Reduced coagulation at high altitude identified by thromboelastography

Clinical Conundrum: Return to High Altitude After Cerebral Venous Sinus Thrombosis

Luks, Andrew M., Thomas G. DeLoughery, Jeffrey H. Gertsch, and Suzy Stokes. Clinical conundrum: return to high altitude after cerebral venous sinus thrombosis. High Alt Med Biol. 00:00-00, 2024.

High Altitude

With ascent to high altitude, barometric pressure declines, leading to a reduction in the partial pressure of oxygen at every point along the oxygen transport chain from the ambient air to tissue mitochondria. This leads, in turn, to a series of changes over varying time frames across multiple organ systems that serve to maintain tissue oxygen delivery at levels sufficient to prevent acute altitude illness and preserve cognitive and locomotor function. This review focuses primarily on the physiological adjustments and acclimatization processes that occur in the lungs of healthy individuals, including alterations in control of breathing, ventilation, gas exchange, lung mechanics and dynamics, and pulmonary vascular physiology. Because other organ systems, including the cardiovascular, hematologic and renal systems, contribute to acclimatization, the responses seen in these systems, as well as changes in common activities such as sleep and exercise, are also addressed. While the pattern of the responses highlighted in this review are similar across individuals, the magnitude of such responses often demonstrates significant interindividual variability which accounts for subsequent differences in tolerance of the low oxygen conditions in this environment.

The benefits of early continuous renal replacement therapy in critically ill patients with acute kidney injury at high-altitude areas: a retrospective multi-center cohort study

Severe hypoxia would aggravate the acute kidney injury (AKI) in high-altitude areas and continuous renal replacement therapy (CRRT) has been used to treat critically ill patients with AKI. However, the characteristics and outcomes of CRRT in critically ill patients at AKI in high altitudes and the optimal timing of CRRT initiation remain unclear. 1124 patients were diagnosed with AKI and treated with CRRT in the ICU, comprising a high-altitude group (n = 648) and low-altitude group (n = 476). Compared with the low-altitude group, patients with AKI at high altitude showed longer CRRT (4.8 vs. 3.7, P = 0.036) and more rapid progression of AKI stages (P < 0.01), but without any significant minor or major bleeding episodes (P > 0.05). Referring to the analysis of survival and kidney recovery curves, a higher mortality but a lower possibility of renal recovery was observed in the high-altitude group (P < 0.001). However, in the high-altitude group, the survival rate of early CRRT initiation was significantly higher than that of delayed CRRT initiation (P < 0.001). The findings showed poorer clinical outcomes in patients undergoing CRRT for AKI at high altitudes. CRRT at high altitudes was unlikely to increase the adverse events. Moreover, early CRRT initiation might reduce the mortality and promote renal recovery in high-altitude patients.

Effects of Hypobaric Hypoxia on Coagulation in Healthy Subjects Exposed to 3,500 m Altitude

Kammerer, Tobias, Anna Walzl, Thomas Müller, Philipp Groene, Giulia Roveri, Rachel Turner, Johanna Roche, Hannes Gatterer, Christoph Siebenmann, and Simon T. Schäfer. Effects of hypobaric hypoxia on coagulation in healthy subjects exposed to 3,500 m altitude. High Alt Med Biol. 24:94-103, 2023. Background: Hypoxia is discussed as a trigger for prothrombotic changes both in intensive care and high altitude medicine. This research study aimed to evaluate the effect of isolated hypobaric hypoxia (HH) on coagulation in females in a highly standardized setting. Methods: Twelve healthy female subjects were studied under HH (equivalent to 3,500 m) and normoxia (NX) during two 4-day sojourns, in a strictly controlled crossover design. Nutrition, fluid intake, hormonal status (i.e., menstrual cycle variation), and physical stress were standardized. Functional coagulation and blood lysis were measured by viscoelastometry and compared between HH and NX. In addition, plasma-based coagulation tests (PBCTs), namely prothrombin time, activated partial thromboplastin time, fibrinogen, factor VIII coagulation activity (FVIII:C), von Willebrand factor antigen (vWF:Ag), and von Willebrand factor ristocetin cofactor activity (vWF:RCo) were measured. Results: Neither for Viscoelastic Haemostatic Assays nor for PBCTs significant changes were found for HH compared with NX (all p > 0.05). Specifically, the lysis ability, as well as clotting time, clot formation, clot amplitude, and maximum clot firmness unchanged were similar between HH and NX. This also applied to all other variables. Conclusion: We demonstrate that moderate HH per se has no influence on blood coagulation in healthy females.

