Influence of temperature on thromboelastometry and platelet aggregation in cardiac arrest patients undergoing targeted temperature management

Rapid and Nondestructive Evaluation of Platelet Function in Whole Blood by Microfluidic Deterministic Cytometry

Platelet size is a determinant of platelet function. Here, a new microfluidic deterministic cytometry packed with S-shaped micropillars (S-MDC) was developed to rapidly and sensitively determine the apparent size (Dapp) of platelets, which was used to evaluate platelet function. The platelet Dapp in the diluted whole blood was rapidly and label-freely measured by S-MDC within 2 min under shear rates (0.4 mm/s) that mimicked physiological conditions. The level of CD62p on platelets scarcely changed before and after platelets went through the whole S-MDC, indicating that the platelet function was nondestructive. Notably, the human platelet Dapp determined before and after thrombin addition by S-MDC was highly coincident with the levels of CD62p on the platelet surface by flow cytometry (r = 0.819), revealing that the human platelet Dapp was available to assess the platelet activation state. In addition, the results of the rat platelet Dapp were consistent with myocardial injury of rats with myocardial ischemia before and after treatment with antiplatelet agents, suggesting that rat platelet Dapp can be used to reflect myocardial injury in vivo outcomes. These findings reveal that S-MDC is a promising technique for screening tests for a bleeding disorder, in addition to monitoring antiplatelet drugs.

Enhanced Blood Clotting After Rewarming From Experimental Hypothermia in an Intact Porcine Model

Introduction: Due to functional alterations of blood platelets and coagulation enzymes at low temperatures, excessive bleeding is a well-recognized complication in victims of accidental hypothermia and may present a great clinical challenge. Still, it remains largely unknown if hemostatic function normalizes upon rewarming. The aim of this study was to investigate effects of hypothermia and rewarming on blood coagulation in an intact porcine model.

Methods: The animals were randomized to cooling and rewarming (n = 10), or to serve as normothermic, time-matched controls (n = 3). Animals in the hypothermic group were immersion cooled in ice water to 25°C, maintained at 25°C for 1 h, and rewarmed to 38°C (normal temperature in pigs) using warm water. Clotting time was assessed indirectly at different temperatures during cooling and rewarming using a whole blood coagulometer, which measures clotting time at 38°C.

Results: Cooling to 25°C led to a significant increase in hemoglobin, hematocrit and red blood cell count, which persisted throughout rewarming. Cooling also caused a transiently decreased white blood cell count that returned to baseline levels upon rewarming. After rewarming from hypothermia, clotting time was significantly shortened compared to pre-hypothermic baseline values. In addition, platelet count was significantly increased.

Discussion/Conclusion: We found that clotting time was significantly reduced after rewarming from hypothermia. This may indicate that rewarming from severe hypothermia induces a hypercoagulable state, in which thrombus formation is more likely to occur.

Hemorrhagic Resuscitation Guided by Viscoelastography in Far-Forward Combat and Austere Civilian Environments: Goal-Directed Whole-Blood and Blood-Component Therapy Far from the Trauma Center

Modern approaches to resuscitation seek to bring patient interventions as close as possible to the initial trauma. In recent decades, fresh or cold-stored whole blood has gained widespread support in multiple settings as the best first agent in resuscitation after massive blood loss. However, whole blood is not a panacea, and while current guidelines promote continued resuscitation with fixed ratios of blood products, the debate about the optimal resuscitation strategy-especially in austere or challenging environments-is by no means settled. In this narrative review, we give a brief history of military resuscitation and how whole blood became the mainstay of initial resuscitation. We then outline the principles of viscoelastic hemostatic assays as well as their adoption for providing goal-directed blood-component therapy in trauma centers. After summarizing the nascent research on the strengths and limitations of viscoelastic platforms in challenging environmental conditions, we conclude with our vision of how these platforms can be deployed in far-forward combat and austere civilian environments to maximize survival.

Mild Therapeutic Hypothermia Alters Hemostasis in ST Elevation Myocardial Infarction Patients

Background and Rationale: Mild therapeutic hypothermia (MTH) is a concept to reduce infarct size and improve outcome after ST-segment elevation myocardial infarction (STEMI). In the STATIM trial, we investigated MTH as an additional therapy for STEMI patients. In the intention-to-treat set, 101 patients were included. No difference in primary and secondary endpoints measured by cardiac magnetic resonance imaging was found. Platelet activation and plasmatic coagulation are key in the pathophysiology of STEMI. In the present study, we investigated the effect of MTH on primary and secondary hemostasis in STEMI patients.

