Waveform Analysis In Snakebite Victims With Hematotoxicity

Overview

In hematotoxic snakebites, due to the lack of a better alternative, 20 minute whole blood clotting test (20'WBCT) or Clotting time remains the standard test in developing countries even though its reliability and sensitivity has been shown to be low. Activated partial thromboplastin time (aPTT) based Clot Waveform Analysis (CWA) is an optic absorbance assay that can be used as a global clotting test. It essentially detects the change in colour of the plasma as coagulation progresses and quantifies the change in the form of a waveform. In this study, the investigators intend to study prospectively the behaviour of clot wave (CW) in hematotoxic bites. A pilot observational study was initially conducted (IEC Ref No. 42/16/IEC/JMMC and RI) and CWA showed changes which provided information earlier than the conventional coagulation studies in the snakebite victims studied. While aPTT or WBCT reflects clotting time, CWA conveys the dynamic process of clot formation. CWA may reveal disorders of clotting in snakebite victims before the conventional tests become abnormal. Here the investigators aim to study the changes in CWA in snakebite victims who develop coagulation disorders in blood

Viperidae bites are quite common in India and are notorious to cause hematotoxicity. In hematotoxic bites, the test recommended to ascertain the development of coagulopathy is a whole blood clotting test (WBCT) as per the current guidelines. Eventhough the reliability and sensitivity of WBCT has been shown to be low, it still remains the standard test. There exists a need to explore other coagulation studies in snakebite to look for a better and efficient alternative. Clot waveform analysis (CWA) is an activated partial thromboplastin time (aPTT)-based optic absorbance assay that can be used as a global clotting test. It has been shown useful in identifying disseminated intravascular coagulation (DIC) in sepsis with high specificity (97.6%) and sensitivity (98%), and the test is recommended by the British Committee for Standards in Hematology guidelines for the diagnosis and treatment of DIC. CWA is based on the traditional aPTT assay. On assessing aPTT with light transmission, a change in the light absorbance is observed as the clot stabilizes by fibrin polymerization. Plotting the milliabsorbance (mAbs) of the sample to time, a curve is obtained which reflects the optical profile that is generated as a clot is formed. This tracing against time gives a qualitative assessment of fibrin polymerization. The delta in absorbance (dAbs) is based on the change in mAbs value from the baseline to the endpoint (plateau) along the Y-axis of the clot curve. The dAbs values of \<100 mAbs denote low fibrinogen samples The normal clot waveform has five main phases: delay, baseline, acceleration, deceleration, and end point. The "delay" period begins at 0 and precedes the "baseline." which denotes the mixing of the reagents and system optimization of light intensity. The "baseline" is the portion of the curve which appears after all reagents have been added to the time and the clot formation begins. The aPTT value is noted at this point (vertical red line). The "acceleration" phase denotes fibrin clot formation, whereas "deceleration" denotes decreasing rate of clot formation. There are two more curves that are plotted in CWA, the first derivative and the second derivatives. They are both derivatives of the absorbance curves. The first derivative reflects the coagulation velocity, whereas the second derivative reflects the acceleration of coagulation. The investigators in this study aim to assess the changes in the CW form in viper-envenomated victims and to compare CWA with standard tests such as prothrombin time (PT) with the international normalized ratio (INR), aPTT, clotting time (CT) (modified Lee and White method) and 20'WBCT( twenty minute whole blood clotting test)