Hemostatic Effects of Bio-Zeolite Gauze and QuikClot Combat Gauze on Major Bleeding in Rabbits Acutely Exposed to High Altitude

Objective: Hemostatic gauze application is an effective way to control major bleeding, which is the most common cause of death in trauma in both civilian and military settings. Coagulation derangement after acute exposure to high altitude might alter the effects of hemostatic gauzes. The present study aimed to observe the hemostatic effects of bio-zeolite gauze (BZG) and QuikClot Combat Gauze® (QCG) on major bleeding in rabbits acutely exposed to high altitude.Methods: Sixty rabbits were randomly and evenly divided into six groups. Animal models of simulated blast- and fragment-induced inguinal major bleeding were prepared in lower altitude and high-altitude areas, and BZG, QCG, and ordinary gauze without hemostatic material were used to control bleeding. The primary outcomes included immediate hemostasis rate, blood loss, and survival rate, while the secondary outcomes included hemodynamic parameters, laboratory examinations, and coagulation-relevant markers.Results: The overall effects of BZG and QCG were better than those of ordinary gauze, with a higher immediate hemostatic rate, less blood loss, and higher survival rate at 90 min after gauze application and higher red blood cell and platelet counts and lower creatinine level at 30 min after gauze application in lower altitude. The concentrations of coagulation factor XII and factor X in rabbits acutely exposed to high altitude were significantly lower than those in lower altitude. At high altitude, the hemostatic effects of BZG did not decrease significantly compared to those in the lower altitude, whereas those of ordinary gauze and QCG decreased significantly at high altitude compared to those in the lower altitude.Conclusions: Coagulation derangement after acute exposure to high altitude has negative effects on ordinary gauze and QCG but has no significant negative hemostatic effects on BZG.

Time Course of Coagulo-Fibrinolytic Derangements During Acclimatization to High Altitude in Rabbits and a Preliminary Study on the Possible Mechanisms

Zhong, Xin, Zhao Ye, Xiaolin Zhou, Renqing Jiang, Yijun Jia, Wenqiong Du, Haoyang Yang, Lin Zhang, Bai Lu, and Zhaowen Zong. Time course of coagulo-fibrinolytic derangements during acclimatization to high altitude in rabbits and a preliminary study on the possible mechanisms. High Alt Med Biol. 00:000-000, 2022. Background: Conflicting data exist regarding changes in the coagulation system during acclimatization to high altitude (HA), which makes the prevention of thromboembolic events difficult. The present study aimed at observing the dynamic changes in the coagulo-fibrinolysis system during acclimatization to HA and at exploring the possible mechanisms. Materials and Methods: Twenty rabbits of both sexes were randomly divided into two groups, including group A rabbits (healthy plain controls) and group B rabbits (acutely exposed to HA). A traditional coagulation test, thromboelastography analysis, and full blood cell count were used to assess the coagulo-fibrinolytic changes at different time points. Plasma was collected to examine the levels of relevant biomarkers. Results: Six hours and 1 day after acute exposure to HA, the coagulo-fibrinolytic system demonstrated a hypercoagulable state. Further, 3 days after exposure to HA, group B rabbits showed hypocoagulability, increased fibrinolysis, and lower clot firmness and 7 days after exposure to HA, delayed coagulation, decreased fibrinolysis, and increased clot firmness were observed. Subsequently, 14, 21, and 28 days after exposure to HA, we found increased clot firmness. Increased platelet counts and concentrations of fibrinogen and plasminogen activator inhibitor-1 contributed to this change. Conclusion: The coagulo-fibrinolytic derangements during acclimatization to HA in rabbits demonstrated a dynamic pattern.

