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Chapter 2 Flashcards

1
Q

How does the endothelium prevent propagation of a clot?

A

Thrombomodulin production results in activation of protein C and subsequent inhibition of factors Va and VIIIa, while local TFPI release reversibly inhibits factor Xa
Endogenous heparin and dermatan sulfate expression results in antithrombin III binding- thus inactivating thrombin and preventing propagation of clot

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2
Q

What is an early mediator of primary hemostasis during endothelial injury?

A

Vasoconstriction, as a result of neuromyogenic reflexes within the vascular smooth muscle

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3
Q

How is vascular contraction further augmented?

A

Paracrine signaling via ADP, thromboxane A2 and serotonin from nearby adherent platelets

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4
Q

What provides an avenue for platelet and leukocyte adhesion

A

Exposure of subendothelial tissue factor and collagen

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5
Q

What improves coagulation protein and platelet binding?

A

Increased endothelial cell production of vWF
Expression of cellular TF and platelet-activating factor (PAF)
Reduced thrombomodulin activity

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6
Q

Origin of platelets and lifespan

A

Derived from bone marrow megakaryocytes

Lifespan of 9-12 days

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7
Q

What percentage of the body’s platelet pool is stored in the spleen?

A

1/3

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8
Q

How is platelet adhesion further strengthened?

A

Presence of vWF, which mediates the binding of collagen with glycoprotein Ib/IX

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9
Q

When does platelet plug formation occur?
When does clot stabilization occur?
What is clot stabilization aided by?

A

Within 1-3 mins of injury
Within 10 mins of injury
Aided in part by negative feedback from endothelial cell PGI2 release

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10
Q

What occurs after platelet plug formation?

A

Procoagulant protein complexes (i.e, prothrombinase, tenase) form on platelet phospholipid surfaces and augment the production of thrombin via the coagulation cascade

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11
Q

What is responsible for the production of all coagulation factors with the exception of VIII and vWF?

A

Liver

VIII and vWF are produced by endothelial cells

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12
Q

How are factors II, VII, IX and X formed

A

Through vit K-dependent reactions

They are of particular importance in pharmacologic anticoagulation

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13
Q

Traditional coagulation pathway

A

Extrinsic (PT/INR) and intrinsic (aPTT) merge into a common pathway

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14
Q

More recent discovery of the coagulation pathway

A

Described in cell-based phases:
Initiation
Amplification
Propagation

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15
Q

Process of initiation

A

TF is released by the injured vascular endothelium
Binds to factor VII to form TF-VIIa complexes
Complex activates factors X and IX to form Xa and IXa
Factors Xa and Va form the Xa-Va complex (prothrombinase complex)
Prothrombinase complex converts small amts of factor II (prothrombin) to factor IIa (thrombin)

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16
Q

Process of amplification

A

Thrombin produced from initiation activates additional factor V, VIII, XI, and platelets through a pos feedback loop

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17
Q

Process of propagation

A

Factors IXa and VIIIa form the factor IXa-VIIIa complex (tenase complex)
Tenase complex converts additional factor X to Xa, which then forms more prothrombinase complexes
Large amts of thrombin are generated, leading to the formation of fibrin from fibrinogen
Fibrin weaves throughout the platelet plug to form a stable fibrin clot

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18
Q

What are important natural anticoagulants?

A

ATIII
Protein C
Protein S

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19
Q

What does ATIII do?

A

Directly inhibits factors IIa (thrombin), IXa, Xa, and XIa

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20
Q

What is protein C?

A

A vit-K dependent natural anticoagulant, which is activated by thrombin-thrombomodulin complexes on the endothelial cell surface following the formation of a clot

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21
Q

What is protein S?

A

A vit-K dependent cofactor in the formation of APC

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22
Q

What are important regulatory and precursor proteins necessary for fibrin degradation?

A

Plasminogen
tPA
a2-antiplasmin

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23
Q

What does tPA do?

A

Acts to convert plasminogen to plasmin, which in turn binds fibrin and degrades the polymer into soluble split products

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24
Q

What does a2-antiplasmin do?

