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PBR: Hematology > Hemostasis > Flashcards

Hemostasis Flashcards

1
Q

What are the four overlapping phases of the hemostatic process?

A

Primary hemostasis, Secondary hemostasis, Clot limitation, and Clot dissolution.

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2
Q

Describe primary hemostasis.

A

Local vasoconstriction and formation of a loose platelet plug.

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3
Q

Describe secondary hemostasis.

A

Circulating coagulation factors, via the clotting cascade, form fibrin that stabilizes the platelet plug.

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4
Q

What are the four steps in the formation of a platelet plug?

A

Adhesion, activation, aggregation, and thrombin activation.

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5
Q

Which bleeding syndrome is associated with a deficiency of GP1b and how does this present clinically?

A

Bernard-Soulier syndrome. Platelets bind poorly to vWF, which results in bleeding gums, significant bleeding with small injuries, and profuse bleeding with menses.

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6
Q

Which bleeding syndrome is associated with a deficiency of the GP2b/3a platelet complex and what is the associated defect?

A

Glanzmann Thrombasthenia. Patients are unable to aggregate platelets.

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7
Q

How does Clopidogrel affect platelet function?

A

It blocks the ADP effects on the platelets, which normally works to induce more platelet activation and thrombogenesis.

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8
Q

What is the presumed factor underlying Prinzmetal angina and how does it work?

A

Thromboxane A2 has vasoconstrictive properties and is the presumed underlying cause of Prinzmetal angina.

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9
Q

During which step in platelet plug formation is the clotting pathway activated?

A

The clotting pathway is activated during step 3 of the platelet plug formation process - aggregation.

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10
Q

Which clotting factors are involved in the intrinsic pathway?

A

Factors 8, 9, 11, and 12

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11
Q

Which clotting factors are involved in the extrinsic pathway?

A

The 7a-tissue factor complex comprises the extrinsic pathway.

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12
Q

Which clotting factor is involved in both the intrinsic and extrinsic pathways?

A

Both pathways converge to activate Factor 10.

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13
Q

Name 4 important hemostatic functions carried out by thrombin.

A

Thrombin is critical in the conversion of fibrinogen to fibrin in the platelet plug, in activating Factor 13 (the resulting Factor 13a interacts with fibrin to make a covalently bonded, stabilized, cross-linked fibrin clot), in stimulating self-regeneration by activating Factors 5, 8, and 11, and in activating platelets as part of primary hemostasis.

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14
Q

Describe the process by which clot size is limited.

A

Clot size limitation occurs because thrombin modulates its own production by combining with an endothelial cell surface protein (thrombomodulin) to activate Protein C. Activated Protein C, combined with Protein S, deactivates Factors 5a and 8a, thereby limiting thrombin production.

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15
Q

Describe the process by which clots are dissolved.

A

Clot dissolution (fibrinolysis) is initiated by tissue plasminogen activator (tPA) released from endothelial cells. tPA catalyzes the conversion of plasminogen to plasmin, which breaks down fibrin and fibrinogen and dissolves the clot.

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16
Q

What would you expect to see clinically in a patient with Protein C or Protein S deficiency?

A

Thrombotic tendency. These patients would present with clots, such as DVTs.

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17
Q

At the bedside, how can you differentiate between a primary hemostatic problem and a coagulation problem?

A

Primary hemostatic problems result in multiple, tiny, superficial hemorrhages (petechiae, ecchymoses, and mucocutaneous bleeding), while coagulation disorders present with deep tissue bleeding such as hematomas and hemarthroses.

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18
Q

Which 5 tests are commonly done in the initial evaluation of a bleeding disorder?

A

PT, PTT, thrombin time, platelet count, and bleeding time (or rapid platelet function analysis (PFA)).

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19
Q

What does prothrombin time (PT) measure?

A

Prothrombin time measures the function of the extrinsic and common coagulation pathways (think Factor 7).

