Thromboelastometry analysis of severe North American pit viper-induced coagulopathy: A case report

Bite First, Bleed Later: How Philippine Trimeresurus Pit Viper Venoms Hijack Blood Clotting

The Philippines has a high diversity of venomous snake species, but there is minimal information on their envenomation effects. This is evidenced by the small number of case reports, the poor reporting of envenomation cases, and the absence of specific antivenoms apart from one against the Philippine cobra (Naja philippinensis). This study sought to profile the action of selected Philippine pit viper venoms on blood coagulation and to investigate whether commercially available non-specific antivenoms can provide adequate protection against these venoms. Venom from the pit vipers Trimeresurus flavomaculatus and Trimeresurus mcgregori were subjected to coagulation assays, antivenom cross-neutralization tests, and thromboelastography. Venoms from both species were able to clot human plasma and isolated human fibrinogen. Consistent with pseudo-procoagulant/thrombin-like activity, the resulting fibrin clots were weak and transient, thereby contributing to net anticoagulation through the depletion of fibrinogen levels. Clotting factors fIXa and fXa were also inhibited by the venoms, further contributing to the net anticoagulant activity. Monovalent and polyvalent antivenoms from the Thai Red Cross Society were effective against both venoms, indicating cross-neutralization of venom toxins; the polyvalent antivenom was able to rescue fibrinogen clotting to a greater degree than the monovalent antivenom. Our findings highlight the coagulopathic effects of these pit viper venoms and suggest the utility of procuring the non-specific antivenoms for areas in the Philippines with a high risk for pit viper envenomation.

The use of rotational thromboelastometry to guide management following Bitis nasicornis envenoming

A man in his thirties presented following Bitis nasicornis envenoming. His coagulation was assessed using rotational thromboelastometry (ROTEM). It identified a subtle abnormality, not detected using standard laboratory assessments of coagulation, and influenced ongoing management. The abnormality resolved following treatment with antivenom. There are few documented cases of using ROTEM to assess patients following haemotoxic envenoming. This case highlights some of the potential benefits and limitations of doing so.

Compendium of medically important snakes, venom activity and clinical presentations in Ghana

BACKGROUND

Snake bite envenoming (SBE) is one neglected tropical disease that has not received the needed attention. The sequelae of burdensome disability and mortality impact the socioeconomic life of communities adversely with little documentation of SBE in health facility records in Ghana. This study details SBE and snake distribution, habits/habitats, type of venom expressed and clinical manifestations.

METHODOLOGY

We conducted a structured thematic desk review of peer reviewed papers, books and reports from repositories including PubMed, World Health Organization (WHO) and Women's & Children's Hospital (WCH) Clinical Toxinology Resources using bibliographic software EndNote and search engine Google Scholar with the following key words; snakes, medical importance, snake bites, venom and venom type, envenomation, symptoms and signs, vaccines, venom expenditure, strike behaviour and venom-metering + Ghana, West Africa, Africa, World. We also reviewed data from the District Health Information Management System (DHIMS) of the Ghana Health Service (GHS). Outcome variables were organized as follows: common name (s), species, habitat/habit, species-specific toxin, clinical manifestation, antivenom availability, WHO category.

FINDINGS

Snake bites and SBE were grouped by the activity of the expressed venom into neurotoxic, cardiotoxic, haemorrhagic, cytotoxic, myotoxic, nephrotoxic and procoagulants. Neurotoxic snake bites were largely due to elapids. Expressed venoms with cardiotoxic, haemorrhagic, nephrotoxic and procoagulant activities principally belonged to the family Viperidae. Snakes with venoms showing myotoxic activity were largely alien to Ghana and the West African sub-region. Venoms showing cytotoxic activity are expressed by a wide range of snakes though more prevalent among the Viperidae family. Snakes with neurotoxic and haemorrhagic venom activities are prevalent across all the agro-ecological zones in Ghana.

CONCLUSION/SIGNIFICANCE

Understanding the characteristics of snakes and their venoms is useful in the management of SBE. The distribution of snakes by their expressed venoms across the agro-ecological zones is also instructive to species identification and diagnosis of SBE.

Correlations between rotational thromboelastometry (ROTEM) and standard coagulation tests following viper snakebites

BACKGROUND

A high prevalence of venom-induced consumption coagulopathy has been reported in individuals with viper snakebites. Rotational thromboelastometry (ROTEM) is a rapid technique that could be advantageous in assessing and monitoring coagulation disorders.

PURPOSE

To explore correlations between ROTEM and standard coagulation tests.

PATIENTS AND METHODS

This prospective observational study was performed among 41 patients with viper envenomation admitted to the Vietnam Poison Control Center from April 2016 to October 2017. Standard coagulation measurements [platelet count, prothrombin time (PT), activated partial thromboplastin time (aPTT), and fibrinogen level] and ROTEM indicators [clotting time (CT), amplitude (at set time: 5 and 10 minutes), clot information time (CFT) and maximum clot firmness (MCF) for extrinsic (EXTEM), intrinsic (INTEM), and fibrin based (FIBTEM) ROTEM] were obtained.

