Hypothermic anticoagulation: testing individual responses to graded severe hypothermia with thromboelastography

Temperature effect on coagulation function in mild hypothermic patients undergoing thoracic surgeries: thromboelastography (TEG) versus standard tests

PURPOSE

Our previous research has revealed that mild hypothermia leads to excessive bleeding in thoracic surgeries, while the underlying mechanism stayed unrevealed by the standard coagulation tests. The research question in this study was as follows: "How does mild hypothermia impair the hemostatic function in patients receiving thoracic surgeries?". The purpose was to detect the disturbed coagulation processes by comparing the TEG parameters in patients receiving active vs. passive warming during thoracic surgeries.

METHODS

Standard coagulation tests and thromboelastography (TEG) were adopted to compare the hemostatic functions in patients receiving active vs. passive warming during thoracic surgeries. Furthermore, blood samples from passive warming group were retested for TEG at actual core body temperatures.

RESULTS

Sixty-four eligible patients were included in this study. TEG revealed that mild hypothermia significantly disturbed coagulation by decreasing MA (59.4 ± 4.5 mm vs. 64.2 ± 5.7 mm, p = 0.04) and α angle (70.4 ± 5.2° vs. 74.9 ± 4.4°, p = 0.05) and prolonging ACT (122.2 ± 19.3 s vs. 117.3 ± 15.2 s, p = 0.01) and K time (1.9 ± 1.0 s vs. 1.3 ± 0.4 min, p = 0.02). TEGs conducted under core body temperatures revealed more impaired coagulation than those incubated at 37 °C. Furthermore, postoperative shivering and waking time were significantly increased in mild hypothermic patients.

CONCLUSION

Mild hypothermia significantly impaired coagulation function in patients receiving thoracic surgeries, which could be detected by TEGs other than the standard coagulation tests. Temperature-adjusted TEGs may provide a preferable method of hemostatic monitoring and transfusion guidance in thoracic surgeries, which warrants further clinical investigations.

Effectiveness of Mild to Moderate Hypothermic Cardiopulmonary Bypass on Early Clinical Outcomes

BACKGROUND

Intraoperative hypothermia is an integral part of cardiopulmonary bypass (CPB), and a precise degree of hypothermia may improve the early clinical outcomes of cardiac surgery. Presently, there is no agreement on an accurate, advantageous temperature range for routine use in CPB. To address this issue, we conducted a retrospective observational study to compare the effects of different hypothermic temperature ranges on primary (inotropic support, blood loss, and platelet count) and secondary (ventilation support and in-hospital stay) outcomes in patients undergoing elective cardiac surgery.

METHODS

Data were retrieved from the medical database of the Cardiovascular Surgery Department, King Edward Medical University, Lahore-Pakistan (a tertiary care hospital), dating from February 2015 to December 2017. Patients were divided into mild (34 °C to 36 °C), intermediate (31 °C to 33 °C), or moderate (28 °C to 30 °C) hypothermic groups.

RESULTS

Out of 275 patients, 245 (89.09%) fit the inclusion criteria. The cohort with mild hypothermic CPB temperatures presented better clinical outcomes in terms of requiring less inotropic support, less blood loss, fewer blood transfusions, improved platelet counts, shorter in-hospital stays, and required less ventilation support, when compared with other hypothermic groups.

CONCLUSIONS

Mild hypothermic CPB (34 °C to 36 °C) may produce better clinical outcomes for cardiac surgery and improve the quality of health of cardiac patients.

Impact of aspirin on bleeding and blood product usage in off-pump and on-pump coronary artery bypass graft surgery

Major bleeding is linked to poorer outcomes following cardiac surgery. Current guidelines recommend continuation of aspirin prior to coronary artery by-pass graft (CABG) but the effect of continuing aspirin in patients with prior indication for aspirin, in particular during off-pump CABG (OPCABG), has not been systematically assessed. In this study, we analysed the effect of continuing aspirin prior to OPCABG and on-pump CABG with respect to bleeding and blood product usage. We compared propensity-matched cohorts of patients who continued aspirin until the day of OPCABG or CABG to controls (no antiplatelet) and to patients discontinuing aspirin 5-7 days prior. Length of hospital stay, 30-day mortality and thromboembolism rates were similar for both OPCABG and CABG. During OPCABG, aspirin-continued patients received more intraoperative red cell units compared to controls without difference in bleeding. Aspirin-continued patients received more blood products perioperatively and bled more than aspirin-discontinued patients undergoing OPCABG. The only difference during CABG was a small increase in the volume of cells salvaged among aspirin-continued patients compared to controls. Current guidelines on the continuation of aspirin prior to CABG and OPCABG are safe. Continuation of aspirin prior to OPCABG may result in more bleeding and blood product usage.

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.

Hypothermia Induced Impairment of Platelets: Assessment With Multiplate vs. ROTEM—An In Vitro Study

Introduction: This experimental in vitro study aimed to identify and characterize hypothermia-associated coagulopathy and to compare changes in mild to severe hypothermia with the quantitative measurement of rotational thromboelastometry (ROTEM) and multiple-electrode aggregometry (MULTIPLATE).

Methods: Whole blood samples from 18 healthy volunteers were analyzed at the target temperatures of 37, 32, 24, 18, and 13.7°C with ROTEM (ExTEM, InTEM and FibTEM) and MULTIPLATE using the arachidonic acid 0.5 mM (ASPI), thrombin receptor-activating peptide-6 32 µM (TRAP) and adenosine diphosphate 6.4 µM (ADP) tests at the corresponding incubating temperatures for coagulation assessment.