The Influence of Environmental Hypoxia on Hemostasis—A Systematic Review

Humans have been ascending to high altitudes for centuries, with a growing number of professional- and leisure-related sojourns occurring in this millennium. A multitude of scientific reports on hemostatic disorders at high altitude suggest that hypoxia is an independent risk factor. However, no systematic analysis of the influence of environmental hypoxia on coagulation, fibrinolysis and platelet function has been performed. To fill this gap, we performed a systematic literature review, including only the data of healthy persons obtained during altitude exposure (&lt;60 days). The results were stratified by the degree of hypoxia and sub-categorized into active and passive ascents and sojourns. Twenty-one studies including 501 participants were included in the final analysis. Since only one study provided relevant data, no conclusions regarding moderate altitudes (1,500–2,500 m) could be drawn. At high altitude (2,500–5,400 m), only small pathophysiological changes were seen, with a possible impact of increasing exercise loads. Elevated thrombin generation seems to be balanced by decreased platelet activation. Viscoelastic methods do not support increased thrombogenicity, with fibrinolysis being unaffected by high altitude. At extreme altitude (5,400–8,850 m), the limited data showed activation of coagulation in parallel with stimulation of fibrinolysis. Furthermore, multiple confounding variables at altitude, like training status, exercise load, fluid status and mental stress, prevent definitive conclusions being drawn on the impact of hypoxia on hemostasis. Thus, we cannot support the hypothesis that hypoxia triggers hypercoagulability and increases the risk of thromboembolic disorders, at least in healthy sojourners.

Evaluation of the altitude impact on a point-of-care thromboelastography analyzer measurement: prerequisites for use in airborne medical evacuation courses

PURPOSE

Hemorrhagic shock is the first cause of preventable death in combat. Evacuations of wounded by aircraft are increasingly used and severely injured patients can spend consequent time in the air, mostly during strategic evacuation. In these situations, monitoring of blood coagulation may be pivotal in the management of blood product transfusion. Viscoelastic-guided transfusion is relevant in these situations. However, evaluation of these devices used in aircraft is lacking, especially the impact of decreased atmospheric pressure. The aim of this study is to evaluate the performance of an easy-to-carry viscoelastic system (TEG^® 6s, Haemonetics).

METHODS

First, TEG^® 6s repeatability, reproducibility, and correlation with chronometric methods and TEG-5000 were assessed on quality controls, healthy volunteers, and patients. Secondly, we tested the influence of vibrations and altitude on TEG^® 6s parameters (0ft vs. 8000 ft = 2428 m) and on quality control samples (normal and hypocoagulable).

RESULTS

TEG^® 6s exhibited good correlation with the reference method and TEG^® 5000. Repeatability and reproducibility CVs were satisfactory. The tests performed in the hypobaric chamber revealed that performance at 0 ft and 8000 ft (2428 m) for 9 out of 13 parameters was not significantly different. However, we showed a significant increasing of CRT.Alpha (p = 0.049), CK.Alpha, CK.MA (p < 0.001 and p < 0.01, respectively) and CFF.MA increased (p < 0.05).

CONCLUSION

Our study provides proof of concept to validate testing in an actual aeromedical situation. Indeed, TEG^® 6s appears to ease of use, resistance to high altitude conditions, and reliability on healthy humans. It is necessary to carry out a study on hemorrhagic injured patients in an aircraft.

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.

Clinical recommendations for high altitude exposure of individuals with pre-existing cardiovascular conditions: A joint statement by the European Society of Cardiology, the Council on Hypertension of the European Society of Cardiology, the European Society of Hypertension, the International Society of Mountain Medicine, the Italian Society of Hypertension and the Italian Society of Mountain Medicine

Take home figure

The current status of viscoelastic testing in septic coagulopathy

Sepsis can be associated with different degrees of coagulopathy, ranging from a mild activation of the coagulation system to disseminated intravascular coagulation (DIC). The evaluation of haemostasis in the context of sepsis is important since it has been shown that anticoagulant therapies were beneficial mainly in patients with sepsis-induced DIC, but not in the general population of septic patients. Sepsis-induced haemostatic disturbances are not adequately reflected by standard coagulation tests (SCTs) which only consider the plasmatic components of the haemostatic system and not the cellular components. In addition, SCTs only assess the initiation phase of coagulation and reflect the activity of pro-coagulant factors, but lack sensitivity for the anticoagulant drive and the fibrinolytic activity. Viscoelastic tests (VET) are whole-blood tests which can assess clot formation and dissociation, and the contribution of both plasmatic and cellular components with a shorter turnaround time compared to SCTs. The use of VET in septic patients has proved useful for the assessment of the fibrinolytic activity, detecting hypercoagulable status and for the diagnosis of DIC and mortality risk prediction. While having relevant advantages over SCTs, the VET also present some blind spots or limitations leaving space for future improvement by the development of new reagents or new viscoelastic parameters.