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20
Q

What does activated partial thromboplastin time (PTT) measure?

A

PTT measures the function of the intrinsic and common coagulation pathways (Factors 8, 9, 11, 12).

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21
Q

What does the thrombin time measure?

A

Thrombin time measures the time of conversion of fibrinogen to fibrin.

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22
Q

What would an increased thrombin time indicate?

A

An increased thrombin time reflects decreased or defective fibrinogen, elevated fibrin degradation products, or the presence of heparin or heparin-like anticoagulants.

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23
Q

What are bleeding time and rapid platelet function analysis testing used to assess?

A

These tests reflect the effectiveness of platelet aggregation, and are used to determine the adequacy of platelet number and function.

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24
Q

A deficiency in which clotting factor does not result in a bleeding disorder?

A

Factor 12

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25
Q

What does a mixing study show?

A

A mixing study is when a patient’s plasma is mixed 1:1 with normal plasma. If the PTT corrects following mixing, the patient has a clotting factor deficiency. If it does not correct, the patient has developed an inhibitor to a clotting factor protein (usually a lupus anticoagulant or Factor 8 inhibitor).

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26
Q

What does it mean if the PTT is prolonged but the PT is normal?

A

There is either a clotting factor deficiency or a circulating clotting factor inhibitor.

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27
Q

What does it mean if the PT is prolonged but the PTT is normal?

A

Factor 7 deficiency, mild liver disease, mild Vitamin K deficiency, or therapeutic Warfarin levels.

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28
Q

Know Figure 24-7 and Table 24-6 ***

A
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29
Q

Which clotting factor is low in children with hemophilia A?

A

Factor 8

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30
Q

What are the expected PT and PTT in hemophilia A?

A

The PTT is elevated but the PT is normal.

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31
Q

What is the inheritance pattern for Hemophilia A?

A

X-linked recessive

32
Q

Which clotting factor deficiencies have X-linked inheritance?

A

Hemophilia A and B

33
Q

What is the classic presentation of a child with hemophilia A/B?

A

Excessive bleeding following neonatal elective circumcision is a classic presentation for hemophilia A/B.

34
Q

What are the common clinical findings in patients with hemophilia A/B?

A

Easy bruising, muscle and joint hemorrhages, and prolonged hemorrhage after surgery or trauma. These patients typically do not have mucosal bleeding or excessive bleeding after minor cuts.

35
Q

What are the plasma level cutoffs for severity of factor deficiency in patients with hemophilia A?

A

Patients with <1% of normal have severe disease. Patients with 1-5% activity have moderate disease, and patients with 6-40% factor activity have mild disease.

36
Q

What is the first step in management of a patient with hemophilia A who presents with head trauma, regardless of presenting symptoms?

A

Start factor therapy immediately in these patients. CT head may be performed after factor therapy has been administered.

37
Q

Bleeding in which extremity is an emergency for patients with hemophilia? What is the recommended management?

A

Bleeding into the forearm of a patient with hemophilia is an emergency because of the risk of compartment syndrome and nerve damage and long-term risk of contractures. Treat with aggressive factor replacement and frequent neurovascular assessment. If compartment syndrome develops, these patients require urgent surgical intervention.

38
Q

What medication can you give to a child with mild hemophilia A (>5% Factor 8) before a tooth extraction? Which test should be done prior to relying on this medication for treatment?

A

DDAVP is a treatment option for some patients with mild factor 8 deficiency because it causes a release of vWF and Factor 8 stores from endothelial cells. A DDAVP challenge should be performed before relying on this response. If the challenge is successful, DDAVP may be used as treatment for an acute bleed and prophylactically for a tooth extraction.

39
Q

How are patients with moderate/severe hemophilia A treated?

A

These patients should receive Factor 8 concentrate when they have acute bleeds.

40
Q

What is the most serious side effect of current factor products?

A

Development of a neutralizing inhibitor (an antibody that inactivates or causes increased clearance of the “foreign” product).