Results: Compared to baseline (37°C) values ROTEM measurements of clotting time (CT) was prolonged by 98% (at 18°C), clot formation time (CFT) was prolonged by 205% and the alpha angle dropped to 76% at 13.7°C (p < 0.001). At 24.0°C CT was prolonged by 56% and CFT by 53%. Maximum clot firmness was only slightly reduced by ≤2% at 13.7°C. Platelet function measured by MULTIPLATE was reduced with decreasing temperature (p < 0.001): AUC at 13.7°C −96% (ADP), −92% (ASPI) and −91% (TRAP).

Conclusion: Hypothermia impairs coagulation by prolonging coagulation clotting time and by decreasing the velocity of clot formation in ROTEM measurements. MULTIPLATE testing confirms a linear decrease in platelet function with decreasing temperatures, but ROTEM fails to adequately detect hypothermia induced impairment of platelets.

Emergency preservation and resuscitation for cardiac arrest from trauma

Patients who suffer a cardiac arrest from trauma rarely survive. Surgical control of hemorrhage cannot be obtained in time to prevent irreversible organ damage. Emergency preservation and resuscitation (EPR) was developed to utilize hypothermia to buy time to achieve hemostasis and allow delayed resuscitation. Large animal studies have demonstrated that cooling to tympanic membrane temperature 10 °C during exsanguination cardiac arrest can allow up to 2 h of circulatory arrest and repair of simulated injuries with normal neurologic recovery. The Emergency Preservation and Resuscitation for Cardiac Arrest from Trauma (EPR-CAT) trial is testing the feasibility and safety of initiating EPR. Study subjects include patients with penetrating trauma who lose a pulse within 5 minutes of hospital arrival and remain pulseless despite standard care. EPR is initiated via an intra-aortic flush of ice-cold saline solution. Following hemostasis, delayed resuscitation and rewarming are accomplished with cardiopulmonary bypass. The primary outcome is survival to hospital discharge without significant neurologic deficits. If trained team members are available, subjects can undergo EPR. If not, subjects can be enrolled as concurrent controls. Ten EPR and 10 control subjects will be enrolled. If successful, EPR could save the lives of trauma patients who are currently dying from exsanguinating hemorrhage.

Which factors have a great impact on coagulopathy and hemostatic impairment after cardiopulmonary bypass in cardiovascular surgery? An analysis based on rotational thromboelastometry

OBJECTIVES

This study aimed to investigate which factors have a great impact on coagulopathy after cardiopulmonary bypass (CPB) using rotational thromboelastometry (ROTEM).

METHODS

Ninety-eight patients undergoing cardiovascular surgery using CPB were enrolled. Data of amplitude 10 min after clotting time (A10) of ROTEM measured routinely before and after CPB were retrospectively collected. ROTEM has some assays by which we can evaluate the capacity of extrinsic coagulation (EXTEM), intrinsic coagulation (INTEM), fibrin polymerization (FIBTEM), and the effect of heparin (HEPTEM). The platelet component, defined as PLTEM, can be calculated by subtracting FIBTEM from EXTEM. Age, sex, total plasma volume, pre-CPB A10, lowest body temperature, in-out balance during CPB, intraoperative bleeding amount, and type of pumps were considered as possible factors. Univariate and multivariate analyses were performed for the rate of change of A10.

RESULTS

The change rate of each A10 had a significant negative correlation with bleeding amount (p < 0.01 for EXTEM, p < 0.01 for INTEM, p = 0.02 for FIBTEM, p < 0.01 for PLTEM). Female sex was a significant contributive predictor for the greater decline of EXTEM (p < 0.01) and INTEM (p < 0.01), positive balance for EXTEM (p < 0.01), FIBTEM (p = 0.01), and PLTEM (p < 0.01), long CPB time for INTEM (p = 0.01), centrifugal pump for FIBTEM (p < 0.01), and large pre-CPB A10 for PLTEM (p < 0.01).

CONCLUSION

In perioperative hemostatic management using ROTEM, attention should be given to the effects of these multiple factors.

Cheap and simple, could it get even cooler? Mild hypothermia and COVID-19

Purpose

The pathophysiology theories of COVID-19 attach the injury of target organs to faulty immune responses and occasionally hyper-inflammation. The damage frequently extends beyond the respiratory system, accompanying cardiovascular, renal, central nervous system, and/or coagulation derangements. Tumor necrosis factor-α (TNF-α) and interleukins (IL)-1 and − 6 suppression may improve outcomes, as experimentally shown. Targeted therapies have been proposed, but mild therapeutic hypothermia—a more multifaceted approach—could be suitable.

Findings

According to evidence derived from previous applications, therapeutic hypothermia diminishes the release of IL-1, IL-6, and TNF-α in serum and at the tissue level. PaCO2 is reduced and the PaO2/FiO2 ratio is increased, possibly lasting after rewarming. Cooling might mitigate both ventilator and infectious-induced lung injury, and suppress microthrombi development, enhancing V/Q mismatch. Improvements in microhemodynamics and tissue O2 diffusion, along with the ischemia-tolerance heightening of tissues, could be reached. Arrhythmia incidence diminishes. Moreover, hypothermia may address the coagulopathy, promoting normalization of both hypo- and hyper-coagulability patterns, which are apparently sustained after a return to normothermia.

Conclusions

As per prior therapeutic hypothermia literature, the benefits regarding inflammatory response and organic damage might be seen. Following the safety-cornerstones of the technique, the overall infection rate and infection-related mortality are not expected to rise, and increased viral replication does not seem to be a concern. Therefore, the possibility of a low cost and widely available therapy being capable of improving COVID-19 outcomes deserves further study.

Hypothermia-Associated Coagulopathy: A Comparison of Viscoelastic Monitoring, Platelet Function, and Real Time Live Confocal Microscopy at Low Blood Temperatures, an in vitro Experimental Study

Introduction

Hypothermia has notable effects on platelets, platelet function, fibrinogen, and coagulation factors. Common laboratory techniques cannot identify those effects, because blood samples are usually warmed to 37°C before analysis and do not fully reflect the in vivo situation. Multiple aspects of the pathophysiological changes in humoral and cellular coagulation remain obscure. This in vitro experimental study aimed to compare the measurements of thromboelastometry (TEM), multiple-electrode aggregometry (MEA) and Real Time Live Confocal Imaging for the purpose of identifying and characterizing hypothermia-associated coagulopathy.