A

Serves as a negative regulator of plasmin and binds and inactivates circulating excess plasmin
Binds continuously secreted plasmin, allowing early clot formation during vascular injury without immediate degradation

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25
What is a nl platelet count?
150-450K/microL of blood
26
What occurs with a platelet count <50,000?
Pts are subject to easy bruising and bleeding?
27
When does spontaneous bleeding occur?
Does not typically occur unless platelet counts are <20K
28
What is considered a nl bleeding time?
Between 2-10 mins
29
What does bleeding time measure?
Qualitative platelet dysfunction
30
What is an abnormal bleeding time? | What is it associated with?
Between 10-15 mins Associated with low-mod risk for bleeding >15 mins is serious risk for spontaneous bleeding and severe platelet dysfunction or thrombocytopenia
31
What does prothrombin time (PT) measure?
The function of the extrinsic and common pathways of the ex vivo coagulation cascade Measures the function of VII, V, X, II and I
32
What is a nl INR?
1.0
33
What prolongs INR? Why?
Warfarin | Due to depletion of vit K-dependent factors II, VII, IX, and X
34
What does aPTT measure?
The ex vivo intrinsic coagulation cascade, compromising high molecular weight kininogen, prekallikrein, and factors XI, IX, VIII, V, X, II, and I
35
What is activated clotting time?
ACT is a test similar to aPTT but used in clinical situations requiring high-dose heparin administration (cardiopulmonary bypass, endovascular interventions, ECMO)
36
What is TEG?
``` Thromboelastography Provides a quantitative measure of all aspects of hemostasis, including: Platelet aggregation Clot strengthening Fibrin cross-linking Fibrinolysis ```
37
Advantages of TEG
Quantification of thrombodynamics Ability to differentiate between platelet and plasma coagulative disorders Rapidity of its results
38
What is the MC congenital bleeding disorder?
vWD
39
Lab findings of vWD
Prolonged bleeding time Mildly prolonged aPTT Abnl platelet binding as measured by a depressed ristocetin cofactor assay
40
Type I vWD inheritance pattern
Autosomal dominant | Characterized by quantitative reduction in vWF levels with nl protein structure and function
41
Type II vWD
Variable inheritance pattern | Characterized by abnl qualitative protein function
42
Type III vWD
Autosomal recessive inheritance pattern | Associated with severe bleeding with absent vWF production
43
First-line therapy for type I and II vWD
DDAVP
44
Tx for type III vWD
Surgical prophylaxis or bleeding | Transfusion with cryoprecipitate or factor VIII: vWF concentrate
45
What is Glanzmann's thrombasthenia?
A rare congenital platelet disorder that is a result of defective or decreased synthesis of glycoprotein IIb/IIIa Platelets are unable to bind fibrinogen and lack the ability to form platelet aggregates
46
Why does platelet dysfunction occur in renal dz?
It's a result of numerous changes to protein function and intraluminal fluid dynamics
47
What bleeding problems are found in uremic pts?
Dysfunctional vWF Decreased thromboxane A2 Altered platelet granules
48
What does anemia cause in renal dz pts?
Decreased platelet adhesion and aggregation
49
Tx of uremic pts
Depends on severity of sx/bleeding risk Dialysis Epo DDAVP/cryoprecipitate
50
What is extracorporeal circuitry? | What does it give rise to?
Cardiopulmonary bypass, ECMO | Abnl platelet activation in part d/t fibrinogen accumulation within the oxygenation membrane
51
What does consumption and loss of platelets from the circulating pool result in?
Thrombocytopenia as well as qualitative dysfunction
52
How are therapeutic anticoagulation levels maintained with extracorporeal circulation?
Systemic unfractionated heparin given IV and intermittently into the extracorporeal circuit
53
Type I HIT
May occur in as many as 10% of pts receiving unfractionated heparin Typically resolves spontaneously within 96 hrs of heparin cessation
54
Type II HIT
Unusual immunologic complication affecting 1-3% of pts
55
Pathology of HIT
Heparin binds with PF4, which is released from platelet alpha granules normally. in HIT, IgG antibodies form against the heparin-PF4 complex within 5-10 days of exposure that in turn, strongly activates platelet adhesion and aggregation
56
When should you raise clinical concern for HIT?
When platelet counts decrease by >50% from preheparin levels
57
What does massive platelet activation and platelet plug formation predispose the pt to?
``` Venous thrombosis Thromboembolism Limb ischemia Stroke MI ```