Methods and Results: Platelet function and morphology were assessed by routine blood count, aggregometry testing, and flow cytometry. Soluble platelet markers were determined by enzyme-linked immunosorbent assay (ELISA) testing. Plasmatic coagulation was measured throughout the study. Platelet count remained unchanged, irrespective of treatment, whereas platelet size decreased in both patient groups. Platelet aggregometry indicated increased platelet reactivity in the MTH group. Furthermore, higher adenosine diphosphate (ADP) plasma levels were found in MTH patients. Expression of glycoprotein IIb/IIIa was increased on platelets of STEMI patients treated with MTH. Lower patient temperatures correlated with longer clotting times and resulted in reduced pH. Lower pH values were positively correlated with longer clotting times.

Conclusion: Present data indicate longer clotting times and higher platelet reactivity in STEMI patients treated with MTH. These changes did not correspond to clinical bleeding events or larger infarct size.

Thromboelastography versus standard coagulation testing in the assessment and reversal of coagulopathy among cirrhotics: a systematic review and meta-analysis

The utility of thromboelastography/thromboelastometry currently has unvalidated clinical benefit in the assessment and reversal of coagulopathy among cirrhotic patients as compared to standard coagulation testing. A novel systematic review and meta-analysis was conducted in order to assess pooled outcome data among patients receiving thromboelastography/thromboelastometry as compared to standard coagulation testing. As compared to standard coagulation testing, there was a significant reduction in the number of patients requiring pRBC, platelet, and fresh frozen plasma transfusions among thromboelastography/thromboelastometry group with pooled OR 0.53 (95% CI 0.32-0.85; P = 0.009), 0.29 (95% CI 0.12-0.74; P = 0.009), and 0.19 (95% CI 0.12-0.31; P < 0.00001), respectively. Similarly, there was a significant reduction in number of pRBC, platelet, and fresh frozen plasma units transfused in the thromboelastography/thromboelastometry group with pooled MD -1.53 (95% CI -2.86 to -0.21; P = 0.02), -0.57 (95% CI -1.06 to -0.09; P = 0.02), and -2.71 (95% CI -4.34 to -1.07; P = 0.001), respectively. There were significantly decreased total bleeding events with pooled OR 0.54 (95% CI 0.31-0.94; P = 0.03) and amount of intraoperative bleeding during liver transplantation with pooled MD -1.46 (95% CI -2.49 to -0.44; P = 0.005) in the thromboelastography/thromboelastometry group. Overall, there was no significant difference in mortality between groups with pooled OR 0.91 (95% CI 0.63-1.30; P = 0.60). As compared to standard coagulation testing, a thromboelastography/thromboelastometry-guided approach to the assessment and reversal of cirrhotic coagulopathy improves overall number of patients exposed to blood product transfusions, quantity of transfusions, and bleeding events.

Postresuscitation Care after Out-of-hospital Cardiac Arrest: Clinical Update and Focus on Targeted Temperature Management

Out-of-hospital cardiac arrest is a major cause of mortality and morbidity worldwide. With the introduction of targeted temperature management more than a decade ago, postresuscitation care has attracted increased attention. In the present review, we discuss best practice hospital management of unconscious out-of-hospital cardiac arrest patients with a special focus on targeted temperature management. What is termed post-cardiac arrest syndrome strikes all organs and mandates access to specialized intensive care. All patients need a secured airway, and most patients need hemodynamic support with fluids and/or vasopressors. Furthermore, immediate coronary angiography and percutaneous coronary intervention, when indicated, has become an essential part of the postresuscitation treatment. Targeted temperature management with controlled sedation and mechanical ventilation is the most important neuroprotective strategy to take. Targeted temperature management should be initiated as quickly as possible, and according to international guidelines, it should be maintained at 32° to 36°C for at least 24 h, whereas rewarming should not increase more than 0.5°C per hour. However, uncertainty remains regarding targeted temperature management components, warranting further research into the optimal cooling rate, target temperature, duration of cooling, and the rewarming rate. Moreover, targeted temperature management is linked to some adverse effects. The risk of infection and bleeding is moderately increased, as is the risk of hypokalemia and magnesemia. Circulation needs to be monitored invasively and any deviances corrected in a timely fashion. Outcome prediction in the individual patient is challenging, and a self-fulfilling prophecy poses a real threat to early prognostication based on clinical assessment alone. Therefore, delayed and multimodal prognostication is now considered a key element of postresuscitation care. Finally, modern postresuscitation care can produce good outcomes in the majority of patients but requires major diagnostic and therapeutic resources and specific training. Hence, recent international guidelines strongly recommend the implementation of regional prehospital resuscitation systems with integrated and specialized cardiac arrest centers.

