Hemostasis and Venipuncture

• Hemostasis is the stoppage of bleeding as a response to an injury whether it be normal vasoconstriction where vessel walls close temporarily, abnormal obstruction like plaque, or coagulation such as litigation.
• Four interrelated responses:

  1. Vasoconstriction - the vessel walls are constricted after an injury, which results in reduced flow of blood in the site of injury
  2. Formation of the primary platelet plug - platelets stick together on the site of hte injury forming a plug
  3. Progression to the stable blood clot
  4. Fibrinolysis or dissolving of clot
• Coagulation / clotting - the process in which the blood changes from a liquid state into a gel that forms the blood clot.
• 3 Types of Protein Need in Coagulation

  1. enzyme precursors that turn into enzymes when activated
  2. cofactors that accelerate enzymatic reactions
  3. substrates which are the substances that are acted on and changed by the enzymes.
• Clotting cascade has two separate but interacting pathways:

  1. extrinsic pathway -activated by external trauma (initiates coagulation)
  2. intrinsic pathway - is activated by trauma inside the bloodstream (produces thrombin). (coagulation phases, namely initiation, amplification, and propagation.)
• Thrombin - produced at the site of injury from the prothrombin. It amplifies coagulation and converts fibrinogen into soluble fibrin.

  -supports the platelet plug formation yb activating factor XI to cross-link fibrin
• Fibrinolysis -process where the fibrin is dissolved. It has two main activities:

  1. reopens intact vessels by dissolving clots
  2. removes hemostatic clots from the tissue as part of the healing process
• Note:

  Liver’s role in hemostasis is to synthesize coagulation factors such as V, VIll, prothrombin, and fibrinogen. This organ produces heparin and bile salts needed for synthesis.
• Hemostatic Disorders

  1. Deep venous thrombosis (DVT) happens when blood clot forms in one or more deep veins, usually in the legs.
  2. Disseminated intravascular coagulation -when the formation of small clots blocks the small blood vessels.
• Hemostatic Disorder

  1. Hemophilia is a disorder involving the lack of sufficient blood- clotting proteins.
  2. Thrombocytopenia is a condition characterized by abnormally low levels of platelets in the blood
• Diagnostic Tests (Hemostasis)

  •Bleeding time • D-dimer

  • Factor assays

  • Fibrin degradation products (FFP)

  • Platelet function assay (PFA)

  • Prothrombin time (PT)

  • Partial thromboplastin time (PTT or APTT)
• Antecubital fossa- called the elbow pit, is the triangular area on the anterior of the elbow, which is a site of major veins.

  -First choice for routine venipuncture because there are several major arm veins called antecubital veins
• H-shaped antecubital veins - refer to a vein arrangement that occurs ni about 70% of the population.
• Median cubital vein - preferred venipuncture site. It isthe easiest to access and least painful forthe patient.
• Cephalic vein - second choice for venipuncture. It is harder to palpate but si usually better when drawing blood from an obese patient.
• Basilic vein - last choice-vein for venipuncture as it is not wellanchored and punctures on this vein are more painful.
• M-shaped antecubital veins -intermediate antebrachial veins, whcih includes median, median cephalic, and median basilic veins.
• M-shaped Antecubital Veins

  1. • Median vein - intermediate antebrachial vein; first-choice vein; safest and less painful
  2. • Median cephalic vein - intermediate cephalic vein; second choice for venipuncture; less likely to roll
  3. • Median basilic vein - intermediate basilic vein; last choice vein because it is more painful
• NOTE:

  Underside of the wrist is never used as avenipuncture site.
• Leg Veins Venipuncture

  5.Leg, ankle, and foot veins must not be used in venipuncture without the permission of a physician due to complications such as thrombosis.
• Arteries -not used for routine blood collection and are limited to

  the collection of arterial blood gas. Special training is needed and the procedure is risky for the patient.