41
Q

How can arthropathy and joint deformity be prevented in patients with hemophilia?

A

Early treatment of bleeding episodes delays or prevents hemophilic arthropathy and subsequent joint deformity. Prophylactic use of factor replacement can reduce arthropathy as well.

42
Q

What is hemophilia B? How is it treated?

A

Factor 9 deficiency (“Christmas disease”). Presentation and management is similar to that of Factor 8 deficiency, but acute bleeds should be treated with Factor 9 concentrate.

43
Q

Which (6) clotting factor deficiencies have autosomal inheritance?

A

Factor 5, 7, 10, 11, 12, and 13 deficiencies are all rare autosomal recessive disorders.

44
Q

What is Factor 11 deficiency?

A

AKA Hemophilia C. It is an autosomal recessive factor deficiency. Bleeding problems are less common than in Factor 8/9 deficiencies, and these patients usually don’t have hemarthroses. These patients tend to have more mucosal bleeding, and severity of illness does not correlate with Factor 11 levels.

45
Q

How is Factor 11 deficiency treated?

A

Tranexamic acid and Ɛ-aminocaproic acid are useful for mucosal bleeding. FFP should be used to treat severe bleeding episodes.

46
Q

Which factor deficiency can be seen in patients with amyloidosis?

A

Factor 10 deficiency.

47
Q

Which clinically significant bleeding disorders will have normal platelet counts, PT, PTT, and bleeding time?

A

Mild vWD, mild hemophilia, and Factor 13 deficiency.

48
Q

How do patients with Factor 13 deficiency present?

A

These patients have severe bleeding problems and severe scarring with superficial wounds but on laboratory testing will have normal PT, PTT, and platelet count.

49
Q

How can the diagnosis of Factor 13 deficiency be made?

A

PT, PTT, platelet count, and bleeding time will all be normal. The screening test is the urea solubility assay, which can be confirmed with the Factor 13 activity assay.

50
Q

How is Factor 13 deficiency treated?

A

Prophylactic Factor 13 replacement is often required to prevent severe bleeding.

51
Q

What (7) conditions can cause DIC?

A

DIC occurs in diseases that promote tissue-factor release: massive direct tissue trauma; production of tumor necrosis factor (especially seen in solid tumors); sepsis; endotoxin production in certain infections; placental tissue substances in obstetric patients with placental abruption, dead fetus, or amniotic fluid embolism; acute promyelocytic leukemia; and rattlesnake or viper envenomation.

52
Q

What is the underlying pathophysiology of DIC?

A

Large amounts of released tissue factor interact with Factor 7 and initiate coagulation. There is excessive thrombin and plasmin produced, resulting in both increased clot formation (via thrombin cleaving fibrinogen to fibrin) and clot breakdown (via plasmin degradation of fibrin clots).

53
Q

What are the lab abnormalities seen in DIC?

A

Prolonged PT and PTT; thrombocytopenia; decreased fibrinogen; elevated D-dimer (produced by the action of plasmin on fibrin); increased thrombin time (due to decreased fibrinogen and increased fibrin degradation products); and RBC fragments (the fibrin strands span the small blood vessels and shear the RBCs).

54
Q

What is DIC and how does it present clinically?

A

DIC is an acquired coagulopathy which occurs in diseases that promote tissue-factor release. It presents with bleeding and symptoms can include petechiae, ecchymosis, hemorrhage, hypotension, tachycardia, altered consciousness, and GI bleeding.

55
Q

How is DIC treated?

A

DIC is treated primarily through treatment of the underlying disorder. With severe bleeding, give FFP and platelets. If fibrinogen is low, give cryoprecipitate as well.

56
Q

Name the (6) Vitamin K dependent coagulation factors.

A

Factors 2, 7, 9, 10, and proteins C and S.

57
Q

What are (4) causes of Vitamin K deficiency?