RESULTS

For INTEM, EXTEM, the FIBTEM, proportions of patients with prolonged CT were 34.1%, 63.4%, and 61.0% respectively and the proportions of patients with decreased MCF were 62.2%, 62.2%, and 35.5%, respectively. Moderate correlations were observed between PT and EXTEM CT (r = 0.627), aPTT and INTEM CT (r = 0.626), fibrinogen and FIBTEM MCF (r = 0.723), and platelet count and EXTEM MCF (0.60).

CONCLUSION

ROTEM indicated a hypocoagulation state in patients with viper snakebite and was moderately correlated with standard coagulation parameters.

Comparison of rotational thromboelastometry parameters with 20-minute whole blood clotting test as a predictor of envenoming in Russell's viper bite patients

BACKGROUND

Coagulopathy is an important and common systemic clinical syndrome caused by snake envenoming. The major clinical effect of Russell's viper (RV) envenoming is haematotoxicity. The 20-min whole blood clotting test (WBCT20) is the standard test for identification of envenoming in resource-limited settings. However, its reliability as a diagnostic test has been questioned. Rotational thromboelastometry (ROTEM) assays different phases of clot formation from initiation to fibrinolysis. Our objective was to compare parameters of ROTEM with WBCT20 and the international normalized ratio (INR) as predictors of envenoming in RV bite patients.

METHODS

Fifty-three patents with RV bite presenting to Anuradhapura Hospital, Sri Lanka were recruited. Epidemiological and clinical data were obtained. Venous blood samples were collected at admission for ROTEM, INR and WBCT20.

RESULTS

A total of 46 of 53 patients with RV bites received antivenom serum (AVS); 74% had a non-clottable WBCT20. All 46 had at least one abnormal ROTEM parameter and 93% had a prolonged EXTEM clotting time (EXTEM-CT). The sensitivity of a prolonged INR was only 55%.

CONCLUSIONS

EXTEM-CT is a better predictor of envenoming and the need for AVS than WBCT20 in RV bites (p=0.02). It provides a numerical value that can be used post-AVS to objectively assess the response and decide on further treatment.

Snakebite Envenomation and Heart: Systematic Review

Snakebite envenomation is a neglected tropical disease which can result in morbidity and mortality. Cardiac implications are poorly understood due to the low frequency of cardiotoxicity combined with a lack of robust information, as snakebites commonly occur in remote and rural areas. This review aims to assess cardiovascular implications of snakebite envenoming and proposes an algorithm for screening of cardiovascular manifestations. A systematic review was performed and 29 articles relating to cardiovascular involvement in snakebite envenomation were selected. Cardiovascular involvement seems to be rare and includes a wide spectrum of outcomes, such as myocardial infarction, ventricular dysfunction, hypotension, cardiac arrest, and myocarditis. In a significant proportion of the cases analyzed (24.39%), the cardiovascular manifestations had major consequences (cardiac arrest, myocardial infarction, malignant ventricular arrhythmias, or death). Clinical monitoring, physical examination, and early electrocardiogram should be considered as key measures to detect cardiovascular involvement in patients with evidence of systemic illness.

Utilization of thromboelastograms in management of Crotalus adamanteus envenomation

BACKGROUND

Crotalinae (pit viper) envenomations are frequently encountered in North American emergency departments. Cases can be complicated by ambiguity in initial species identification as well as timing and duration of current antivenin treatment. Recently, thromboelastography (TEG) has emerged as an enhanced real-time monitoring parameter for snake envenomations that may aid in management of venom-induced consumptive coagulopathy.

CASE

A 61-year-old snake handler presented with severe coagulopathy and hypofibrinogenemia following envenomation from her pet eastern diamondback rattlesnake (Crotalus adamanteus). Her coagulopathy transiently improved with Crotalidae Polyvalent Immune Fab (Ovine) (FabAV) but would repeatedly rebound following cessation of antivenin over the next 10 days. Serial TEGs were successfully utilized to identify and corroborate fibrinolysis while predicting clot formation prior to routine coagulation studies.

DISCUSSION

Traditional coagulation parameters have not always been ideal when treating severe coagulopathy from pit viper envenomations and may not identify active fibrinolysis for several hours. In this case of C. adamanteus envenomation, TEG proved to be useful in demonstrating improvements in clotting function prior to standard laboratory measures, which further guided antivenin therapy.

