. 34.89 ± 0.76°C, p<0.001), temperature at the end of the procedure (36.47 ± 0.51 vs. 35.17 ± 0.75°C, p<0.001), and temperature upon arrival to the CTU (36.35 ± 0.44 vs. 35.07 ± 0.78°C, p<0.001) were significantly higher in the water-circulating group as compared to the forced-air group.

Conclusion

A quality improvement process led to selection of a new warming device that virtually eliminated perioperative hypothermia at our institution. Patients warmed with the new device were significantly less likely to experience intraoperative hypothermia and were significantly more likely to be normothermic upon arrival to the CTU.