mbbs ims msu

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mbbs ims msu

  1. 1. Bleeding Time (BT)<br />
  2. 2. The bleeding time test is used to evaluate how well a person&apos;s blood is clotting. <br />The test evaluates <br />how long it takes the vessels cut to constrict and <br />how long it takes for platelets in the blood to seal off the hole. <br />Blood vessel defects, platelet function defects, along with many other conditions can result in prolonged bleeding time. <br />Definition<br />
  3. 3. Two techniques<br />Duke’s method : Earlobe (Obsolete)<br />Ivy’s method : Forearm (Today use)<br />
  4. 4. An incision 5 mm long x 1 mm deep is made on the lateral aspect of the surface of the forearm and the time to cessation of bleeding is measured. <br />Constant pressure (supplied by a sphygmomanometer) of 40 mm Hg. is applied and a disposable incision device is used to standardize the procedure. <br />Provided that fibrinogen levels and platelet count is normal, this procedure will detect defective platelet function and is used as a screening test for inherited and acquired platelet defects.<br />Ivy’s method Principle<br />
  5. 5. Incision vs Puncture<br />Incision<br />Puncture<br />
  6. 6. Specimen<br />The test is performed on forearms only <br />Small children may have to be restrained as excessive movement may render performance difficult and may invalidate the test. <br />The patient should be advised as to the possibility of some scaring. <br />An accurate drug history is often useful to the interpretation of the test. <br />The test may be performed routinely if the platelet count is in excess of 100,000/mm3 and a free arm is available. <br />
  7. 7. Equipment<br />stopwatch<br />sphygmomanometer (blood pressure cuff)<br />filter paper (Whatman No 1)<br />Surgicutt tm Automated Incision Making Instrument or lancet or Blade<br />70% alcohol prep<br />butterfly bandages<br />Surgicutt<br />Blade<br />Lancet<br />
  8. 8. Calibration and Control<br />Calibration: None<br />Quality Control:<br />No external QC is available. Care must be taken to standardize the procedure. <br />The protocol must followed exactly!<br />
  9. 9. Select a site on the patient&apos;s arm on the lateral aspect surface that is free of veins, bruises, edematous areas, and scars and is approximately 5 cm below the antecubital crease.<br />Clean the site with the alcohol prep.<br />Place the sphygmomanometer around the patient&apos;s arm approximately two inches above the elbow and maintain 40 mm Hg. <br />Make the incision by pushing the lancet into the skin (1/2 the length), then remove the device. <br />Discard the device in a &quot;sharps&quot; container.<br />Procedure<br />
  10. 10. Start the timing device and blot the edge of the incision at 30-second intervals with the filter paper. Do not touch the incision with the filter paper.<br />Note the time that bleeding stops and report to the nearest 30 seconds. <br />Note: If the bleeding time exceeds 15 minutes:<br />stop the procedure <br />apply pressure to stop the bleeding <br />To minimize scaring, bandage with a bandage is applied perpendicular to the incision.<br />10<br />Procedure<br />
  11. 11.
  12. 12. Note<br />Expected results:Normal Values: 2- 9 minutes.<br />In general not exceed 6 minutes.<br />
  13. 13. Errors producing false positive results<br />Blood pressure cuff maintained too high (&gt;40mm Hg.) <br />Incision too deep, caused by excessive pressure on the incision device. <br />Disturbing the clot with the filter paper. <br />Low fibrinogen (&lt;100 mg/dl) or platelet count (100,00 /mm3). <br />Drug ingestion affecting platelet function (e.g. asprin) <br />Errors producing false negative results<br />Blood pressure cuff maintained too low (&lt;40 mm Hg). <br />Incision too shallow. <br />Sources of error<br />
  14. 14. The bleeding time test is primarily a test of platelet function. It is usually significantly prolonged in the case of congenital or acquired platelet defects. Disease states in which abnormal bleeding times may be found include:<br />Von Willebrand&apos;s Disease<br />Sensitivity to Asprin<br />Clinical significance<br />
  15. 15. Function of Platelets<br />Stop bleeding from a damaged vessel<br />* Hemostasis<br />Three Steps involved in Hemostasis<br />1. Vascular Spasm<br />2. Formation of a platelet plug<br />3. Blood coagulation (clotting)<br />
  16. 16. Steps in Hemostasis<br />*DAMAGE TO BLOOD VESSEL LEADS TO:<br />Vascular Spasm:<br /><ul><li>Immediate constriction of blood vessel
  17. 17. Vessel walls pressed together – become “sticky”/adherent to each other
  18. 18. Minimize blood loss</li></li></ul><li>Steps in Hemostasis<br />2. Platelet Plug formation:<br /> a. PLATELETS attach to exposed collagen<br />b. Aggregation of platelets causes release of chemical mediators (ADP, Thromboxane A2)<br />c. ADP attracts more platelets<br />d. Thromboxane A2<br /> * promotes aggregation & more ADP<br /> Leads to formation of platelet plug !<br />
  19. 19. (+) Feedback promotes formation of platelet Plug <br />
  20. 20. Thrombin<br />Final Step in Hemostasis<br />Blood Coagulation (clot formation):<br />Transformation of blood from liquid to solid<br />Clot reinforces the plug<br />Multiple cascade steps in clot formation<br />Fibrinogen (plasma protein)Fibrin<br />
  21. 21. Factor X<br />Thrombin in Hemostasis<br />
  22. 22. Clotting Cascade<br />Participation of 12 different clotting factors (plasma glycoproteins)<br />Factors are designated by a roman numeral<br />Cascade of proteolytic reactions<br />Intrinsic pathway / Extrinsic pathway<br />Common Pathway leading to the formation of a fibrin clot !<br />
  23. 23. X<br />Hageman factor (XII)<br /> inactive <br /> active <br />CLOT !<br />
  24. 24. Clotting Cascade<br />Intrinsic Pathway:<br />Stops bleeding within (internal) a cut vessel<br />Foreign Substance (ie: in contact with test tube)<br />Factor XII (Hageman Factor)<br />Extrinsic pathway:<br />Clots blood that has escaped into tissues<br />Requires tissue factors external to blood<br />Factor III (Tissue Thromboplastin) <br />
  25. 25. Clotting Cascade<br />Fibrin :<br />Threadlike molecule-forms the meshwork of the clot<br />Entraps cellular elements of the blood forms CLOT<br />Contraction of platelets pulls the damaged vessel close together:<br />Fluid squeezes out as the clot contracts (Serum)<br />
  26. 26. Clot dissolution <br />Clot is slowly dissolved by the “fibrin splitting” enzyme called Plasmin<br />Plasminogenis the inactive pre-cursor that is activated by Factor XII (Hageman Factor) (simultaneous to clot formation)<br />Plasmin gets trapped in clot and slowly dissolves it by breaking down the fibrin meshwork<br />
  27. 27. Clot formation:Too much or too little of a good thing…<br />Too much:<br />Inappropriate clot formation is a thrombus (free-floating clots are emboli)<br />An enlarging thrombus narrows and can occlude vessels<br />Too little:<br />Hemophilia- too little clotting- can lead to life-threatening hemorrhage (caused from lack of one of the clotting factors)<br />Thrombocyte deficiency (low platelets) can also lead to diffuse hemorrhages<br />

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