General Approach in Investigation of Hemostasis The Islamic University – Gaza Faculty of Health Science Medical Technology Department General Approach in Investigation of Hemostasis Lecture 2: Bleeding Time

Introduction When blood vessels are damaged, Hemostasis (clot formation) will arrest bleeding. This process is divided into three phases: Vascular Phase - Cutting or damaging blood vessels leads to vascular spasm of the smooth muscle in the vessel wall. This produces a vasoconstriction which will slow or even stop blood flow. This response will last up to 30 minutes and is localized to the damaged area.

Platelet phase - Damaged endothelial cells lining the blood vessel release von Willebrand's Factor. This substance makes the surfaces of the endothelial cells "sticky". This condition may, by itself, be enough to close small blood vessels. In larger blood vessels, platelets begin to stick to the surfaces of endothelial cells. This effect is called Platelet Adhesion. The platelets that adhere to the vessel walls now begin to secrete Adenosine diphosphate (ADP) which is released from "stuck" platelets. This material causes the aggregation of nearby free platelets which attach to the fixed platelets and each other. This aggregation of platelets leads to the formation of a platelet plug.

Coagulation Phase - Begins 30 seconds to several minutes after phases I and II have commenced. The overall process involves the formation of the insoluble protein Fibrin from the plasma protein Fibrinogen through the action of the enzyme Thrombin. Fibrin forms a network of fibers which traps blood cells and platelets forming a thrombus or clot. This phase followed by : Clot Retraction - After 2 or 3 days, the clot begins to contract. Platelets in the clot contain contractile proteins. These proteins pull the edges of the wound together and reduces the chance of further hemorrhage. This activity also assists the repair processes.

Fibrinolysis - Dissolution of the clot Fibrinolysis - Dissolution of the clot. The breakdown of the clot is due to the production of a powerful proteolytic enzyme Plasmin. Plasmin is formed through the same chemical pathway that produces thrombin. These reactions demonstrate that materials which induce clot formation (Thrombin and Factor XII) will eventually assist in the breakup of the clot.

Coagulation Tests Tests of the Vascular Platelet Phase of Haemostasis: Bleeding Time (BT) Tests of the Coagulation Cascade: Clotting Time ( CT) or Coagulation time Activated Partial Thromboplastin Time (APTT). Prothrombin Time (PT). Tests of Fibrinolysis and the Mechanisms That Control Hemostasis: Fibrin Degradation Products (FDP)

Bleeding Time (BT) Principle The bleeding time is dependent upon The bleeding time test is a useful tool to test for platelet plug formation and capillary integrity. Occasionally, the bleeding time test will be ordered on a patient scheduled for surgery. The bleeding time is dependent upon The efficiency of tissue fluid in accelerating the coagulation process Capillary function and The number of blood platelets present and their ability to form a platelet plug.

Bleeding Time (BT) Prolonged bleeding times are generally found when The platelet count is below 50,000/µL When there is platelet dysfunction. Four procedures are currently in use for determining the bleeding time: The Duke method. The Ivy Method. The Mielke Method. The Simplate or Surgicutt Method.

Duke Method With the Duke method, the patient is pricked with a special needle or lancet, preferably on the earlobe or fingertip, after having been swabbed with alcohol. The prick is about 3–4 mm deep. The technician then wipes the blood every 30 seconds with a filter paper. The test ceases when bleeding ceases. The usual time is about 1–3 minutes. No repeat testing is allowed due to space. The test causes nervousness in the patient. This test method is the easiest to perform, but is the least standardized and has the less precision and accuracy.

Ivy Method In the Ivy method, a blood pressure cuff is placed on the upper arm and inflated to 40 mmHg to control capillary tone and to improve the sensitivity and reproducibility– this will maintain constant pressure within the capillaries and help standardize the procedure. A sterile, disposable blood lancet is used to make a shallow incision that is 1 millimeter deep on the underside of the forearm. Every 30 seconds, filter paper is used to draw off the blood. The time from when the incision is made until all bleeding has stopped is measured. (Or use the following:) • 20 mm Hg for infants weighing 1,000 grams or less (This is approximately 2 pounds, 3ounces. • 25 mm Hg for infants weighing 1,000 grams--2,000 grams (This is approximately 2 pounds, 3 ounces to 4 pounds, 6 ounces.) • 30 mm Hg for infants weighing 2,000 grams or more (This is approximately 4 pounds, 6 ounces or greater) • For infants older than 5 months use 40 mm Hg.

The test is finished when bleeding has stopped completely. Ivy Method The test is finished when bleeding has stopped completely. A prolonged bleeding time may be a result from decreased number of thrombocytes or impaired blood vessels. However, it should also be noted that the depth of the puncture or incision may be the source of error. Normal values fall between 2 – 7 minutes depending on the method used. The greatest source of variation in this test is largely due to difficulty in performing a standardized puncture. This usually leads to erroneously low results.

Mielke Method A Modification of the Ivy Method. A Bard-Parker or similar disposable blade is used, along with a rectangular polystyrene or plastic template that contains a standardized slit. The blade is placed in a special handle containing a gauge in order to standardize the depth of the incision. The same procedure as described for the Surgicutt method is employed.

Mielke Method

Advantages of this method include: Mielke Method Advantages of this method include: That the surgical incision more closely approximates the patient’s haemostatic response to surgery, when compared to the puncture in the Ivy Method. The depth of the incision can be controlled. Disadvantages of this method include: Patient anxiety, due to open blade. Small scars might form.