Methods

Blood samples were drawn from 18 healthy volunteers and incubated for 30 min before being analyzed at the target temperatures (37, 32, 24, 18, and 13.7°C). At each temperature thromboelastometry and multiple-electrode aggregometry were measured. Real Time Live Confocal Imaging was performed at 4, 24, and 37°C. The images obtained by Real Time Live Confocal Imaging were compared with the functional results of thromboelastometry and multiple-electrode aggregometry.

Results

Thromboelastometry standard parameters were impaired at temperatures below baseline 37°C (ANOVA overall effect, p < 0.001): clotting time was prolonged by 27% at 13.7°C and by 60% at 18°C (p < 0.044); clot formation time was prolonged by 157% (p < 0.001). A reduction in platelet function with decreasing temperatures was observed (p < 0.001); the area under the curve at 13.7°C was reduced by 96% (ADP test), 92% (ASPI test), and 91% (TRAP test) of the baseline values. Temperature-associated changes in coagulation were visualized with Real Time Live Confocal Imaging. Molecular changes such as the temperature-associated decrease in the fibrin network are paralleled by cellular effects like the lesser activity of the platelets as a result of decreased temperature. The maximum clot firmness (MCF) in TEM only changed slightly within the temperature range tested.

Conclusion

The inhibitory effects of temperature on clot formation were visualized with Real Time Live Confocal Microscopy and compared with standard point-of-care testing. Inhibition of clotting factors and impaired platelet function are probably a result of hypothermia-induced impairment of thrombin. Measurement of MCF in TEM does not fully concur with Real Time Live Confocal Microscopy or MEA in hypothermia.

Hypothermic circulatory arrest induced coagulopathy: rotational thromboelastometry analysis

Objectives

Hypothermic circulatory arrest (HCA) has been considered to cause coagulopathy during cardiac surgery. However, coagulopathy associated with HCA has not been understood clearly in details. The objective of this study is to analyze the details of coagulopathy related to HCA in cardiac surgery by using rotational thromboelastometry (ROTEM).

Methods

We retrospectively analyzed 38 patients who underwent elective cardiac surgery (HCA group = 12, non-HCA group = 26) in our hospital. Blood samples were collected before and after cardiopulmonary bypass (CPB). Standard laboratory tests (SLTs) and ROTEM were performed. We performed four ROTEM assays (EXTEM, INTEM, HEPTEM and FIBTEM) and analyzed the following ROTEM parameters: clotting time (CT), clot formation time (CFT), maximum clot firmness (MCF) and maximum clot elasticity (MCE). The amount of perioperative bleeding, intraoperative transfusion and perioperative data were compared between the HCA and non-HCA group.

Results

Operation time and hemostatic time were significantly longer in the HCA group, whereas CPB time had no difference between the groups. The amount of perioperative bleeding and intraoperative transfusion were much higher in the HCA group. SLTs showed no difference between the groups both after anesthesia induction and after protamine reversal. In ROTEM analysis, MCE contributed by platelet was reduced in the HCA group, whereas MCE contributed by fibrinogen had no difference.

Conclusion

Our study confirmed that the amount of perioperative bleeding and intraoperative transfusion were significantly higher in the HCA group. ROTEM analysis would indicate that clot firmness contributed by platelet component is reduced by HCA in cardiac surgery.

Hypothermia-induced activation of the splenic platelet pool as a risk factor for thrombotic disease in a mouse model

BACKGROUND

Hypothermia, either therapeutically induced or accidental (ie, an involuntary decrease in core body temperature to <35°C), results in hemostatic disorders. However, it remains unclear whether hypothermia enhances or inhibits coagulation, especially in severe hypothermia. The present study evaluated the thrombocytic and hemostatic changes in hypothermic mice.

METHODS

C57Bl/6 mice were placed at an ambient temperature of -20°C under general anesthesia. When the rectal temperature decreased to 15°C, 10 mice were immediately euthanized, while another 10 mice were rewarmed, kept in normal conditions for 24 hours, and then euthanized. These treatments were also performed in 20 splenectomized mice.

RESULTS

The hypothermic mice had adhesion of CD62P-positive platelets with high expression of von Willebrand factor (vWF) in their spleens, while the status of the peripheral platelets was unchanged. Furthermore, the plasma levels of platelet factor 4 (PF4) and pro-platelet basic protein (PPBP), which are biomarkers for platelet degranulation, were significantly higher in hypothermic mice than in control mice, indicating that hypothermia activated the platelets in the splenic pool. Thus, we analyzed these biomarkers in asplenic mice. There was no increase in either PF4 or PPBP in splenectomized hypothermic mice. Additionally, the plasma D-dimer elevation and microthrombosis were caused in rewarmed mice, but not in asplenic rewarmed mice.

CONCLUSIONS

Our results indicate that hypothermia leads to platelet activation in the spleen via the upregulation of vWF, and this activation causes hypercoagulability after rewarming.

Increased Fibrinolysis as a Specific Marker of Poor Outcome After Cardiac Arrest

Supplemental Digital Content is available in the text.

Objectives:

Recent data suggest that early increased fibrinolysis may be associated with unfavorable prognosis in cardiac arrest. The current study aimed to assess whether there is an optimal fibrinolysis cutoff value as determined by thrombelastometry at hospital admission to predict poor outcome in a cohort of adult patients with out-of-hospital cardiac arrest.

Design:

Prospective observational cohort study.

Setting:

Emergency department of a 2.100-bed tertiary care facility in Vienna, Austria, Europe.