58
Labs for HIT
Serotonin release assay (SRA) Heparin-induced platelet aggregation assay (HIPA) ELISA
59
What is one of the more common screening tests in clinical use for HIT?
ELISA
60
Tx of HIT
Immediate cessation of all heparin therapies Non-heparin-based anticoagulation strategies unless clinical CI Avoidance of platelet transfusion is appropriate to help propagation of white clot
61
Idiopathic thrombocytic purpura (ITP)
An acquired d/o rising from pathologic destruction of platelets d/t autoantibody formation
62
When does ITP commonly occur?
Time of infection (often viral) OR | altered immune homeostasis (malignancy, lymphoproliferative d/os, concurrent autoimmune dz)
63
Dx of ITP
Clinical and one of exclusion
64
Tx of ITP
With platelet count of <30K, initially prevention of bleeding Include glucocorticoids and IVIG 2nd line is splenectomy If surgery is CIed, rituximab
65
Pathology of hemophilia A/B
A is deficiency of factor VIII B is deficiency of factor IX Impaired formation of tenase (VIII-IXa) complex, impacting the amplification phase of coagulation and leading to decreased factor Xa and thrombin creation
66
Sx of hemophilia A/B
Mucosal bleeding Excessive bleeding during circumcision Hemarthrosis Intracranial hemorrhage
67
Labs for hemophilia A/B
Elevated aPTT | Decreased factor VIII or IX levels
68
Tx of hemophilia A
Recombinant factor VIII Cryoprecipitate transfusion Desmopressin
69
Tx of hemophilia B
Recombinant factor IX | FFP or cryoprecipitate transfusion
70
DIC
Results from unchecked activation of the normal coagulation response with loss of localization Sepsis is the MCC of DIC
71
Pathophys of DIC
Stems from systemic microvascular activation of platelets, diffuse activation of clotting factors, deposition of fibrin with microangiopathic thrombosis, and subsequent fibrinolytic pathway inactivation
72
Dx of DIC
Clinical dx of exclusion | Schistocytes on peripheral blood smear
73
Tx of DIC
Maintain an INR <1.5 and platelet count >50K
74
Tx of bleeding secondary to hepatic failure
Correction of factor and platelet deficiencies with blood component management
75
When is hypothermia commonly seen?
Altered coagulation as a result of: Trauma Massive resuscitation Extended exposure to open body cavities during procedures Iatrogenic hypothermia for cerebral or myocardial protection
76
What is hypothermia associated with?
Impaired platelet function | Decreased collagen-induced platelet aggregation
77
Tx of hypothermia
Treat underlying cause Limit evaporative heat loss Mild (>34 degrees Celsius)- passive rewarming techniques Moderate (30-34 Celsius)- active rewarming Severe (<30 Celsius)- External passive and active rewarming, internal rewarming
78
Definition of massive transfusion
Replacement of a pts blood volume with packed RBCS (pRBCs) in a 24-hr period or acute transfusion of over half the pt's blood volume per hr
79
What is the massive transfusion protocol?
1:1:1 ratio of pRBC, FFP and platelet administration
80
What is the MC hereditary procoagulant d/o?
Factor V Leiden
81
Pathology of factor V Leiden
Mutation of the factor V protein prevents APC-mediated inactivation, thereby increasing risk for uncontrolled clot formation
82
Dx of factor V Leiden
aPTT with and without APC
83
Tx of factor V Leiden
No lifelong anticoagulation, only in thromboembolic events
84
What does ATIII do?
Inactivates thrombin and factors Xa, IXa, and XIa
85
What is the MC site of thrombosis in an ATIII deficiency?
Iliofemoral DVT
86
Dx of ATIII deficiency
ATIII-heparin cofactor assay
87
Tx of ATIII deficiency
FFP transfusion or ATIII concentrate
88
Dx of protein C/S deficiency
Serum protein C and S levels below the nl limits
89
What is the MC clinical manifestation of C/S deficiency?
Venous thromboembolism
90
What is a known RF for pts with decreased protein C and S levels d/t a transient procoagulant state during initiation of the drug?
Warfarin-induced skin necrosis
91
When should postponement of surgery occur?
Postpone beyond 6 wks for bare-metal stenting and 6 mos for drug-eluting stenting for noncardiac surgery pts If not possible, continue dual antiplatelet therapy
92
MOA of ASA
NSAID that irreversibly inhibit clyclooxygenase isoforms (COX-1 and COX-2) Maintains its effects for the lifespan of the platelet
93
MOA of ticlopidine, prasugrel and clopidogrel
Irreversibly inhibit activity of the ADP-P2Y receptor on the platelet membrane, which in turn impairs glycoprotein IIb/IIIa-mediated platelet cross-linking and aggregation