Simplate / Surgicutt Method The Preferred Method Modified From the Ivy Method. The first bleeding time device introduced was the Simplate. The Simplate device has a trigger and spring method for the blade. The blade has a depth of 1.0 mm and a width of 5.0 mm. Another brand name is the Surgicutt.

Advantages of this method include: Simplate / Surgicutt Method Advantages of this method include: Instrument is a sterile, standardized, easy to use device that makes a uniform incision. Instrument is a spring activated surgical steel blade which is housed in a plastic unit. This eliminates variability of blade incision. This method is the most standardized method of all the bleeding time procedures. Disadvantages of this method include: Slight scarring can occur so patient should be informed.

Materials Blood pressure cuff Sterile, disposable blood lancet, capable of a puncture 5 mm wide and 1 mm deep Stopwatch Whatman No. 1 circular filter paper Alcohol pads Gloves Butterfly bandage

Preparation of the Patient After proper greeting and identification of the patient, explain the test for patient. It is critical that you ask the patient whether or not they have taken aspirin, aspirin containing compounds (many over the counter medications contain aspirin) or blood thinners such as heparin or Coumadin recently. These drugs will cause a falsely abnormal bleeding time and the test should not be done.

Procedure Greet and identify the patient. Explain the procedure to the patient. Obtain a history about aspirin or aspirin containing compounds taken within last 7 - 10 days. Select a site on the patient's forearm approximately three fingers widths below the bend in the elbow that is free of visible subcutaneous veins. Cleanse the outer surface of the patient's forearm by moving the alcohol pad in concentric circles from the incision site outward; allow to air dry. Place a blood pressure cuff on the patient's arm above the elbow. Turn the knob on the bulb of the sphygmomanometer until it stops. Squeeze the bulb to inflate the sphygmomanometer. Inflate the cuff and maintain pressure at 40 mm Hg.

Procedure Remove the Surgicutt device from the blister pack, being careful not to contaminate or touch the blade-slot surface. Remove the safety clip. Holding the skin tight, depress the “trigger” on the bleeding time device. The puncture must be performed within 30 to 60 seconds of inflation of the blood pressure cuff. Simultaneously start the stopwatch. After 30 seconds have passed blot (do not wipe) the blood with the filter paper. The filter paper must not touch the wound on the arm. Blot the site at regular thirty second intervals. Rotate the filter paper after each 30 seconds. When bleeding ceases and blood no longer is drawn to the filter paper, stop the watch and release the blood pressure cuff by turning the knob next to the bulb in the opposite direction used to inflate the cuff. Remove the blood pressure cuff.

Appropriately discard all used materials and wash hands. Procedure Record the bleeding time. Bleeding time is determined to the nearest 30 seconds. If bleeding continues for more than 15 minutes, the procedure should be discontinued, and pressure applied to the wound sites. After ensuring that the bleeding has stopped, carefully bandage the site. Appropriately discard all used materials and wash hands.

Result Normal Values 2.5 – 9.5 minutes The critical Value for bleeding time is > 15 min. If the puncture site is still bleeding after 15 minutes, discountinue the test apply pressure to the site. Document and report the results to the clinician. DID YOU KNOW? Bleeding time is shorter in men than in women by an average of about 30 seconds. This is probably because men have slightly more red blood cells than do women, and the higher the red cell count, the more efficient the platelets.

Calibration , Quality Control Calibration: None Quality Control: No external QC is available. Care must be taken to standardize the procedure. The protocol must followed exactly!

Sources of Error If the patient has taken aspirin or aspirin-containing compounds 7 to 10 days prior to the procedure, the bleeding time may be prolonged. The technician must determine the patient's history concerning aspirin ingestion to ensure quality results. About 20 different medications, including antihistamines and nonsteroidal anti-inflammatory drugs such as aspirin and ibuprofen, impair the platelets' ability to stick to wounds, and therefore produce a longer bleeding time. Results may be affected by an improperly performed puncture. A puncture that is too shallow, too deep, or in an inappropriate location will adversely affect test results. The alcohol must be completely dried before making the puncture. If residual alcohol is on a puncture site, the bleeding time will be erroneously prolonged. Aspirin • Naficillin • Indomethacin • Nitrofurantoin • Naproxen • Penicillin • Dextran • Piperacillin • Heparin • Ticarcillin • Prostacyclin • Aminocaproic acid • Ampicillin • Ethanol • Azlocillin • Halothane • Carbenicillin • Nitroglycerin • Mithramycin • Radiographic contrast agents • Moxalxtam

Sources of Error If the technician does not initiate timing of the procedure simultaneously with the puncture, the results will be adversely affected. If the technician allows the filter paper to touch the wound, the platelet clot may be dislodged, causing falsely elevated results. If the stopwatch has not been appropriately calibrated, it may keep incorrect time. Stopwatches should be calibrated on a regular basis as a part of the quality assurance program. The direction of the incision should be consistent. A horizontal incision gives a longer bleeding time than a vertical incision The bleeding time is prolonged in thrombocytopenia, hereditary and acquired platelet dysfunctions, von Willebrand's disease, a fibrinogenemia, severe hypofibrinogenemia, and some vascular bleeding disorders

Sources of Error 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.