Patients:

Patients with out-of-hospital cardiac arrest of presumed cardiac origin, subjected to targeted temperature management, who had achieved return of spontaneous circulation at admission were analyzed.

Interventions:

None.

Measurements and Main Results:

Fibrinolysis was assessed by thrombelastometry at the bedside immediately after hospital admission and is given as maximum lysis (%). The outcome measure was the optimal cutoff for maximum lysis at hospital admission to predict poor outcome (a composite of Cerebral Performance Category 3–5 or death) at day 30, assessed by receiver operating characteristic curve analysis. Seventy-eight patients (61% male, median 59 yr) were included in the study from March 2014 to March 2017. Forty-two patients (54%) had a poor 30-day outcome including 23 nonsurvivors (30%). The maximum lysis cutoff at admission predicting poor 30-day outcome with 100% specificity (95% CI, 90–100%) was greater than or equal to 20%. Tissue-type plasminogen activator antigen levels were likewise elevated in patients with poor neurologic outcome or death 52 ng/mL (interquartile range, 26–79 ng/mL) versus 29 ng/mL (interquartile range, 17–49 ng/mL; p = 0.036).

Conclusions:

Increased fibrinolysis at admission assessed by thrombelastometry specifically predicts poor outcome in cardiac arrest with presumed cardiac etiology.

Hypothermia, pH, and Postoperative Red Blood Cell Transfusion in Massively Transfused Adult Cardiac Surgery Patients: A Retrospective Cohort Study

OBJECTIVE

To determine the relationships between hypothermia and pH at surgery end and postoperative red blood cell (RBC) transfusion in massively transfused adult cardiac surgery patients.

DESIGN

Retrospective cohort study.

SETTING

Single tertiary care, academic medical center.

PARTICIPANTS

A total of 395 adult patients having cardiac surgery with cardiopulmonary bypass who were massively transfused during an 8-year period. Patients were excluded if they did not receive an antifibrinolytic drug during surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Body temperature and pH at surgery end were recorded. Postoperative RBC transfusion, a surrogate for postoperative bleeding, was the study's primary outcome. Secondary outcomes were postoperative fresh frozen plasma (FFP) transfusion, postoperative platelet transfusion, reoperation for bleeding, and mortality. Patients with hypothermia did not have more postoperative RBC transfusion (p = 0.56), but patients with acidosis or alkalosis received more RBCs after surgery (p = 0.04). There were no differences in secondary outcomes between groups. In multivariate analysis, both acidosis and alkalosis were independently associated with postoperative RBC transfusion (p = 0.01 and p < 0.0001).

CONCLUSION

Hypothermia at surgery end has no association with postoperative RBC transfusion in massively transfused cardiac surgery patients, but pH derangements are associated with increased postoperative transfusion. Thus, normalization of blood pH may be important in reducing postoperative bleeding in massively transfused cardiac surgery patients.

Thermoregulation as a disease tolerance defense strategy

Physiological responses that occur during infection are most often thought of in terms of effectors of microbial destruction through the execution of resistance mechanisms, due to a direct action of the microbe, or are maladaptive consequences of host-pathogen interplay. However, an examination of the cellular and organ-level consequences of one such response, thermoregulation that leads to fever or hypothermia, reveals that these actions cannot be readily explained within the traditional paradigms of microbial killing or maladaptive consequences of host-pathogen interactions. In this review, the concept of disease tolerance is applied to thermoregulation during infection, inflammation and trauma, and we discuss the physiological consequences of thermoregulation during disease including tissue susceptibility to damage, inflammation, behavior and toxin neutralization.

Acidosis induced by carbon dioxide insufflation decreases heparin potency: a risk factor for thrombus formation

Background:

Since the introduction of CO2 insufflation during open heart surgery in our hospital, we incidentally observed thrombus formation in the dissected heart, in the pericardium and in the cardiotomy reservoir of the cardiopulmonary bypass system. Furthermore, we measured very high levels of pCO2, causing severe acidosis, in stagnant blood in the pericardium and cardiotomy reservoir.

Objectives:

In this in vitro study, we assessed the influence of acidosis and hypothermia on heparin potency and thrombin formation.

Methods:

We assessed heparin potency in function of pH (pH 5.0-7.4) and temperature (24-37°C) by comparing the activated partial thromboplastin time in platelet-poor plasma between samples with and without unfractionated heparin. We measured thrombin formation in platelet-poor plasma by means of fluorescent, calibrated, automated thrombography in function of pH (pH 5.0-7.4) and temperature (24-37°C). The parameters of interest were the endogenous thrombin potential and the peak amount of thrombin generation.

Results:

The major finding of this study is the significant decrease in the efficiency of unfractionated heparin in delaying thrombus formation at acidotic (pH 5.0-7.0) conditions (p=0.034-0.05). Furthermore, we found that thrombin formation is significantly increased at hypothermic (24-34°C) conditions (p=<0.001-0.01).

Conclusions:

Based on the results of our in-vitro study, we conclude that acidosis may lead to a decreased heparin potency. Acidosis, as induced by CO2 insufflation, may predispose patients to incidental thrombus formation in stagnant blood in the open thorax and in the cardiotomy reservoir. Hypothermia might further increase this risk. Therefore, we recommend reconsidering the potential advantages and disadvantages of using CO2 insufflation during cardiopulmonary bypass.

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

BACKGROUND

Coagulation can be visualised using whole blood coagulation analyses such as thromboelastometry and platelet aggregation tests; however, the role of temperature in the analyses is ambiguous. The aim was to examine whether temperature influences the whole blood coagulation tests.