A

Low stores (neonates), liver disease, decreased dietary absorption (no dietary intake of leafy greens, malabsorption, broad spectrum antibiotics), and antagonists (warfarin).

58
Q

What disorder are infants at risk for if they do not receive Vitamin K at birth?

A

Vitamin K deficiency bleeding (formerly known as hemorrhagic disease of the newborn).

59
Q

Why are individuals with protein C deficiency at risk for warfarin-related skin necrosis?

A

Initially, warfarin therapy causes a prothrombotic effect, which outweighs the antithrombotic effect on Factor 7. This is especially likely to happen if the patient is Protein C deficient. All patients starting warfarin therapy should be on heparin or LMWH until a therapeutic warfarin dose is achieved to prevent this complication.

60
Q

What is the appropriate management of a patient with clinical signs of bleeding and vitamin K deficiency?

A

Administer vitamin K in addition to FFP or nonactivated prothrombin complex concentrate. Vitamin K won’t take effect for ~8 hours, so the FFP is needed to control bleeding in the interim.

61
Q

What would the the expected laboratory abnormality in patients with lupus anticoagulants? How would these patients present clinically?

A

Lupus anticoagulants result in a prolonged PTT and thrombosis, not bleeding.

62
Q

Which infants are at higher risk for development of renal vein thrombosis?

A

Infants with a history of birth asphyxia, shock, and/or sepsis are at increased risk of developing endothelial cell injury leading to renal vein thrombus formation. It is also more common in infants of diabetic mothers and in those with congenital hypercoagulable states.

63
Q

How do infants with renal vein thrombosis typically present?

A

Almost all patients present with at least one of the following: gross hematuria, unilateral or bilateral flank mass, and thrombocytopenia.

64
Q

What is the most common cause of DVT in children?

A

The most common cause of DVT in children is the presence of a central venous catheter.

65
Q

What are the three naturally occuring anticoagulants?

A

Proteins C and S, and antithrombin.

66
Q

How do protein C and protein S function as anticoagulants?

A

Activated protein C, in conjunction with its cofactor, protein S, cleaves activated Factors 5 and 8, rendering them inactive. Factors 5 and 8 are necessary cofactors in the clotting cascade, so their inactivation prevents clot formation.

67
Q

How does antithrombin function as an anticoagulant?

A

Antithrombin inhibits thrombin.

68
Q

Which congenital thrombophilias result in neonatal purpura fulminans in infancy?

A

Infants who are homozygous for Protein C or S deficiency have neonatal purpura fulminans, with life-threatening thrombosis.

69
Q

What is Factor 5 Leiden?

A

It is an inherited thrombophilia (activated Protein C resistance) which increases the risk of venous thrombosis 5-8 fold.

70
Q

What are the (3) most common anticoagulants used in children?

A

Unfractionated heparin, low-molecular-weight heparin, and warfarin.

71
Q

When is tPA used in children?

A

tPA use is reserved for children with severe life or limb-threatening arterial or venous thrombosis.

72
Q

What is the mechanism of action of tPA?

A

tPA increases the conversion of plasminogen to plasmin in the presence of fibrin, which helps to break down fibrin clots. However, it also results in systemic fibrin lysis and can result in serious bleeding.

73
Q

How much is a 10 ml/kg RBC transfusion expected to increase the hemoglobin?

A

A transfusion of 10 ml/kg typically raises the hemoglobin by 2.5-3 g/dL.

74
Q

How much elemental iron is present in a unit of pRBCs?

A

250 mg

75
Q

What are 3 potential complications of RBC transfusion?

A

Hemolytic reaction (life-threatening, with fever, chills, flank pain, and oozing from IV sites), febrile nonhemolytic reaction (fever and chills only), and urticarial reaction (hives without other allergic symtoms).

76
Q

How much would a unit of random-donor platelets be expected to raise the platelet count?

A

~50 x 109/L

PBR: Hematology (9 decks)

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