Thromboelastometry and Platelet Function during Acclimatization to High Altitude

Interaction between hypoxia and coagulation is important given the increased risk of thrombotic diseases in chronically hypoxic patients who reside at sea level and in residents at high altitude. Hypoxia alters the proteome of platelets favouring a prothrombotic phenotype, but studies of activation and consumption of specific coagulation factors in hypoxic humans have yielded conflicting results. We tested blood from 63 healthy lowland volunteers acclimatizing to high altitude (5,200 m) using thromboelastometry and assays of platelet function to examine the effects of hypoxia on haemostasis. Using data from two separate cohorts of patients following identical ascent profiles, we detected a significant delay in clot formation, but increased clot strength by day 7 at 5,200 m. The latter finding may be accounted for by the significant rise in platelet count and fibrinogen concentration that occurred during acclimatization. Platelet function assays revealed evidence of platelet hyper-reactivity, with shortened PFA-100 closure times and increased platelet aggregation in response to adenosine diphosphate. Post-expedition results were consistent with the normalization of coagulation following descent to sea level. These robust findings indicate that hypoxia increases platelet reactivity and, with the exception of the paradoxical delay in thromboelastometry clotting time, suggest a prothrombotic phenotype at altitude. Further work to elucidate the mechanism of platelet activation in hypoxia will be important and could impact upon the management of patients with acute or chronic hypoxic respiratory diseases who are at risk of thrombotic events.

Effects of profound hypoxemia on coagulation & fibrinolysis in normal individuals

Hypoxia has been proposed to enhance, diminish, or have no effect on laboratory measures of coagulation or clinical thrombosis. Further, there usually are significant pathological or environmental factors concurrently present with hypoxia. Thus, the goal of the present investigation was to determine whether whole blood or plasmatic coagulation and fibrinolytic kinetics would change in response to progressive hypoxia to a systemic oxygenation (SpO2) of 70%. Healthy, conscious volunteers (n = 9) breathing a hypoxic mixture of gases during an in-vivo validation of noninvasive cerebral oximetry had blood samples collected and assessed with thrombelastography at normoxia and after SpO2 of 70%. A mild release of endogenous heparin-like activity occurred that diminished plasmatic coagulation, and a mild increase in clot lysis time also was noted. Further investigation to determine whether these phenomena occur in more chronic, less hypoxic states as sources of hypocoagulation or thrombophilia is needed.

Caudwell Xtreme Everest: An Overview

The Caudwell Xtreme Everest (CXE) expedition in the spring of 2007 systematically studied 222 healthy volunteers as they ascended from sea level to Everest Base Camp (5300 m). A subgroup of climbing investigators ascended higher on Everest and obtained physiological measurements up to an altitude of 8400 m. The aim of the study was to explore inter-individual variation in response to environmental hypobaric hypoxia in order to understand better the pathophysiology of critically ill patients and other patients in whom hypoxaemia and cellular hypoxia are prevalent. This paper describes the aims, study characteristics, organization and management of the CXE expedition.

Hypoxia Induces a Prothrombotic State Independently of the Physical Activity

Hypoxia (oxygen deprivation) is known to be associated with deep vein thrombosis and venous thromboembolism. We attempted to get a better comprehension of its mechanism by going to high altitude, thereby including the potential contributing role of physical activity. Two groups of 15 healthy individuals were exposed to hypoxia by going to an altitude of 3900 meters, either by climbing actively (active group) or transported passively by cable car (passive group). Both groups were tested for plasma fibrinogen, von Willebrand factor and factor VIII levels, fibrinolysis, thrombin generating capacity, heart rate, oxygen saturation levels and blood pressure. As a control for the passive group, 7 healthy volunteers stayed immobile in bed for 7 days at normoxic conditions. The heart rate increased and oxygen saturation levels decreased with increasing altitude. Fibrinolysis and fibrinogen levels were not affected. Factor VIII and von Willebrand factor levels levels increased significantly in the active group, but not in the passive group. Plasma thrombin generation remained unchanged in both the active and passive group with increasing altitude and during 7 days of immobility in healthy subjects. However, by applying whole blood thrombin generation, we found an increased peak height and endogenous thrombin potential, and a decreased lagtime and time-to-peak with increasing levels of hypoxia in both groups. In conclusion, by applying whole blood thrombin generation we demonstrated that hypoxia causes a prothrombotic state. As thrombin generation in plasma did not increase, our results suggest that the cellular part of the blood is involved in the prothrombotic phenotype induced by hypoxia.