METHODS

We included 40 patients treated with targeted temperature management (33 ± 1 °C) after out-of-hospital cardiac arrest. The blood samples were obtained on hypothermia and normothermia. Each blood sample was analysed simultaneously at 33 °C and 37 °C by thromboelastography (ROTEM®) employing the assays EXTEM®, INTEM®, FIBTEM® and HEPTEM®, and by Multiplate®Analyzer, using COLtest®, ADPtest®, ASPItest® and TRAPtest® as agonists. Data on antithrombotic drugs were collected systematically from medical records, and data were analysed using repeated measurement analysis of variance (ANOVA).

RESULTS

The ROTEM® analyses showed increased clotting time, lower maximum velocity and increased time to maximum velocity (all p values <0.02) when performed at 33 °C compared with 37 °C, irrespective of the patients being hypothermic (median 33.1 °C) or normothermic (median 37.5 °C). However, EXTEM® time to maximum velocity showed no difference between the analyses performed at 33 °C and 37 °C when the patients were hypothermic (p = 0.83). No differences were found in maximum clot firmness (all p values >0.09) analysed at 33 °C and 37 °C, independent of the body temperature. In the hypothermic blood sample, no difference was found when using the COLtest®, ASPItest® or TRAPtest® to compare platelet aggregation analysed at 33 °C and 37 °C (all p values >0.19), but platelet aggregation was significantly higher using the ADPtest® (p < 0.001) when analysed at 33 °C. In the normothermic blood sample, the TRAPtest® showed no difference (p = 0.73) when performed at 33 °C; however, significantly lower aggregation was found using the COLtest® and ASPItest® (all p values <0.001), while a higher aggregation at 33 °C was found using the ADPtest® (p = 0.003).

CONCLUSION

ROTEM® analyses seemed not to be dependent on body temperature but showed a slower initiation of coagulation when analysed at 33 °C compared with 37 °C. The Multiplate®Analyzer results were dependent on the temperature used in the analyses and the body temperature. In whole blood coagulation tests, the temperature used in the analyses should be kept at 37 °C irrespective of the patient's body temperature being 33 °C or 37 °C.

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

BACKGROUND

Anesthesia, critical illness, and trauma are known to alter thermoregulation, which can potentially affect coagulation and clinical outcome. This in vitro preclinical study explores the relationship between temperature change and hemostasis using a recently validated viscoelastic technique. We hypothesize that temperature change will cause significant alterations in the microstructural properties of clot.

METHODS

We used a novel viscoelastic technique to identify the gel point of the blood. The gel point identifies the transition of the blood from a viscoelastic liquid to a viscoelastic solid state. Furthermore, identification of the gel point provides 3 related biomarkers: the elastic modulus at the gel point, which is a measure of clot elasticity; the time to the gel point (TGP), which is a measure of the time required to form the clot; and the fractal dimension of the clot at the gel point, df, which quantifies the microstructure of the clot. The gel point measurements were performed in vitro on whole blood samples from 136 healthy volunteers over a temperature range of 27°C to 43°C.

RESULTS

There was a significant negative correlation between increases in temperature, from 27°C to 43°C, and TGP (r = -0.641, P < 0.0005). Conversely, significant positive correlations were observed for both the elastic modulus at the gel point (r = 0.513, P = 0.0008) and df (r = 0.777, P < 0.0005) across the range of 27°C to 43°C. When temperature was reduced below 37°C, significant reductions in df and TGP occurred at ≤32°C (Bonferroni-corrected P = 0.0093) and ≤29°C (Bonferroni-corrected P = 0.0317), respectively. No significant changes were observed when temperature was increased to >37°C.

CONCLUSIONS

This study demonstrates that the gel point technique can identify alterations in clot microstructure because of changes in temperature. This was demonstrated in slower-forming clots with less structural complexity as temperature is decreased. We also found that significant changes in clot microstructure occurred when the temperature was ≤32°C.

Asphyxia by Drowning Induces Massive Bleeding Due To Hyperfibrinolytic Disseminated Intravascular Coagulation

OBJECTIVE

To date, no study has systematically investigated the impact of drowning-induced asphyxia on hemostasis. Our objective was to test the hypothesis that asphyxia induces bleeding by hyperfibrinolytic disseminated intravascular coagulation.

DESIGN

Observational study.

SETTING

A 2,100-bed tertiary care facility in Vienna, Austria, Europe.

PATIENTS

All cases of drowning-induced asphyxia (n=49) were compared with other patients with cardiopulmonary resuscitation (n=116) and to patients with acute promyelocytic leukemia (n=83). Six drowning victims were investigated prospectively. To study the mechanism, a forearm-ischemia model was used in 20 volunteers to investigate whether hypoxia releases tissue plasminogen activator.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Eighty percent of patients with drowning-induced asphyxia developed overt disseminated intravascular coagulation within 24 hours. When compared with nondrowning cardiac arrest patients, drowning patients had a 13 times higher prevalence of overt disseminated intravascular coagulation at admission (55% vs 4%; p<0.001). Despite comparable disseminated intravascular coagulation scores, acute promyelocytic leukemia patients had higher fibrinogen but lower d-dimer levels and platelet counts than drowning patients (p<0.001). Drowning victims had a three-fold longer activated partial thromboplastin time (124 s; p<0.001) than both nondrowning cardiac arrest and acute promyelocytic leukemia patients. Hyperfibrinolysis was reflected by up to 1,000-fold increased d-dimer levels, greater than 5-fold elevated plasmin antiplasmin levels, and a complete absence of thrombelastometric clotting patterns, which was reversed by antifibrinolytics and heparinase. Thirty minutes of forearm-ischemia increased tissue plasminogen activator 31-fold (p<0.001).

CONCLUSIONS

The vast majority of drowning patients develops overt hyperfibrinolytic disseminated intravascular coagulation, partly caused by hypoxia induced tissue plasminogen activator release. Antifibrinolytics and heparinase partially reverse the abnormal clotting patterns. Severe activated partial thromboplastin time prolongation may be a marker of combined hyperfibrinolytic afibrinogenemia and autoheparinization in drowning-related asphyxia.

