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mbbs ims msu

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    mbbs ims msu mbbs ims msu Presentation Transcript

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