94
When to use clopidogrel
ACS Recent MI or CVA Established PAD
95
When to use prasugrel
ACS during PCI | It is found to inhibit platelet aggregation more rapidly and consistently compared to clopidogrel
96
When to use cilostazol
Intermittent peripheral arterial claudication Prevents vasoconstriction and smooth muscle proliferation May require up to 1 yr before symptomatic relief is noticeable
97
CIs of cilostazol
Dx of heart failure
98
What are abciximab, eptifibatide, and tirofiban used for?
Adjuncts to heparin and ASA therapy
99
What do heparin and LMWH do?
Increase ATIII activity | Primarily affects intrinsic and common pathways of in vitro coagulation
100
How do you measure heparin and LMWH efficacy?
aPTT needs to be 1.5-2.5x the baseline aPTT value
101
What is the onset of therapeutic warfarin anticoagulation
Takes at least 24-72 hrs | Principally affects extrinsic and common pathways of in vitro coagulation
102
How to measure effect of warfarin
PT and INR
103
MOA of direct thrombin inhibitors (DTI) | Examples of DTI
Inactivates circulating and clot-bound thrombin Argatroban and bivalirudin Dabigatran
104
When to use argatroban
Those with contraindication to heparin
105
Monitoring of argatroban
aPTT
106
What is bivalirudin approved for?
Pts with ACS undergoing PCI
107
What is dabigatran used for?
Tx/prevention of DVT, PE, non-valvular atrial fibrillation-associated stroke
108
What are apixaban, roxaban, and edoxaban approved for?
VTE and nonvalvular a fib
109
Measurement of apixaban, roxaban, and edoxaban
Anti-factor Xa activity
110
What is r-tPA approved for?
Acute STEMI Acute ischemic stroke Acute massive PE
111
Use of oxidized regenerated cellulose products
Frequently used as topical mesh placed on sites of bleeding to promote coagulation
112
Use of gelatin matrix products
Can absorb blood up to 40x their weight and serve as the foundation of a hemostatic plug
113
Use of topical thrombin and fibrin sealants
Commonly used bioactive topicals that augment hemostasis via directed factor II (topical thrombin) or fibrinogen (fibrin) application
114
MOA of aminocaproic acid
Interferes with fibrinolysis by competitively blocking the fibrin-binding site on plasminogen, thereby preventing conversion to plasmin
115
Use of aminocaporic acid
``` Prevention of fibrinolytic bleeding d/t: Cardiac surgery Congenital hematologic dz Cirrhosis Malignancy ```
116
Use of tranexamic acid
Hemophiliac pts undergoing dental procedures | Tx of menorrhagia
117
Uses of desmopressin
DI Nocturia Management of bleeding secondary to hemophilia A, type I and 2 vWD, and prevention of surgical bleeding in hemophiliac pts
118
Dosing of desmopressin in perioperative vWD and hemophilia A pts
30 mins IV or 2 hrs IN prior to the procedure
119
What does protamine sulfate do?
Reverses the effects of heparin
120
What does phytonadione (vit K) do?
Antagonizes the effects of warfarin
121
What does each unit of pRBCs contain?
200 mL of RBC concentrate and an additional 100 mL of preservation solution
122
What do pRBCs do?
Raise the recipient hematocrit approximately 3-4%
123
Derivation of FFP and FP-24
Donor whole blood that has been separated and frozen within 8 (FFP) and 24 (FP-24) hrs
124
When are FFP and FP-24 indicated?
Tx of multiple coagulation factor deficiencies, massive transfusion protocols, and when specific factor concentrates are not available
125
What are components of cryoprecipitate?
Fibrinogen Factor VIII Factor XIII vWF
126
Indications of cryoprecipitate
Massive transfusion protocols Hypofibrinogenemia Factor VIII deficiencies when factor concentrates are not available Bleeding associated with vWD when factor concentrates or DDAVP are not available
127
Platelet concentration dose and efficacy
Contain around 7 x 10 to the 6th platelets per 50 mL | Each unit should increase platelet levels by at least 5K
128
Indications for platelet transfusions
``` Massive transfusion Hereditary platelet dysfunction Drug-induced platelet dysfunction Cardiopulmonary bypass surgery-related platelet destruction Platelet underproduction ```
129
What should platelet counts be in preparation for surgical procedures?
>50K
130
What are isolated and recombinant factors currently available?
``` Fibrinogen concentrate Recombinant thrombin Recombinant factors VIII and IX vWF concentrate Antithrombin concentrate Of particular note in surgical populations: prothrombin complex concentrates (PCCs) and recombinant factor VIIa ```

Surgery (30 decks)

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