Therapeutic Hypothermia and the Risk of Hemorrhage: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Current guidelines recommend a period of moderate therapeutic hypothermia (TH) for comatose patients after cardiac arrest to improve clinical outcomes. However, in-vitro studies have reported platelet dysfunction, thrombocytopenia, and coagulopathy, results that might discourage clinicians from applying TH in clinical practice. We aimed to quantify the risks of hemorrhage observed in clinical studies.Medline and Embase were searched from inception to October 2015.Randomized controlled trials (RCTs) comparing patients undergoing TH with controls were selected, irrespective of the indications for TH. There were no restrictions for language, population, or publication year.Data on study characteristics, which included patients, details of intervention, and outcome measures, were extracted.Forty-three trials that included 7528 patients were identified from 2692 potentially relevant references. Any hemorrhage was designated as the primary outcome and was reported in 28 studies. The pooled results showed no significant increase in hemorrhage risk associated with TH (risk difference [RD] 0.005; 95% confidence interval [CI] -0.001-0.011; I, 0%). Among secondary outcomes, patients undergoing TH were found to have increased risk of thrombocytopenia (RD 0.109; 95% CI 0.038-0.179; I 57.3%) and transfusion requirements (RD 0.021; 95% CI 0.003-0.040; I 0%). The meta-regression analysis indicated that prolonged duration of cooling may be associated with increased risk of hemorrhage.TH was not associated with increased risk of hemorrhage despite the increased risk of thrombocytopenia and transfusion requirements. Clinicians should cautiously assess each patient's risk-benefit profile before applying TH.

Operative Strategies and Outcomes in Type a Aortic Dissection after the Enactment of a Multidisciplinary Aortic Surgery Team

Objective

The purpose of this study was to compare operative strategies and patient outcomes in acute type A aortic dissection (ATAAD) repairs before and after the implementation of a multi-disciplinary aortic surgery team.

Methods

Between May 2005 and July 2014, 101 patients underwent ATAAD repair at our institution. A dedicated multidisciplinary aortic surgery team (experienced aortic surgeon, perfusionists, cardiac anesthesiologists, nurses, and radiologists) was formed in 2010. We retrospectively compared ATAAD repair outcomes in patients before (2005–2009, N = 39) and after (2010–2014, N = 62) implementation of our program. Expected operative mortality was calculated using the International Registry of Acute Aortic Dissection preoperative predictive model.

Results

This study demonstrated a significant reduction in operative mortality after implementation of the aortic surgery program (30.8% vs. 9.7%; P = 0.014). There was also an increase in the complexity of surgical technique and perfusion strategies with fewer postoperative complications related to respiratory (P < 0.0001) and renal failure (P = 0.034). Baseline demographics were similar, and there was no statistically significant difference in International Registry of Acute Aortic Dissection predictive variables between the 2 groups. However, there was a 3.5-fold reduction in the observed-to-expected (O/E) operative mortality ratio. There was a 50% increase in volume with a significant number of patients being admitted directly to our aortic center for ATAAD repair, thus avoiding delay in operation related to transfers from a secondary hospital.

Conclusions

Patient outcomes are improved when the surgical treatment of ATAAD is managed by a high-volume multidisciplinary aortic surgery team.

Efficacy of enteral ticagrelor in hypothermic patients after out-of-hospital cardiac arrest

Introduction

Delivery of crushed ticagrelor via a nasogastric tube is a widely spread off-label use in unconscious patients following out-of-hospital cardiac arrest (OHCA). Notwithstanding the importance of a potent dual antiplatelet therapy in these patients, the efficacy of crushed ticagrelor after OHCA has not been established yet.

Methods

In a prospective, single-center, observational trial, 38 consecutive MI patients after OHCA were included. 27 patients (71.1 %) underwent mild induced hypothermia. The primary outcome was platelet inhibition at 24h measured by impedance aggregometry.

Results

There was sufficient platelet inhibition in most patients after OHCA. In all hypothermic patients, there was an adequate platelet inhibition by ticagrelor at 24 h (p < 0.001). 15 patients (39.5 %) had significant gastroesophageal reflux and one patient with significant reflux had inadequate platelet inhibition at 24 h. There were no stent thrombosis or recurrent atherothrombotic events in these patients.

Conclusion

Administration of crushed ticagrelor via a nasogastric tube reliably inhibited platelet function in vitro and in vivo regardless of the presence of hypothermia in MI patients. Thus, platelet inhibition can be reliably achieved in MI patients during neuroprotective hypothermia following OHCA.

Localized hypothermia aggravates bleeding in the collagenase model of intracerebral hemorrhage

Animal studies testing whether therapeutic hypothermia is neuroprotective after intracerebral hemorrhage (ICH) have been inconclusive. In rodents, ICH is often produced in the striatum by infusing collagenase, which causes prolonged hemorrhaging from multiple vessels. Our previous data shows that this bleeding (hematoma) is worsened by systemic hypothermia given soon after collagenase infusion. In this study we hypothesized that localized brain hypothermia would also aggravate bleeding in this model (0.2 U of collagenase in 1.2 μL of saline). We also evaluated cooling after intrastriatal thrombin infusion (1 U in 30 μL of saline)-a simplified model of ICH thought to cause bleeding. Focal hypothermia was achieved by flushing cold water through an implanted cooling device attached to the skull underneath the temporalis muscle of adult rats. Previous work and data at this time shows this method cools the striatum to ∼33°C, whereas the body remains normothermic. In comparison to normothermic groups, cooling significantly worsened bleeding when instituted at 6 hours (∼94 vs. 42 μL, p=0.018) and 12 hours (79 vs. 61 μL, p=0.042) post-ICH (24-hour survival), but not after a 24-hour delay (36-hour survival). Rats were cooled until euthanasia when hematoma size was determined by a hemoglobin-based spectrophotometry assay. Cooling did not influence cerebral blood volume after just saline or thrombin infusion. The latter is explained by the fact that thrombin did not cause bleeding beyond that caused by saline infusion. In summary, local hypothermia significantly aggravates bleeding many hours after collagenase infusion suggesting that bleeding may have confounded earlier studies with hypothermia. Furthermore, these findings serve as a cautionary note on using cooling even many hours after cerebral bleeding.