Whole blood platelet aggregation kinetics under cardiopulmonary bypass: A pilot study

Assessing the platelets' functional status during surgery on cardiopulmonary bypass is challenging. This study used multiple electrode impedance aggregometry (Multiplate^®) to create a timeline of platelet aggregation changes as induced by cardiopulmonary bypass in antiplatelet-naive patients undergoing elective surgery for mitral valve regurgitation. We performed six consecutive measurements (T1: pre-operatively, T2: after heparinization, T3: 3 min after establishment of cardiopulmonary bypass, T4: immediately after administration of cardioplegia, T5: 5 min after administration of cardioplegia, and T6: 45 min after administration of cardioplegia). Platelet aggregation was determined after stimulation with 3.2-μg/mL collagen, 6.4-μM adenosine diphosphate, and 32-μM thrombin receptor activating peptide. Five patients were included (age: 64 ± 10 years, one female). We observed a decrease in hematocrit levels by -17.1% ± 3.7% (T1 vs T6) with a drop after establishment of cardiopulmonary bypass (T2 vs T3) and slightly decreasing platelet counts by -6.2% ± 7.7% (T1 vs T6). Immediately after establishment of cardiopulmonary bypass (T2 vs T3), we observed reduced platelet aggregation responses for stimulation with adenosine diphosphate (-19.7% ± 12.8%) and thrombin receptor activating peptide (-19.3% ± 6.3%). Interestingly, we found augmented platelet aggregation for all stimuli 45 min after administration of cardioplegia (T5 vs T6) with the strongest increase for collagen (+83.4% ± 42.8%; adenosine diphosphate: +39.0% ± 37.2%; thrombin receptor activating peptide: +34.5% ± 18.5%). Thus, after an initial drop due to hemodilution upon establishment of cardiopulmonary bypass, platelet reactivity increased over time which was not outweighed by decreasing platelet counts due to mechanical platelet destruction and absorption. These findings have implications for rational transfusion, peri-operative antiplatelet therapy, and for the management of patients on other extracorporeal support, such as extracorporeal life support or extracorporeal membrane oxygenation.

Platelet indices and outcome after cardiac arrest

BACKGROUND

Platelet variables, including platelet distribution width (PDW) and mean platelet volume (MPV), have been associated with outcome in critically ill patients. We evaluated these variables in patients after cardiac arrest (CA).

METHODS

All adult CA patients admitted to the intensive care unit (ICU) over an 8-year period (2006-2014) and treated with targeted temperature management were included. We retrieved all data concerning CA characteristics as well as platelet count, PDW and MPV on the first 2 days of admission. Unfavorable 3-month neurological outcome was defined as a cerebral performance category score of 3-5.

RESULTS

We included 384 patients (age 62 [52-75] years; 270/384 male): 231 patients (60%) died within 30-days and 246 patients (64%) had an unfavorable 3-month neurological outcome. On admission, platelet count, PDW and MPV were 87 [126-261] *10³cells/mm³, 17 [16.3-17.3]% and 8.3 [7.6-9.2] μm³, respectively. Platelet count decreased significantly over the first 2 days, whereas PDW and MPV did not change significantly. There were no significant differences between the values on admission or time-courses of platelet count, PDW or MPV between survivors and non-survivors or between patients with unfavorable and favorable neurological outcome.

CONCLUSIONS

In our cohort of post-CA patients, PDW and MPV were not associated with outcome.

Adaptation of global hemostasis to therapeutic hypothermia in patients with out-of-hospital cardiac arrest: Thromboelastography study

BACKGROUND

The use of mild therapeutic hypothermia (MTH) in patients after out-of-hospital cardiac arrest (OHCA) who are undergoing primary percutaneous coronary intervention (pPCI) can protect patients from thromboembolic complications. The aim of the study was to evaluate the adaptive mecha- nisms of the coagulation system in MTH-treated comatose OHCA survivors.

METHODS

Twenty one comatose OHCA survivors with acute coronary syndrome undergoing imme- diate pPCI were treated with MTH. Quantitative and qualitative analyses of physical clot properties were performed using thromboelastography (TEG). Two analysis time points were proposed: 1) during MTH with in vitro rewarming conditions (37°C) and 2) after restoration of normothermia (NT) under normal (37°C) and in vitro cooling conditions (32°C).