Novel Treatment Strategy for Patients with Venom-Induced Consumptive Coagulopathy from a Pit Viper Bite

Pit viper venom commonly causes venom-induced consumptive coagulopathy (VICC), which can be complicated by life-threatening hemorrhage. VICC has a complex pathophysiology affecting multiple steps of the coagulation pathway. Early detection of VICC is challenging because conventional blood tests such as prothrombin time (PT) and activated partial thromboplastin time (aPTT) are unreliable for early-stage monitoring of VICC progress. As the effects on the coagulation cascade may differ, even in the same species, the traditional coagulation pathways cannot fully explain the mechanisms involved in VICC or may be too slow to have any clinical utility. Antivenom should be promptly administered to neutralize the lethal toxins, although its efficacy remains controversial. Transfusion, including fresh frozen plasma, cryoprecipitate, and specific clotting factors, has also been performed in patients with bleeding. The effectiveness of viscoelastic monitoring in the treatment of VICC remains poorly understood. The development of VICC can be clarified using thromboelastography (TEG), which shows the procoagulant and anticoagulant effects of snake venom. Therefore, we believe that TEG may be able to be used to guide hemostatic resuscitation in victims of VICC. Here, we aim to discuss the advantages of TEG by comparing it with traditional coagulation tests and propose potential treatment options for VICC.

Comparison of thromboelastography versus conventional coagulation tests in simulated Crotalus atrox envenomation using human blood

INTRODUCTION

Pit viper bites are a source of significant morbidity and mortality. Pit viper bites can cause venom-induced consumptive coagulopathy (VICC), typically evaluated with laboratory-based conventional coagulation tests (CCTs). However, CCTs require a laboratory and average 1 h to conduct. Thromboelastography (TEG) provides real-time, point-of-care tests of coagulation that are fast and require no separate laboratory facilities, which could be advantageous in both hospital and austere settings. However, the relative efficacy of TEG versus CCTs was unclear, particularly at low venom concentrations. Therefore, the objectives of this study were to test human blood with various concentrations of pit viper venom using CCTs and TEG to determine dose-dependent changes, lowest observed effect concentration (LOEC), and sensitivity to detecting samples out of normal diagnostic range.

METHODS

Blood samples from 20 volunteers were mixed with varying concentrations of western diamond back rattlesnake (Crotalus atrox) venom based on the mouse LD50_IV (none, 0.5%, 1%, 2%, 33%, 66%, and 100% LD50_IV). Samples were split and assessed with both CCTs including prothrombin time (PT), international normalized ratio (INR), partial thromboplastin time (PTT), fibrinogen, and D-dimer, along with TEG measures of reaction time (R), kinetic time (K), rate of clot formation (α-angle), and clot strength (MA). Data were analyzed as dose-dependent concentration-based changes in raw values and in percent of samples exceeding diagnostic thresholds using ANOVA and nonparametric statistics at the p < .05 threshold.

RESULTS

All evaluations showed significant concentration-dependent changes, and 100% of samples exceeded diagnostic thresholds at 33%LD50_IV and above, save D-dimer. At 0.5%LD50_IV, R, K, α-angle, PT, and INR were significantly different from controls, and at 1%LD50_IV, mean values exceeded diagnostic thresholds for R, K, α-angle, MA, PT, and INR, but not for PTT, D-dimer, or fibrinogen. At 2%LD50_IV, 100% of samples were out of normal range for K, α-angle, and PT_. CONCLUSION: TEG is effective in coagulopathy evaluations of in vitro simulated pit viper envenomation. At low venom concentrations, TEG performed as well or better than the majority of CCTs. These findings provide empirical evidence supporting the use of TEG to rapidly and accurately evaluate VICC.

Thromboelastography with Platelet Studies (TEG® with PlateletMapping®) After Rattlesnake Envenomation in the Southwestern United States Demonstrates Inhibition of ADP-Induced Platelet Activation As Well As Clot Lysis

INTRODUCTION

Hematologic effects of North American rattlesnake envenomation can include fibrinogenolysis and thrombocytopenia, depending on species, geography, and other variables. During treatment, these effects are routinely monitored through assessment of fibrinogen concentrations and platelet counts. However, these tests provide no information about fibrinolysis or platelet dysfunction, both of which can also occur with venom from some species.

METHODS

This was a retrospective chart review of patients admitted to a quaternary care academic hospital (Banner - University Medical Center Phoenix) in the southwestern United States for treatment of rattlesnake envenomation, over an approximately 1-year period from March 2017 through April 2018. Patients who had thromboelastography with platelet studies (TEG® with PlateletMapping®) during their care were included.

RESULTS

Twelve patients were identified for this study. Four patients exhibited inhibition of ADP-induced platelet activation: one had normal fibrinogen and platelet count, two had concurrent hypofibrinogenemia, and one had concurrent thrombocytopenia. Crotalidae polyvalent immune Fab (ovine) reversed platelet inhibition in the single patient for whom serial thromboelastographs were available. Fibrinolysis was present in seven patients and resolved in the two patients with serial thromboelastographs.

CONCLUSIONS

Inhibition of ADP-induced platelet aggregation and fibrinolysis occurred independent of hypofibrinogenemia and thrombocytopenia, indicating fibrinogen concentration (or protime) and platelet count monitoring alone is insufficient to assess the extent of hematologic toxicity in rattlesnake envenomation. Crotalidae polyvalent immune Fab (ovine) reversed platelet inhibition in one case, suggesting platelet inhibition could also be used in treatment decisions. Fibrinolysis could also be reversed, although the timing to antivenom administration was less clear.