Mild induced hypothermia: effects on sepsis-related coagulopathy--results from a randomized controlled trial

INTRODUCTION

Coagulopathy associates with poor outcome in sepsis. Mild induced hypothermia has been proposed as treatment in sepsis but it is not known whether this intervention worsens functional coagulopathy.

MATERIALS AND METHODS

Interim analysis data from an ongoing randomized controlled trial; The Cooling And Surviving Septic shock (CASS) study. Patients suffering severe sepsis/septic shock are allocated to either mild induced hypothermia (cooling to 32-34°C for 24hours) or control (uncontrolled temperature).

TRIAL REGISTRATION

NCT01455116. Thrombelastography (TEG) is performed three times during the first day after study enrollment in all patients. Reaction time (R), maximum amplitude (MA) and patients' characteristics are here reported.

RESULTS

One hundred patients (control n=50 and intervention n=50; male n=59; median age 68years) with complete TEG during follow-up were included. At enrollment, 3%, 38%, and 59% had a hypocoagulable, normocoagulable, and hypercoagulable TEG clot strength (MA), respectively. In the hypothermia group, functional coagulopathy improved during the hypothermia phase, measured by R and MA, in patients with hypercoagulation as well as in patients with hypocoagulation (correlation between ΔR and initial R: rho=-0.60, p<0.0001 and correlation between ΔMA and initial MA: rho=-0.50, p=0.0002). Similar results were not observed in the control group neither for R (rho=-0.03, p=0.8247) nor MA (rho=-0.15, p=0.3115).

CONCLUSION

Mild induced hypothermia did seem to improve functional coagulopathy in septic patients. This improvement of functional coagulopathy parameters during the hypothermia intervention persisted after rewarming. Randomized trials are warranted to determine whether the positive effect on sepsis-related coagulopathy can be transformed to improved survival.

Temperature effects on haemostasis in whole blood from ticagrelor- and aspirin-treated patients with acute coronary syndrome

BACKGROUND

Comatose survivors after cardiac arrest are treated with mild induced hypothermia and potent platelet- inhibiting drugs after coronary stenting. Previous studies have shown an increased incidence of stent thrombosis during clopidogrel and aspirin treatment in conjunction with induced hypothermia. The aim of this study was to investigate the in vitro effect of induced hypo- and hyperthermia on blood from patients undergoing ticagrelor- and aspirin-mediated platelet inhibition.

METHODS

Whole blood from 15 patients with acute coronary syndrome who were treated with ticagrelor and aspirin and from eight healthy volunteers was incubated for 1 hour at 28, 33, 37, and 39°C.

RESULTS

In blood from patients with acute coronary syndrome, the activated clotting time (Sonoclot) was prolonged in mild hypothermic (33°C) compared to normothermic (37°C) samples. Sonoclot, clotting rate and platelet function were decreased in hypothermic compared to normothermic samples. Platelet-induced activation and aggregation (Multiplate) was unchanged in mild hypothermic compared to normothermic samples. In contrast, mild hypothermia supported increased platelet activation as measured with flow cytometry with up-regulation of PAC-1 and P-selectin on the platelet surface.

CONCLUSION

In acute coronary syndrome patients treated with ticagrelor and aspirin, in vitro hypothermia to 33°C markedly increased platelet activity measured with flow cytometry, whereas viscoelastic coagulation test (Sonoclot) revealed a hypocoagulative response. Prospective clinical trials studying platelet inhibition at different temperatures and correlating changes in platelet function to bleeding or stent occlusion are needed.

Platelet aggregation and clot formation in comatose survivors of cardiac arrest treated with induced hypothermia and dual platelet inhibition with aspirin and ticagrelor; a prospective observational study

INTRODUCTION

We conducted a prospective observational study in cardiac arrest survivors treated with mild induced hypothermia, evaluating different platelet function tests at hypo- and normothermia. We also investigated the relation between gastric emptying and vasodilator stimulated phosphoprotein (VASP).

METHODS

Comatose survivors of out of hospital cardiac arrest were included and divided into two groups, depending on whether dual platelet inhibition with peroral ticagrelor and aspirin was given or not. The first blood samples (T1) were collected 12-24 hours after reaching target temperature (33°C) and were compared to blood samples collected 12-28 hours after reaching normothermia (37°C) (T2) within each group. All samples were analysed by Sonoclot viscoelasticity, flow cytometry based VASP and with multiple electrode aggregometry, Multiplate®; adenosine diphosphate (ADP), collagen (COL), thrombin receptor agonist peptide (TRAP) and arachidonic acid (ASPI). Sonoclot and Multiplate® instruments were set on in vivo temperatures. Gastric secretion from the nasogastric tube was measured to assess absorption of per orally administered antiplatelet drugs. Differences between T1 and T2 within each group were calculated using Wilcoxon matched pairs signed test. Significance levels were set at P <0.01.

RESULTS

In total, 23 patients were included. In patients with dual platelet inhibition (n =14) Multiplate®-analyses showed no changes in ADP stimulated platelets. COL, TRAP and ASPI aggregations were higher at T2 compared to T1. Sonoclot-analyses showed that activated clotting time (ACT) was unchanged but both clot rate (CR) and platelet function (PF) were higher at T2 compared to T1. VASP decreased from 53 ± 28(T1) to 24 ± 22(T2), (P <0.001). The average volume of gastric secretion aspirated before T1 correlated well with VASP (T1), r =0.81 (P <0.001). In patients with no platelet inhibition, (n =9) similar changes between T1 and T2 were seen as in patients with dual platelet inhibition while VASP was unchanged.