RESULTS

During MTH compared to NT, reaction time (R) was lengthened, clot kinetic parameter (a) was significantly reduced, but no effect on clot strength (MA) was observed. Finally, the coagulation index (CI) was significantly reduced with clot fibrinolysis attenuated during MTH. The clot lysis time (CLT) was shortened, and clot stability (LY60) was lower compared with those values during NT. In vitro cooling generally influenced clot kinetics and reduced clot stability after treatment.

CONCLUSIONS

Thromboelastography is a useful method for evaluation of coagulation system dysfunc- tion in OHCA survivors undergoing MTH. Coagulation impairment in hypothermia was associated with a reduced rate of clot formation, increased weakness of clot strength, and disturbances of fibrinoly- sis. Blood sample analyses performed at 32°C during MTH, instead of the standard 37°C, seems to enhance the accuracy of the evaluation of coagulation impairment in hypothermia.

Prolonged targeted temperature management compromises thrombin generation: A randomised clinical trial

AIM

To investigate whether prolonged compared with standard duration of targeted temperature management (TTM) compromises coagulation.

METHODS

Comatose survivors after out-of-hospital cardiac arrest (n=82) were randomised to standard (24h) or prolonged (48h) duration of TTM at 33±1°C. Blood samples were drawn 22, 46 and 70h after attaining the target temperature. Samples were analysed for rotational thromboelastometry (ROTEM^® (EXTEM^®, INTEM^®, FIBTEM^® and HEPTEM^®)) and thrombin generation using the Calibrated Automated Thrombogram^® assay.

RESULTS

With the 22-h sample, we revealed no difference between groups in the ROTEM^® and thrombin generation results beside a slightly higher EXTEM^® and INTEM^® maximum velocity in the prolonged group (p-values≤0.04). With the 46-h sample, ROTEM^® showed no differences when using EXTEM^®; however, 11% (p<0.01) longer clotting time and 12% (p<0.01) longer time to maximum velocity were evident in the prolonged group than in the standard group when using INTEM^®. The prolonged group had reduced thrombin generation compared with the standard group as indicated by 30% longer lag time (p=0.04), 106nM decreased peak concentration (p<0.001), 36% longer time to peak (p=0.01) and 411 nM*minute decreased endogenous thrombin potential (p<0.001). With the 70-h sample, no differences in ROTEM^® results were found between groups. However, the prolonged group had reduced thrombin generation indicated by longer lag time, decreased peak concentration and longer time to peak (all p-values≤0.02) compared with the standard group.

CONCLUSION

Prolonged TTM in post-cardiac arrest patients impairs thrombin generation. ClinicalTrials.gov identifier: NCT02258360.

Post-cardiac arrest level of free-plasma DNA and DNA-histone complexes

BACKGROUND

Plasma DNA-histone complexes and total free-plasma DNA have the potential to quantify the ischaemia-reperfusion damages occurring after cardiac arrest. Furthermore, DNA-histone complexes may have the potential of being a target for future treatment. The aim was to examine if plasma DNA-histone complexes and the levels of total free-plasma DNA were elevated in post-cardiac arrest patients compared with healthy individuals, and to examine if these biomarkers were capable of predicting mortality.

METHODS

We included 42 comatose out-of-hospital cardiac arrest patients and collected blood samples after 22, 46 and 70 h. Samples for DNA-histone complexes were quantified by Cell Death Detection ELISA^plus . The total free-plasma DNA analyses were quantified with qPCR by analysing the Beta-2 microglobulin gene. The control group comprised 40 healthy individuals.

RESULTS

We found no difference in the level of DNA-histone complexes between the 22-h sample and healthy individuals (P = 0.10). In the 46-h sample, there was an increased level of DNA-histone complexes in non-survivors compared with survivors 30 days after the cardiac arrest (P < 0.01) and the area under the ROC curve was 0.78 (95% confidence interval: 0.59;0.96). The level of total free-plasma DNA was increased in the 22-h sample compared with healthy individuals (P < 0.001) but no significant difference was found between non-survivors and survivors 30 days after the cardiac arrest (all P ≥ 0.06).

CONCLUSION

An increased level of DNA-histone complexes was associated with increased mortality and that the level of total free-plasma DNA was elevated post-cardiac arrest.