Influence of Acute Normobaric Hypoxia on Hemostasis in Volunteers with and without Acute Mountain Sickness

INTRODUCTION

The aim of the present study was to investigate whether a 12-hour exposure in a normobaric hypoxic chamber would induce changes in the hemostatic system and a procoagulant state in volunteers suffering from acute mountain sickness (AMS) and healthy controls.

MATERIALS AND METHODS

37 healthy participants were passively exposed to 12.6% FiO2 (simulated altitude hypoxia of 4,500 m). AMS development was investigated by the Lake Louise Score (LLS). Prothrombin time, activated partial thromboplastin time, fibrinogen, and platelet count were measured and specific methods (i.e., thromboelastometry and a thrombin generation test) were used.

RESULTS

AMS prevalence was 62.2% (LLS cut off of 3). For the whole group, paired sample t-tests showed significant increase in the maximal concentration of generated thrombin. ROTEM measurements revealed a significant shortening of coagulation time and an increase of maximal clot firmness (InTEM test). A significant increase in maximum clot firmness could be shown (FibTEM test).

CONCLUSIONS

All significant changes in coagulation parameters after exposure remained within normal reference ranges. No differences with regard to measured parameters of the hemostatic system between AMS-positive and -negative subjects were observed. Therefore, the hypothesis of the acute activation of coagulation by hypoxia can be rejected.

Physical activity at altitude: challenges for people with diabetes: a review

BACKGROUND

A growing number of subjects with diabetes take part in physical activities at altitude such as skiing, climbing, and trekking. Exercise under conditions of hypobaric hypoxia poses some unique challenges on subjects with diabetes, and the presence of diabetes can complicate safe and successful participation in mountain activities. Among others, altitude can alter glucoregulation. Furthermore, cold temperatures and altitude can complicate accurate reading of glucose monitoring equipment and storage of insulin. These factors potentially lead to dangerous hyperglycemia or hypoglycemia. Over the last years, more information has become available on this subject.

PURPOSE

To provide an up-to-date overview of the pathophysiological changes during physical activity at altitude and the potential problems related to diabetes, including the use of (continuous) blood glucose monitors and insulin pumps. To propose practical recommendations for preparations and travel to altitude for subjects with diabetes.

DATA SOURCES AND SYNTHESIS

We researched PubMed, medical textbooks, and related Internet sites, and extracted human studies and data based on relevance for diabetes, exercise, and altitude.

LIMITATIONS

Given the paucity of controlled trials regarding diabetes and altitude, we composed a narrative review and filled in areas lacking diabetes-specific studies with data obtained from nondiabetic subjects.

CONCLUSIONS

Subjects with diabetes can take part in activities at high, and even extreme, altitude. However, careful assessment of diabetes-related complications, optimal preparation, and adequate knowledge of glycemic regulation at altitude and altitude-related complications is needed.

Inhibitory effect of nitrite on coagulation processes demonstrated by thrombelastography

Nitric oxide (NO) can be generated by two-step reduction pathway in which nitrate is converted first into nitrite and then into NO via several mechanisms, as well as from arginine by endogenous nitric oxide synthase (NOS). We have recently shown that nitrite ions in the presence of erythrocytes inhibit platelet aggregation and activation, as measured by aggregometry and flow cytometric analysis of P-selectin, through its reduction to NO under partially deoxygenated conditions. In the current study, we investigated how nitrite may affect overall clotting processes via modulating platelet function using thrombelastography (TEG). We measured three major TEG parameters, reaction time (R, time to initial fibrin formation), α angle (velocity of clot growth) and maximum amplitude (MA, maximum clot strength) using blood from healthy volunteers. An NO donor (DEANONOate) showed inhibitory effects on all TEG parameters in platelet rich plasma (PRP) and whole blood, resulting in delayed R, decreased angle, and reduced MA in a dose dependent manner. Nitrite ions also exhibited inhibitory effects in whole blood at 20% hematocrit, and this was greatly enhanced under hypoxic conditions, being demonstrable at 0.1 μM concentration. Neither compound changed any TEG parameters in plasma. Our results suggest that nitrite affects overall blood clotting and that TEG may be used to follow this process. Further the physiological effects of factors which determine NO bioavailability, such as endogenous levels of blood and tissue nitrite, may be useful as biomarkers for predicting hemostatic potential.