CONCLUSIONS

We have demonstrated increased platelet aggregation and strengthened clot formation over time in out of hospital cardiac arrest patients treated with hypothermia. In patients on oral dual platelet inhibition, the effect of ticagrelor was delayed, probably due to slow gastric emptying.

Therapeutic temperature management after cardiac arrest and the risk of bleeding: systematic review and meta-analysis

AIM

Prognosis after cardiac arrest in the era of modern critical care is still poor with a high mortality of approximately 90%. Around 30% of the survivors have neurological impairments. Targeted temperature management (TTM) is the only treatment option which can improve mortality and neurological outcome. It is so far unclear if bleeding complications occur more often in patients undergoing TTM treatment.

METHODS

We conducted a systematic literature research in September 2013 including three major databases i.e. MEDLINE, EMBASE and CENTRAL. All studies were rated in respect to the ILCOR Guidelines and concerning their level of evidence and quality. We then performed a meta-analysis on bleeding disposition under TTM.

RESULTS

We initially found 941 studies out of which 34 matched our requirements and were thus included in our overview. Five studies including 599 patients were summarized in a meta-analysis concerning bleeding complications of all severities. There was a trend toward higher bleeding in patients treated with TTM (RR: 1.30, 95% CI: 0.97-1.74) which did not reach significance (p=0.085). Seven studies with an overall 599 patients were included in our meta-analysis on bleeding requiring transfusion. There was no significant difference in the incidence of severe bleeding with a risk ratio of 0.97 (95% CI: 0.61-1.56, p=0.909).

CONCLUSIONS

The data included in our meta-analysis indicate that, concerning the risk of bleeding, TTM is a safe method for patients after cardiac arrest. We did not observe a significantly higher risk for bleeding in patients undergoing TTM.

Cardiac resuscitation and coagulation

Cardiac arrest and its treatment options are frequently associated with significant derangements in coagulation. This review article highlights coagulopathies commonly encountered in cardiac arrest and during treatment with hypothermia, thrombolysis, and extracorporeal membrane oxygenation.

Thrombin generation and fibrin clot formation under hypothermic conditions: an in vitro evaluation of tissue factor initiated whole blood coagulation

BACKGROUND

Despite trauma-induced hypothermic coagulopathy being familiar in the clinical setting, empirical experimentation concerning this phenomenon is lacking. In this study, we investigated the effects of hypothermia on thrombin generation, clot formation, and global hemostatic functions in an in vitro environment using a whole blood model and thromboelastography, which can recapitulate hypothermia.

METHODS

Blood was collected from healthy individuals through venipuncture and treated with corn trypsin inhibitor, to block the contact pathway. Coagulation was initiated with 5pM tissue factor at temperatures 37°C, 32°C, and 27°C. Reactions were quenched over time, with soluble and insoluble components analyzed for thrombin generation, fibrinogen consumption, factor (f)XIII activation, and fibrin deposition. Global coagulation potential was evaluated through thromboelastography.

RESULTS

Data showed that thrombin generation in samples at 37°C and 32°C had comparable rates, whereas 27°C had a much lower rate (39.2 ± 1.1 and 43 ± 2.4 nM/min vs 28.6 ± 4.4 nM/min, respectively). Fibrinogen consumption and fXIII activation were highest at 37°C, followed by 32°C and 27°C. Fibrin formation as seen through clot weights also followed this trend. Thromboelastography data showed that clot formation was fastest in samples at 37°C and lowest at 27°C. Maximum clot strength was similar for each temperature. Also, percent lysis of clots was highest at 37°C followed by 32°C and then 27°C.

CONCLUSIONS

Induced hypothermic conditions directly affect the rate of thrombin generation and clot formation, whereas global clot stability remains intact.

Impaired bioavailability and antiplatelet effect of high-dose clopidogrel in patients after cardiopulmonary resuscitation (CPR)

PURPOSE

Bioavailability of clopidogrel in the form of crushed tablets administered via nasogastric tube (NGT) has not been established in patients after cardiopulmonary resuscitation. Therefore, we performed a study comparing pharmacokinetic and pharmacodynamic response to high loading dose of clopidogrel in critically ill patients after cardiopulmonary resuscitation (CPR) with patients scheduled for elective coronary angiography with stent implantation.

METHODS

In the NGT group (nine patients, after cardiopulmonary resuscitation, mechanically ventilated, therapeutic hypothermia), clopidogrel was administered in the form of crushed tablets via NGT. Ten patients undergoing elective coronary artery stenting took clopidogrel per os (po) in the form of intact tablets. Pharmacokinetics of clopidogrel was measured with high-performance liquid chromatography (HPLC) before and at 0.5, 1, 6, 12, 24 h after administration of a loading dose of 600 mg. In five patients in each group, antiplatelet effect was measured with thrombelastography (TEG; Platelet Mapping) before and 24 h after administration.

RESULTS

The carboxylic acid metabolite of clopidogrel was detected in all patients in the po group. In eight patients, the maximum concentration was measured in the range of 0.5-1 h after the initial dose. In four patients in the of NGT group, the carboxylic acid metabolite of clopidogrel was undetectable and in the remaining patients was significantly delayed (peak values at 12 h). All patients in the po group reached clinically relevant (>50 %) inhibition of thrombocyte adenosine diphosphate (ADP) receptor after 24 h compared with only two in the NGT group (p = 0.012). There was a close correlation between peak of inactive clopidogrel metabolite plasmatic concentration and inhibition of the ADP receptor (r = 0.79; p < 0.001).

CONCLUSION

The bioavailability of clopidogrel in critically ill patients after cardiopulmonary resuscitation is significantly impaired compared with stable patients. Therefore, other drugs, preferentially administered intravenously, should be considered.